•NiMgAl-layered double hydroxides derived Ni catalysts for NH3 decomposition.•Catalyst of certain constitution showed high efficiency and excellent durability.•Superior performance is associated with the Mg site synergism toward Ni.•“Spillover effect” of surface hydrogen accounts for a higher turnover frequency.The NiMgAl-layered double hydroxides, with the stoichiometric ratios of Mg/Ni and Mg/Al being 0–9 and 0–3, respectively, were synthesized and employed as the Ni catalyst precursors for NH3 decomposition. The resulting catalyst of the certain Ni, Mg, and Al contents showed high catalytic efficiency and outstanding durability for the target reaction. The features of cost effective (with only Mg and Al elements besides Ni), easy fabrication, and thermally durable are attractive for large-scale operation. The characterizations revealed the related changes in structure and property, such as the Ni particle size and distribution, the reduction of Ni2+ species, the Ni-oxide matrix interaction, the surface basicity as well as the adsorption/desorption behavior of hydrogen, in line with the stoichiometry of Ni, Mg, and Al in the samples. The superior catalytic activity and stability are thought to be associated with the structurally isolated active Ni species by the oxide matrix and the synergism between Ni-Mg sites. Particularly, the “spillover effect” of surface hydrogen accounts for a higher turnover frequency.Download high-res image (193KB)Download full-size image

In this study, the morphologically uniform Co3O4 cubes (c-Co3O4), hexagonal plates (h-Co3O4) and tetrakaidecahedrons (t-Co3O4) were carefully synthesized and the crystalline facets of (001), (111), and (112) were identified. Au nanoparticles (3.1–3.3 nm) were deposited on the three Co3O4 entities, which were achieved to obtain specific Au–Co3O4 interfaces. A detailed comparison was made on the basis of their unique interfacial structures and catalytic behaviors. H2-TPR and XPS investigations revealed the important variations in reactivity of surface oxygen, surface Co3+/Co2+ ratio, evolution of surface oxygen vacancies as well as Au oxidation state upon Au loading and pretreatments. The enhanced CO oxidation by Au deposition, and particularly He- and in situ-pretreatments, has been elucidated in light of the structural specialties associated with the three facets of Co3O4 substrates and the corresponding Au–Co3O4 interfaces. The consequent activity enhancement for Co3O4 substrate and Au–Co3O4 interface was verified: (001) > (112) > (111), and Au/(112) > Au/(001) > Au/(111). The results of Au/h-Co3O4 also suggest that both Au cluster and Co3O4 structural feature can have a profound effect on the catalytic behaviour of generated interface. The present study extends the insights into the interface-dependent CO oxidation over the controllably prepared Au–Co3O4 interfacial structures.

Spherically shaped Co3O4 particles were synthesized by one-pot solvothermal treatment of Co(NO3)2 in n-octanol that is free of structure-directing agents or pore formers. Au nanoparticles (2–4 nm) dispersed on the Co3O4 substrates were fabricated using deposition–precipitation method. The as-synthesized Co3O4 (without calcination) and the corresponding Au-containing catalyst achieved complete CO oxidation at 90 °C and 80 °C, respectively. Upon calcination, the condensed Co3O4 formed on which uniform dispersion of small-sized flat Au entities (3.0 ± 0.6 nm) with large Au–Co3O4 interfaces was established, showing complete CO oxidation at 110 °C. These two types of catalysts were found to be extremely durable even when operated in a period beyond 70 h under certain conditions. The calcined Co3O4-based Au catalyst can outperform Au/d-Co3O4 in both activity and stability when subjected to a pre-reaction at 350 °C for 5 h. The yolk–shell type Co3O4@SiO2 catalysts synthesized by controllable acid-etching of Co3O4 cores demonstrated an optimal Co3O4 core–SiO2 shell interaction and a suitable Co3O4 core particle size for CO oxidation. Both Co3O4 substrates and Au/Co3O4 systems were found to encounter substantial activity enhancement by in situ pretreatment. The pretreatment resulted in (i) transformation of AuOx to Au0, (ii) higher fraction of surface Co3+, and (iii) suitably lower concentration of surface oxygen adspecies, accounting for the enhanced activities.

