Three-dimensionally ordered macroporous La0.6Sr0.4MnO3 (3DOM LSMO) supported manganese oxide and gold (yAu/zMnOx/3DOM LSMO; y = 1.76–6.85 wt %; z = 8 wt % (weight percent of Mn2O3)) nanocatalysts were fabricated by means of in situ poly(methyl methacrylate)-templating and gas bubble-assisted poly(vinyl alcohol)-protected reduction methods. The 3DOM LSMO support possessed a rhombohedral crystal structure and a surface area of 22–25 m2/g. MnOx and Au nanoparticles (NPs) (3.2–3.8 nm) were well dispersed on the surface of 3DOM LSMO. Catalytic performance of the samples for toluene oxidation was found to be well related to their surface adsorbed oxygen species concentrations and low-temperature reducibility. Among the as-prepared samples, 5.92Au/8MnOx/3DOM LSMO performed the best at a space velocity of 20 000 mL/(g h): the T50% and T90% (corresponding to toluene conversion of 50 and 90%) were 205 and 220 °C, respectively. The apparent activation energies (52.8–68.5 kJ/mol) obtained over the yAu/8MnOx/3DOM LSMO samples were much smaller than those (79.3–89.5 kJ/mol) obtained over the bulk LSMO supported counterparts. We believe that the excellent catalytic performance of 5.92Au/8MnOx/3DOM LSMO might be ascribed to the large surface area, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Au NPs or MnOx and 3DOM LSMO.

Three-dimensionally (3D) mesoporous single-crystalline CaO nano- and microparticles with tri-, tetra-, and hexagonal morphologies have been successfully fabricated using a surfactant (P123, CTAB, or PEG) assisted hydrothermal dissolution−recrystallization strategy with irregular nonporous CaO powders as the starting material. The as-synthesized calcium oxide samples are characterized by means of techniques such as X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy/selected area electron diffraction, Fourier-transfer infrared spectroscopy, thermogravimetric analysis/differential scanning calorimetry, and N2 adsorption−desorption. It is shown that the introduction of a surfactant has an important effect on the morphology and pore structure of the synthesized CaO samples. With P123 or PEG as template, a higher hydrothermal temperature and longer hydrothermal time favor the generation of more regular morphological CaO entities with a higher surface area. Among the surfactants adopted in the present work, PEG is the most effective in the fabrication of high-surface-area 3D mesoporous CaO. Under the conditions of hydrothermal temperature of 240 °C and hydrothermal time of 72 h in the presence of PEG and after calcination at 600 °C for 3 h in an oxygen flow, one can obtain a single-crystalline 3D mesoporous CaO material with a surface area of 257 m2/g. The possible formation mechanism of single-crystalline 3D wormhole-like mesoporous CaO is also discussed. These high-surface-area mesoporous CaO samples exhibit excellent CO2 adsorption behavior. The highest amount of CO2 desorbed from the CaO hydrothermally fabricated with PEG at 240 °C for 72 h and calcination at 600 °C for 3 h achieves 770 μmol CO2/g. It is suggested that the rise in surface area and the formation of 3D wormhole-like mesopores contribute to the enhanced CO2 adsorption capacity of CaO.

To overcome deactivation of Pd-based catalysts at high temperatures, we herein design a novel pathway by introducing a certain amount of CoO to the supported Au–Pd alloy nanoparticles (NPs) to generate high-performance Au–Pd–xCoO/three-dimensionally ordered macroporous (3DOM) Co3O4 (x is the Co/Pd molar ratio) catalysts. The doping of CoO induced the formation of PdO–CoO active sites, which was beneficial for the improvement in adsorption and activation of CH4 and catalytic performance. The Au–Pd–0.40CoO/3DOM Co3O4 sample performed the best (T90% = 341 °C at a space velocity of 20 000 mL g–1 h–1). Deactivation of the 3DOM Co3O4-supported Au–Pd, Pd–CoO, and Au–Pd–xCoO nanocatalysts resulting from water vapor addition was due to the formation and accumulation of hydroxyl on the catalyst surface, whereas deactivation of the Pd–CoO/3DOM Co3O4 catalyst at high temperatures (680–800 °C) might be due to decomposition of the PdOy active phase into aggregated Pd0 NPs. The Au–Pd–xCoO/3DOM Co3O4 nanocatalysts exhibited better thermal stability and water tolerance ability compared to the 3DOM Co3O4-supported Au–Pd and Pd–CoO nanocatalysts. We believe that the supported Au–Pd–xCoO nanomaterials are promising catalysts in practical applications for organic combustion.

•Au–Pd–xM (M = Mn, Cr, Fe, Co) particles are fabricated and well dispersed on the 3DOM Mn2O3 surface.•Au–Pd–0.21Co/3DOM Mn2O3 exhibits the best catalytic activity for CH4 oxidation.•Au–Pd–0.22Fe/3DOM Mn2O3 shows the best catalytic activity for o-xylene oxidation.•M doping can enhance the oxygen activation and methane adsorption ability.Palladium-based catalysts are highly active for eliminating volatile organic compounds. Reducing the use of noble metals and enhancing performance of a catalyst are always desirable. The three-dimensionally ordered macroporous (3DOM) Mn2O3-supported transition metal M (M = Mn, Cr, Fe, and Co)-doped Au–Pd nanoparticles (NPs) with an Au–Pd–xM loading of 1.86–1.97 wt% were prepared using the modified polyvinyl alcohol-protected reduction method. It is found that the Au–Pd–xM NPs with a size of 3.6–4.4 nm were highly dispersed on the surface of 3DOM Mn2O3. The 1.94 wt% Au–Pd–0.21Co/3DOM Mn2O3 and 1.94 wt% Au–Pd–0.22Fe/3DOM Mn2O3 samples performed the best for the oxidation of methane and o-xylene, respectively. The methane oxidation rate at 340 °C (339.0 × 10−6 mol/(gPd s)) over 1.94 wt% Au–Pd–0.21Co/3DOM Mn2O3 was three times higher than that (93.8 × 10−6 mol/(gPd s)) over 1.97 wt% Au–Pd/3DOM Mn2O3, and the o-xylene reaction rate at 140 °C (2.59 μmol/(gN s) over 1.94 wt% Au–Pd–0.22Fe/3DOM Mn2O3 was two times higher than that (0.93 μmol/(gN s) over 1.97 wt% Au–Pd/3DOM Mn2O3. It is concluded that doping a certain amount of the transition metal to Au–Pd/3DOM Mn2O3 could modify the microstructure of the alloy NPs, thus improving the oxygen activation and methane adsorption ability. We are sure that the M-doped Au–Pd/3DOM Mn2O3 materials are promising catalysts for the efficient removal of volatile organic compounds.The transition metal M (M = Mn, Cr, Fe, and Co)-doped Au–Pd/3DOM Mn2O3 nanocatalysts show super catalytic performance for methane and o-xylene oxidation, which is attributed to the enhanced oxygen activation and methane adsorption ability.Download high-res image (298KB)Download full-size image

•Hydrothermal stability of CuSSZ-13 decreases with increasing the Si/Al ratio.•Hydrothermal aging leads to the drop in amount of isolated Cu2+ species.•Transformation of Cu2+ species to aggregated CuO induces SSZ-13 structure collapse.•The aggregated CuO species gives rise to deactivation of CuSSZ-13.The hydrothermal stability of the CuSSZ-13 samples with various Si/Al ratios was examined. The NO conversions in the NH3-SCR and NH3 oxidation were measured. Physicochemical properties of the samples were characterized by means of a number of analytical techniques. It is shown that the NH3-SCR activity and hydrothermal stability of the CuSSZ-13 samples decreased with the rise in Si/Al ratio. Such decreases were attributed to the drop in the amount of the isolated Cu2+ in the D6R and CHA cage of the CuSSZ-13 samples. Part of the isolated Cu2+ ions were transformed to CuO after hydrothermal aging treatment, especially in the high-Si/Al-ratio samples. A large amount of the aggregated CuO destroyed the skeleton structure of SSZ-13, leading to the deactivation of the samples.Reaction steps of standard SCR on isolated Cu2+ ions of CuSSZ-13 catalyst.Download high-res image (103KB)Download full-size image

The Fe-modified sepiolite-supported Mn–Cu mixed oxide (CuxMny/Fe-Sep) catalysts were prepared using the co-precipitation method. These materials were characterized by means of the XRD, N2 adsorption–desorption, XPS, H2-TPR, and O2-TPD techniques, and their catalytic activities for CO and ethyl acetate oxidation were evaluated. The results show that catalytic activities of the CuxMny/Fe-Sep samples were higher than those of the Cu1/Fe-Sep and Mn2/Fe-Sep samples, and the Mn/Cu molar ratio had a distinct influence on catalytic activity of the sample. Among the CuxMny/Fe-Sep and Cu1Mn2/Sep samples, Cu1Mn2/Fe-Sep performed the best for CO and ethyl acetate oxidation, showing the highest reaction rate and the lowest T50 and T90 of 4.4 × 10− 6 mmol·g− 1·s− 1, 110, and 140 °C for CO oxidation, and 1.9 × 10− 6 mmol·g− 1·s− 1, 170, and 210 °C for ethyl acetate oxidation, respectively. Moreover, the Cu1Mn2/Fe-Sep sample possessed the best low-temperature reducibility and the lowest temperature of oxygen desorption as well as the highest surface Mn4 +/Mn3 + and Cu2 +/CuO atomic ratios. It is concluded that factors, such as the strong interaction between the Cu or Mn and the Fe-Sep support, good low-temperature reducibility, and good mobility of chemisorbed oxygen species, might account for the excellent catalytic activity of Cu1Mn2/Fe-Sep.CO conversion as a function of temperature over the as-prepared catalysts at SV = 60,000 ml·g− 1·h− 1.Download high-res image (168KB)Download full-size image

•3DOM LaMnAl11O19 is prepared using the polymethyl methacrylate-templating method.•Pd/3DOM LaMnAl11O19 is prepared via polyvinyl alcohol-protected reduction route.•0.97 wt% Pd/3DOM LaMnAl11O19 performs the best in methane combustion.•0.97 wt% Pd/3DOM LaMnAl11O19 is catalytically stable in methane combustion.•3DOM structure, Pd NPs, Oads, reducibility, and Pd–support interaction govern the activity.Three-dimensionally ordered macroporous (3DOM) LaMnAl11O19 and 0.97 wt% Pd/3DOM LaMnAl11O19 samples with a good-quality 3DOM structure have been prepared using the poly(methyl methacrylate) (PMMA)-templating and polyvinyl alcohol (PVA)-protected reduction methods, respectively. The Pd nanoparticles (NPs) with a size of 2–5 nm were uniformly dispersed on the macropore wall surface of 3DOM LaMnAl11O19. Due to the highest adsorbed oxygen species concentration and the best low-temperature reducibility, the 0.97 wt% Pd/3DOM LaMnAl11O19 sample showed the best catalytic activity for methane combustion, with the reaction temperatures (T10%, T50%, and T90%) required for achieving methane conversions of 10, 50, and 90% being 259, 308, and 343 °C at SV = 20,000 mL/(g h), respectively. The 0.97 wt% Pd/3DOM LaMnAl11O19 catalyst was catalytically stable, whereas the 0.98 wt% Pd/3DOM Mn2O3 sample was partially deactivated after 50 h of methane oxidation. The introduction of 3.0 vol% H2O or 2.0 vol% CO2 to the reaction system resulted in the reversible deactivation of 0.97 wt% Pd/3DOM LaMnAl11O19, but the addition of 100 ppm SO2 led to the irreversible deactivation of the catalyst. It is concluded that the good-quality 3DOM structure, uniformly dispersed Pd NPs, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Pd NPs and 3DOM LaMnAl11O19 were accountable for the good catalytic performance of 0.97 wt% Pd/3DOM LaMnAl11O19.Download full-size image

Ordered mesoporous Mn2O3 (meso-Mn2O3) and meso-Mn2O3-supported Pd, Pt, and Pd-Pt alloy x(PdyPt)/meso-Mn2O3; x = (0.10−1.50) wt%; Pd/Pt molar ratio (y) = 4.9−5.1 nanocatalysts were prepared using KIT-6-templated and poly(vinyl alcohol)-protected reduction methods, respectively. The meso-Mn2O3 had a high surface area, i.e., 106 m2/g, and a cubic crystal structure. Noble-metal nanoparticles (NPs) of size 2.1−2.8 nm were uniformly dispersed on the meso-Mn2O3 surfaces. Alloying Pd with Pt enhanced the catalytic activity in methane combustion; 1.41(Pd5.1Pt)/meso-Mn2O3 gave the best performance; T10%, T50%, and T90% (the temperatures required for achieving methane conversions of 10%, 50%, and 90%) were 265, 345, and 425 °C, respectively, at a space velocity of 20000 mL/(g·h). The effects of SO2, CO2, H2O, and NO on methane combustion over 1.41(Pd5.1Pt)/meso-Mn2O3 were also examined. We conclude that the good catalytic performance of 1.41(Pd5.1Pt)/meso-Mn2O3 is associated with its high-quality porous structure, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interactions between Pd-Pt alloy NPs and the meso-Mn2O3 support.Alloying Pd with Pt enhanced the catalytic performance in methane combustion. 1.41(Pd5.1Pt)/meso-Mn2O3 showed the highest activity because of its large surface area, high Oads concentration, good low-temperature reducibility, and strong Pd-Pt alloy and Mn2O3 interactions.Download high-res image (124KB)Download full-size image

•3D mesoporous PdxPt alloys are synthesized via a KIT-6-templating route.•The Pd2.41Pt sample performs the best in methane combustion.•PdO–PtO2 is the main active site for methane combustion.•Pd2.41Pt shows good thermal stability and good resistance to CO2 and H2O.•Methane can be more readily activated over the PdxPt alloys than over the Pd.Mesoporous cubic PdxPt (x = 0.43–8.52) alloys with surface areas of 26–32 m2/g were synthesized using the KIT-6-templating method. Physicochemical properties of the materials were characterized by means of various techniques, and their catalytic activities were evaluated for methane combustion. It is found that the Pd and Pt were uniformly distributed in the PdxPt alloys. The addition of Pt to Pd exerted a significant effect on the redox property of Pd. The PdxPt alloys possessed a higher methane activation ability than the monometallic Pd. The oxidized Pd–Pt (i.e., PdO–PtO2) were more active than the metallic Pd0–Pt0. The Pd2.41Pt sample performed the best for methane combustion (T10%, T50%, and T90% were 272, 303, and 322 °C at SV = 100,000 mL/(g h); TOFPd, TOFPt, TOFPd + Pt, and specific reaction rate at 280 °C were 0.85 × 10−3 s−1, 1.98 × 10−3 s−1, 0.59 × 10−3 s−1, and 4.46 μmol/(gcat s), respectively). The deactivation of the Pd2.41Pt sample induced by 2.5–5.0 vol% CO2 or H2O addition was reversible, but its deactivation due to 100 ppm SO2 introduction was irreversible. It is concluded that the excellent catalytic performance of the Pd2.41Pt sample was associated with its good mesoporous structure, Pd–Pt alloy and PdO–PtO2 coexistence, and good methane and oxygen activation ability.Mesoporous PdxPt (x = 0.43–8.52) alloys are synthesized via a KIT-6-templating route. The excellent catalytic performance of the Pd2.41Pt sample is associated with its mesoporous structure, Pd–Pt alloy and PdO–PtO2 coexistence, and good methane and oxygen activation ability.Download full-size image

