Black TiO2 obtained by hydrogenation has attracted enormous attention due to its unusual photocatalytic activity. In this contribution, a novel photocatalyst containing both a titanate–anatase heterostructure and a surface disordered shell was in situ synthesized by using a one-step hydrogenation treatment of titanate nanowires at ambient pressure, which exhibited remarkably improved photocatalytic activity for water splitting under simulated solar light. The as-hydrogenated catalyst with a heterostructure and a surface disordered shell displayed a high hydrogen production rate of 216.5 μmol·h–1, which is ∼20 times higher than the Pt-loaded titanate nanowires lacking of such unique structure. The in situ-generated heterostructure and hydrogenation-induced surface disorder can efficiently promote the separation and transfer of photoexcited electron–hole pairs, inhibiting the fast recombination of the generated charge carriers. A general synergistic effect of the heterostructure and the surface disordered shell on photocatalytic water splitting is revealed for the first time in this work, and the as-proposed photocatalyst design and preparation strategy could be widely extended to other composite photocatalytic systems used for solar energy conversion.Keywords: heterostructure; hydrogenation; photocatalytic; surface disorder; water splitting

•Full CO conversion (100%) over CMC-0.05 is achieved at 108 °C.•Below 117 °C the selectivity of O2 to CO2 over CMC-0.05 is always 100%.•Doping of Mn can increase oxygen vacancies and improve catalyst reducibility.•The real Cu species during CO PROX are revealed by in-situ DRIFTS and XANES.A series of CuMnCeO catalysts with 10% CuO (weight loading) and variable atomic ratios of Mn/Mn + Ce (0, 0.02, 0.05 or 0.10) were synthesized by co-precipitation and employed for CO preferential oxidation (CO PROX). After doping a small amount of manganese into ceria, the catalysts show improved catalytic performance as compared with the undoped one, especially the catalyst with the Mn/Mn + Ce atomic ratio of 0.05 (CMC-0.05) which displays the lowest temperatures for half CO conversion (T50 = 73 °C) and full CO conversion (T100 = 108 °C). In addition, it also exhibits the widest temperature window of full CO conversion (108–149 °C) and 100% selectivity of oxygen to CO2 below 117 °C. As revealed by XRD and UV-Raman, the presence of appropriate amount of Mn cannot only enhance the formation of Ce–Cu–Mn–O ternary oxide solid solution with fluorite structure, inhibiting the growth of CeO2 crystallite size, but also increase the oxygen vacancies. The results of H2-TPR and XPS indicate that the reducibility and amount of surface oxygen species of CMC-0.05 are also improved, both of which are beneficial to catalytic performance. In situ XANES results suggest that the bulk copper species still remain as Cu2+ ions below 200 °C even in H2-rich CO PROX atmosphere; however, the in-situ DRIFTS spectra indicate that during CO PROX below 120 °C the surface copper species are Cu+ ions which are regarded as the main active sites for CO PROX; above 120 °C Cu0 species appear, which enhance H2 oxidation, decreasing the oxygen to CO2 selectivity.

•AgxAu1−x/TiO2 was prepared via a facile photoreduction and a replacement reaction.•AgxAu1−x/TiO2 exhibits tunable SPR frequencies in visible light region.•The improved visible light absorption remarkably enhances RhB photodegradation.•The mixed AgxAu1−x/TiO2 catalysts with different Ag/Au ratios show better activity.A series of AgxAu1−x/TiO2 photocatalysts with tunable surface plasmon resonance (SPR) frequencies were successfully prepared via a facile photoreduction combined with a simple replacement reaction between Ag and Au3+ ions. These two reactions react synergistically, resulting in the formation of Ag–Au alloy on TiO2. The as-prepared AgxAu1−x/TiO2 plasmonic photocatalysts exhibiting different colors absorb the visible light with different wavelengths, improving the utilization efficiency of the incident light with distinct frequencies. For RhB degradation, these catalysts containing Ag–Au alloy show much higher visible light-responsive photocatalytic activity than the commercial P25 and the single supported Ag or Au catalysts. By mixing the catalysts AgxAu1−x/TiO2 with different SPR frequencies, the photocatalytic activity can be further improved due to the widened visible light absorption range.

A series of Bi2S3/(BiO)2CO3 composite photocatalysts with different loadings of amorphous Bi2S3 were successfully synthesized through an ultrasonic-assisted ion-exchange reaction between thioacetamide (CH3CSNH2) and (BiO)2CO3, and characterized by XRD, XPS, BET, EELS, EDX, SEM, TEM/HRTEM, UV–Vis, and photoluminescence (PL) techniques. The results of TEM/HRTEM, EELS, and EDX indicate that the composite catalyst Bi2S3/(BiO)2CO3 has been successfully synthesized with the deposited Bi2S3 present in amorphous state on the surface of (BiO)2CO3. The activities of the catalysts for RhB degradation under visible light show that the catalyst prepared under ultrasonic is more active than the one synthesized without ultrasonic. The optimized sample Bi2S3/(BiO)2CO3 (U5.0) exhibits a much higher activity, about 4.8 times to that of pure (BiO)2CO3. Based upon the band structures of Bi2S3/(BiO)2CO3, it is deduced that the migration of the visible light-induced electrons from the conduction band of Bi2S3 to that of (BiO)2CO3 should have facilitated the separation of photogenerated carriers, as confirmed by the suppressed photoluminescence spectra. Using different scavengers, the ·O2− and holes are clearly identified as the main oxidative species for RhB photodegradation. In light of these observations, a potential photocatalytic mechanism of RhB degradation over Bi2S3/(BiO)2CO3 is proposed.

The ordered TiO2 nanotube array (NA)-supported ferric oxide nanoparticles with adjustable content and controllable particulate size were prepared through a facile light-assisted cyclic magnetic adsorption (LCMA) method. Multiple techniques such as SEM, TEM, EDX, XRD, EXAFS, XPS, UV–vis absorption, and TG were employed to study the structure and properties of the catalysts. The influencing factors upon soot combustion including the annealing temperature and loading of the active component in Fe2O3/TiO2–NA were also investigated. An obvious confinement effect on the catalytic combustion of soot was observed for the ferric oxide nanoparticles anchored inside TiO2 nanotubes. On the basis of the catalytic performance and characterization results, a novel domain-confined multiple collision enhanced soot combustion mechanism was proposed to account for the observed confinement effect. The design strategy for such nanotube array catalysts with domain-confined macroporous structure is meaningful and could be well-referenced for the development of other advanced soot combustion catalysts.Keywords: confinement effect; Fe2O3/TiO2−nanotubes; magnetic adsorption; multiple collision; soot combustion

Black TiO2 was usually obtained via hydrogenation at high pressure and high temperature. Herein, we reported a facile hydrogenation of TiO2 in the presence of a small amount of Pt at relatively low temperature and atmospheric pressure. The hydrogen spillover from Pt to TiO2 accounts well for the greatly enhanced hydrogenation capability. The as-synthesized Pt/TiO2 exhibits remarkably improved photocatalytic activity for water splitting.