By regulating the H2O/SiO2 molar ratio (n = 13.8, 16.9, 20.1, 26.3), NaY zeolites of different particle sizes (NaY-n, 50–400 nm) were synthesized, and NaY-n was modified with disodium hydrogen phosphate, Na2HPO4. The as-prepared catalysts are highly effective for the dehydration of sustainable lactic acid (LA) to produce acrylic acid (AA). Through the optimization of NaY particle size and Na2HPO4 loading, AA yields as high as 74.3% can be achieved under mild conditions (340 °C). In terms of employed feed rate of lactic acid and amount of catalyst, the AA formation rate is 12.0 mmol gcat−1 h−1, the highest ever reported for LA dehydration to AA. Employing slightly low Si/Al ratios in NaY-n can modify catalyst acidity, while pre-applied Na+ ion-exchange and following Na2HPO4 loading can effectively reduce the number of acid sites, particularly the Brønsted ones on NaY-n. Equally important structural features of NaY-n are their shorter pore channels (or even incompletely developed zeolite texture) and relatively larger Sexternal/SBET ratio, which favors quick product departure from the catalyst surface, and reduces the possibility of side reactions occurring inside the long channels. The appropriate surface acidity together with unique structural features of NaY-n ensure efficient LA conversion with high dehydration selectivity. Higher surface concentrations of Na+ on Na2HPO4/NaY-n also favor sodium lactate meanwhile suppressing poly-lactate as well as preventing carbon formation, corresponding to superior performance as well as improved durability of Na2HPO4/NaY-n.

•Pre-hydrolysis approach to direct synthesis of Fe, Al-, and Cr-incorporated SBA-15.•No need in mineral acids addition and in situ incorporation of cations in host framework.•Flexible metal content with M/Si molar ratio up to 0.05 (Fe, Cr)–0.08 (Al).•Metal content can also be readily controlled by varying the pre-hydrolysis period.•As-synthesised Fe-SBA-15 shows good (hydro)thermal stability and enhanced B/L acidity.The Fe-incorporated mesoporous SBA-15 materials with the Fe content up to a Fe/Si molar ratio = 0.05 were synthesised via pre-hydrolysis of tetraethyl orthosilicate (TEOS) employing P123 triblock copolymer as the template. The synthetic strategy is the hydrolysis of Fe salt precursor can provide acidic medium essential for the pre-hydrolysis of TEOS. Different Fe/Si ratios and TEOS pre-hydrolysis periods were employed to modify the structure and texture of the Fe-incorporated SBA-15. The impact of Fe sources (ferric nitrate, ferric chloride, and ferric sulfate) on the characteristics of Fe-SBA-15 has also been investigated. Ferric nitrate showed the best effect among the three Fe sources. UV–Vis study reveals that besides the four-coordinated iron species, the iron oxide domains may also exist in the samples. Pyridine adsorption IR study demonstrates enhancement in Brønsted and Lewis acidity of as-synthesised Fe-SBA-15 materials, potential as solid acid catalyst or catalyst support. Moreover, the employed treatments (700 °C for 10 h in air and 600 °C for 3 h in 100% steam) verified good thermal and hydrothermal stability of the derived Fe-SBA-15. For comparison, Al- and Cr-incorporated SBA-15, with the Al/Si and Cr/Si molar ratio of 0.08 and 0.05 respectively, were also synthesised through the same strategy.