•Ordered mesoporous Co3O4 (meso-Co3O4) is prepared via the KIT-6-templating route.•meso-CoO and meso-CoOx are fabricated from meso-Co3O4 via a reduction process.•meso-CoOx with the largest surface Co2+ amount performs best for o-xylene oxidation.•Surface Co2+ species are beneficial for oxygen activation.•Active oxygen species formed in the Co2+ sites are mainly O2− and/or O22−.Cobalt oxide is a typical transition metal oxide that exhibits high catalytic activity for the total oxidation of volatile organic compounds. In this study, a reduction process in a glycerol solution was adopted to generate mesoporous CoO (meso-CoO) or CoOx (meso-CoOx) from mesoporous Co3O4 (meso-Co3O4). The obtained samples were rich in Co2+ species and exhibited high catalytic activity for o-xylene oxidation. The meso-CoOx sample with the largest surface Co2+ amount performed the best: The o-xylene conversion at 240 °C was 83%, and the reaction rate over meso-CoOx was nine times higher than that over meso-Co3O4. It is found that the samples with more surface Co2+ species possessed better oxygen activation ability, and the Co2+ species were the active sites that favored the formation of highly active O2− and O22− (especially O2−) species.Download high-res image (128KB)Download full-size image

•3DOM BiVO4 is fabricated via the polymethyl methacrylate-templating route.•Fe2O3/3DOM BiVO4 is prepared by the incipient wetness impregnation method.•0.97Fe2O3/3DOM BiVO4 possesses the highest Oads density.•Fe2O3-3DOM BiVO4 heterojunction inhibits recombination of charge carriers.•0.97Fe2O3/3DOM BiVO4 shows excellent activity and stability for 4-NP degradation.The three-dimensionally ordered macroporous (3DOM) BiVO4 and its supported iron oxide (xFe2O3/3DOM BiVO4, x = 0.18, 0.97, and 3.40 wt%) photocatalysts were prepared using the ascorbic acid-assisted polymethyl methacrylate-templating and incipient wetness impregnation methods, respectively. Physicochemical properties of the materials were characterized by means of numerous analytical techniques, and their photocatalytic activities were evaluated for the degradation of 4-nitrophenol under visible light illumination. It is found that the BiVO4 possessed a high-quality 3DOM architecture with a monoclinic crystal phase, and the Fe2O3 was highly dispersed on the surface of 3DOM BiVO4. The xFe2O3/3DOM BiVO4 samples much outperformed the 3DOM BiVO4 sample, and 0.97Fe2O3/3DOM BiVO4 showed the best photocatalytic performance (98% 4-nitrophenol was degraded in the presence of 0.6 mL H2O2 within 30 min of visible light illumination) and excellent photocatalytic stability. The introduction of H2O2 to the reaction system could promote the photodegradation of 4-nitrophenol by providing the active OH species generated via the reaction of photoinduced electrons and H2O2. The pseudo-first-order reaction rate constants (0.0876–0.1295 min−1) obtained over xFe2O3/3DOM BiVO4 were much higher than those (0.0033–0.0395 min−1) obtained over 3DOM or Bulk BiVO4 and Fe2O3/Bulk BiVO4, with the 0.97Fe2O3/3DOM BiVO4 sample exhibiting the highest rate constant. The enhanced photocatalytic performance of 0.97Fe2O3/3DOM BiVO4 was associated with its unique porous architecture, high surface area, Fe2O3 − BiVO4 heterojunction, good light-harvesting ability, high adsorbed oxygen species concentration, and excellent separation efficiency of photogenerated electrons and holes as well as the photo-Fenton degradation process.0.97Fe2O3/3DOM BiVO4 exhibits excellent photocatalytic activity for 4-NP degradation, which is mainly associated with its unique porous structure, Fe2O3–BiVO4 heterojunction, and excellent separation efficiency of photoinduced electrons/holes as well as the photo-Fenton degradation process.Download high-res image (137KB)Download full-size image

The effects of the hydrothermal aging temperature on the catalytic performance and stability of CuSSZ-13 catalysts with various Cu/Al ratios were studied. The conversions of NO and NH3 were tested in the standard NH3-SCR reactions. The NH3-SCR activity of the catalysts decreased with the increasing hydrothermal aging temperature. Remarkably, the reduction was more significant as the Cu/Al ratio increased. The physicochemical properties of the samples were characterized by means of a number of analytical techniques. The results show that the hydrothermal stability of the CuSSZ-13 catalyst decreased with the increase in the hydrothermal aging temperature and Cu/Al ratio in the catalyst. Such a decrease was attributed to a drop in the number of isolated Cu2+ (in D6R and CHA cage). The transformation of the Cu2+ ions into new species (Cu2+ on Al2O3) depended on the collapse of the SSZ-13 structure after the hydrothermal aging treatment and was more likely to appear in the high Cu/Al-ratio samples and at a higher aging temperatures. The phase transformation of Cu2+ to agglomerated CuxO also occurred during the hydrothermal aging process. The formation of a large number of CuxO species might destroy the SSZ-13 structure, leading to deactivation of the catalyst.

Ordered meso/macroporous metal oxides have gained increasing attention in heterogeneous catalysis arising from their large surface areas and pore volumes, elevated catalytic activity and good thermal stability. Compared to nonporous metal oxides, their most prominent feature is the ability to interact with molecules not only at their exterior surface but also within the large interior surface of the material. The past decade has witnessed substantial advances in the synthesis of new porous metal oxides with ordered structures for use in a wide range of applications. By recalling some of the classical fundamentals of porous materials, this review examines the recent developments in ordered meso- and macro-porous metal oxide catalysts for heterogeneous catalysis. Additionally, we outline the current challenges in the field of nanoparticle-based catalysis, including the role played by the morphology (size, shape, and porosity) of ordered meso/macroporous metal oxides, and provide a perspective on the need for further advances in porous materials so that their contribution to heterogeneous catalysis can continue to expand.

The Pd catalyst supported on cryptomelane-type manganese oxide octahedral molecular sieve (OMS-2) were prepared. The effect of Pd loading on the catalytic oxidation of carbon monoxide, toluene, and ethyl acetate over xPd/OMS-2 has been investigated. The results show that the Pd loading plays an important role on the physicochemical properties of the xPd/OMS-2 catalysts which outperform the Pd-free counterpart with the 0.5Pd/OMS-2 catalyst being the best. The temperature for 50% conversion was 25, 240 and 160 °C, and the temperature for 90% conversion was 55, 285 and 200 °C for oxidation of CO, toluene, and ethyl acetate, respectively. The lowtemperature reducibility and high oxygen mobility of xPd/OMS-2 are the factors contributable to the excellent catalytic performance of 0.5Pd/OMS-2.

Bimetallic Au–Pd alloy nanoparticles (NPs) dispersed on nanohybrid three-dimensionally ordered macroporous (3DOM) La0.6Sr0.4MnO3 (LSMO) perovskite catalysts were fabricated via the l-lysine-mediated colloidal crystal-templating and reduction routes. The obtained AuPd/3DOM LSMO samples possess a nanovoid-like 3DOM construction with well-dispersed Au–Pd alloy NPs (2.05–2.35 nm in size) on the internal walls of the macropores. The Au–Pd alloy presence favored catalytic activity for methane combustion. The 3DOM LSMO support exhibits three key attributes: (i) a large surface area (32.0–33.8 m2/g) which aids high dispersion of the noble metal NPs on the support surface; (ii) abundant Brønsted acid sites which facilitate reactant adsorption and activation; and (iii) thermal stability. AuPd/3DOM LSMO has been synthesized with beneficial properties, including a richness of adsorbed oxygen species, increased oxidized noble metal species, low-temperature reducibility, and strong noble metal–3DOM LSMO interaction, all contributing to provide enhanced activity and a structure with high thermal and hydrothermal stability. In situ diffuse reflectance infrared Fourier transform spectroscopy studies revealed that including Au in the bimetallic system accelerated the reaction rate and altered the reaction pathway for methane oxidation by enriching the adsorbed oxygen species and decreasing the bonding strength between the reaction intermediates and the Pd atoms.Keywords: bimetallic gold−palladium catalyst; methane combustion; strontium-substituted lanthanum manganite; synergism; three-dimensionally ordered macroporous perovskite

•Ordered mesoporous Cr2O3 (meso-Cr2O3) is fabricated via the KIT-6-templating route.•xAu1Pd2/meso-Cr2O3 are prepared using the polyvinyl alcohol-protected reduction method.•The 1.95Au1Pd2/meso-Cr2O3 sample performs the best for toluene oxidation.•Oads concentration, low-temp. reducibility, and AuPd–Cr2O3 interaction govern the activity.Three-dimensionally ordered mesoporous Cr2O3 (meso-Cr2O3) and its supported Au, Pd, and Au–Pd (0.90 wt% Au/meso-Cr2O3, 1.00 wt% Pd/meso-Cr2O3, and xAu1Pd2/meso-Cr2O3 (x = 0.50–1.95 wt%) catalysts were prepared using the KIT-6-templating and polyvinyl alcohol-protected reduction methods, respectively. Physicochemical properties of the samples were characterized by means of numerous techniques, and their catalytic activities were evaluated for the oxidation of toluene. It is found that the meso-Cr2O3 with a high surface area of 74 m2/g was rhombohedral in crystal structure and the noble metal nanoparticles (NPs) with a size of 2.9–3.7 nm were uniformly dispersed on the surface of meso-Cr2O3. The 1.95Au1Pd2/meso-Cr2O3 sample performed the best: the T10%, T50%, and T90% (temperatures required for achieving toluene conversions of 10, 50, and 90%) were 87, 145, and 165 °C at a space velocity of 20,000 mL/(g h), respectively, and the apparent activation energy was the lowest (31 kJ/mol) among all of the samples. The effect of moisture on the catalytic activity of the 1.95Au1Pd2/meso-Cr2O3 sample was also examined. It is concluded that the excellent catalytic performance of 1.95Au1Pd2/meso-Cr2O3 was associated with its small Au–Pd particle size, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Au–Pd NPs and meso-Cr2O3.Three-dimensionally ordered mesoporous Cr2O3 (meso-Cr2O3) and its supported Au–Pd (xAu1Pd2/meso-Cr2O3) catalysts were prepared using the KIT-6-templating and PVA-protected reduction methods, respectively. The small noble metal particle size, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Au–Pd NPs and meso-Cr2O3 were responsible for the excellent catalytic performance of 1.95Au1Pd2/meso-Cr2O3.

•A Pd/Fe2O3/BiVO4 hybrid with optical structure, heterojunction, and plasmonic effect is fabricated.•Modification by amorphous Fe2O3 nanofilms and Pd nanoclusters improves the property of 3DOM BiVO4.•Novel nanoarchitecture shows superior ability to harvest light and generate efficient charge carriers.•Synergistic low-crystalline interface favors the improvement in phenol degradation and water splitting.Through effectively harvesting and converting solar energy, photocatalysis has become one of the most important technologies in wastewater decontamination and hydrogen production. Currently, extensive studies are being conducted to develop photocatalysts with advanced features, such as visible-light response, heterogeneous nanoarchitecture, plasmonic effect, and excellent optical behavior. Finding efficient utilization technique to improve photocatalytic performance motivates researchers all over the world. Herein, we demonstrate the design of a visible-light-driven Pd/Fe2O3/BiVO4 hybrid with 3D ordered macro-/mesoporous (3DOM) nanoarchitecture for efficiently photocatalytic organic degradation and photoelectrochemical (PEC) water splitting. The hybrid photocatalyst exhibited two-tier bandgap energies and possessed enhanced ability to harvest visible light and separate photo-induced carriers. It is shown that, over the Pd/Fe2O3/3DOM-BiVO4 photocatalyst, not only the refractory phenol could be rapidly degraded into CO2 and H2O, but also the photoconversion efficiency was greatly improved in water splitting to generate H2. The excellent photocatalytic performance of Pd/Fe2O3/BiVO4 was associated with the construction of low-crystalline plasmonic heterointerfaces through the 3DOM framework. The produced synergistic action enabled the hybrid material to absorb the sunlight adequately and transfer the photoexcited carriers expediently to drive phenol degradation or hydrogen evolution from water.Harmonizing virtues of periodically optical structure, heterojunction, and plasmonic effect, the Pd/Fe2O3/3DOM BiVO4 hybrid shows excellently visible-light photocatalytic performance for phenol degradation and water splitting.

•3DOM CeO2–Al2O3 with ordered mesopore walls is fabricated via the PMMA-templating route.•3DOM 26.9CeO2–Al2O3 displays a bimodal macro/mesoporous architecture.•3DOM 26.9CeO2–Al2O3 supported noble metal is prepared via the polymer-protective reduction.•0.27Pt/3DOM 26.9CeO2–Al2O3 performs the best in toluene oxidation.•Oads content, reducibility, and noble metal—support interaction govern the catalytic activity.Three-dimensionally ordered macro-/mesoporous 26.9 wt% CeO2–Al2O3 (denoted as 3DOM 26.9CeO2–Al2O3)-supported noble metal nanocatalysts (xM/3DOM 26.9CeO2–Al2O3, x = 0.27–0.81 wt%; M = Au, Ag, Pd, and Pt) were prepared using the polymethyl methacrylate-templating and polyvinyl pyrrolidone- or polyvinyl alcohol-protected reduction methods, respectively. It is shown that the xM/3DOM 26.9CeO2–Al2O3 samples displayed a high-quality 3DOM architecture with a bimodal pore (macropore size = 180–200 nm and mesopore size = 4–6 nm) structure and a surface area of 102–108 m2/g, with the noble metal nanoparticles (3–4 nm in size) being highly dispersed on the 3DOM 26.9CeO2–Al2O3 surface. The 0.27Pt/3DOM 26.9CeO2–Al2O3 sample performed the best (T90% = 198 °C at space velocity = 20,000 mL/(g h)) for toluene oxidation. The addition of moisture to the feedstock induced a positive effect on catalytic activity. The apparent activation energies obtained over the xM/3DOM 26.9CeO2–Al2O3 samples were in the range of 46–100 kJ/mol, with the 0.27Pt/3DOM 26.9CeO2–Al2O3 sample possessing the lowest apparent activation energy. It is concluded that the good catalytic performance of 0.27Pt/3DOM 26.9CeO2–Al2O3 was associated with its higher adsorbed oxygen species concentration, better low-temperature reducibility, and stronger interaction between Pt and 3DOM 26.9CeO2–Al2O3 as well as the unique bimodal porous structure.