•Ce-substitution greatly improves the DME SR performance of ZnAlCex catalysts.•The optimized CeO2 content in ZnAlCex catalysts is 20% by weight.•The presence of Ce in ZnAlCex can enhance H2 desorption at lower temperature.•ZnAlCex catalysts exhibit much lower CO selectivity than Cu-based one.•The catalyst ZnAlCe0.2 shows very high catalytic stability even at 420 °C.Ce-substituted ternary oxide catalysts ZnAlCex were prepared and employed in dimethyl ether steam reforming (DME SR) to produce hydrogen. XRD, XAFS (XANES & EXAFS), H2O-TPD, CH3OH-TPD and TPSR techniques were used for catalyst characterization. It is found that the catalytic performance of these catalysts is dependent on Ce content. The catalyst containing 20 wt% CeO2 exhibits the best catalytic performance. Its calculated TOF (0.034 s−1) is nearly three times to that of ZnAlO. The kinetic results reveal that the addition of 20 wt% CeO2 to ZnAlCex greatly decreases the apparent activation energy (Ea) of DME SR, due to the formation of new reaction sites such as Ce4+–O–Zn2+ linkages. XRD and EXAFS analyses indicate that Ce addition can not only decrease the crystallite size of ZnO and ZnAl2O4, but also tune the relative contents of them. The results of H2O-TPD and CH3OH-TPD show that Ce addition can lower H2 desorption temperature, which accounts well for the better catalytic performance of ZnAlCex. It is worth noting that the Zn-based catalysts display much lower CO selectivity than the Cu-based one, especially the Ce-substituted ZnAlCex. Start-off durability tests demonstrate that this series of catalysts also possess high catalytic stability.

•Non-stoichiometric Cu/Ce0.978Cu0.022O2 − δ catalyst is highly active for CO PROX.•The temperatures for 50% and 100% CO conversion are only 73 °C and 115 °C.•The selectivity of oxygen to CO2 can reach as high as 100% at full CO conversion.•Ce1 − xCuxO2 − δ solid solution remarkably promotes the reducibility of the catalysts.•Cu+ and Cu0 are the main active sites for CO and H2 oxidation, respectively.A series of Ce1 − xCuxO2 − δ non-stoichiometric solid solutions and their supported copper catalysts CuO/Ce1 − xCuxO2 − δ (x = 0, 0.005, 0.022, 0.043) were prepared by co-precipitation and deposition–precipitation, respectively. The CuO/Ce1 − xCuxO2 − δ catalysts show high performance for CO preferential oxidation (CO PROX). Multiple techniques of N2 sorption (BET), XRD, Laser Raman spectroscopy (LRS), HRTEM, H2-TPR, O2-TPO, N2O chemisorption and in-situ DRIFTS were used for catalyst characterization. The results of XRD, LRS and H2-TPR conformably indicate that a small amount of Cu2 + ions can be incorporated into the lattice of CeO2, forming non-stoichiometric solid solutions Ce1 − xCuxO2 − δ, which shows much better reducibility than pure CeO2. The supported CuO/Ce1 − xCuxO2 − δ catalysts exhibit remarkably enhanced activity for CO PROX as compared with CuO/CeO2, especially the catalyst CuO/Ce0.978Cu0.022O2 − δ containing 15% Cu, which displays the best CO PROX performance, showing not only the lowest temperature (115 °C) for CO total conversion, but also the 100% selectivity of O2 to CO2 at this temperature. Several aspects including the presence of more oxygen vacancies, the improved reducibility, and stronger capability for CO chemisorption of this catalyst account well for its superior performance for CO PROX. Based upon the in-situ DRIFTS study, it is revealed that Cu+ is the main active site for CO oxidation, while Cu0 is more active for H2 activation and oxidation.

A non-platinic lean NOx trap catalyst MnOx-K2CO3/K2Ti8O17 (K2CO3 loading: 25 wt %) was prepared via successive impregnation, which exhibits a large NOx storage capacity (3.21 mmol/g), a high NOx reduction percentage (98.5%) and an ultralow selectivity of NOx to N2O (0.3%). The catalyst was characterized by multiple techniques including XRD, SEM/HRTEM, EXAFS, FT-IR, CO2-TPD and in situ DRIFTS. Except for K2O, -OK groups, surface K2CO3 and bulk or bulk-like K2CO3, an unknown titanate phase with a K/Ti atomic ratio higher than 2/8 is identified, which is also active and regenerative for NOx storage and reduction. In-situ DRIFTS results reveal that NOx is mainly stored as bidentate nitrates and bidentate nitrite species in the catalyst. The appearance of negative bands around 1555 and 1575 cm–1 (C═O stretching vibration in bidentate carbonates) suggests the involvement of carbonates in NOx storage. Based upon the characterization results, a carbonate-involved NOx storage/reduction mechanism was proposed.

The catalyst obtained through the co-precipitation of Mn(Ac)2 and (NH4)2CO3 (denoted as Mn–Ac–NH4) displays the highest performance for soot oxidation. Compared with other MnOx catalysts, the catalyst Mn–Ac–NH4 exhibits much better reducibility and more uniform sponge-like nanostructure. The characterization results indicate that the oxygen species on the surface of Mn–Ac–NH4 are more active for soot combustion. The NO species can also be captured and oxidized by these oxygen species, generating more reactive NO2 which can enhance soot oxidation.

•Soot combustion on Co2.5Mg0.5Al1–x%Lax%O is greatly enhanced by La substitution.•The optimal substitution amount of La in Co2.5Mg0.5Al1–x%Lax%O catalysts is x = 10.•La-substitution has remarkably improved the redox property of the catalysts.•A nitrate/NO2 assisted soot combustion mechanism is revealed by in-situ DRIFTS.A series of hydrotalcite-derived multicomponent oxide catalysts Co2.5Mg0.5Al1–x%Lax%O (denoted as CMALax, x = 0, 5, 8, 10 or 15) with different La contents were synthesized by co-precipitation, and employed for catalytic soot combustion and NOx storage at lean condition. It is found that the La-substituted catalysts are more active than the one without La for soot combustion and NOx storage. Among all the catalysts CMALax, CMALa10 (x = 10) exhibits the highest catalytic performance, showing the largest NOx storage capacity (300 μmol/g) and the lowest temperature for the maximal soot oxidation rate (Tm = 388 °C). The results of H2-TPR and O2-TPD indicate that the La-substitution can enhance the redox properties and increase the amount of surface lattice oxygen species of the catalysts. The results of soot combustion kinetics show that the apparent activation energy of CMALa10 is the lowest (92.75 kJ/mol). Based upon the catalytic performance and in situ DRIFTS characterization, a nitrate and/or NO2 enhanced soot combustion mechanism over CMALa10 was proposed. It is revealed that at low temperature the stored nitrate can directly promote soot ignition, while at high temperature the NO2 species arising from NO oxidation or nitrate decomposition act as the main active species for soot combustion.

Photochemical synthesis is a promising strategy for the control of both the size and shape of silver nanoprisms; however, the mechanism of nanoprism formation under irradiation still remains as a mystery. Intermediates, which often contain abundant information about the reaction process, are significant to the understanding of reaction mechanisms. Unfortunately, intermediates are usually hard to be acquired due to the fast reaction rate. Herein, we successfully slow down the conversion rate of the photochemical reactions by enlarging the solution volume and removing morphology-directing agent bis(p-sulfonatophe-nyl) phenylphosphine dihydrate dipotassium. Nanorods and nanotrapezoids were found to be the key intermediates for the photoinduced formation of silver nanoprisms with ~100 nm edge length, especially the nanorods which have never identified as the intermediates for silver nanoprism formation. Characterization methods including time-dependent ultraviolet-visible spectroscopy, high resolution transmission electron microscopy (TEM and HRTEM), and selected area electron diffraction were employed to characterize these intermediates. Based upon the revealed evidences, a plausible metamorphosis-like photochemical growth route for the formation of Ag nanoprisms via the intermediates of nanorods and nanotrapezoid is proposed.