A novel synthetic strategy has been adopted to deposit Au nanoparticles (NPs) (ca. 5 nm) on a hollow FeOx substrate using Au/β-FeOOH hybrid nanocrystals as the precursor. Through the encapsulation of Au/β-FeOOH by SiO2 shells and the calcination step, the Au/β-FeOOH can be transformed into Au/FeOx with the hollow structural feature. Because of the protective SiO2 shells, aggregation of the Au NPs is effectively prohibited, and the hemispherical morphology of the Au particles is essentially retained. The Au/FeOx hollow composite is obtained by removing the SiO2 shells, and the Au NPs in the final Au/FeOx hollow composite are small-sized yet stable enough because of the calcination history. The derived Au/FeOx hollow composite shows a substantial pretreatment effect on CO oxidation: with a pretreatment in the reaction feed at 180 °C for 0.5 h, the hollow Au/FeOx shows the T100 of CO oxidation decreasing from 180 to 88 °C. O2 temperature-programmed desorption and X-ray photoelectron spectroscopy characterizations revealed that the pretreatment may result in (i) the creation of electron holes in the p-type FeOx substrate and electron deficiency of Au nanoparticles as well as a strong Au–FeOx interaction; (ii) appropriate coverage of oxygen adspecies on the Au NPs; and (iii) increased surface oxygen density, especially at the Au–FeOx boundary region, as a result of the spillover effect of oxygen adspecies from Au NPs. All of these features are responsible for an overall enhanced activity of CO oxidation and better durability of the Au/FeOx hollow composite.Keywords: akagenite; CO oxidation; gold; hematite; hollow nanostructures; pretreatment effect

We reported the morphology-directed synthesis of Co3O4 nanotubesvia interfacial reaction of NaOH with pre-fabricated CoC2O4·2H2O nanorods based on modified Kirkendall effect. The as-obtained Co3O4 nanotubes showed excellent activity and durability in catalytic combustion of CH4.

CuO nanostructures of different morphologies were synthesized and compared for catalytic benzene combustion. XRD patterns of various CuO nano-crystallites suggest the monoclinic CuO structure. The dominant crystal planes of various CuO nanostructures are identified by means of HRTEM and electron diffraction. The amount of oxygen adspecies was found to be strongly dependent on the orientation of crystal planes. The activity of benzene combustion over major crystal planes of CuO nanostructures is: (200) > (111) > (01) > (001), consistent with the order of the corresponding density of terminate Cu2+ ions on which both benzene and oxygen are activated.

Alkali phosphates-modified NaY zeolites were developed as catalysts for efficient conversion of lactic acid to acrylic acid. The catalytic performance was optimized in terms of the type and loading of alkali phosphates, reaction temperature, liquid hourly space velocity, and lactic acid concentration. A high acrylic acid yield of 58.4% was achieved at 340 °C over 14 wt % Na2HPO4/NaY. The physicochemical properties of the catalysts were investigated by various techniques including NH3-TPD, pyridine adsorption-FTIR, Raman, and MAS 31P NMR. Introduction of alkali phosphates to NaY zeolite results in a decline of surface acidity. The results of FTIR, Raman, and MAS 31P NMR investigations on the fresh and used catalysts suggest that sodium phosphate is largely transformed to sodium lactate during the reaction. The phosphates and the in situ generated sodium lactate function as highly active species for the target reaction.Keywords (keywords): acrylic acid; alkali phosphate; dehydration; lactic acid; NaY

The core–shell structured microcapsular-like Ru@SiO2 reactor is proved to be the most efficient material known to date for COx-free hydrogen production via ammonia decomposition for fuel cells application. The very active Ru core particles can retain good stability even at high temperatures (up to 650 °C) thanks to the protection of the inert SiO2 nano-shell.

Hierarchically porous intestine-like SnO2 hollow nanostructures of different dimension were successfully synthesized via a facile, organic template free, H2O2-assisted method at room temperature. The morphology as well as texture (congregated solid sphere, intestine-like solid nanostructure, hollow core–shell one, and intestine-like hollow one) of SnO2 materials can be controlled by varying H2O2 concentration and the size of intestine-like hollow SnO2 can be tuned in the range of 20–120 nm by changing SnSO4 concentration. The hierarchically porous intestine-like SnO2 has high specific surface area (142 m2 g−1). The gas-sensing behaviors of the intestine-like SnO2 material to different gas probes such as ethanol, H2, CO, methane, and butane have been investigated; among them a high selectivity to ethanol was achieved.

In the present study the intestine-like binary SnO2/TiO2 hollow nanostructures are one-pot synthesized in aqueous phase at room temperature via a colloid seeded deposition process in which the intestine-like hollow SnO2 spheres and Ti(SO4)2 are used as colloid seeds and Ti-source, respectively. The novel core (SnO2 hollow sphere)-shell (TiO2) nanostructures possess a large surface area of 122 m2/g (calcined at 350 °C) and a high exposure of TiO2 surface. The structural change of TiO2 shell at different temperatures was investigated by means of X-ray diffraction and Raman spectroscopy. It was observed that the rutile TiO2 could form even at room temperature due to the presence of SnO2 core and the unique core-shell interaction.