Three-dimensionally ordered macro/mesoporous Ce0.6Zr0.3Y0.1O2 (3DOM CZY) supported high-dispersion Pt nanoparticles (x wt % Pt/3DOM CZY, x = 0.6, 1.1, and 1.7) were successfully synthesized via the cetyltrimethylammonium bromide/triblock copolymer P123 assisted gas bubbling reduction route. The 3DOM CZY and x wt % Pt/3DOM CZY samples exhibited a high surface area of 84–94 m2/g. Pt nanoparticles (NPs) with a size of 2.6–4.2 nm were uniformly dispersed on the surface of 3DOM CZY. The 1.1 wt % Pt/3DOM CZY sample showed excellent catalytic performance, giving a T90% value at 598 °C at gas hourly space velocity (GHSV) of 30000 mL/(g h) and the highest turnover frequency (TOFPt) of 6.98 × 10–3 mol/(molPt s) at 400 °C for methane combustion. The apparent activation energy (64 kJ/mol) over 1.1 wt % Pt/3DOM CZY was much lower than that (95 kJ/mol) over Bulk CZY. The effects of water vapor and SO2 on the catalytic activity of 1.1 wt % Pt/3DOM CZY were also examined. It is concluded that the excellent catalytic activity of 1.1 wt % Pt/3DOM CZY was associated with its high oxygen adspecies concentration, good low-temperature reducibility, and strong interaction between Pt NPs and CZY as well as large surface area and unique nanovoid-walled 3DOM structure.Keywords: ceria-zirconia-yttria solid solution; mesoporous wall; methane combustion; supported Pt nanoparticle; three-dimensionally ordered macropore

The Ce0.6Zr0.3Y0.1O2 (CZY) nanorods and their supported gold and palladium alloy (zAuxPdy/CZY; z = 0.80–0.93 wt%; x or y = 0, 1, 2) nanoparticles (NPs) were prepared using the cetyltrimethyl ammonium bromide-assisted hydrothermal and polyvinyl alcohol-protected reduction methods, respectively. Physicochemical properties of the samples were characterized by means of numerous analytical techniques, and their catalytic activities were evaluated for the oxidation of toluene. It is shown that the CZY in zAuxPdy/CZY was cubic in crystal structure, surface areas of CZY and zAuxPdy/CZY were in the range 68–77 m2 g−1, and the Au–Pd NPs with a size of 4.6–5.6 nm were highly dispersed on the surface of CZY nanorods. Among all the samples, 0.90Au1Pd2/CZY possessed the highest adsorbed oxygen concentration and the best low-temperature reducibility, and performed the best: T50% and T90% (temperatures required for achieving toluene conversions of 50 and 90%) were 190 and 218 °C at a space velocity of 20000 mL (g h)−1, respectively. The partial deactivation due to water vapor introduction was reversible. The active sites might be the surface oxygen vacancies on CZY, oxidized noble metal NPs, and/or interfaces between noble metal NPs and CZY. The apparent activation energies (37–43 kJ mol−1) obtained over 0.90–0.93AuxPdy/CZY were much lower than that (88 kJ mol−1) obtained over CZY for toluene oxidation. It is concluded that the excellent catalytic performance of 0.90Au1Pd2/CZY was associated with its high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Au–Pd NPs and CZY nanorods as well as good dispersion of Au–Pd NPs.

Using a mixture of NaNO3 and NaF as molten salt and MnSO4 and AgNO3 as metal precursors, 0.13 wt % Ag/Mn2O3 nanowires (0.13Ag/Mn2O3-ms) were fabricated after calcination at 420 °C for 2 h. Compared to the counterparts derived via the impregnation and poly(vinyl alcohol)-protected reduction routes as well as the bulk Mn2O3-supported silver catalyst, 0.13Ag/Mn2O3-ms exhibited a much higher catalytic activity for toluene oxidation. At a toluene/oxygen molar ratio of 1/400 and a space velocity of 40 000 mL/(g h), toluene could be completely oxidized into CO2 and H2O at 220 °C over the 0.13Ag/Mn2O3-ms catalyst. Furthermore, the toluene consumption rate per gram of noble metal over 0.13Ag/Mn2O3-ms was dozens of times as high as that over the supported Au or AuPd alloy catalysts reported in our previous works. It is concluded that the excellent catalytic activity of 0.13Ag/Mn2O3-ms was associated with its high dispersion of silver nanoparticles on the surface of Mn2O3 nanowires and good low-temperature reducibility. Due to high efficiency, good stability, low cost, and convenient preparation, 0.13Ag/Mn2O3-ms is a promising catalyst for the practical removal of volatile organic compounds.

Nitrogen-doped TiO2-bronze@g-C3N4 (TiO2 (B)@g-C3N4) two-dimensional binary heterojunctions were constructed based on seeding-induced growth through a microwave-assisted solvothermal process and subsequent thermal treatment in a vacuum. The morphology of the TiO2 (B) nanosheets could be controlled by tuning the concentration of the Ti precursor, which determined the enhanced photoelectron activity. The optimal photocatalytic activity for the degradation of methyl orange (MO) under low-intensity visible-light illumination was obtained at a TiO2 (B)/g-C3N4 molar ratio of 1:1, which was 12.7 and 7.9 times higher than that of pure g-C3N4 and P25, respectively. The photocatalytic activity was further enhanced by about 7.7% after in situ N-doping. The improvement in photocatalytic activity of N-doped TiO2 (B)@g-C3N4 hetero-nanojunctions was attributable to the strong absorption in the visible-light region and better separation of photogenerated electron–hole pairs at the nanojunction interface, a result due to the large contact area between N-doped TiO2 (B) and g-C3N4 nanosheets. We have explained the photocatalytic degradation of MO molecules largely in terms of the direct oxidation by the photogenerated holes and partly by the contribution of the superoxide radicals.

In the present study, nanodisk-like Fe2O3 was first prepared using the hydrothermal method, and then its supported gold catalysts (xAu/Fe2O3 nanodisk, x = 0.71–6.55 wt %) were fabricated using the polyvinyl alcohol-protected reduction method. Under the reaction conditions of toluene concentration = 1000 ppm, toluene/O2 molar ratio = 1/400, and space velocity = 20 000 mL/(g h), 6.55Au/Fe2O3 nanodisk performed the best (T50% = 200 °C and T90% = 260 °C). The apparent activation energies (46–50 kJ/mol) obtained over the xAu/Fe2O3 nanodisk were smaller than that (65 kJ/mol) obtained over the Fe2O3 nanodisk for toluene oxidation. We conclude that the high oxygen adspecies concentration, good low-temperature reducibility, and strong interaction between Au nanoparticles and the Fe2O3 nanodisk are responsible for the high catalytic performance of the 6.55Au/Fe2O3 nanodisk.

The Ce0.6Zr0.3Y0.1O2 (CZY) nanorods and its supported nanosized gold (xAu/CZY, Au loading (x) = 0.4–4.7 wt %) were prepared using the cetyltrimethylammonium bromide-assisted hydrothermal and polyvinylpyrrolidone-protected reduction methods, respectively. Physicochemical properties of the samples were characterized by means of numerous analytical techniques, and their catalytic activities were evaluated for the oxidation of CO and toluene. It is shown that the CZY in xAu/CZY was cubic in crystal structure, surface areas of CZY and xAu/CZY were in the range of 68–79 m2/g, and the Au nanoparticles (NPs) with a size of 3.1–3.9 nm were well dispersed on the surface of CZY nanorods. Among the xAu/CZY samples, the 4.7Au/CZY sample possessed the highest adsorbed oxygen concentration and the best low-temperature reducibility, and showed the highest catalytic activity at a space velocity of 20 000 mL/(g h): the T50% and T90% (temperatures required for achieving reactant conversions of 50 and 90%) were 32 and 60 °C for CO oxidation and 218 and 265 °C for toluene oxidation, respectively. Deactivation of water vapor addition was reversible, a result due to the competitive adsorption of H2O and toluene as well as oxygen on the sample surface. The apparent activation energies (27–37 and 39–53 kJ/mol) obtained over xAu/CZY were lower than those (42 and 88 kJ/mol) obtained over CZY for CO and toluene oxidation, respectively. On the basis of the characterization results and activity data, we conclude that the excellent catalytic performance of 4.7Au/CZY was associated with its higher oxygen adspecies concentration, better low-temperature reducibility, and stronger interaction between Au NPs and CZY nanorods as well as better Au NPs dispersion.

Three-dimensionally macroporous perovskite-type oxides EuFeO3 (EFO-3DOM, EFO-sucrose-1, EFO-sucrose-2, and EFO-sucrose-3, respectively) have been prepared using the polymethyl methacrylate-templating method in the absence or presence of sucrose. Physicochemical properties of the materials were characterized by means of a number of analytical techniques, and their catalytic activities were evaluated for the total oxidation of toluene. It is shown that all of the EFO samples were of single-phase orthorhombic crystal structure with a 3DOM architecture. The sucrose addition during the preparation process had a great effect on the surface area and porous structure of the final product. A clear correlation of surface area, surface oxygen species concentration, and low-temperature reducibility with the catalytic performance was observed. The EFO-sucrose-1 catalyst performed the best, giving the T50% and T90% of 312 and 347 °C at space velocity = 20,000 mL/(g h), respectively. The apparent activation energies of the 3DOM-structured EFO samples were in the range of 82–97 kJ/mol. It is concluded that the higher surface area and oxygen adspecies concentration and better low-temperature reducibility account for the good catalytic activity of EFO-sucrose-1.

High-surface-area and well-ordered mesoporous Fe-incorporated SBA-15 (xFe-SBA-15) and SBA-15-supported FeOx (yFeOx/SBA-15) with the Fe surface density between 0.09 to 1.11 Fe-atom/nm2 have been prepared using the one-step synthesis and incipient wetness impregnation methods, respectively. Physicochemical properties of these materials were characterized by means of numerous techniques, and their catalytic activities for the combustion of toluene were evaluated. It is found that the xFe-SBA-15 and yFeOx/SBA-15 samples possessed rod- or chain-like morphologies. The Fe species were of high dispersion when the Fe surface density was lower than 0.76 Fe-atom/nm2 in xFe-SBA-15 and 0.64 Fe-atom/nm2 in yFeOx/SBA-15. At a similar Fe surface density and space velocity, the xFe-SBA-15 catalysts showed better activity than the yFeOx/SBA-15 catalysts, in which the xFe-SBA-15 catalyst with Fe surface density 0.59 Fe-atom/nm2 performed the best. It is concluded that the good performance of the xFe-SBA-15 sample with Fe surface density 0.59 Fe-atom/nm2 was associated with its large surface area, high Fe species dispersion, and good low-temperature reducibility.

A series of Ag nanoparticles (NPs) supported on three-dimensionally ordered macroporous (3DOM) La0.6Sr0.4MnO3 (yAg/3DOM La0.6Sr0.4MnO3; y = 0, 1.57, 3.63, and 5.71 wt %) were successfully prepared with high surface areas (38.2–42.7 m2/g) by a facile novel reduction method using poly methacrylate colloidal crystal as template in a dimethoxytetraethylene glycol (DMOTEG) solution. Physicochemical properties of these materials were characterized by means of numerous techniques, and their catalytic activities were evaluated for the combustion of methane. It is shown that the yAg/3DOM La0.6Sr0.4MnO3 materials possessed unique nanovoid-like 3DOM architectures, and the Ag NPs were well dispersed on the inner walls of macropores. Among the La1–xSrxMnO3 (x = 0.2, 0.4, 0.6, 0.8) and yAg/3DOM La0.6Sr0.4MnO3 (y = 0, 1.57, 3.63, and 5.71 wt %) samples, 3.63 wt % Ag/3DOM La0.6Sr0.4MnO3 performed the best, giving T10%, T50%, and T90% (temperatures corresponding to methane conversion =10, 50, and 90%) of 361, 454, and 524 °C, respectively, and the highest turnover frequency (TOFAg) value of 1.86 × 10–5 (mol/molAg s) at 300 °C. The apparent activation energies (39.1–37.5 kJ/mol) of the yAg/3DOM La0.6Sr0.4MnO3 samples were much lower than that (91.4 kJ/mol) of the bulk La0.6Sr0.4MnO3 sample. The effects of water vapor and sulfur dioxide on the catalytic activity of the 3.63 wt % Ag/3DOM La0.6Sr0.4MnO3 sample were also examined. It is concluded that its super catalytic activity was associated with its high oxygen adspecies concentration, good low-temperature reducibility, large surface area, and strong interaction between Ag and La0.6Sr0.4MnO3 as well as the unique nanovoid-walled 3DOM structure.

Three-dimensionally ordered macroporous Co3O4 (3DOM Co3O4) and its supported gold (xAu/3DOM Co3O4, x = 1.1–8.4 wt%) nanocatalysts were prepared using the polymethyl methacrylate-templating and bubble-assisted polyvinyl alcohol-protected reduction methods, respectively. The 3DOM Co3O4 and xAu/3DOM Co3O4 samples exhibited a surface area of 22–27 m2 g−1. The Au nanoparticles with a size of 2.4–3.7 nm were uniformly deposited on the macropore walls of 3DOM Co3O4. There were good correlations of oxygen adspecies concentration and low-temperature reducibility with catalytic activity of the sample for CO and toluene oxidation. Among 3DOM Co3O4 and xAu/3DOM Co3O4, the 6.5Au/3DOM Co3O4 sample performed the best, giving a T90% (the temperature required for achieving a conversion of 90%) of −35 °C at a space velocity of 20000 mL g−1 h−1 for CO oxidation and 256 °C at a space velocity of 40000 mL g−1 h−1 for toluene oxidation. The effect of water vapor was more significant in toluene oxidation than in CO oxidation. The apparent activation energies (26 and 74 kJ mol−1) over 6.5Au/3DOM Co3O4 were lower than those (34 and 113 kJ mol−1) over 3DOM Co3O4 for CO and toluene oxidation, respectively. It is concluded that the higher oxygen adspecies concentration, better low-temperature reducibility, and strong interaction between Au and 3DOM Co3O4 were responsible for the excellent catalytic performance of 6.5Au/3DOM Co3O4.