A series of nonplatinic ceria-based oxides supported catalysts LaCoO3/K2CO3/S (S=CeO2, Ce0.75Zr0.25O2 or 5%Y/Ce0.75Zr0.25O2) were prepared by successive impregnation and employed for lean-burn NOx trapping. It is found that the doping of Zr or YZr into CeO2 facilitates the formation of CeZrO binary or YCeZrO ternary solid solutions, increasing the specific surface area and improving the redox property of ceria. The results of EXAFS and H2-TPR reveal that the LaCoO3 in the solid solution supported catalysts possesses higher dispersion and better reducibility than that in CeO2 supported one. The result of O2-TPD shows that the surface active oxygen species are remarkably increased after loading LaCoO3 on the supports. The YCeZrO ternary solid solution supported catalyst containing 5 wt % K2CO3 exhibits the best performance for NO oxidation and reduction at 350 °C, showing a high NO-to-NO2 conversion (66.5%) at lean condition, and a very high NOx reduction percentage (98.2%) and an extremely high NOx-to-N2 selectivity (98.8%) at rich condition in the absence of CO2. After addition of 5 vol % CO2 in the atmosphere, the NOx reduction percentage during NOx storage and reduction tests can still be maintained at high level (above 90%) in the temperature region of 350–400 °C. The results of FT-IR, CO2-TPD and in situ DRIFTS indicate that the potassium in catalysts exists as −OK groups, K2O, bulk or bulk-like K2CO3. At low K2CO3 loading (≤5 wt %), NOx is stored as nitrates with diverse coordination structures, while at higher K2CO3 loading (8 wt %) it is mainly stored as bulk nitrates without forming nitrites. Based upon all characterizations, a carbonate-involved NOx storage and reduction mechanism is revealed in molecular level.

Herein, we introduce a specially designed domain-confined macroporous catalyst, namely, the Co3O4 nanocrystals anchored on a TiO2 nanotube array catalyst, which was synthesized by using the mercaptoacetic acid induced surface-grafting method. This catalyst exhibits much better performance for catalytic soot combustion than the conventional TiO2 powder supported one in gravitational contact mode (GMC).

A simple and feasible contact mode called gravitational contact mode (GCM) was developed for the first time to imitate the practical state between soot and catalyst. By simulating rainwater adsorption on a lawn in nature, we synthesized a lawn-like CuO nanorods array, which exhibited rather good catalytic activity for diesel soot combustion under GCM. Moreover, the CuO nanorods array could serve as a support for composite catalysts through a sequential chemical bath deposition method and exhibited higher catalytic activity than a traditional supported catalyst. The monolithic macroscopic structure of such a catalyst shows its potential for large-scale preparation and application.

A series of CuZnAlCeO catalysts with Zn partially substituted by Ce were prepared by co-precipitation, and employed for hydrogen production via dimethyl ether steam reforming (DME SR). The catalytic activity of these catalysts largely depends on CeO2 content. The catalyst containing 10 wt% CeO2 exhibits the best catalytic performance. The techniques of X-ray diffraction (XRD), N2O chemisorption, X-ray absorption fine structure (XAFS, including XANES and EXAFS), temperature-programmed reduction (H2-TPR) and CO desorption (CO-TPD) were used for catalyst characterization. The results of XRD, H2-TPR and N2O chemisorption conformably indicate that partial substitution of Zn by Ce can remarkably improve the dispersion of Cu species. The presence of Ce could not only inhibit the sintering of Cu species, but also improve the reducibility of copper oxides. The CO-TPD results clearly indicate that the two catalysts with 5 and 10 wt% CeO2 possess higher CO-chemisorption capability than others, which is consistent with the results of Cu dispersion. The linear fitting results of XANES spectra reveal that these two catalysts also contain higher amount of Cu+ species, which determines their better catalytic performance for DME SR.Highlights► Substitution of Zn by Ce can improve the DME SR performance of CuZnAlO catalyst. ► The optimal content of CeO2 in substituted CuZnAlCeO catalysts is 10% by weight. ► The presence of CeO2 can enhance the dispersion and reducibility of Cu species. ► The catalyst with more Cu+ species shows higher capability for CO chemisorption.

A mesoporous perovskite, LaCoO3, with a high specific surface area of 75 m2 g−1 was synthesized by a nano-casting method. Its related NOx storage/reduction catalyst K/LaCoO3, which contains no noble metals, exhibits excellent de-NOx performance under alternating lean/rich conditions, showing a high NOx reduction efficiency of 97.0% and a high NOx to N2 selectivity of 97.3%.

For the first time we synthesized mesoporous CeO2 nanosheets with single-crystal-like, ultrathin and uniform-sized structures through the thermal decomposition of specially prepared intermediates of Ce(OH)CO3 nanosheets. The resulting single-crystal-like CeO2 porous nanosheets are only 2.4 nm thick, as measured by AFM. BET analysis indicated that the pores of the nanosheets were centered at 3.7 nm. A novel structure transformation mechanism from 1D to 0D, then to a 2D assembly was clearly revealed. Moreover, such ultrathin CeO2 porous nanosheets exhibited much higher photocatalytic activity for dye degradation than that of polycrystalline CeO2 nanoparticles.

•GQDs anchored TiO2 nanotubes array (TiO2-NA) or CdS/TiO2-NA was synthesized.•GQDs improved the light quantum efficiency of both TiO2-NA and CdS/TiO2-NA.•Loading GQDs into TiO2-NA or CdS/TiO2-NA enhances their activity for H2O splitting.•Light-filtering effect of graphene sheets is weakened by breaking them into GQDs.The inversely structured TiO2 nanotubes-array (TiO2-NA) and CdS-modified TiO2 nanotubes-array (CdS/TiO2-NA) with graphene quantum dots (GQDs) anchored inside were prepared through a facile impregnation method. The catalysts were characterized by multiple techniques of SEM, TEM, XRD, Raman spectroscopy, XPS, TG and diffuse reflectance UV/Vis absorption spectroscopy. The results of TEM, XPS and Raman spectroscopy indicate that the GQDs were really formed and successfully anchored into the TiO2-NA and CdS/TiO2-NA. The activity evaluation results show that the hydrogen evolution rate during photocatalytic water splitting was greatly improved after loading GQDs into TiO2-NA and CdS/TiO2-NA. By breaking graphene into GQDs, the light-filtering effect of graphene was remarkably inhibited as compared with that of conventional large graphene sheets. Moreover, the overall morphology of TiO2 nanotube array could be well maintained after anchoring GQDs inside, which is favorable to mass transfer. The catalyst design strategy proposed in present work can be extended to other photocatalytic systems.

A series of carbonate-based lean-burn NOx trap (LNT) catalysts Pt–K2CO3/ZrO2 with different K2CO3 loading were prepared by sequential impregnation, which show extremely good performance for lean NOx storage and reduction. The catalyst containing 15 wt % K2CO3 exhibits a large NOx storage capacity of 2.16 mmol/g and a very high NOx reduction percentage of 99%. Multiple techniques including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), temperature-programmed decomposition (TPD), Fourier-transform infrared spectroscopy (FT-IR), and in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) were employed for catalyst characterization. The results of XRD, FT-IR, and HR-TEM conformably show that, at room temperature, the K species exist as amorphous K2CO3; while at NOx storage temperature (350 °C), three kinds of K species including −OK groups, K2O, and K2CO3 are simultaneously present in the catalysts as revealed by in situ DRIFTS, TPD, and FT-IR results. Surface carbonates are identified as the most active species for NOx storage, showing the best NOx storage performance. Higher K2CO3 loading than 15 wt % leads to the formation of more bulk or bulk-like K2CO3 species, which are unfavorable to NOx storage. As K2CO3 loading is 10 wt % or less, the NOx is mainly stored as nitrates species such as monodentate nitrates, ionic nitrates, and bridging bidentate nitrates, while at higher K2CO3 loading, the NOx is only stored as bidentate nitrite species. The presence of excess amount of K2CO3 can decrease the ability of the catalysts for NO adsorption and oxidation, making the NOx oxidized only to nitrite species.