The present investigation showed that the surface cobalt silicate and CoOx cluster anchored to SBA-15 are highly efficient heterogeneous catalysts for the cyclohexane partial oxidation with air-like O2 (20%)-N2 (80%) mixture as oxidant in the continuously stirred tank reactor at 413 K and 1.0 MPa. Typically, selectivity of 84.6% at cyclohexane conversion of 14.5% can be achieved in a period of 2 h reaction. The performance of Co-catalyst is affected by the nature of Co species introduced to SBA-15. The surface cobalt silicate with higher proportion of “isolated” Co2+ sites shows better result than the well dispersed CoOx clusters mainly on the internal surface of SBA-15. Furthermore, different preparation method also influences the porosity of SBA-15 and accessibility to Co sites, which may in turn affect on the reaction performance.

Cyclohexane oxidation was operated in a continuously stirred tank reactor at system pressures of 0.6–1.0 MPa under an air-like O2/N2 atmosphere (rather than pure O2). Catalytic performance was investigated over Au nanoparticles (size: 3–8 nm) hosted by SBA-15 as well as Au particles (>60 nm) deposited on MCM-41, and high turnover frequencies of desired products were detected over the former. Based on intrinsic activities of representative catalysts, we derived a size-sensitivity feature of cyclohexane oxidation over Au particles.

Mesoporous zirconia–yttria (ZYO) and ceria–zirconia–yttria (CZYO) have been synthesized for the first time from simple inorganic salts rather than expensive alkoxides in aqueous medium using CTAB as template. The approach is simple and economical. The fabricated ZYO and CZYO materials show typical mesoporous characteristics. The surface areas are 200 and 139 m2 g−1 and the average pore diameters are ca. 5.7 and 6.8 nm, respectively. The framework of the meso-materials show high crystallinity, and the mesopores are narrow in pore size distribution and show interconnected feature. The high thermal stability and the large surface area at temperature as high as 550 °C suggests that the materials are suitable for high-temperature catalytic applications.

•SnO2 crystallites of regular morphology synthesized and the exposed crystal facets identified.•Au NPs (2.2–2.4 ± 0.7 nm) monodispersed on the structurally defined SnO2 substrates.•Certain Au/SnO2 interfaces created for detailed comparison in the target reactions.•Specific Au–SnO2 facet interaction having strong impact on the interfacial properties.•Significance of distinctive Au/SnO2 interfacial structures governing the reaction pathways.SnO2 crystallites of regular morphology [rhombic dodecahedra (r.d-SnO2), elongated octahedra (e.o-SnO2), and octahedra (o-SnO2)], together with low-dimensional rod-clusters (r.c-SnO2) and plates (p-SnO2), were controllably synthesized. Based on (HR)TEM, SEM, and SEAD characterizations, the SnO2 facets were identified as {1 1 1}, {1 1 0}, and {1 0 1}. Au nanoparticles of 2.2–2.4 nm with narrow particle size deviation (±0.6–0.7 nm) were monodispersed on the SnO2 substrates. Au/SnO2 interfacial structures with structurally defined oxide substrate and comparable Au particle size and morphology were accomplished. The systems achieved made it possible to study the distinct interfaces in catalytic benzene combustion and methanol oxidation. H2 TPR, O2 TPD, and XPS characterizations revealed that the specific Au–SnO2 interaction has a strong effect on the reactivity of surface and bulk lattice oxygen, the oxidation state of surface Sn atoms, and the sort and relative concentration of surface oxygen adspecies. The Au/SnO2{1 1 0} and Au/SnO2{1 0 1} interfaces favor selective oxidation of methanol, whereas Au/SnO2{1 1 1} enhances total oxidation of both benzene and methanol. These interfacial structures were rather stable in both reactions. Through structural analysis of SnO2 facets, the evolution of active oxygen species and the possible reaction pathways of benzene combustion have been proposed. The involved reaction pathways are notably influenced by the specific Au/SnO2 interfacial structure and the nature of the reactant molecule, as well as the reaction temperature. The current study gained insight into the significance of specific Au/SnO2 facets determining the catalytic activity of benzene and methanol oxidation.Download high-res image (142KB)Download full-size image