α-Fe2O3 nanowires deposited diatomite was prepared using a precipitation–deposition method with FeCl3 as metal source and (NH2)2CO aqueous solution as precipitating agent. Physicochemical properties of the samples were characterized by means of numerous techniques, and their efficiency for the removal of As(III) and As(V) was determined. It is found that the solution pH value, reaction temperature, reaction time, and FeCl3 concentration had effects on the α-Fe2O3 amount loaded on the diatomite. Parameters, such as adsorbent amount, adsorption time, adsorption temperature, pH value, and initial As(III) or As(V) concentration, could influence the As(III) or As(V) removal efficiency of the α-Fe2O3 nanowires/diatomite sample (prepared with a 8 wt% FeCl3 aqueous solution at pH = 4.5 and 50 °C for 35 h) for the removal of As(III) and As(V). Over the α-Fe2O3/diatomite sample at pH = 3.5, the maximal As(III) and As(V) adsorption capacities were 60.6 and 81.2 mg g−1, and the maximal As(III) and As(V) removal efficiency was 99.98 and 100%, respectively. The Langmuir model was more suitable for the adsorption of As(V), whereas the Freundlich model was more suitable for the adsorption of As(III). The adsorption mechanism of the sample was also discussed.

Highly dispersed Ag nanoparticles supported on high-surface-area 3DOM La0.6Sr0.4MnO3 were successfully generated via the dimethoxytetraethylene glycol-assisted gas bubbling reduction route. The macroporous materials showed super catalytic performance for methane combustion.

Uniform hollow spherical rhombohedral LaMO3 and solid spherical cubic MOx (M = Mn and Co) NPs were fabricated using the PMMA-templating strategy. Hollow spherical LaMO3 and solid spherical MOx NPs possessed surface areas of 21–33 and 21–24 m2/g, respectively. There were larger amounts of surface-adsorbed oxygen species and better low-temperature reducibility on/of the hollow spherical LaMO3 samples than on/of the solid spherical MOx samples. Hollow spherical LaMO3 and solid spherical MOx samples outperformed their nanosized counterparts for oxidation of CO and toluene, with the best catalytic activity being achieved over the solid spherical Co3O4 sample for CO oxidation (T50% = 81 °C and T90% = 109 °C) at space velocity = 10 000 mL/(g h) and the hollow spherical LaCoO3 sample for toluene oxidation (T50% = 220 °C and T90% = 237 °C) at space velocity = 20 000 mL/(g h). It is concluded that the higher surface areas and oxygen adspecies concentrations and better low-temperature reducibility are responsible for the excellent catalytic performance of the hollow spherical LaCoO3 and solid spherical Co3O4 NPs. We believe that the PMMA-templating strategy provides an effective route to prepare uniform perovskite-type oxide and transition-metal oxide NPs.

Three-dimensionally (3D) ordered mesoporous β-MnO2-supported Au nanocatalysts (Au/β-MnO2(urea), Au/β-MnO2(NaOH), and Au/β  -MnO2(Na2CO3)MnO2(Na2CO3)) with an Au loading of 5 wt.% were prepared by the deposition–precipitation method using urea, NaOH and Na2CO3 as precipitating agent, respectively. The physicochemical properties of the materials were characterized by means of numerous analytical techniques, and their catalytic activities were evaluated for the complete oxidation of CO, benzene, and toluene. It is shown that the nature of precipitating agent had an important influence on the physicochemical properties of the β-MnO2 support, Au nanoparticles, and Au/β-MnO2 catalysts. Among the three Au/β-MnO2 samples, the Au/β-MnO2(NaOH) showed the highest surface atomic ratios of Mn3+/Mn4+, Oads/Olatt, and Au3+/Au0. The loading of gold could greatly modify the reducibility of Au/β-MnO2 via the strong interaction between the gold and the β-MnO2 support, and the Au/β-MnO2(NaOH) sample possessed the best low-temperature reducibility. Gold loading resulted in a significant enhancement in catalytic activity of β-MnO2. The three Au/β-MnO2 catalysts outperformed the Au-free β-MnO2 catalyst, among which the Au/β-MnO2(NaOH) one showed the best catalytic activity (T50% and T100% = 48 and 70 °C for CO oxidation, 200 and 250 °C for benzene oxidation, and 170 and 220 °C for toluene oxidation, respectively). It is concluded that factors, such as the better gold dispersion, higher surface Au3+ and oxygen adspecies concentrations, better low-temperature reducibility, stronger synergistic action between the gold and the support as well as the high-quality 3D ordered mesoporous structure of the support, might be responsible for the excellent catalytic performance of Au/β-MnO2(NaOH).Graphical abstractHighlights► 3D ordered mesoporous β-MnO2 with a high surface area is prepared via the KIT-6-templating route. ► 5 wt.% Au/β-MnO2 catalysts are prepared via the deposition–precipitation route. ► The nature of precipitant has an important impact on the physicochemical property of the product. ► Gold loading results in a significant enhancement in catalytic activity of β-MnO2. ► Au dispersion, Au3+ and Oads contents, reducibility, and porosity govern catalytic activity.

Porous LaFeO3 (LFO) samples with surface areas of 15–26 m2/g and orthorhombic structures were prepared via a glucose-assisted hydrothermal route. Physicochemical properties of the materials were characterized by means of a number of techniques, and their catalytic activities were evaluated for toluene combustion. It is found that the sample (LFO-170) derived at a hydrothermal temperature of 170 °C possessed the highest surface area and surface oxygen concentration and the best low-temperature reducibility. Among the LFO samples, the LFO-170 sample showed the best performance for toluene combustion, giving the T10%, T50%, and T90% of 180, 250, and 270 °C at space velocity=20,000 mL/(g h), respectively. The apparent activation energies of the LFO samples were 50–55 kJ/mol. We believe that the high surface area and surface oxygen concentration and good low-temperature reducibility were responsible for the good catalytic performance of the LFO-170 sample.Graphical abstractPorous LaFeO3 is prepared by the glucose-assisted hydrothermal method. The good catalytic performance of porous LaFeO3 for toluene combustion is ascribed to high surface area and Oads concentration and good reducibility.Highlights► 3D porous LaFeO3 is prepared by the glucose-assisted hydrothermal method. ► A suitable hydrothermal temperature is needed for 3D porous LaFeO3 formation. ► 3D porous LaFeO3 is high in surface area and Oads content and good in reducibility. ► 3D porous LaFeO3 performs well in the combustion of toluene. ► Catalytic activity is governed by surface area, Oads concentration, and reducibility.

Fluoride-doped BiVO4 with the F/Bi molar ratios of 0, 0.09, 0.13, and 0.29 (denoted as BiVO4–F0, BiVO4–F0.09, BiVO4–F0.13, and BiVO4–F0.29, respectively) were synthesized using the hydrothermal strategy with the hydrothermally derived BiVO4 as the precursor and NH4F as the fluoride source. Physicochemical properties of the materials were characterized by means of a number of analytical techniques. Photocatalytic activities of the fluoride-doped BiVO4 samples were evaluated for the degradation of phenol under visible-light irradiation. It is shown that compared to the undoped BiVO4–F0 sample, the fluoride-doped BiVO4 samples retained the monoclinic structure, but possessed higher surface areas and oxygen adspecies concentration, better light-absorbing performance, and lower bandgap energies. Among the four samples, the porous spherical BiVO4–F0.29 sample exhibited the best photocatalytic activity for the degradation of phenol in the presence of a small amount of H2O2 under visible-light illumination. It is concluded that the higher surface area and oxygen adspecies concentration, stronger optical absorbance performance, and lower bandgap energy were responsible for the excellent photocatalytic performance of BiVO4–F0.29 for the photocatalytic degradation of phenol.Graphical abstractHighlights► F-doped monoclinic BiVO4 with porous structures are obtained hydrothermally. ► The BiVO4–F0.29 sample possesses the highest Oads concentration. ► The BiVO4–F0.29 sample possesses the lowest bandgap energy. ► The BiVO4–F0.29 sample performs the best for phenol photodegradation. ► Surface area, Oads concentration, and bandgap energy govern photocatalytic activity.

Three-dimensionally ordered macroporous (3DOM) monoclinic InVO4 and its supported chromia (yCrOx/3DOM InVO4, y denotes as the weight percentage of Cr2O3, y = 5, 10, 15, and 20 wt%) photocatalysts were fabricated using the ascorbic acid-assisted polymethyl methacrylate-templating and incipient wetness impregnation methods, respectively. Physicochemical properties of the materials were characterized by means of a number of analytical techniques. Photocatalytic activities of the samples were evaluated for the degradation of rhodamine B (RhB) in the presence of H2O2 under visible-light illumination. Compared to 3DOM InVO4 and 15CrOx/bulk InVO4, yCrOx/3DOM InVO4 showed much better visible-light-driven photocatalytic performance for RhB degradation, with the 15CrOx/3DOM InVO4 sample performing the best. It is concluded that the CrOx loading, higher surface area and surface oxygen vacancy density and lower bandgap energy as well as the better quality of 3DOM structure were responsible for the good photocatalytic performance of 15CrOx/3DOM InVO4 for the degradation of RhB.

Porous S-doped bismuth vanadate with an olive-like morphology and its supported cobalt oxide (y wt% CoOx/BiVO4−δS0.08, y = 0.1, 0.8, and 1.6) photocatalysts were fabricated using the dodecylamine-assisted alcohol-hydrothermal and incipient wetness impregnation methods, respectively. It is shown that the y wt% CoOx/BiVO4−δS0.08 photocatalysts were single-phase with a monoclinic scheetlite structure, a porous olive-like morphology, a surface area of 8.8–9.2 m2/g, and a bandgap energy of 2.38–2.41 eV. There was the co-presence of surface Bi5+, Bi3+, V5+, V3+, Co3+, and Co2+ species in y wt% CoOx/BiVO4−δS0.08. The 0.8 wt% CoOx/BiVO4−δS0.08 sample performed the best for methylene blue degradation under visible-light illumination. The photocatalytic mechanism was also discussed. We believe that the sulfur and CoOx co-doping, higher oxygen adspecies concentration, and lower bandgap energy were responsible for the excellent visible-light-driven catalytic activity of 0.8 wt% CoOx/BiVO4−δS0.08.Graphical abstractThe good photocatalytic performance of 0.8 wt% CoOx/BiVO4−δS0.08 for methylene blue degradation is ascribed to the S- and CoOx-doping, high Oads content, and low bandgap energy.Highlights► Porous S-doped BiVO4-supported CoOx are prepared by the impregnation method. ► 0.8 wt% CoOx/BiVO4−δS0.08 possesses the highest surface oxygen species concentration. ► 0.8 wt% CoOx/BiVO4−δS0.08 possesses the lower bandgap energy. ► 0.8 wt% CoOx/BiVO4−δS0.08 performs the best for methylene blue photodegradation. ► S- and CoOx-doping, Oads content, and bandgap energy govern photocatalytic activity.

Three-dimensionally ordered macroporous (3DOM) La0.6Sr0.4Fe0.8Bi0.2O3−δ (LSFB) were prepared using the surfactant (Pluronic F127, poly(ethylene glycol), l-lysine or xylitol)-assisted polymethyl methacrylate-templating method. Physicochemical properties of the materials were characterized by means of a number of analytical techniques, and their catalytic activities were evaluated for the combustion of toluene. It is shown that the LSFB samples were of 3DOM-architectured single-phase orthorhombic crystal structure. The nature of surfactant and solvent could influence the pore structures and surface areas of the LSFB samples. The Fe4+/Fe3+ or Oads/Olatt molar ratio and low-temperature reducibility correlated with the catalytic performance of the LSFB sample. The porous LSFB samples much outperformed the bulk counterpart, with the LSFB sample derived with xylitol showing the best catalytic activity (the temperatures required for 50 and 90% toluene conversions were 220 and 242 °C at 20,000 mL/(g h), respectively). Apparent activation energies of the porous LSFB samples were in the range of 46–74 kJ/mol. It is concluded that the high oxygen adspecies concentration and good low-temperature reducibility were responsible for the excellent catalytic activity of the porous LSFB sample derived with xylitol.Graphical abstractHighlights► 3DOM La0.6Sr0.4Fe0.8Bi0.2O3−δ are prepared by the surfactant-assisted PMMA-templating method. ► The nature of surfactant and solvent influences the pore structure of La0.6Sr0.4Fe0.8Bi0.2O3−δ. ► Porous La0.6Sr0.4Fe0.8Bi0.2O3−δ outperforms the bulk counterpart for toluene combustion. ► Catalytic activity is governed by the Oads concentration and low-temperature reducibility.

Nanosized rod-like, wire-like, and tubular α-MnO2 and flower-like spherical Mn2O3 have been prepared via the hydrothermal method and the CCl4 solution method, respectively. The physicochemical properties of the materials were characterized using numerous analytical techniques. The catalytic activities of the catalysts were evaluated for toluene oxidation. It is shown that α-MnO2 nanorods, nanowires, and nanotubes with a surface area of 45–83 m2/g were tetragonal in crystal structure, whereas flower-like spherical Mn2O3 with a surface area of 162 m2/g was of cubic crystal structure. There were the presence of surface Mn ions in multiple oxidation states (e.g., Mn3+, Mn4+, or even Mn2+) and the formation of surface oxygen vacancies. The oxygen adspecies concentration and low-temperature reducibility decreased in the order of rod-like α-MnO2 > tube-like α-MnO2 > flower-like Mn2O3 > wire-like α-MnO2, in good agreement with the sequence of the catalytic performance of these samples. The best-performing rod-like α-MnO2 catalyst could effectively catalyze the total oxidation of toluene at lower temperatures (T50% = 210 °C and T90% = 225 °C at space velocity = 20 000 mL/(g h)). It is concluded that the excellent catalytic performance of α-MnO2 nanorods might be associated with the high oxygen adspecies concentration and good low-temperature reducibility. We are sure that such one-dimensional well-defined morphological manganese oxides are promising materials for the catalytic elimination of air pollutants.