A series of polytitanate nanobelt supported lean-burn NOx trap catalysts Pt-xK2CO3/K2Ti8O17 with different weight loading of K2CO3 (x = 0%, 5%, 15%, 20%, 25%, or 30%) were synthesized by successive impregnation. The nanobelt support K2Ti8O17 displays a specific surface area as high as 302 m2/g, and the corresponding catalysts Pt-xK2CO3/K2Ti8O17 show excellent NOx storage performance. As K2CO3 loading increases from 5% to 30%, the NOx storage capacity (NSC) exhibits a volcano-type altering tendency with the maximum appearing at 25% (2.68 mmol/g); the highest NOx reduction efficiency of 99.2% was also achieved over this catalyst in cyclic alternative lean/rich atmospheres. Further increase of K2CO3 loading induces the formation of more bulk or bulk-like K2CO3 species, decreasing the performance of the catalysts for NOx storage and reduction. HR-TEM and FT-IR results indicate that the K species exist as highly dispersed phases including K2O, K2CO3, and −OK groups, which are undetectable by X-ray diffraction (XRD) even at the K2CO3 loading of 30%. Several carbonate species with different thermal stability and reactivity are identified by FT-IR and CO2-TPD. In situ diffuse reflectance FT-IR (DRIFTS) reveals that at low K2CO3 loading (<20%) NOx is mainly stored as monodentate nitrates and monodentate nitrites, while at higher K2CO3 loading NOx is mainly stored as bidentate nitrite species, which results from the decrease of oxidation ability of the catalysts due to the potential covering of K2CO3 on Pt sites.

The Au/MnOx–CeO2 catalysts used for CO preferential oxidation were prepared by deposition–precipitation with ultrasonic assistance. The effect of calcination temperature (150–350 °C) on the structures and catalytic performance of the catalysts was systematically investigated. It is found that the catalyst Au/MnOx–CeO2 calcined at 250 °C exhibits the best catalytic performance, giving not only the highest CO conversion of 90.9% but also the highest selectivity of oxygen to CO2 at 120 °C. The results of XRD, TEM and XPS indicate that this catalyst possesses the smallest particle size, the highest dispersion of Au species and the largest amount of surface adsorbed oxygen species, which are favorable to CO oxidation. The H2-TPR results reveal that the selectivity of oxygen to CO2 is mainly determined by the reducibility of Au species in the catalysts. The strong interaction between Au species and the support in Au/MnOx–CeO2-250 decreases its capability for H2 dissociation and oxidation, leading to high selectivity of oxygen to CO2.Highlights► Au/MnOx–CeO2 catalysts are prepared by a novel ultrasonic-assisted DP method. ► The sample Au/MnOx–CeO2 calcined at 250 °C shows the highest CO PROX performance. ► The selectivity of O2 to CO2 is mainly determined by the reducibility of Au species. ► Ultrasonic increases Au-support interaction, inhibiting H2 activation and oxidation.

A series of CuZnAl1−xZrxO catalysts with different weight ratios of ZrO2/(Al2O3 + ZrO2) were prepared by co-precipitation and used for catalytic production of hydrogen via the route of dimethyl ether steam reforming (DME SR). Multiple techniques such as N2 physisorption, X-ray diffraction (XRD), temperature-programmed reduction by hydrogen (H2-TPR), N2O chemisorption and X-ray absorption fine structure (XAFS, including XANES and EXAFS) were employed for catalyst characterization. It is found that the relative contents of Al and Zr greatly influence the catalytic performance of the catalysts including DME conversion, H2 yield and CO/CO2 selectivity. The catalyst CuZnAl0.8Zr0.2O shows not only the highest DME conversion but also the highest H2 yield in the whole reaction temperature region of 300–425 °C. Poorly crystallized CuO and ZnO phases were identified by XRD for CuZnAl1−xZrxO catalysts. The crystallinity of them increases with the decrease of Al content. The partial substitution of Al by Zr improves both the reducibility and the dispersion of copper species as revealed by H2-TPR results. The N2O chemisorption and Cu K-edge XAFS results conformably indicate that the Cu species in CuZnAl0.8Zr0.2O possesses the highest dispersion. In addition, after used in DME SR reaction, the catalyst CuZnAl0.8Zr0.2O possesses the highest Cu+/Cu0 ratio, as calculated by Cu K-edge XANES fitting. The lowest CO selectivity during DME SR over this catalyst is highly related to the highest Cu+/Cu0 ratio.Highlights► Zr-substituted CuZnAl1−xZrxO is very efficient for H2 production via DME SR route. ► The optimal amount of Zr in CuZnAl1−xZrxO is 20 wt% by ZrO2/(Al2O3 + ZrO2) ratio. ► Zr-substitution improves both the reducibility and the dispersion of Cu oxides. ► Presence of more Cu+ species in CuZnAl1−xZrxO effectively inhibits CO formation.

The CuO–CeO2 catalyst (CuO loading: 15 wt%) was prepared by a novel chemisorption-hydrolysis method, and employed for the preferential oxidation of CO (CO PROX) in H2-rich stream. For comparison, several other conventional methods such as impregnation, co-precipitation and deposition-precipitation were also used to prepare the catalyst. It is found that the CuO–CeO2 catalyst prepared by chemisorption-hydrolysis method exhibits the best catalytic performance, giving not only the widest temperature window (120–170 °C) for CO complete conversion, but also the highest oxygen to CO2 selectivity of 99.9% at 120 °C. The results of XRD, N2O chemisorption and in-situ FT-IR conformably indicate that this catalyst possesses the highest dispersion of Cu species, which facilitates the formation of Cu+ carbonyl species, and simultaneously prevents the adsorption and oxidation of H2. With the increase of reaction temperature, Cu+ is gradually reduced to Cu0, enhancing the adsorption and oxidation of H2, as a result, the selectivity of oxygen towards CO2 is lowered obviously. The presence of CO2 and H2O exhibits negative effects on the catalytic performance, shortening the activity window to 150–170 °C region and decreasing the CO2 selectivity to 87% at the temperature for the initial 100% conversion of CO. Based on the above study, a potential reaction pathway for CO PROX over the CuO–CeO2 catalyst is proposed.Highlights► Chemisorption-hydrolysis is a novel route for synthesizing CuO–CeO2 used for CO PROX. ► Superhigh selectivity (99.9%) of O2 to CO2 is achieved at 120 °C over CuO–CeO2(CH). ► CuO–CeO2(CH) possesses the highest Cu dispersion, increasing O2 to CO2 selectivity. ► Below 120 °C H2 adsorption is totally inhibited by the formation of Cu+–CO species.