•The PEG-derived vanadium phosphorus oxides fabricated as catalysts for the target reaction.•The highest formation rate of desired products (19.8 μmol gcat−1 min−1) known to date.•An efficient VPO catalyst demands a higher fraction of δ-VOPO4 in catalyst constitution.•Medium strong acid sites of high density are also responsible for the superior activity.•The VOPO4 and (VO)2P2O7 specimen in balanced amount maximized catalyst performance.Vanadium phosphorus oxides (VPOs) fabricated by employing poly ethylene glycol (PEG) additive were used as catalysts for efficient conversion of acetic acid (methyl acetate) and formaldehyde to acrylic acid (methyl acrylate). The highest formation rate (19.8 μmol gcat−1 min−1) of desired products (acrylic acid + methyl acrylate) was accomplished over a VPO catalyst comprising mainly vanadyl pyrophosphate ((VO)2P2O7) and vanadyl phosphate in δ form (δ-VOPO4). This catalyst is nearly three times more active than the analogue reported in literature. The VPO catalyst activated in 1.5% butane–air is superior to that activated in air or nitrogen. Different from the PEG-derived VPO catalysts for n-butane oxidation to maleic anhydride, a better VPO catalyst for the current reaction requires a higher fraction of δ-VOPO4 entity and contains the medium strong acid sites of high density. Through systematic catalyst characterizations and evaluations, an unambiguous correlation between catalyst structure/constitution and performance was established.Graphical abstractDownload high-res image (172KB)Download full-size image

Ni nanoparticles (NPs) of narrow size distribution encapsulated inside meso- and microporous silica were prepared through in situ reduction of NiO NPs coated with silica. By varying preparation parameters, the mean size of Ni NPs can be fine-tuned in the range 6–45 nm. It was found that with variation in core size, microcapsular cavity, and shell porosity, the as-obtained Ni@meso-SiO2 catalysts for the partial oxidation of methane to synthesis gas are notably different in catalytic activity and durability. The catalyst activity and durability are essentially determined by the size of the Ni cores, and also somewhat by the porosity of SiO2 shells, as well as the extent of core–shell interaction, which is influenced by the microcapsular cavity structure. The Ni-350@meso-SiO2 catalyst with Ni NPs of ca. 6 nm and SiO2 shells with 3–4 nm mesopores is superior in both activity and durability, giving CH4 conversion of ∼93%, H2 selectivity of 92–93% (750 °C and GHSV = 72,000 mL g−1 h−1), and TOFCH4 of 37.9 s−1.Graphical abstractNi nanoparticles with controllable size and a narrow size distribution encapsulated inside meso- and microporous silica were prepared for partial oxidation of methane. The Ni-350@meso-SiO2 catalyst with Ni particles of ca. 6 nm is superior in both activity and durability at 750 °C and gas hourly space velocity (GHSV) of 72,000 mL h−1 g−1.Download high-res image (53KB)Download full-size imageHighlights► Ni nanoparticles (6–45 nm) encapsulated by silica shell of different porosity. ► Catalysts are highly active for partial oxidation of methane to synthesis gas. ► Ni size, shell porosity, and core-shell interaction determine catalyst activity and durability. ► Ni-350@meso-SiO2 with Ni cores of 6 nm is superior in both activity and durability.