Three-dimensionally (3D) ordered macroporous (3DOM) La0.6Sr0.4FeO3-δ (LSF-F127, LSF–PEG, LSF–PEG–EtOH, and LSF–Lysine) with mesoporous or nanovoid-like skeletons were prepared using the surfactant (Pluronic F127, poly(ethylene glycol) (PEG) or l–lysine)-assisted polymethyl methacrylate (PMMA)-templating method in aqueous or 40% ethanol aqueous solution. It is shown that the LSF samples displayed a 3DOM architecture and were of a single-phase orthorhombic crystal structure. The nature of surfactant and solvent could influence the pore structure and surface area of the final product. Treating the LSF precursor first in N2 at 500 °C and then in air at 750 °C favored the formation of 3DOM-structured La0.6Sr0.4FeO3−δ. The porous LSF catalysts performed well in toluene combustion, with LSF–PEG showing the best catalytic performance (T10% = 54 °C, T50% = 225 °C and T90% = 280 °C at 20,000 mL/(g h)). It is concluded that the excellent catalytic performance of 3DOM-structured LSF is associated with their larger surface areas, higher oxygen adspecies concentrations, better low-temperature reducibility, and high-quality 3DOM structures.Graphical abstract3DOM-structured La0.6Sr0.4FeO3−δ (LSF-F127, LSF–PEG, LSF–PEG–EtOH, and LSF–Lysine) were prepared using the surfactant (F127, PEG or l–lysine)-assisted PMMA-templating method in aqueous or 40% ethanol aqueous solution. The excellent catalytic performance of 3DOM LSF for toluene combustion is related to the large surface area, high oxygen adspecies concentration, and good low-temperature reducibility as well as the high-quality 3DOM structure.Highlights► 3DOM La0.6Sr0.4FeO3−δ are prepared by the surfactant-aided PMMA-templating method. ► Surfactant addition favors the formation of mesoporous or nanovoid-like skeletons. ► 3DOM La0.6Sr0.4FeO3−δ are high in Oads content and good in low-temp. reducibility. ► 3DOM La0.6Sr0.4FeO3−δ catalysts perform well in the combustion of toluene. ► Surface area, Oads content, and reducibility account for the good catalytic activity.

Diatomite materials coated with antimony-doped tin oxide (ATO) were prepared by the co-precipitation method, and characterized by means of the techniques, such as X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, selected-area electron diffraction, X-ray fluorescence spectroscopy, and N2 adsorption–desorption measurement. It was shown that the coated ATO possessed a tetragonal rutile crystal structure, and the ATO-coated diatomite materials had a multi-pore (micro- meso-, and macropores) architecture. The porous ATO-coated diatomite materials exhibited excellent electrical conductive behaviors. The best conductive performance (volume resistivity = 10 Ω cm) was achieved for the sample that was prepared under the conditions of Sn/Sb molar ratio = 5.2, Sn/Sb coating amount = 45 wt%, pH = 1.0, and reaction temperature = 50 °C. Such a conductive porous material is useful for the applications in physical and chemical fields.Graphical abstractAntimony-doped tin oxide (ATO)-coated diatomite with porous structures are fabricated using the co-precipitation method. The porous ATO-coated diatomite material shows excellent conductive performance.Highlights► Sb-doped SnO2 (ATO)-coated diatomite materials with porous structures are prepared. ► Sn/Sb ratio, ATO coating amount, pH value, and temperature influence resistivity. ► Porous ATO-coated diatomite materials show excellent conductive performance. ► The lowest resistivity of the porous ATO-coated diatomite sample is 10 Ω cm.

Three-dimensionally (3D) ordered macroporous (3DOM) iron oxides with nanovoids in the rhombohedrally crystallized macroporous walls were fabricated by adopting the dual-templating [Pluronic P123 and poly(methyl methacrylate) (PMMA) colloidal microspheres] strategy with ferric nitrate as the metal precursor in an ethanol or ethylene glycol and methanol mixed solution and after calcination at 550 °C. The possible formation mechanisms of such architectured materials were discussed. The physicochemical properties of the materials were characterized by means of techniques such as XRD, TGA/DSC, FT-IR, BET, HRSEM, HRTEM/SAED, UV−vis, XPS, and H2-TPR. The catalytic properties of the materials were also examined using toluene oxidation as a probe reaction. It is shown that 3DOM-structured α-Fe2O3 without nanovoids in the macroporous walls was formed in the absence of P123 during the fabrication process, whereas the dual-templating strategy gave rise to α-Fe2O3 materials that possessed high-quality 3DOM structures with the presence of nanovoids in the polycrystalline macropore walls and higher surface areas (32−46 m2/g). The surfactant P123 played a key role in the generation of nanovoids within the walls of the 3DOM-architectured iron oxides. There was the presence of multivalent iron ions and adsorbed oxygen species on the surface of each sample, with the trivalent iron ion and oxygen adspecies concentrations being different from sample to sample. The dual-templating fabricated iron oxide samples exhibited much better low-temperature reducibility than the bulk counterpart. The copresence of a 3DOM-structured skeleton and nanovoids in the macropore walls gave rise to a drop in the band-gap energy of iron oxide. The higher oxygen adspecies amounts, larger surface areas, better low-temperature reducibility, and unique nanovoid-containing 3DOM structures of the iron oxide materials accounted for their excellent catalytic performance in the oxidation of toluene.

Hexagonally crystallized CaCO3 materials with flower-like, belt-like, network-like, coralloid, and hexagonal and rectangular parallelepiped morphologies were selectively fabricated using the surfactant (cetyltrimethylammonium bromide, sodium dodecyl sulfate, poly(N-vinyl-2-pyrrolidone or poly(ethylene glycol) (PEG)) mediated solvo- or hydrothermal strategy with CaO powders as Ca source in an oleic acid (OA)/ethanol, OA/ethylene glycol or water solvent, respectively. The as-obtained materials were characterized by means of the techniques, such as X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry, Fourier transform infrared spectroscopy, high-resolution scanning electron microscopy, high-resolution transmission electron microscopy, selected-area electron diffraction, and N2 adsorption–desorption measurement. It is shown that the morphology of the CaCO3 product was associated with the nature of surfactant and solvent and solvo- or hydrothermal temperature. The surfactant-free fabricated CaCO3 particles were cube-like in morphology. The rise in solvo- or hydrothermal temperature favored the enhancement in surface area of the CaCO3 product. Among the as-fabricated CaCO3 samples, the one derived hydrothermally with PEG at 240 °C possessed the highest surface area (134 m2/g). Such a high-surface-area wormhole-like mesoporous CaCO3 sample could decompose below 800 °C to mesoporous CaO with high surface area (110 m2/g). This reversible regeneration feature makes the mesoporous calcite useful in gas adsorption and separation as well as catalysis. The possible mechanisms for the multiply morphological CaCO3 formation have also been discussed.Graphical abstractCalcite-type CaCO3 with multiple morphologies and porous structures are selectively fabricated using the surfactant-mediated solvo- or hydrothermal strategy with CaO as Ca source in an organic or aqueous solvent. The high-surface-area (134 m2/g) CaCO3 derived hydrothermally with PEG at 240 °C for 72 h can decompose to mesoporous CaO with a high surface area (110 m2/g) below 800 °C.Research highlights► Surfactant-assisted solvo- or hydrothermal method favors the generation of porous CaCO3. ► Surfactant, solvent and solvo- or hydrothermal temperature determine CaCO3 morphology. ► CaCO3 obtained hydrothermally with PEG at 240 °C possesses a high surface area of 134 m2/g. ► Porous CaCO3 can decompose below 800 °C to mesoporous CaO with a high surface area of 110 m2/g.

MgO nano/microparticles with multiple morphologies and porous structures have been fabricated via the surfactant (poly(N-vinyl-2-pyrrolidone, poly(ethylene glycol) (PEG), cetyltrimethylammonium bromide, oleylamine or triblock copolymer P123 or F127) assisted solvo- or hydrothermal route in a dodecylamine or oleic acid solvent. The as-fabricated MgO samples were characterized by means of numerous techniques. It is shown that the obtained MgO samples were single-phase and of cubic in crystal structure; the particle morphology and pore architecture mainly depended upon the surfactant, solvent, and solvo- or hydrothermal temperature adopted. The solvothermal process resulted in polycrystalline MgO, whereas the hydrothermal one gave rise to single-crystalline MgO. Surface areas (8–169 m2 g−1) of the MgO samples derived solvothermally were lower than those (181–204 m2 g−1) of the MgO counterparts derived hydrothermally, with the mesoporous MgO generated after the PEG-assisted hydrothermal treatment at 240 °C for 72 h possessing the highest surface area. CO2 adsorption capacities of the MgO samples were in good agreement with their surface areas, and the mesoporous MgO derived hydrothermally with PEG at 240 °C for 72 h exhibited the largest CO2 uptake (368 μmol g−1) below 350 °C. We believe that such a high low-temperature adsorption capacity renders the mesoporous magnesia material useful in the utilization of acidic gas adsorption.Graphical abstractCubic-crystallized MgO with multiple morphologies and porous structures are selectively fabricated using the surfactant-mediated solvo- or hydrothermal methods with MgO as Mg source in an organic (OA or DA) or aqueous medium. The high-surface-area (204 m2 g−1) MgO derived hydrothermally with PEG at 240 °C for 72 h exhibits the largest CO2 uptake (368 μmol g−1) below 350 °C.Highlights► Surfactant-assisted solvo- or hydrothermal strategy favors the generation of porous MgO. ► Surfactant, solvent and solvo/hydrothermal temperature govern MgO shape and pore structure. ► MgO obtained hydrothermally with PEG at 240 °C possesses a high surface area of 204 m2 g−1. ► The MgO (surface area, 204 m2 g−1) exhibits the largest CO2 uptake (368 μmol g−1) below 350 °C.

Monoclinic BiVO4 single-crystallites with polyhedral, rod-like, tubular, leaf-like, and spherical morphologies have been fabricated using the triblock copolymer P123-assisted hydrothermal strategy with bismuth nitrate and ammonium metavanadate as metal source and various bases as pH adjustor. The physicochemical properties of the materials were characterized by means of the XRD, TGA/DSC, Raman, HRSEM, HRTEM/SAED, XPS, and UV–vis techniques. The photocatalytic activities of the as-fabricated BiVO4 samples were measured for the photodegradation of methylene blue (MB) under visible-light irradiation. It is shown that factors, such as the pH value of precursor solution, the introduction of surfactant, the nature of alkaline source, and the hydrothermal temperature, have a crucial influence on the particle architecture of the BiVO4 product. Among the as-fabricated BiVO4 samples, the ones derived hydrothermally with P123 at pH = 6 or 10 possessed excellent optical absorption performance both in UV- and visible-light regions and hence showed outstanding photocatalytic activities for the addressed reaction. The unusually high visible-light-driven catalytic performance of monoclinically crystallized rod-like and tubular BiVO4 single-crystallites is associated with the higher surface areas and concentrations of surface oxygen defects, and unique particle morphologies. The possible formation mechanisms of such multiple morphological BiVO4 materials have also been discussed.

Three-dimensionally ordered macroporous (3DOM) europium oxide and samarium oxide with mesoporous walls and cubic crystal structures have been successfully fabricated with polymethyl methacrylate (PMMA) as hard template and F127, sucrose, and l-lysine as surfactant. The as-fabricated rare earth oxides were characterized by means of X-ray diffraction, thermogravimetric analysis, differential scanning calorimetric analysis, Fourier-transform infrared spectroscopy, scanning electron microscope, transmission electron microscopy, selected-area electron diffraction, nitrogen adsorption–desorption, ultraviolet–visible diffuse reflectance spectroscopy, and photoluminescence spectroscopy. It is shown that the as-fabricated Eu2O3 and Sm2O3 samples displayed 3DOM architectures with polycrystalline wormhole-like mesoporous walls. The nature of surfactant and solvent and calcination parameter had important effects on the pore structure and surface area of the final product. The introduction of surfactant and the carbonization of sucrose or l-lysine favored the enhancement in surface area of the 3DOM-structured materials, with the 3DOM Eu2O3 and Sm2O3 samples derived in the presence of sucrose possessing the highest surface area of 36.8 and 32.6 m2 g−1, respectively. The 3DOM Eu2O3 and Sm2O3 samples showed much better UV-light absorption capacity than their bulk counterparts. The PL study revealed that the luminescent properties could be modified by tailoring the pore structure of Eu2O3 and Sm2O3. The unique physical properties associated with the generation of 3DOM skeletons and wormhole-like mesoporous walls make such materials useful for the applications in optics and heterogeneous catalysis.Graphical abstractThree-dimensionally ordered macroporous (3DOM) Eu2O3 and Sm2O3 with mesopore walls can be fabricated by the surfactant-assisted PMMA-templating method. 3DOM Eu2O3 obtained with sucrose possesses a surface area up to 37 m2 g−1. 3DOM Eu2O3 and Sm2O3 show strong UV-light absorption. By tailoring the pore structure of Eu2O3 and Sm2O3, the luminescent property can be modified.Highlights► 3DOM Eu2O3 and Sm2O3 with mesopore walls are fabricated by the PMMA-templating method. ► Surfactant addition and carbonization process favor the formation of the 3DOM structure. ► 3DOM Eu2O3 obtained with sucrose possesses a surface area up to about 37 m2 g−1. ► 3DOM Eu2O3 and Sm2O3 show excellent UV-light absorption. ► The luminescent property can be modified by tailoring the pore structure of Eu2O3 and Sm2O3.

A series of La1-xSrxM1-yFeyO3 (M = Mn, Co; x = 0, 0.4; y = 0.1, 1.0) perovskite-type oxide catalysts have been fabricated via a strategy of citric acid complexation coupled with hydrothermal treatment. The materials are characterized by a number of analytical techniques. The oxidation of toluene is used as a probe reaction for the evaluation of catalytic performance. It is found that both La0.6Sr0.4FeO3 and LaFeO3 exhibit high activities. The partial substitution of manganese and cobalt with iron can significantly improve the catalytic performance of La0.6Sr0.4MnO3 and La0.6Sr0.4CoO3. At toluene/O2 molar ratio = 1/200 and space velocity = 20 000 h−1, the catalytic activity decreases in the sequence of La0.6Sr0.4Co0.9Fe0.1O3 > La0.6Sr0.4FeO3 > La0.6Sr0.4Mn0.9Fe0.1O3 > LaFeO3 > La0.6Sr0.4CoO3 > La0.6Sr0.4MnO3. Compared to the Fe-free counterparts, the La0.6Sr0.4Mn0.9Fe0.1O3 and La0.6Sr0.4Co0.9Fe0.1O3 catalysts are, respectively, 50 and 85 °C lower with regard to the temperature required for complete toluene oxidation. Toluene can be completely oxidized at 245 °C over La0.6Sr0.4Co0.9Fe0.1O3. The excellent catalytic performance of La0.6Sr0.4Co0.9Fe0.1O3 can be attributed to the presence of (i) Fe3+−O−Fe4+ couples, (ii) a transition of electronic structure, and (iii) a trace amount of Co3O4.