A series of lean-burn NOx trap catalysts Pt/K/TiO2–Al2O3–La2O3 were prepared by sequential impregnation with the support synthesized using a superior polymerized complex method. The effect of La2O3 addition to the support on the structures, NOx storage capacity (NSC) and sulfur-resistance of Pt/K/TiO2–Al2O3 catalysts was investigated carefully. TG/DTA, FT-IR, N2 physisorption, in-situ DRIFTS, H2-TPR, NH3-TPD and CO-chemisorption techniques were employed for catalyst characterization. It is found that the NSC of Pt/K/TiO2–Al2O3 is greatly increased by La2O3 addition due to the remarkably increased specific surface area of the support and the improved Pt dispersion. Higher Pt dispersion corresponds to stronger oxidation ability and larger NSC of the catalysts. The catalyst with a weight ratio of La2O3/(TiO2 + Al2O3 + La2O3) = 3% always shows the highest NSC at both fresh and regenerated states. In-situ DRIFT spectra show that NOx is mainly stored as nitrate species at 350 °C. The Pt/K/TiO2–Al2O3–La2O3 catalysts show much better desulfation performance and much higher NSC recovery efficiency than TiO2–Al2O3 or La2O3 supported ones, especially the catalyst containing 3% La2O3 in the support, which exhibits an NSC recovery efficiency as high as 91%. From the view of both NOx storage and sulfur-resistance, this catalyst is more promising for practical lean-burn NOx removal.Highlights► A superior polymerized complex method was used to prepare TiO2–Al2O3–La2O3 support. ► The NOx storage capacity of Pt/K/TiO2–Al2O3 is greatly increased by La2O3 addition. ► La2O3 addition obviously increases the SBET of the support and the dispersion of Pt. ► La2O3 addition can also improve the sulfur-resisting performance of Pt/K/TiO2–Al2O3. ► The optimal content of La2O3 in the whole support TiO2 + Al2O3 + La2O3 is 3% by weight.

The nanometric substituted perovskite catalysts La1−xKxCo1−yNiyO3−δ (x = 0, 0.1; y = 0, 0.05, 0.1) were synthesized by citric acid complexation method, and employed for soot combustion, NOx storage and simultaneous NOx-soot removal. Their structures and physico-chemical properties were characterized by XRD, EXAFS, BET, SEM, H2-TPR, and XPS techniques. When K and Ni are simultaneously introduced into LaCoO3 catalyst, soot combustion is largely accelerated, with the temperature (Tm) for maximal soot conversion lowered by at least 50 °C; moreover, NOx reduction by soot is also facilitated. The La0.9K0.1Co0.95Ni0.05O3−δ catalyst exhibits not only the lowest Tm (367 °C) temperature but also the highest soot combustion rate (67.3 μg/s g catalyst). Meanwhile, the NOx reduction percentage over this catalyst can reach 21%. The kinetic results show that the activation energy for soot combustion over La0.9K0.1Co0.95Ni0.05O3−δ (81.34 kJ mol−1) is much lower than that over LaCoO3 (107.7 kJ mol−1). The H2-TPR and XPS results show that the La0.9K0.1Co0.95Ni0.05O3−δ catalyst possesses better redox properties, more tetravalent cobalt ions and larger amount of surface adsorbed oxygen species, which determines its novel performance for soot combustion, NOx storage and soot-NOx removal.Graphical abstractHighlights► La1−xKxCo1−yNiyO3−δ show better performance for soot combustion and soot-NOx removal. ► More Co4+ ions and oxygen vacancies are formed in La1−xKxCo1−yNiyO3−δ catalysts. ► Substituted catalysts La1−xKxCo1−yNiyO3−δ possess larger amount of adsorbed oxygen. ► Soot combustion activation energy is largely decreased by simultaneous substitution.

Mesoporous binary oxides TiO2–Al2O3 were prepared by citric acid complexation-organic template decomposition method using nonionic p-octyl polyethylene glycol phenyl ether (OP) and cationic cetyltrimethyl-ammonium bromide (CTAB) as co-templates; the corresponding NSR catalysts Pt/K/TiO2–Al2O3 were prepared by successive wetness impregnation. Multiple techniques including N2 physisorption, XRD, HR-TEM, NH3-TPD, H2-TPR and H2-chemisorption were employed for catalyst characterization. It is found that the support prepared using OP and CTAB as co-templates possesses much larger specific surface area (309 m2/g) than those prepared using CTAB as single template (275 m2/g) or using conventional co-precipitation (250 m2/g); meanwhile, this support exhibits the largest amount of surface acidic sites as indicated by NH3-TPD results, which makes its supported catalyst show the best sulfur-resistance performance among the catalysts with the support prepared by different methods. The results of H2-chemisorption and HR-TEM conformably indicate that this catalyst also possesses the highest dispersion of Pt, which determines its best NOx storage and reduction performance at lean/rich cycles, giving a mean NOx reduction percentage as high as 95 %.

Herein, we introduce a La1−xSrxCoO3 perovskite catalyst, substituting for Pt containing LNT catalysts, to remove efficiently NOx from lean-burn engines. The NOx storage/reduction occurred alternatively on the perovskite in successive lean/rich atmospheres, and the NOx conversion reached 71.4% with 100% selectivity to N2 at 300 °C.

A facile strategy to correlate the thermal decomposition of inorganic–organic hybrid with the Kirkendall effect appearing during the oxidation process of sulfides into oxides has been developed to synthesize hierarchical-porous-structured metal oxide microspheres by using ceria as the model system. The as-prepared hierarchical-porous-structured ceria with micropores, mesopores and macropores (HC3M) possesses a very high surface area (over 290 m2 g−1) and high thermal stability. We have also demonstrated that the pore size of mesopores in HC3M can be modulated by controlling the oxidation and decomposition temperature of the hybrid precursors. Our preliminary results of the preferential oxidation of carbon monoxide in the H2-rich stream (PROX) show that both the conversion and selectivity of the Cu/HC3M catalyst are obviously higher than those of Cu/CeO2 particles. The improved catalytic activity may be attributed to the high dispersion and the smaller size of Cu on HC3M, the high specific surface area and unique hierarchical porous structure of HC3M support. Thus, the hierarchical-porous-structured ceria is expected to find promising applications in catalysis, sensors and fuel cells. In addition, the method to convert inorganic–organic hybrid sulfides into oxides can be successfully extended to the synthesis of hierarchical-porous-structured Y-doped and La-doped ceria with the modulated composition. Through the designed preparation of inorganic–organic hybrid sulfides, selenides or tellurides followed by the oxidation and thermal decomposition at suitable temperature, we believe that this conversion of hybrid materials into oxides might be extended to fabricate other hierarchical-porous-structured oxides with improved physical and/or chemical properties.

A series of the BaFeO3 − x perovskite catalysts was synthesized by a sol-gel method using citric acid and/or EDTA as complexants with a purpose to improve their sulfur-resistance by forming a uniform perovskite structure at a low calcination temperature, i.e. 750 °C. The thermogravimetry results show that almost no carbonate was formed after calcination of the xerogel precursor with the complexants' molar ratio of CA/EDTA ≤ 1.5, which was convinced by the in situ DRIFT spectra results of the Ba–Fe-1 catalyst during the SO2/O2 sorption. It indicates that, after adding EDTA into the complexants, the metal ions of the raw material could be mixed homogeneously and react stoichiometrically by calcination at 750 °C to form a uniform perovskite structure. Accordingly, the obtained Ba–Fe-1 perovskite presented a performed sulfur-resistance. Moreover, the seriously damaged structure of the BaFeO3 − x perovskite by reduction could be in situ regenerated by calcination under lean conditions at 400 °C, which is within the operating temperature zone of the aftertreatment system of diesel to meet the real commercial demands.Research highlights► The BaFeO3 − x perovskite was prepared by a sol-gel method. ► The BaFeO3 − x perovskite was used as a NOx storage-reduction catalyst. ► Addition of EDTA made the metal ions mix homogeneously in the sol. ► Complexants with CA/EDTA ≤ 1.5 could produce a uniform perovskite structure. ► The uniformed BaFeO3 − x perovskite has a good sulfur-resistance.