The bimetallic Co–Ni nanoparticles that are encapsulated by porous silica shell were synthesized for partial oxidation of methane to syngas. By carefully tuning the Co/Ni ratios of core–shell structured catalysts, the catalytic activity can be efficiently modified: CoNi2@SiO2 > Ni@SiO2 > CoNi@SiO2 > Co2Ni@SiO2 > > Co@SiO2. The CoNi2@SiO2 catalyst outperforms the other counterparts at a reaction temperature of 700 °C. The proper alloying of Co and Ni metals cannot only enhance catalyst activity but also suppress carbon deposition during the reaction. The encapsulation of the nanoparticles of Co–Ni alloy can also effectively prevent aggregation of core alloy nanoparticles.The Co–Ni nanoparticles encapsulated by porous silica shells were synthesized for the partial oxidation of methane to syngas. CoNi2@SiO2 outperforms the other counterparts at 700 °C. Proper alloying of Co and Ni metals enhanced catalyst activity and also suppressed coke deposition while the core–shell structure improved the resistance against core particle sintering.Download full-size imageHighlights► The Co–Ni nanoparticles encapsulated by porous silica shells are synthesized. ► Activity order: CoNi2@SiO2 > Ni@SiO2 > CoNi@SiO2 > Co2Ni@SiO2 > > Co@SiO2. ► Proper alloying of Co–Ni cores enhances activity meanwhile suppresses coke formation. ► The core–shell structure also effectively prevents core particles from sintering.

VPO catalysts supported on ZrO2 and H3PO4-treated ZrO2 were prepared for the first time by means of precipitation–deposition in an organic medium. The physicochemical properties of the catalysts were investigated by the BET, XRD, TEM, Raman, XPS, and H2-TPR techniques. It was found that the way of H3PO4 treatment conducted on ZrO2 has a significant effect on the nature of the support, as well as on the state and structure of the VPO component loaded on it. The discrepancies in the synergistic interaction between VPO and the different supports induce variation in catalytic performance. The change in VPO loading is found to have an effect on catalyst efficiency. At 673 K, the MA yield is 61 mol% over the 36%VPO/(H3PO4)-p-ZrO2 catalyst, the best performance achieved so far among the supported VPOs.

Mo1.00VxTe0.20Nb0.16On (x=0.35–0.50) mixed-metal oxide catalysts were synthesized through ultrasonic and hydrothermal treatments. Both TeO2 and H6TeO6 were used as tellurium sources. The enhanced dispersion of TeO2 by ultrasonic treatment is crucial for obtaining an active and selective MoVTeNbO catalyst for acrylic acid (AA) formation from propane oxidation. The TeO2-derived Mo1.00VxTe0.20Nb0.16On (x=0.35–0.41) are superior to their H6TeO6-derived counterparts; propane conversion and AA selectivity over the Mo1.00V0.41Te0.20Nb0.16On is 55% and 60 mol% at 380 °C, respectively, giving an AA formation rate of 22.3 μmol g−1 min−1. Based on the physicochemical properties of the catalysts, we propose that the ultrasonic treatment can give rise to (i) enhanced presence of the orthorhombic Te2M20O57 (M=Mo, V, Nb) and hexagonal Te0.33MO3.33 (M=Mo, V, Nb) phases, (ii) surface enrichment of Te, (iii) enhanced reactivity of lattice oxygen, (iv) an increase in MoOTe and VOTe entities, and (v) better isolation of active sites.

We reported the morphology-directed synthesis of Co3O4 nanotubesvia interfacial reaction of NaOH with pre-fabricated CoC2O4·2H2O nanorods based on modified Kirkendall effect. The as-obtained Co3O4 nanotubes showed excellent activity and durability in catalytic combustion of CH4.

The core–shell structured microcapsular-like Ru@SiO2 reactor is proved to be the most efficient material known to date for COx-free hydrogen production via ammonia decomposition for fuel cells application. The very active Ru core particles can retain good stability even at high temperatures (up to 650 °C) thanks to the protection of the inert SiO2 nano-shell.

CuO nanostructures of different morphologies were synthesized and compared for catalytic benzene combustion. XRD patterns of various CuO nano-crystallites suggest the monoclinic CuO structure. The dominant crystal planes of various CuO nanostructures are identified by means of HRTEM and electron diffraction. The amount of oxygen adspecies was found to be strongly dependent on the orientation of crystal planes. The activity of benzene combustion over major crystal planes of CuO nanostructures is: (200) > (111) > (01) > (001), consistent with the order of the corresponding density of terminate Cu2+ ions on which both benzene and oxygen are activated.