Highly ordered mesoporous MnO2 and Co3O4 are prepared by adopting an SBA-16-based nanocasting strategy under ultrasonic irradiation and characterized by means of numerous techniques. It is shown that the as-fabricated manganese and cobalt oxides possess well-ordered mesoporous architectures with polycrystalline pore walls. With the assistance of ultrasonic waves, the metal precursors can readily diffuse from the bulk solution to the inner pores of the silica template. The repeated four-step fabrication process, filling → filtration → washing → calcination, is beneficial for preventing the formation of manganese or cobalt oxide nanoparticles on the external surfaces of the template and facilitating more metal precursors to fill the mesopore channels of the template. After removal of the silica template by a 2 mol/L NaOH aqueous solution, the as-received highly ordered mesoporous MnO2 and Co3O4 exhibit a surface area of up to 266 and 313 m2/g, respectively, which is about 2−3 times higher than that reported in the literature. The mesoporous MnO2 and Co3O4 samples are more readily reduced at low temperatures and show much better catalytic performance for toluene complete oxidation than their bulk counterparts. The excellent performance of the mesoporous materials is ascribed to their ordered mesoporous structure, better reducibility, and high surface area.

The YBa2Cu3O7 nano/microsized single crystallites with spherical and rod-like morphologies were fabricated hydrothermally. The catalytic performance of the materials was evaluated for methane combustion. It is shown that there was a clear relationship between the α-oxygen desorption or initial H2 consumption rate and catalytic activity. The single-crystalline perovskite-like cuprate catalysts outperformed the polycrystalline counterpart. The good catalytic performance of the hydrothermally derived YBa2Cu3O7 single crystallites is associated with more α-oxygen adspecies, better low-temperature reducibility, high-quality single crystallinity, and unique morphology.

yAu/SnO2 (y = 1–5 wt%) and 1 wt% Pt- or Pd-doped 3Au/SnO2 catalysts were prepared by the co-precipitation method. It is observed that the 3Au/SnO2 catalyst showed the best performance (T100% = 166 °C). The pretreatment of 3Au/SnO2 in CO obviously decreased the catalytic activity due to the reduction of oxidized gold species to metallic Au0. Pd- or Pt-doping to 3Au/SnO2 brought about a significant enhancement in performance, with the T100% value being 74 and 93 °C, respectively. It is concluded that the oxidized gold species were more active than metallic Au0 and the remarkable improvement in catalytic activity due to Pd or Pt doping was associated with the presence of strong interaction of Pd or Pt with Au.

By adopting the strategy of triblock copolymer (Pluronic P123) or cetyltrimethylammonium bromide (CTAB) assisted hydrothermal treatment, we fabricated cubic fluorite-type Ce0.6Zr0.3Y0.1O2 (CZY) solid solution polycrystallites with various morphologies. These materials were characterized by means of techniques such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected-area electron diffraction, X-ray photoelectron spectroscopy, thermogravimetry, laser Raman, Fourier-transfer infrared spectroscopy, hydrogen temperature-programmed reduction, and surface area measurements. It is found that the nanorod-like, microspherical, microbowknot-like, and micro-octahedral CZY particles were respectively generated hydrothermally with CTAB at 120 °C for 72 h and with P123 at 100, 120, and 240 °C for 48 h after calcination at 550 °C for 3 h. There was a copresence of Ce3+ and Ce4+ in the CZY samples that led to the formation of oxygen vacancies. We observed a good correlation of low-temperature reducibility with the morphology of the CZY samples. The reducibility of these nano- and micromaterials at low temperatures (240−550 °C) enhanced in the order micro-octahedral CZY < microspherical CZY < microbowknot-like CZY < nanorod-like CZY. The formation mechanism of CZY with various morphologies was discussed.

Three-dimensionally (3D) ordered macroporous (3DOM) MgO, γ-Al2O3, Ce0.6Zr0.4O2, and Ce0.7Zr0.3O2 with polycrystalline mesoporous walls have been successfully fabricated with the triblock copolymer EO106PO70EO106 (Pluronic F127) and regularly packed monodispersive polymethyl methacrylate (PMMA) microspheres as the template and magnesium, aluminum, cerium and zirconium nitrate(s), or aluminum isopropoxide as the metal source. The as-synthesized metal oxides were characterized by means of techniques such as X-ray diffraction (XRD), thermogravimetric analysis/differential scanning calorimetry (TGA/DSC), Fourier transform infrared (FT-IR), high-resolution scanning electron microscopy (HRSEM), high-resolution transmission electron microscopy/selected area electron diffraction (HRTEM/SAED), BET, carbon dioxide temperature-programmed desorption (CO2-TPD), and hydrogen temperature-programmed reduction (H2-TPR). It is shown that the as-fabricated MgO, γ-Al2O3, Ce0.6Zr0.4O2, and Ce0.7Zr0.3O2 samples possessed single-phase polycrystalline structures and displayed a 3DOM architecture; the MgO, Ce0.6Zr0.4O2, and Ce0.7Zr0.3O2 samples exhibited worm-hole-like mesoporous walls, whereas the γ-Al2O3 samples exhibited 3D ordered mesoporous walls. The solvent (ethanol or water) nature and concentration, metal precursor, surfactant, and drying condition have an important impact on the pore structure and surface area of the final product. The introduction of surfactant F127 to the synthesis system could significantly enhance the surface areas of the 3DOM metal oxides. With PMMA and F127 in a 40% ethanol solution, one can generate well-arrayed 3DOM MgO with a surface area of 243 m2/g and 3DOM Ce0.6Zr0.4O2 with a surface area of 100 m2/g; with PMMA and F127 in an ethanol−HNO3 solution, one can obtain 3DOM γ-Al2O3with a surface area of 145 m2/g. The 3DOM MgO and 3DOM γ-Al2O3 samples showed excellent CO2 adsorption behaviors, whereas the 3DOM Ce0.6Zr0.4O2 sample exhibited exceptional low-temperature reducibility. The unique physicochemical properties associated with the copresence of 3DOM and mesoporous walls make these porous materials ideal candidates for applications in heterogeneous catalysis and CO2 adsorption.

Mesoporous chromia with ordered three-dimensional (3D) hexagonal polycrystalline structures were fabricated at 130, 180, 240, 280, and 350 °C in an autoclave through a novel solvent-free route using KIT-6 as the hard template. The as-obtained materials were characterized (by means of X-ray diffraction, transmission electron microscopy, N2 adsorption−desorption, temperature-programmed reduction, and X-ray photoelectron spectroscopy techniques) and tested as a catalyst for the complete oxidation of toluene and ethyl acetate. We found that with a high surface area of 106 m2/g and being multivalent (Cr3+, Cr5+, and Cr6+), the chromia (meso-Cr-240) fabricated at 240 °C is the best among the five in catalytic performance. According to the results of the temperature-programmed reduction and X-ray photoelectron spectroscopy investigations, it is apparent that the coexistence of multiple chromium species promotes the low-temperature reducibility of chromia. The excellent performance of meso-Cr-240 is because of good 3D mesoporosity and low-temperature reducibility as well as the high surface area of the chromia. The combustion follows a first-order reaction with respect to toluene or ethyl acetate in the presence of excess oxygen, and the corresponding average activation energy is 79.8 and 51.9 kJ/mol, respectively, over the best-performing catalyst.

Under mild reaction conditions, uniform La(OH)3 nanorods were fabricated in large scale by a facile template-free solution method. The as-prepared sample was characterized by a number of techniques. It is found that the La(OH)3 nanorods are hexagonal in structure and single-crystalline, with the diameter and length of 6–30 and 45–200 nm, respectively. The surface area of the nanorods is up to 113 m2/g. We attribute the high surface area to the use of 1-propanol/H2O mixed solvent and the rapid cooling of sample to 0 °C. A formation mechanism of the rodlike crystal is tentatively suggested. The reported solution-phase process may be a facile and low-cost approach for the generation of high surface area single-crystalline nanorods of other rare earth hydroxides.

La1−xSrxMnO3−δ (x = 0.4, 0.5, and 0.6) catalysts were fabricated hydrothermally from KMnO4, MnCl2 (KMnO4/MnCl2 molar ratio = 3/7), and stoichiometric amounts of lanthanum and strontium nitrates in KOH solution. The physicochemical properties of the materials were characterized by a number of analytical techniques. It was found that the La1−xSrxMnO3−δ samples fabricated at 250 °C are single-crystalline perovskite-type oxides in the form of microcubes. The as-fabricated La1−xSrxMnO3−δ materials display various states of oxygen nonstoichiometry. The total amount of oxygen vacancies and Mn4+ in the catalysts decreases in the order of La0.5Sr0.5MnO3−δ > La0.4Sr0.6MnO3−δ > La0.6Sr0.4MnO3−δ. It has been found that the trends of catalyst reducibility and catalytic performance of the three catalysts follow a similar order. We observed 100% toluene conversion at 255 °C over the La0.5Sr0.5MnO3−δ catalyst, 113 °C lower than that observed over a polycrystalline La0.5Sr0.5MnO3−δ catalyst prepared by calcination at 950 °C. The excellent performance of the former can be related to the high Mn4+/Mn3+ ratio, distinct oxygen nonstoichiometry, and single-crystalline structure of the catalyst.Single-crystalline perovskite-type oxide La1−xSrxMnO3−δ microcubes are fabricated via a hydrothermal route. 100% toluene conversion is achieved over the La0.5Sr0.5MnO3−δ catalyst at 255 °C, which is 113 °C lower than that over the polycrystalline La0.5Sr0.5MnO3−δ catalyst. The excellent performance is related to the high Mn4+/Mn3+ ratio, distinct oxygen nonstoichiometry, and single-crystalline structure.

By adopting the strategy of dissolution−recrystallization under hydrothermal conditions (at 240 °C for 72 h) in the presence of a triblock copolymer (Pluronic P123), we fabricated nano- and microparticles of single-crystalline MgO of rectangular parallelepiped and hexagonal prism morphologies. The MgO crystallites display three-dimensional wormholelike mesopores and have a surface area as high as 298 m2/g even after calcination at 550 °C for 3 h.

La1−xSrxMO3−δ (M = Co, Mn; x = 0, 0.4) catalysts have been fabricated via a strategy of citric acid complexing and hydrothermal treatment. The oxidation of toluene was used as a probe reaction for the evaluation of catalytic performance. The materials were characterized by a number of techniques. We observed that the catalytic activity (evaluated by the temperature required for 80% conversion of toluene, T80%) increased in the sequence of LaMnO3.10 (T80% = 295 °C) < LaCoO2.89 (T80% = 246 °C) < La0.6Sr0.4MnO3.03 (T80% = 233 °C) < La0.6Sr0.4CoO2.76 (T80% = 219 °C) at toluene/O2 molar ratio = 1/400 and space velocity = 20 000 h−1. Moreover, CO2 and H2O were the only products for toluene oxidation over the catalysts. It is concluded that factors such as enriched structural defects (oxygen vacancies) and good Mn4+/Mn3+ or Co3+/Co2+ redox ability are responsible for the excellent catalytic performance of the La1−xSrxMO3−δ nanomaterials.

Single-crystalline nanowires and nanorods of cubic perovskite-type La0.6Sr0.4CoO3-δoxides have been fabricated by a hydrothermal method and characterized by a number of analytical techniques. Compared to the polycrystalline La0.6Sr0.4CoO3-δ catalyst, the single-crystalline materials exhibit much better catalytic activity for the complete oxidation of toluene. The excellent performance can be attributed to the distinct oxygen nonstoichiometry and single-crystalline structure of the materials.

Nanoparticles of Ce0.6Zr0.35Y0.05O2 (CZY) solid solution have been prepared by the CTAB (hexadecyltrimethyl ammonium bromide), CTAB-EG (ethylene glycol) templating, and CTAB-EG-NaCl (in which the pores of the precursor synthesized by the CTAB-EG method is filled by a certain amount of NaCl) method, respectively. The physical properties of these materials were characterized by means of techniques such as X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and N2 adsorption-desorption measurements. The CZY samples synthesized by the above three methods display wormhole-like mesoporous morphology and cubic crystal structures. The materials are narrow in pore size distribution (averaged pore diameter = 5.3–7.1 nm), high in surface areas (95–119 m2/g), and large in pore volumes (0.16–0.18 cm3/g). It has been demonstrated that the introduction of NaCl is capable of retaining the pore structures of solid nanomaterials at high-temperature calcination.

•3DOM La0.6Sr0.4MnO3 (LSMO) is prepared by polymethyl methacrylate-templating method.•xAu/LSMO catalysts are prepared by the polyvinyl alcohol-protected reduction method.•xAu/LSMO perform excellently in the oxidation of CO and toluene.•Activity is governed by Oads content, reducibility, and strong Au–LSMO interaction.Three-dimensionally ordered macroporous (3DOM) La0.6Sr0.4MnO3 (LSMO) and its supported gold (xAu/LSMO, x = 3.4–7.9 wt%) catalysts were prepared using the polymethyl methacrylate-templating and gas-bubble-assisted polyvinyl alcohol-protected reduction methods, respectively. There were good correlations of surface-adsorbed oxygen species concentration and low-temperature reducibility with the catalytic activity of the sample for CO and toluene oxidation. Among the LSMO and xAu/LSMO samples, 6.4Au/LSMO performed the best, giving T50% and T90% values of −19 and 3 °C for CO oxidation and 150 and 170 °C for toluene oxidation, respectively. The apparent activation energies (31–32 and 44–48 kJ/mol) obtained over xAu/LSMO were much lower than those (45 and 59 kJ/mol) obtained over LSMO for the oxidation of CO and toluene, respectively. It is concluded that higher oxygen adspecies concentration, better low-temperature reducibility, and strong interaction between Au and LSMO are responsible for the excellent catalytic performance of 6.4Au/LSMO.Graphical abstract3DOM-structured La0.6Sr0.4MnO3 (LSMO) and xAu/LSMO (x = 3.4–7.9 wt%) are prepared using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods, respectively. The high Oads concentration, good low-temperature reducibility, and strong Au–LSMO interaction are responsible for excellent catalytic performance of 6.4Au/LSMO for CO and toluene oxidation. Download high-res image (396KB)Download full-size image

•CoxPd are prepared using the modified polyvinyl alcohol-protected reduction method.•CoxPd nanoparticles displayed core-shell (core: Pd; shell: Co) structure.•CoxPd nanoparticles with a core-shell structure exhibit super thermal stability.•CoxPd/3DOM CeO2 possess good O2 and CH4 adsorption abilities.•CoxPd/3DOM CeO2 perform well in methane oxidation.Three-dimensionally ordered macroporous CeO2 (3DOM CeO2) and its supported Pd@Co (CoxPd/3DOM CeO2, x (Co/Pd molar ratio) = 2.4–13.6) nanocatalysts were prepared using the polymethyl methacrylate-templating and modified polyvinyl alcohol-protected reduction methods, respectively. The Pd@Co particles displayed a core-shell (core: Pd; shell: Co) structure with an average size of 3.5–4.5 nm and were well dispersed on the surface of 3DOM CeO2. The CoxPd/3DOM CeO2 samples exhibited high catalytic performance and super stability for methane oxidation, with the Co3.5Pd/3DOM CeO2 sample showing the highest activity (T90% = 480 °C at space velocity of 40,000 mL/(g h) and excellent stability in the temperature range 400–800 °C. The apparent activation energies (58–73 kJ/mol) obtained over CoxPd/3DOM CeO2 were much lower than those (104–112 kJ/mol) over Co/3DOM CeO2 and 3DOM CeO2 for methane oxidation, with the Co3.5Pd/3DOM CeO2 sample possessing the lowest apparent activation energy (58 kJ/mol). It is concluded that the excellent catalytic performance of Co3.5Pd/3DOM CeO2 was associated with its good abilities to adsorb oxygen and methane as well as the unique core-shell structure of CoPd nanoparticles.Download high-res image (110KB)Download full-size image