As a novel and rather convenient method, ultrasonic pretreatment was employed for the preparation of nanostructured Au/MnOx–CeO2 (Mn/Ce = 1:1) catalysts which were used for CO preferential oxidation. The effects of synthesis pH (7.0–11.0) and Au loading (0.5–5.0 wt.%) on the performance of these catalysts were systematically investigated. It is found that the Au(1.0)/MnOx–CeO2-10.0 with 1.0 wt.% Au prepared at pH = 10.0 exhibits the best catalytic performance, giving not only the highest CO conversion of 90.9% but also the highest oxygen to CO2 selectivity of 47.8% at 120 °C. The results of XRD, HR-TEM and XPS indicate that this catalyst possesses the highest dispersion of Au species and the largest amount of surface adsorbed oxygen species, which facilitates CO oxidation. The H2-TPR results reveal that the selectivity of oxygen to CO2 is mainly determined by the reducibility of Au species in the catalysts. The strong interaction between Au species and the supports in the catalyst Au(1.0)/MnOx–CeO2-10.0 decreases its capability for H2 dissociation, effectively inhibiting the hydrogen spillover, as a result, the selectivity of oxygen to CO2 is remarkably increased.Highlights► Au/MnOx–CeO2 catalysts are prepared by a novel ultrasonic-assisted DP method. ► The sample Au/MnOx–CeO2 (1.0 wt.% Au, pH = 10.0) shows the highest CO PROX performance. ► The selectivity of O2 to CO2 is mainly determined by the reducibility of Au species. ► Ultrasonic increases Au-support interaction, inhibiting H2 activation and oxidation.

A series of Ce1−xZrxO2 (x = 0, 0.1, 0.2, 0.3) solid solution supported lean-burn NOx trap (LNT) catalysts K/LaCoO3/Ce1−xZrxO2 were prepared by successive impregnation. After sulfation the supported perovsikte LaCoO3 was well maintained; reducing treatment partly destroyed the perovsikte, but it can be well recovered by re-oxidation treatment. Based on NOx storage and sulfur-resisting performance of the catalysts, the optimal atomic ratio of Zr in Ce1−xZrxO2 support is x = 0.2. The catalyst K/LaCoO3/Ce0.8Zr0.2O2 exhibits much better NOx storage capacity than the Pt-based catalyst Pt/K/Ce0.8Zr0.2O2, which is highly related to its stronger capability for NO to NO2 oxidation. During NOx storage much larger amounts of nitrate and nitrite species were identified by in situ DRIFTS over perovskite-based catalysts than over Pt-based one. The H2-TPR results reveal that after deep sulfation little sulfur species were deposited on the catalyst K/LaCoO3/Ce1−xZrxO2, showing strong sulfur-resisting ability. As a result, it is thought that the full replacement of Pt by perovskite LaCoO3 in the corresponding LNT catalysts is feasible.

The hydrotalcite-based MnxMg3−xAlO catalysts with different Mn:Mg atomic ratios were synthesized by coprecipitation, and employed for soot combustion, NOx storage and simultaneous soot-NOx removal. It is shown that with the increase of Mn content in the hydrotalcite-based MnxMg3−xAlO catalysts the major Mn-related species vary from MnAl2O4 and Mg2MnO4 to Mn3O4 and Mn2O3. The catalyst Mn1.5Mg1.5AlO displays the highest soot combustion activity with the temperature for maximal soot combustion rate decreased by 210 °C, as compared with the Mn-free catalyst. The highly reducible Mn4+ ions in Mg2MnO4 are identified as the most active species for soot combustion. For NOx storage, introduction of Mn greatly influences bulk NOx storage, with the adsorbed NOx species varying from linear nitrites to ionic and chelating bidentate nitrates gradually. The coexistence of highly oxidative Mn4+ and highly reductive Mn2+ in Mn1.0Mg2.0AlO is favorable to the simultaneous soot-NOx removal, giving a NOx reduction percentage of 24%. In situ DRIFTS reveals that the ionic nitrate species are more reactive with soot than nitrites and chelating bidentate nitrates, showing higher NOx reduction efficiency.

A series of lean-burn NOx trap (LNT) catalysts Pt/K/Al2O3–TiO2–ZrO2 were prepared by sequential impregnation. By altering support calcination temperature and K loading, the distribution state of the storage medium K on different catalysts is carefully investigated. Pyridine-IR results show that a lot of hydroxyl groups exist on the supports calcined at low temperatures (<800 °C), which can react with the supported K2CO3, possibly forming –OK groups. The in situ DRIFTS results indicate that the dominant NOx storage species are monodentate or/and bidentate nitrates. As the calcination temperature is increased to 800 °C or higher, much less hydroxyl groups are detected on the surface of Al2O3–TiO2–ZrO2. In this case, most potassium exists in the form of K2CO3 on Al2O3–TiO2–ZrO2, which can transform to free ionic nitrates during NOx storage. High K loading and high calcination temperature facilitate the formation of K2CO3, which possesses higher NOx storage efficiency but lower sulfur resisting and regeneration ability than –OK groups.

A series of lithium-based lean-burn NOx trap catalysts Pt/Li/TiO2–Al2O3 were prepared by sequential impregnation. The doping of TiO2 into the support Al2O3 significantly enhances the sulfur-resistance performance of the catalyst Pt/Li/Al2O3. On TiO2–Al2O3 mixed oxides, the Pt and lithium species are more highly dispersed, giving higher NOx storage capacity, as compared with those on Al2O3 and TiO2. In situ DRIFTS reveals that the NOx storage on Pt/Li/TiO2–Al2O3 mainly proceeds on –OLi sites forming bidentate nitrate species at 500 °C. The catalyst Pt/Li/TiO2–Al2O3 with 40% TiO2 in the support is the most promising one applicable to the lean-burn NOx abatement.

The noble metal free perovskite-type BaFeO3−x catalyst has been synthesized by a sol−gel method containing a small amount of spinel and carbonate. NOx is stored on both perovskite and carbonate, and the formed nitrate on the perovskite can be transferred to the neighboring carbonates to regenerate the storage sites on the perovskite. During the sulfation process, both perovskite and carbonate can be sulfated, and the sulfate species formed on the former one is more easily reduced. The poison of the perovskite catalyst is mainly due to the sulfation of the carbonate. The NOx storage capacity of the sulfated BaFeO3-950 catalyst, on which a trace amount of carbonate exists, drops only 14% comparing with the fresh catalyst. The iron atoms surrounding the barium atoms closely in the crystal lattice of the perovskite inhibit the sulfation of the barium, inducing a high sulfur tolerance.

A series of mesoporous MnOx−CeO2 binary oxide catalysts with high specific surface areas were prepared by surfactant-assisted precipitation. The CO and C3H8 oxidation reactions were used as model reactions to evaluate their catalytic performance. The techniques of N2 adsorption/desorption, XRD, XPS, TPR, TPO, TPD, and in situ DRIFTS were employed for catalyst characterization. It is found that the activity for CO and C3H8 oxidation of the catalysts exhibits a volcano-type behavior with the increase of Mn content. The catalyst with a Mn/Ce ratio of 4/6, possessing a high specific surface area of 215 m2/g, exhibits the best catalytic activity, which is related not only to its highest reducibility and oxygen-activation ability, as revealed by TPR and TPO, but also to the formation of more active oxygen species on the MnOx−CeO2 interface as identified by TPD. After the addition of a small amount of Pd to the MnOx−CeO2 catalyst, its activity for CO oxidation is greatly enhanced, due to the acceleration of gas-phase oxygen activation and transferring via spillover. However, the activity for C3H8 oxidation is hardly promoted due to the different reaction pathways for CO and C3H8 oxidation. For CO oxidation, the gas-phase oxygen activated by Pd can directly react with the adsorbed CO to form CO2, while, for C3H8 oxidation, which takes place at a much higher temperature than CO oxidation, the C−H bond activation and cleavage may be mainly driven by the active oxygen species on the interface between MnOx and CeO2. The addition of Pd shows little effect on the active interface oxygen species, so no promotion upon C3H8 oxidation is observed.