By regulating the H2O/SiO2 molar ratio (n = 13.8, 16.9, 20.1, 26.3), NaY zeolites of different particle sizes (NaY-n, 50–400 nm) were synthesized, and NaY-n was modified with disodium hydrogen phosphate, Na2HPO4. The as-prepared catalysts are highly effective for the dehydration of sustainable lactic acid (LA) to produce acrylic acid (AA). Through the optimization of NaY particle size and Na2HPO4 loading, AA yields as high as 74.3% can be achieved under mild conditions (340 °C). In terms of employed feed rate of lactic acid and amount of catalyst, the AA formation rate is 12.0 mmol gcat−1 h−1, the highest ever reported for LA dehydration to AA. Employing slightly low Si/Al ratios in NaY-n can modify catalyst acidity, while pre-applied Na+ ion-exchange and following Na2HPO4 loading can effectively reduce the number of acid sites, particularly the Brønsted ones on NaY-n. Equally important structural features of NaY-n are their shorter pore channels (or even incompletely developed zeolite texture) and relatively larger Sexternal/SBET ratio, which favors quick product departure from the catalyst surface, and reduces the possibility of side reactions occurring inside the long channels. The appropriate surface acidity together with unique structural features of NaY-n ensure efficient LA conversion with high dehydration selectivity. Higher surface concentrations of Na+ on Na2HPO4/NaY-n also favor sodium lactate meanwhile suppressing poly-lactate as well as preventing carbon formation, corresponding to superior performance as well as improved durability of Na2HPO4/NaY-n.

Spherically shaped Co3O4 particles were synthesized by one-pot solvothermal treatment of Co(NO3)2 in n-octanol that is free of structure-directing agents or pore formers. Au nanoparticles (2–4 nm) dispersed on the Co3O4 substrates were fabricated using deposition–precipitation method. The as-synthesized Co3O4 (without calcination) and the corresponding Au-containing catalyst achieved complete CO oxidation at 90 °C and 80 °C, respectively. Upon calcination, the condensed Co3O4 formed on which uniform dispersion of small-sized flat Au entities (3.0 ± 0.6 nm) with large Au–Co3O4 interfaces was established, showing complete CO oxidation at 110 °C. These two types of catalysts were found to be extremely durable even when operated in a period beyond 70 h under certain conditions. The calcined Co3O4-based Au catalyst can outperform Au/d-Co3O4 in both activity and stability when subjected to a pre-reaction at 350 °C for 5 h. The yolk–shell type Co3O4@SiO2 catalysts synthesized by controllable acid-etching of Co3O4 cores demonstrated an optimal Co3O4 core–SiO2 shell interaction and a suitable Co3O4 core particle size for CO oxidation. Both Co3O4 substrates and Au/Co3O4 systems were found to encounter substantial activity enhancement by in situ pretreatment. The pretreatment resulted in (i) transformation of AuOx to Au0, (ii) higher fraction of surface Co3+, and (iii) suitably lower concentration of surface oxygen adspecies, accounting for the enhanced activities.

In this study, the morphologically uniform Co3O4 cubes (c-Co3O4), hexagonal plates (h-Co3O4) and tetrakaidecahedrons (t-Co3O4) were carefully synthesized and the crystalline facets of (001), (111), and (112) were identified. Au nanoparticles (3.1–3.3 nm) were deposited on the three Co3O4 entities, which were achieved to obtain specific Au–Co3O4 interfaces. A detailed comparison was made on the basis of their unique interfacial structures and catalytic behaviors. H2-TPR and XPS investigations revealed the important variations in reactivity of surface oxygen, surface Co3+/Co2+ ratio, evolution of surface oxygen vacancies as well as Au oxidation state upon Au loading and pretreatments. The enhanced CO oxidation by Au deposition, and particularly He- and in situ-pretreatments, has been elucidated in light of the structural specialties associated with the three facets of Co3O4 substrates and the corresponding Au–Co3O4 interfaces. The consequent activity enhancement for Co3O4 substrate and Au–Co3O4 interface was verified: (001) > (112) > (111), and Au/(112) > Au/(001) > Au/(111). The results of Au/h-Co3O4 also suggest that both Au cluster and Co3O4 structural feature can have a profound effect on the catalytic behaviour of generated interface. The present study extends the insights into the interface-dependent CO oxidation over the controllably prepared Au–Co3O4 interfacial structures.