•High-surface-area 3DOM La0.6Sr0.4MnO3 is prepared by the PMMA-templating method.•Surfactant addition is critical in 3DOM structure formation with nanovoid-like walls.•The calcination procedure is a key step in the formation of 3DOM structure.•3DOM La0.6Sr0.4MnO3-DP3 performs best in the combustion of methane.•Surface area, Oads, and reducibility determine the activity of 3DOM La0.6Sr0.4MnO3.Three-dimensionally ordered macroporous rhombohedral La0.6Sr0.4MnO3 (3DOM LSMO) with nanovoids was prepared using polymethyl methacrylate (PMMA) microspheres as a hard template and dimethoxytetraethylene glycol (DMOTEG), ethylene glycol, polyethylene glycol (PEG400), l-lysine, or triblock copolymer (Pluronic P123) as a surfactant. Physicochemical properties of the materials were characterized by a number of analytical techniques, and their catalytic activities for the combustion of methane were evaluated. It is shown that the morphology of the sample depended strongly on the nature of the surfactant added during the fabrication process. The macropore sizes and surface areas of the 3DOM LSMO materials were 165–214 nm and 32–40 m2/g, respectively. It is found that addition of appropriate amounts of DMOTEG and PEG400 was beneficial for the generation of high-quality 3DOM-structured La0.6Sr0.4MnO3 (denoted as LSMO-DP1, LSMO-DP3, LSMO-DP5, derived with a DMOTEG /PEG400 ratio of 0.2, 0.6, and 1.0, respectively). The LSMO-DP3 catalyst derived with 3.0 mL of DMOTEG and 5.0 mL of PEG400 possessed the highest oxygen species concentration and surface area and best low-temperature reducibility, and hence exhibited a good catalytic activity (T10% = 437 °C, T50% = 566 °C, and T90% = 661 °C at GHSV = 30,000 mL/(g h)) for methane combustion. The apparent activation energies of the 3DOM LSMO samples were estimated to be 56.5–75.2 kJ/mol, with the LSMO-DP3 sample showing the lowest apparent activation energy (56.6 kJ/mol).Graphical abstractRhombohedrally crystallized 3DOM La0.6Sr0.4MnO3 (LSMO) catalysts with a high surface area of 32–42 m2/g were prepared by the PMMA-templating method. The 3DOM LSMO-DP3 catalyst derived with 3.0 mL of dimethoxytetraethylene glycol and 5.0 mL of polyethylene glycol shows excellent activity for the combustion of methane.Download high-res image (263KB)Download full-size image

Three-dimensionally ordered macroporous (3DOM) single-phase rhombohedral perovskite-type oxide LaMnO3 materials with nanovoid skeletons were prepared using the poly(methyl methacrylate)-templating methods with the assistance of surfactant (poly(ethylene glycol) (PEG) or triblock copolymer (Pluronic P123)). The nature of surfactant influenced the pore structure of the LaMnO3 sample. The use of PEG400 alone led to a 3DOM-structured LaMnO3 without nanovoid skeletons; with the addition of PEG400 and P123, however, one could prepare LaMnO3 samples with high-quality 3DOM structures, nanovoid skeletons, and high surface areas (37–39 m2/g). Under the conditions of toluene concentration = 1000 ppm, toluene/O2 molar ratio = 1:400, and space velocity = 20,000 mL/(g h), the porous LaMnO3 samples were superior to the bulk counterpart in catalytic performance, with the nanovoid-containing 3DOM-structured LaMnO3 catalyst performing the best (the temperatures for toluene conversions of 50% and 90% were 222–232 and 243–253 °C, respectively). The apparent activation energies (57–62 kJ/mol) over the 3DOM-structured LaMnO3 catalysts were much lower than that (97 kJ/mol) over the bulk LaMnO3 catalyst. We believe that the excellent performance of the 3D macroporous LaMnO3 materials in catalyzing the combustion of toluene might be due to factors such as large surface area, high oxygen adspecies concentration, good low-temperature reducibility, and unique nanovoid-containing 3DOM structure of the materials.Graphical abstractThrough the surfactant-assisted PMMA-templating method, we prepared three-dimensionally ordered macroporous (3DOM) LaMnO3 catalysts with nanovoid skeletons. It is found that the excellent performance of the catalysts in toluene combustion can be related to the high surface area and oxygen adspecies concentration as well as low-temperature reducibility of 3DOM LaMnO3.Download high-res image (260KB)Download full-size imageHighlights► Rhombohedral 3DOM LaMnO3 is prepared by surfactant-assisted PMMA-templating method. ► Surfactant addition is critical in the formation of 3DOM structure with nanovoid walls. ► 3DOM LaMnO3 is high in surface area and Oads concentration and good in reducibility. ► 3DOM LaMnO3 performs excellently in the combustion of toluene. ► Catalytic activity is governed by surface area, Oads, and reducibility of 3DOM LaMnO3.

•Ordered mesoporous cobalt oxide (meso-Co3O4) is obtained via KIT-6-templating route.•xAu/meso-Co3O4 nanocatalysts are prepared using the colloidal deposition method.•Au nanoparticles are highly dispersed inside the mesoporous channels of meso-Co3O4.•xAu/meso-Co3O4 perform well in the oxidation of CO, benzene, toluene, and o-xylene.•There is a strong interaction between Au nanoparticles and meso-Co3O4.Three-dimensionally ordered mesoporous Co3O4 (meso-Co3O4) and its supported gold (xAu/meso-Co3O4, x = 3.7–9.0 wt%) nanocatalysts were prepared using the KIT-6-templating and polyvinyl alcohol-protected colloidal deposition methods, respectively. The meso-Co3O4 and xAu/meso-Co3O4 samples exhibited a high surface area of 91–94 m2/g. The Au nanoparticles with a size of 1–5 nm were uniformly deposited inside the mesoporous channels of meso-Co3O4. There were good correlations of oxygen adspecies concentration and low-temperature reducibility with catalytic activity of the sample for CO or BTX (benzene, toluene, and o-xylene) oxidation. Among meso-Co3O4 and xAu/meso-Co3O4, the 6.5Au/meso-Co3O4 sample performed the best, giving the T90% (the temperature required for achieving a CO or BTX conversion of 90%) of −45, 189, 138, and 162 °C for the oxidation of CO, benzene, toluene, and o-xylene, respectively. The apparent activation energies (23 and 45–55 kJ/mol) over 6.5Au/meso-Co3O4 were much lower than those (48 and 72–92 kJ/mol) over bulk Co3O4 for CO and BTX oxidation, respectively. The effects of water vapor, carbon dioxide, and sulfur dioxide on the catalytic activity of the 6.5Au/meso-Co3O4 sample were also examined. It is concluded that the higher surface area and oxygen adspecies concentration, better low-temperature reducibility, and strong interaction between Au and meso-Co3O4 were responsible for the excellent catalytic performance of 6.5Au/meso-Co3O4.Download high-res image (167KB)Download full-size image

Perovskite-like oxide La2-xSrxCuO4 (x = 0, 1) single crystallites with microrod-like morphologies and tetragonal crystal structures were prepared hydrothermally at 240°C with poly(ethylene glycol) (PEG) or hexadecyltrimethyl ammonium bromide (CTAB) as a surfactant and after calcination at 850°C. The physicochemical properties of the materials were characterized by means of XRD, BET, SEM, TEM/SAED (selected-area electron diffraction), XPS and H2-TPR techniques. It is found that doping Sr2+ to La2CuO4 lattice enhanced the catalytic activity for methane combustion and the LaSrCuO4 catalyst derived from PEG is the best among the tested ones. It is concluded that factors, such as adsorbed oxygen species concentration, reducibility and surface area, determined the catalytic performance of such single-crystalline materials.

The NiO samples (NiO-HMTA, NiO-HMTA-PEG, NiO-HMTA-PVP, and NiO-urea, respectively) with a surface area of 31 −66 m2/g and porous nanoflower- and nanourchin-like morphologies were prepared via the hydrothermal route with hexamethylenetetramine (HMTA) or urea as precipitator in the absence or presence of surfactant (poly(ethylene glycol) (PEG) or polyvinyl pyrrolidone (PVP)). It is shown that NiO-HMTA-PVP possessed the highest surface area and Oads concentration and the best reducibility. The NiO-HMTA-PVP catalyst performed the best (T50% = 253 °C and T90% = 266 °C). The excellent catalytic activity of NiO-HMTA-PVP was associated with its large surface area, high Oads concentration, and good reducibility.Download full-size imageHighlights► NiO nanoflowers and nanourchins are prepared by the hydrothermal method. ► NiO nanoflowers and nanourchins show a surface area of 31–66 m2/g. ► NiO nanoflower derived with PVP is high in Oads content and good in reducibility. ► NiO nanoflower derived with PVP performs excellently for toluene combustion. ► High surface area and Oads content and good reducibility governs catalytic activity.

Nanometer perovskite-type oxides La1−xSrxMO3−δ (M = Co, Mn; x = 0, 0.4) have been prepared using the citric acid complexing-hydrothermal-coupled method and characterized by means of techniques, such as X-ray diffraction (XRD), BET, high-resolution scanning electron microscopy (HRSEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD), and temperature-programmed reduction (TPR). The catalytic performance of these nanoperovskites in the combustion of ethylacetate (EA) has also been evaluated. The XRD results indicate that all the samples possessed single-phase rhombohedral crystal structures. The surface areas of these nanomaterials ranged from 20 to 33 m2 g−1, the achievement of such high surface areas are due to the uniform morphology with the typical particle size of 40–80 nm (as can be clearly seen in their HRSEM images) that were derived with the citric acid complexing-hydrothermally coupled strategy. The XPS results demonstrate the presence of Mn4+ and Mn3+ in La1−xSrxMnO3−δ and Co3+ and Co2+ in La1−xSrxCoO3−δ, Sr substitution induced the rises in Mn4+ and Co3+ concentrations; adsorbed oxygen species (O−, O2−, or O22−) were detected on the catalyst surfaces. The O2-TPD profiles indicate that Sr doping increased desorption of the adsorbed oxygen and lattice oxygen species at low temperatures. The H2-TPR results reveal that the nanoperovskite catalysts could be reduced at much lower temperatures (<240 °C) after Sr doping. It is observed that under the conditions of EA concentration = 1000 ppm, EA/oxygen molar ratio = 1/400, and space velocity = 20,000 h−1, the catalytic activity (as reflected by the temperature (T100%) for EA complete conversion) increased in the order of LaCoO2.91 (T100% = 230 °C) ≈ LaMnO3.12 (T100% = 235 °C) < La0.6Sr0.4MnO3.02 (T100% = 190 °C) < La0.6Sr0.4CoO2.78 (T100% = 175 °C); furthermore, there were no formation of partially oxidized by-products over these catalysts. Based on the above results, we conclude that the excellent catalytic performance is associated with the high surface areas, good redox properties (derived from higher Mn4+/Mn3+ and Co3+/Co2+ ratios), and rich lattice defects of the nanostructured La1−xSrxMO3−δ materials.

The three-dimensional mesoporous calcium oxide (meso-CaO) supported chromium–vanadium binary oxide catalysts yCrOx/10 wt.% VOx/meso-CaO (i.e., yCr/10V/meso-CaO, y = 0–4 wt.%; the VOx and CrOx weight percentages referred to the mass contents of V2O5 and Cr2O3 in the catalysts, respectively) were prepared via an incipient wetness impregnation route and characterized by means of XRD, BET, SEM, TEM/SAED (selected-area electron diffraction), Raman, and H2-TPR (temperature-programmed reduction) techniques. The catalytic performance of the materials was evaluated for the oxidative dehydrogenation (ODH) of isobutane. It is found that the meso-CaO and yCr/10V/meso-CaO displayed wormhole-like mesoporous structures, VOx and/or CrOx were highly dispersed in the form of mono- and polyvanadate or polychromate on the surface of the meso-CaO support. The H2-TPR results indicate that 2Cr/10V/meso-CaO exhibited the best low-temperature reducibility among the as-prepared catalysts. Under the conditions of isobutane/oxygen molar ratio = 1/2, space velocity = 30,000 mL/(g h), and temperature = 540 °C, a maximal C4-olefins yield of 15% with the corresponding C4-olefins selectivity of 79% was achieved over the 2Cr/10V/meso-CaO catalyst. It is concluded that the good dispersion of CrOx and VOx domains and low-temperature reducibility of the catalyst as well as the strong basicity and three-dimensional wormhole-like mesoporosity of the CaO support were responsible for the excellent catalytic performance of 2Cr/10V/meso-CaO for the ODH of isobutane.

High-surface area and well-ordered mesoporous Cr-incorporated SBA-15 (Cr-SBA-15) and SBA-15-supported chromia (CrOx/SBA-15) with Cr surface density = 0.05–1.11 Cr-atom/nm2 have been prepared, respectively, using the one-step synthesis and incipient wetness impregnation method, and characterized by AAS, XRD, BET, ESEM, TEM, XPS, laser Raman, UV-Vis, FT-IR, and H2-TPR. It is observed that the Cr-SBA-15 and CrOx/SBA-15 samples showed an evolution of surface morphology from long chain-shaped to short rod-like and further to an irregularly spherical architecture at elevated Cr content, which might arise from the interaction of Cr ions or CrOx domains with SBA-15. There were co-presence of tetrahedrally coordinated mono- and poly-chromate (Cr6+) as well as octahedrally coordinated Cr3+ species in Cr-SBA-15 and CrOx/SBA-15, with the Cr6+ species being dominant at Cr surface density ≤0.22 Cr-atom/nm2 in Cr-SBA-15 and Cr ≤0.54 Cr-atom/nm2 in CrOx/SBA-15, whereas the amount of the Cr3+ species increased markedly at Cr surface density ≥0.53 Cr-atom/nm2 due to the formation of crystal Cr2O3 phase. Maximal Cr incorporation into Cr-SBA-15 and one monolayer surface CrOx coverage on CrOx/SBA-15 occurred at Cr surface density ≤0.53 Cr-atom/nm2 and <1.11 Cr-atom/nm2, respectively. The CrOx/SBA-15 samples exhibited better reducibility than the Cr-SBA-15 samples, with the best reducibility exhibited at Cr surface densities of 0.54 and 0.12 Cr-atom/nm2, respectively.