A series of nano-gold catalysts supported on binary oxides MOx–CeO2 (atomic ratio M/Ce = 1:1, M = Mn, Fe, Co, Ni) are prepared by deposition–precipitation (DP). An innovative and rather convenient ultrasonic pretreatment of the support is employed for Au/MnOx–CeO2 preparation. It is found that for preferential CO oxidation Au/MnOx–CeO2 is more active than Au/CeO2. Ultrasonic pretreatment of MnOx–CeO2 further promotes the performance of Au/MnOx–CeO2, with CO conversion increased by 24 % at 120 °C. Meanwhile, the selectivity of oxygen to CO2 is promoted in the whole temperature range, especially in 80–120 °C, the selectivity is increased by 15–21%. HR-TEM and XRD results indicate that ultrasonic pretreatment is favorable to the formation of much smaller gold nanoparticles (<5 nm). The characterization of XPS, UV–vis DRS, H2-TPR and CO-TPR confirms that the strong interaction between Au and the support effectively inhibits the dissociation and oxidation of H2 over the ultrasonically pretreated catalyst Au/MnOx–CeO2, making it highly selective to CO oxidation.

Nanorods and nanoparticles of CeO2 were successfully synthesized and used as support of Pd/CeO2 catalysts. It is found that the nanorods show obvious advantages as the support, compared with the nanoparticles. Low efficiency in the formation of reduced Pd, and partial encapsulation of Pd species account for the poor activity of Pd supported on CeO2 nanoparticles. On the contrary, a favorable interaction between Pd and the crystal planes [1 1 0] and [1 0 0] of CeO2 nanorods effectively promotes the reducibility of Pd species, resulting in much better catalytic performance of Pd/CeO2 catalyst for CO oxidation.

A mesoporous NSR catalyst Pt/BaCO3–Al2O3 was synthesized by using tri-block copolymer P123 as template. Systematic comparative studies on the structural and catalytic performance between the mesoporous catalyst and the conventional impregnated one were performed. N2 physisorption, XRD, TPD were employed for their structural characterization. In situ DRIFTS, TPR, TEM were used for investigation of the catalytic behaviors for NOx and SOx sorption, as well as desulfation. The results of structural characterization show that mesoporous Pt/BaCO3–Al2O3 exhibits high surface area (261 m2 g−1 after calcination at 600 °C), uniform pore size with a diameter of ca. 5 nm and high thermal stability up to 800 °C. The Ba-containing species are highly dispersed in three-dimensions and strongly interacted with Al2O3, and all the BaCO3 presents as LT-BaCO3 (BaCO3 with low thermal stability). By contrast, most of the Ba species in the impregnated sample exist predominantly as HT-BaCO3 (BaCO3 with high thermal stability) and are enriched on the surface. As a result, the mesoporous sample possesses great advantages in serving as NSR catalysts, such as enhanced NOx trapping ability, lower sulfation degree, and higher desulfation extent, as compared with the impregnated one. In addition, after NOx and SOx sorption, no bulk phases of barium nitrates and sulfates were observed in the mesoporous catalyst, while they are evidently formed on the impregnated one. In a word, the mesoporous structure is of great significance in achieving high dispersion of barium species and better performance for NOx storage and regeneration of the catalyst.

A series of mesoporous multicomponent mixed oxide catalysts La-Mn-Ce-O with various ratios of (nLa+nMn)/(nLa+nMn+nCe) were prepared by citric acid complexation-organic template decomposition (CAC-OTD) method. For comparison, the sample with the same composition was also prepared by conventional coprecipitation method. The results of N2 adsorption/desorption showed that the samples prepared by using CAC-OTD method possessed relatively large specific surface area and uniform pore diameter distribution (3.4.4.4 nm). The results of X-ray diffraction (XRD) identified the formation of La-Ce and Mn-Ce solid solution. Mn species were not detected by XRD. The results of X-ray photoelectron spectroscopy (XPS) showed that there was a strong electronic state interaction between Mn and Ce species, resulting in the formation of Mn 2p shake-up peak. Such interaction enhanced the transfer of oxygen species from Ce to Mn oxide and therefore increased the redox activity of the samples. The sample with the strongest shake-up peak showed the highest oxidation activity. The results of temperature programmed reduction (TPR) showed that the manganese species in the samples prepared by using CAC-OTD method were easier to be reduced, which was relevant to the oxidation activity of the catalysts. The results of activity evaluation showed that the light-off temperature of the LMC(0.5)-500 sample was about 50°C lower than that of the sample prepared by using coprecipitation method. The samples prepared by using CAC-OTD method showed good thermal stability.

The mesoporous catalysts La–Co–Ce–O were successfully prepared in one step by citric acid complexation-organic template decomposition method, which show large surface area (up to 157 m2/g), narrow pore diameter distribution (3.7∼3.9 nm), good thermal stability and high activity for CO and C3H8 oxidation. Based on the structural characterization results, it is found that the predominant Co phases are Co3O4 crystallites, and the activities of these mesoporous catalysts are not proportional to the amounts of surface cobalt atoms, but mainly related to the physical structure of the catalysts and the effective interaction between cobalt and cerium species. When the surface Co/Ce atomic ratio is close to 1, the catalytic synergy effect between them is maximized.

A series of Li-based lean-burn NOx trap (LNT) catalysts Pt/Li/TiO2–MOx (M = Al, Zr, Si, Sn) were prepared by sequential impregnation with the supports TiO2–MOx synthesized by co-precipitation. The support effect on the NOx storage and sulfur-resisting performance of Pt/Li/TiO2–MOx catalysts was investigated carefully. The NOx storage capacity of fresh Pt/Li/TiO2 is greatly improved by doping with Al2O3 or ZrO2 due to the remarkably increased specific surface area and the oxidation ability of the catalysts. HR-TEM and H2-chemisorption results reveal that the oxidation ability of Pt/Li/TiO2–MOx is mainly determined by Pt crystallite size. Larger Pt crystallites correspond to stronger oxidation ability. The regeneration of sulfated Pt/Li/TiO2–MOx strongly depends on the total acidity of the supports, including Brønsted and Lewis acid; the supports with larger acidity possess higher ability of sulfur-resistance and regeneration. The results of in situ DRIFTS show that over Pt/Li/TiO2–MOx (M = Al, Zr, Si, Sn) NOx is mainly stored as ionic nitrate species at 350 °C. Taking the NSC and regeneration ability into account, the catalyst Pt/Li/TiO2–Al2O3 is the most promising one for practical application.Graphical abstractDownload high-res image (145KB)Download full-size imageHighlights► The BET area and acidity of TiO2 are increased by the addition of MOx (M = Al/Zr/Si). ► The NOx storage capacity of Pt/Li/TiO2 is enhanced by MOx(M = Al/Zr/Si/Sn) addition. ► The ability of the catalysts for NO to NO2 oxidation is related to Pt particle size. ► The sulfur-resistance and regeneration of the catalysts depends on support acidity.