The three-dimensional (3D) macroporous orthorhombically crystallized perovskite-like oxides La2CuO4 were prepared using the polymethyl methacrylate (PMMA) microsphere-templating strategy with nitrates of lanthanum and copper as metal source and a mixed solution of methanol and ethylene glycol as solvent in the absence or presence of citric acid and after calcination at various atmospheres. The as-prepared materials were characterized by means of X-ray diffraction, N2 adsorption-desorption, scanning electron microscopy, X-ray photoelectron spectroscopy, and hydrogen temperature-programmed reduction. Catalytic activities of the materials were evaluated for the combustion of methane. The catalyst (La2CuO4-1) prepared with PMMA and citric acid possessed a 3D ordered macroporous (3DOM) structure and a surface area up to 46 m2/g, whereas the one (La2CuO4-2) prepared with PMMA but without citric acid exhibited a 3D wormhole-like macroporous structure and a surface area of 39 m2/g. There was the presence of a trace amount of La2O2CO3 phase in the La2CuO4-1 and La2CuO4-2 catalysts. The calcination procedure (first in N2 flow at 700 °C and then in air flow at 300 and 800 °C, respectively) was crucial in forming the 3D porous structure of La2CuO4. The as-obtained catalysts had overstoichiometric oxygen. The La2CuO4-1 catalyst showed better low-temperature reducibility than the La2CuO4-2 and La2CuO4-Citrate (derived from the conventional citric acid-complexing route) catalysts. The 3D porous La2CuO4 materials performed well in catalyzing the oxidation of methane, with the La2CuO4-1 catalyst showing the best performance (the temperature for 90% CH4 conversion = 672 °C (reaction rate = ca. 40 mmol/(g h)) at CH4/O2 molar ratio = 1/10 and space velocity = 50,000 mL/(g h). It is concluded that the excellent catalytic performance of La2CuO4-1 was mainly related to the higher surface area, better low-temperature reducibility, and 3DOM architecture.Graphical abstractThe citric acid-assisted PMMA-templating strategy can generate La2CuO4 with a three-dimensional ordered macroporous (3DOM) structure and a high surface area of 46 m2/g. It is found that the high surface area, good low-temperature reducibility, and porous structure of the 3DOM-structured La2CuO4 are responsible for the excellent catalytic performance for the oxidation of methane.Download high-res image (270KB)Download full-size imageHighlights► Citric acid-assisted PMMA-templating strategy can generate 3DOM-structured La2CuO4. ► The calcination procedure is a key step in the formation of 3D macroporous structure. ► 3DOM and wormhole-like macroporous structured La2CuO4 possess high surface areas. ► 3DOM-structured La2CuO4 exhibits good low-temperature reducibility. ► Low-temperature reducibility, surface area, and 3D porosity govern catalytic activity.

Nanosized α-MnO2-supported silver catalysts (xAg/nano-MnO2, x = 0–10.0 wt%) were prepared by the incipient wetness impregnation method and characterized by means of numerous analytical techniques. Catalytic activities of the materials were evaluated for the oxidation of CO and benzene. It is shown that the loading of silver on nano-MnO2 could significantly modify the catalytic activities and the catalytic performance of xAg/nano-MnO2 strongly depended upon the Ag loading, among which 5Ag/nano-MnO2 performed the best for the addressed reactions. The excellent performance of 5Ag/nano-MnO2 was associated with the highly dispersed Ag, good low-temperature reducibility, and synergism at the interface of Ag and MnO2 nanodomains.Graphical abstractNanosized α-MnO2-supported silver catalysts (xAg/nano-MnO2, x = 0–10.0 wt%) are prepared by the incipient wetness impregnation method. It is shown that the catalytic performance strongly depends upon the Ag loading and 5Ag/nano-MnO2 performs the best for CO and benzene oxidation; such excellent performance is associated with the highly dispersed Ag, good low-temperature reducibility, and synergism between the Ag and MnO2 nanodomains.Download high-res image (175KB)Download full-size imageHighlights► There is a strong interaction between Ag and nano-MnO2 nanodomains. ► Ag loading promotes the reducibility of nano-MnO2. ► Ag-loaded nano-MnO2 catalysts perform well in the oxidation of CO and benzene. ► 5Ag/nano-MnO2 shows the best catalytic activity for both reactions. ► Ag dispersion, reducibility, and synergism determine catalytic performance.

Perovskite-type oxide La0.5Sr0.5MnO3−δ catalysts were fabricated hydrothermally at 220, 240, 250 or 270 °C for 50 h (denoted as LSMO-220, LSMO-240, LSMO-250, and LSMO-270, respectively). We characterized the materials by a number of analytical techniques. It was found that the La0.5Sr0.5MnO3−δ samples are single-crystalline cubic perovskite-type oxides in the form of microcubes. The as-fabricated samples displayed various surface and bulk compositions that can be related to the discrepancy in treatment temperature. The surface Mn/(La + Sr + Mn) ratio and the initial H2 consumption rate at low-temperatures increase according to the sequence of LSMO-240 < LSMO-270 < LSMO-220 < LSMO-250. We observed that the surface Mn4+/Mn3+ ratio and catalytic performance of the materials follow a similar order. The temperature for 100% toluene conversion over LSMO-250 was 280 °C. The excellent performance of the materials can be related to (i) Mn surface enrichment, (ii) high Mn4+/Mn3+ ratio, (iii) oxygen nonstoichiometry, and (iv) single-crystalline structure of the catalysts.

The nano-sized polycrystalline Ce0.6Zr0.3Y0.1O2 (CZY) support was fabricated adopting the cetyltrimethyl ammonium bromide (CTAB)-assisted hydrothermal treatment method and the CZY-supported nano-sized gold catalysts, y% AuOx/CZY (y% represents the Au weight percentage, y = 0.2–10.0), were prepared using an in situ reduction procedure with HAuCl4 as Au source, NaBH4 as reducing agent, and poly(N-vinyl-2-pyrrolidone) (PVP) as surfactant. We characterized the physicochemical properties of these materials by means of the XRD, Brunauer-Emmett-Teller (BET), high-resolution scanning electron microscopic (HRSEM), high-resolution transmission electron microscopic (HRTEM)/selected area electron diffraction (SAED), XPS, and hydrogen temperature-programmed reduction (H2-TPR) techniques, and examined their catalytic activities for the combustion of methane. It is observed that the CZY and gold were nanoparticles with the diameter of 5–50 and 2–20 nm, respectively. At a lower gold loading (y ≤ 0.6), the gold mainly existed in a highly dispersed AuOx (Au3+) domain on the CZY surfaces; at a higher gold loading (y ≥ 1.0), the gold were present in the form of metallic Au0 cluster as well as dispersed AuOx domains. With the introduction of gold, the reducibility of the y% AuOx/CZY catalysts was improved significantly, possibly due to the synergistic action between the nano-sized gold and the nanocrystalline CZY. Among the y% AuOx/CZY catalysts, the one at y = 0.2 showed the best activity for methane combustion. It is suggested that the good catalytic performance of CZY-supported gold materials with a lower gold loading (<1.0%) is associated with the high dispersion of AuOx domains, high atomic ratio of Au3+/Au0, nano-sized Au and CZY particles, and good reducibility.

•3DOM CoFe2O4 is fabricated via the polymethyl methacrylate-templating route.•MnOx/3DOM CoFe2O4 is prepared by the incipient wetness impregnation method.•Pd–Pt/MnOx/3DOM CoFe2O4 is obtained using the PVA-protected reduction method.•1.87Pd2.1Pt/6.70MnOx/3DOM CoFe2O4 performs excellently in CH4 combustion.•Pd–Pt alloy, Oads, reducibility, and metal-support interaction govern the activity.Three-dimensionally ordered macroporous (3DOM) CoFe2O4, zMnOx/3DOM CoFe2O4 (z = 4.99–12.30 wt%), and yPd–Pt/6.70 wt% MnOx/3DOM CoFe2O4 (y = 0.44–1.81 wt%; Pd/Pt molar ratio = 2.1–2.2) have been prepared using the polymethyl methacrylate microspheres-templating, incipient wetness impregnation, and bubble-assisted polyvinyl alcohol-protected reduction strategies, respectively. All of the samples were characterized by means of various techniques. Catalytic performance of the samples was measured for methane combustion. It is shown that the as-prepared samples exhibited a high-quality 3DOM structure (103 ± 20 nm in pore size) and a surface area of 19–28 m2/g, and the noble metal or alloy nanoparticles (NPs) with a size of 2.2–3.0 nm were uniformly dispersed on the macropore wall surface of 3DOM CoFe2O4. The loading of MnOx on CoFe2O4 gave rise to a slight increase in activity, however, the dispersion of Pd–Pt NPs on 6.70MnOx/3DOM CoFe2O4 significantly enhanced the catalytic performance, with the 1.81Pd2.1Pt/6.70MnOx/3DOM CoFe2O4 sample showing the highest activity (T10% = 255 °C, T50% = 301 °C, and T90% = 372 °C at a space velocity of 20,000 mL/(g h)). We believe that the excellent catalytic activity of 1.81Pd2.1Pt/6.70MnOx/3DOM CoFe2O4 was related to its well-dispersed Pd–Pt alloy NPs, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between MnOx or Pd–Pt NPs and 3DOM CoFe2O4.

•g-C3N4 is fabricated by directly heating guanidine hydrochloride.•Fe2O3/g-C3N4 is prepared by the incipient wetness impregnation method.•0.5 wt% Fe2O3/g-C3N4 possesses the highest adsorbed oxygen species concentration.•Fe2O3–g-C3N4 heterojunction inhibits the recombination of photoinduced charge carriers.•0.5 wt% Fe2O3/g-C3N4 shows excellent photocatalytic activity for 4-NP degradation.Graphitic carbon nitride and its supported iron oxide (x wt% Fe2O3/g-C3N4, x = 0.1–0.8) photocatalysts were fabricated using the guanidine hydrochloride calcination and incipient wetness impregnation methods, respectively. The x wt% Fe2O3/g-C3N4 photocatalysts contained a two-dimensional nanosheet structure with high dispersion of Fe2O3 nanoparticles (2–3 nm in size), a surface area of 27–29 m2/g, and a bandgap energy of 1.92–2.68 eV. The 0.5 wt% Fe2O3/g-C3N4 sample showed the highest photocatalytic activity (90% 4-nitrophenol (4-NP) was degraded within 40 min of visible-light illumination). Effects of pH value, H2O2 amount, and initial 4-NP concentration on activity of the typical sample were also examined. It is concluded that the enhanced photocatalytic activity of 0.5 wt% Fe2O3/g-C3N4 was associated with its unique two-dimensional layered structure, Fe2O3-g-C3N4 heterojunction, high surface oxygen adsorbed species concentration, and easy transfer and separation of photogenerated charge carriers.0.5 wt% Fe2O3/g-C3N4 exhibits excellent photocatalytic performance for 4-nitrophenol degradation, which is associated with its unique two-dimensional layered structure, Fe2O3–g-C3N4 heterojunction, and excellent separation efficiency of photoinduced electrons and holes.

Highly dispersed Ag nanoparticles supported on high-surface-area 3DOM La0.6Sr0.4MnO3 were successfully generated via the dimethoxytetraethylene glycol-assisted gas bubbling reduction route. The macroporous materials showed super catalytic performance for methane combustion.

Ordered meso/macroporous metal oxides have gained increasing attention in heterogeneous catalysis arising from their large surface areas and pore volumes, elevated catalytic activity and good thermal stability. Compared to nonporous metal oxides, their most prominent feature is the ability to interact with molecules not only at their exterior surface but also within the large interior surface of the material. The past decade has witnessed substantial advances in the synthesis of new porous metal oxides with ordered structures for use in a wide range of applications. By recalling some of the classical fundamentals of porous materials, this review examines the recent developments in ordered meso- and macro-porous metal oxide catalysts for heterogeneous catalysis. Additionally, we outline the current challenges in the field of nanoparticle-based catalysis, including the role played by the morphology (size, shape, and porosity) of ordered meso/macroporous metal oxides, and provide a perspective on the need for further advances in porous materials so that their contribution to heterogeneous catalysis can continue to expand.

The effects of the hydrothermal aging temperature on the catalytic performance and stability of CuSSZ-13 catalysts with various Cu/Al ratios were studied. The conversions of NO and NH3 were tested in the standard NH3-SCR reactions. The NH3-SCR activity of the catalysts decreased with the increasing hydrothermal aging temperature. Remarkably, the reduction was more significant as the Cu/Al ratio increased. The physicochemical properties of the samples were characterized by means of a number of analytical techniques. The results show that the hydrothermal stability of the CuSSZ-13 catalyst decreased with the increase in the hydrothermal aging temperature and Cu/Al ratio in the catalyst. Such a decrease was attributed to a drop in the number of isolated Cu2+ (in D6R and CHA cage). The transformation of the Cu2+ ions into new species (Cu2+ on Al2O3) depended on the collapse of the SSZ-13 structure after the hydrothermal aging treatment and was more likely to appear in the high Cu/Al-ratio samples and at a higher aging temperatures. The phase transformation of Cu2+ to agglomerated CuxO also occurred during the hydrothermal aging process. The formation of a large number of CuxO species might destroy the SSZ-13 structure, leading to deactivation of the catalyst.

α-Fe2O3 nanowires deposited diatomite was prepared using a precipitation–deposition method with FeCl3 as metal source and (NH2)2CO aqueous solution as precipitating agent. Physicochemical properties of the samples were characterized by means of numerous techniques, and their efficiency for the removal of As(III) and As(V) was determined. It is found that the solution pH value, reaction temperature, reaction time, and FeCl3 concentration had effects on the α-Fe2O3 amount loaded on the diatomite. Parameters, such as adsorbent amount, adsorption time, adsorption temperature, pH value, and initial As(III) or As(V) concentration, could influence the As(III) or As(V) removal efficiency of the α-Fe2O3 nanowires/diatomite sample (prepared with a 8 wt% FeCl3 aqueous solution at pH = 4.5 and 50 °C for 35 h) for the removal of As(III) and As(V). Over the α-Fe2O3/diatomite sample at pH = 3.5, the maximal As(III) and As(V) adsorption capacities were 60.6 and 81.2 mg g−1, and the maximal As(III) and As(V) removal efficiency was 99.98 and 100%, respectively. The Langmuir model was more suitable for the adsorption of As(V), whereas the Freundlich model was more suitable for the adsorption of As(III). The adsorption mechanism of the sample was also discussed.