Nanosheets-constructed ZnO spheres with novel three-dimensional (3D) fluffy structure were successfully synthesized by a facile one-step solvothermal method. Each fluffy ZnO sphere possesses a diameter of 2–3 μm, consisting of crossed nanosheets with an average thickness of ∼20 nm. Such special hollow 3D structure makes larger surface area and more active sites exposed during the reaction, facilitating the transportation of reactants and products and increasing the reaction rate. The activity measurement for Rhodamine B photodegradation shows that such fluffy ZnO spheres do possess much higher photocatalytic activity than other commonly reported nanostructured ZnO, such as nanoflowers, nanospiraldisks, nanodumbbells and nanorods. The results of photoluminescence spectra show that the fluffy spheres show much higher electron–hole segregation efficiency than other ZnO materials. Through one-pot synthesis Ag is readily doped on the fluffy spheres and strongly interacts with them, further improving the photocatalytic performance of ZnO. Based on the properties and characterization results, a special growth mechanism for such fluffy ZnO spheres is proposed, and the photocatalytic reaction mechanism is also discussed.Graphical abstractDownload full-size imageResearch highlights▶ Nanosheets-constructed fluffy ZnO spheres were successfully synthesized. ▶ The fluffy ZnO is more active than other nano-ZnO for Rhodamine B photodegradation. ▶ Doping Ag on the fluffy ZnO spheres further improves its photocatalytic activity. ▶ A special growth mechanism for such fluffy ZnO spheres is proposed.

Several nanosized catalysts Co3O4–CeO2 with varying compositions were synthesized by a surfactant-template method and further promoted by a small amount of Pd (0.5 wt%). These catalysts exhibit uniform mesoporous structure and high surface area (>100 m2 g−1). The Co3O4 crystallites in these catalysts are encapsulated by nanosized CeO2 with only a small fraction of Co ions exposing on the surface and strongly interacting with CeO2. Such structure maximizes the interaction between Co3O4 and CeO2 in three dimensions, resulting in unique redox properties. The introduction of Pd prominently enhances both the reduction and oxidation performance of the catalysts, due to hydrogen or oxygen spillover. These catalysts prepared by surfactant-template method exhibit excellent oxidation performance, especially the ones promoted with Pd, which show markedly enhanced CO oxidation activity even at room temperature. Based upon the results of structural properties, redox behaviors and in situ DRIFTS study, two different reaction pathways over Co3O4–CeO2 and Pd/Co3O4–CeO2 are proposed.

Several nanosized catalysts Co3O4–CeO2 with varying compositions were synthesized by a surfactant-template method and further promoted by a small amount of Pd (0.5 wt%). These catalysts exhibit uniform mesoporous structure and high surface area (>100 m2 g−1). The Co3O4 crystallites in these catalysts are encapsulated by nanosized CeO2 with only a small fraction of Co ions exposing on the surface and strongly interacting with CeO2. Such structure maximizes the interaction between Co3O4 and CeO2 in three dimensions, resulting in unique redox properties. The introduction of Pd prominently enhances both the reduction and oxidation performance of the catalysts, due to hydrogen or oxygen spillover. These catalysts prepared by surfactant-template method exhibit excellent oxidation performance, especially the ones promoted with Pd, which show markedly enhanced CO oxidation activity even at room temperature. Based upon the results of structural properties, redox behaviors and in situ DRIFTS study, two different reaction pathways over Co3O4–CeO2 and Pd/Co3O4–CeO2 are proposed.

Nanostructured Co3O4−CeO2 and CuO−CeO2 catalysts with the specific surface areas exceeding 100 m2 g−1 were synthesized by a surfactant-templated method. The catalytic performance of these catalysts was investigated using the total oxidation of CO and C3H8 as model reactions. The results show that the Co3O4−CeO2 catalysts are less active for CO oxidation but are more active for C3H8 oxidation as compared with the CuO-CeO2 catalysts. Moreover, the Co3O4−CeO2 catalysts exhibit a volcano-type performance for CO oxidation with the cobalt content increasing. The in situ diffuse reflectance infrared spectroscopy (DRIFTS) study shows that CO is adsorbed mainly as carbonyl (2106 cm−1) and bidentate carbonate (1568 and 1281 cm−1) on CuO−CeO2, and only as bidentate carbonate (1591 and 1268 cm−1) on Co3O4−CeO2. On the basis of the results of structural characterization, redox properties, and in situ DRIFTS study, the active sites for CO and C3H8 oxidation are identified, respectively. Carbon monoxide oxidation preferentially occurs at the interface between CeO2 and CuO or Co3O4, whereas propane oxidation takes place on the neighboring surface lattice oxygen sites in CuO or Co3O4 crystallites. The different requirements of the active sites are determined by the different reaction mechanisms and the rate-determining steps. It is also found that the introduction of a small amount of Pd to Co3O4−CeO2 can remarkably promote the CO oxidation activity, but it hardly enhanced the C3H8 oxidation activity of the catalyst. The different reaction mechanisms, on molecular level, are identified and discussed in detail.

For the first time we synthesized mesoporous CeO2 nanosheets with single-crystal-like, ultrathin and uniform-sized structures through the thermal decomposition of specially prepared intermediates of Ce(OH)CO3 nanosheets. The resulting single-crystal-like CeO2 porous nanosheets are only 2.4 nm thick, as measured by AFM. BET analysis indicated that the pores of the nanosheets were centered at 3.7 nm. A novel structure transformation mechanism from 1D to 0D, then to a 2D assembly was clearly revealed. Moreover, such ultrathin CeO2 porous nanosheets exhibited much higher photocatalytic activity for dye degradation than that of polycrystalline CeO2 nanoparticles.

A facile strategy to correlate the thermal decomposition of inorganic–organic hybrid with the Kirkendall effect appearing during the oxidation process of sulfides into oxides has been developed to synthesize hierarchical-porous-structured metal oxide microspheres by using ceria as the model system. The as-prepared hierarchical-porous-structured ceria with micropores, mesopores and macropores (HC3M) possesses a very high surface area (over 290 m2 g−1) and high thermal stability. We have also demonstrated that the pore size of mesopores in HC3M can be modulated by controlling the oxidation and decomposition temperature of the hybrid precursors. Our preliminary results of the preferential oxidation of carbon monoxide in the H2-rich stream (PROX) show that both the conversion and selectivity of the Cu/HC3M catalyst are obviously higher than those of Cu/CeO2 particles. The improved catalytic activity may be attributed to the high dispersion and the smaller size of Cu on HC3M, the high specific surface area and unique hierarchical porous structure of HC3M support. Thus, the hierarchical-porous-structured ceria is expected to find promising applications in catalysis, sensors and fuel cells. In addition, the method to convert inorganic–organic hybrid sulfides into oxides can be successfully extended to the synthesis of hierarchical-porous-structured Y-doped and La-doped ceria with the modulated composition. Through the designed preparation of inorganic–organic hybrid sulfides, selenides or tellurides followed by the oxidation and thermal decomposition at suitable temperature, we believe that this conversion of hybrid materials into oxides might be extended to fabricate other hierarchical-porous-structured oxides with improved physical and/or chemical properties.

A mesoporous perovskite, LaCoO3, with a high specific surface area of 75 m2 g−1 was synthesized by a nano-casting method. Its related NOx storage/reduction catalyst K/LaCoO3, which contains no noble metals, exhibits excellent de-NOx performance under alternating lean/rich conditions, showing a high NOx reduction efficiency of 97.0% and a high NOx to N2 selectivity of 97.3%.

Black TiO2 was usually obtained via hydrogenation at high pressure and high temperature. Herein, we reported a facile hydrogenation of TiO2 in the presence of a small amount of Pt at relatively low temperature and atmospheric pressure. The hydrogen spillover from Pt to TiO2 accounts well for the greatly enhanced hydrogenation capability. The as-synthesized Pt/TiO2 exhibits remarkably improved photocatalytic activity for water splitting.