Hollow nanostructured materials are widely used in catalysis. Besides the large surface area, well-defined active sites, and delimited cavities, the favorable catalytic performance of hollow nanostructured catalysts can be ascribed to the enrichment of reactant molecules around active species implemented by the hollow chambers. Previous studies found the enrichment of reactant is induced by surface curvature, but understanding of the structural effect still needs quantitative discussion. Herein, we elucidate the curvature effect by building nanotube assembled hollow spheres with controllable morphology. By using experimental and computational methods, we demonstrate that with increased hollow-sphere size, the reactant concentration inside hollow sphere decreases while the diffusion flux increases, both affecting the reaction rate. This balancing effect between adsorption and diffusion induced by surface curvature suggests a unique strategy to design more efficient and selective hollow nanostructured catalysts.

CeO2-supported copper species have been reported as an active catalyst for the hydrogenation of carbon–oxygen bonds (CO, CO2, furfural, esters, etc.). However, the identification of active sites remains challenging. Herein, we prepared a series of rod-shaped ceria-supported copper catalysts with different copper sizes (single-atom, 1.4 nm nanoclusters, 3.0 nm and 6.8 nm nanoparticles) and applied them for methyl acetate (MA) hydrogenation. The structure and chemical environment of copper species were detected, and the surface Cu0 and Cuσ+ species and defects (oxygen vacancy and M–[O x ]–Ce solid solution) were quantitatively measured. To identify the active sites for MA hydrogenation, we also prepared contrast samples with increased surface defects or with reduced Cu0–Cuσ+ species. It is demonstrated that the Cu0–Cuσ+ species rather than oxygen vacancies or M–[O x ]–Ce solid solution are the primary active sites for MA hydrogenation. From the results of in situ experiments and various chemisorption and density functional theory calculations, the Cu0–Cuσ+ interface located at the surface Cu deposits is evidenced to play the key role in enhancing the adsorption and activation of MA. The turnover frequency of Cu/CeO2 catalysts for MA hydrogenation is linearly increased with the increase of the Cu0–Cuσ+ interfacial perimeter. This insight into active sites for carbon–oxygen bond hydrogenation may provide guidance for high-performance catalyst design.

Hydrogenation of dimethyl oxalate (DMO) is one of the key steps in the route of ethylene glycol (EG) production from syngas. Cu/SiO 2 catalysts prepared by the ammonia evaporation method are reported to present excellent catalytic performance for selective DMO hydrogenation and used in industry. However, the selectivity of EG and the long-term stability of catalysts still require improvement. Herein, we used silane coupling agents to selectively and efficiently cover the surface isolated hydroxyl groups on Cu/SiO 2 by the post-grafting method, which exhibited a prominently promotion effect on reducing the selectivity of by-products (C 3 -C 4 OH) and enhancing the catalytic stability. Characterization results suggested that both the density and intensity of the basic sites decreased significantly after the coverage of hydroxyl groups, resulting in the reduction of C 3 -C 4 OH selectivity, thus increasing the EG selectivity. Meanwhile, the coke and blocked pore structure induced by excessive methyl glycolate (MG) adsorption and polymerization on surface hydroxyl groups could be the main reason for catalyst deactivation. After the surface modification, MG desorption was greatly facilitated, which improved the stability in DMO hydrogenation. Furthermore, the effect of different silane coupling agents ended with amino or alkyl groups was studied as well. These insights concerning the effect of covering hydroxyl groups by silane coupling agents on selectivity and stability may provide practical guidance for the design and fabrication of Cu/SiO 2 catalysts for the industrial application.

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Reducible oxides supported copper‐based catalysts have been widely used in ester hydrogenations due to their excellent catalytic performance. However, the role of surface oxygen vacancies is still unclear. Here, we fabricated four copper‐based catalysts using different shaped CeO2 nanocrystals as supports for the hydrogenation of methyl acetate (MA) to ethanol. The catalytic activities significantly changed depending on the morphology of supports in the order of rod>cube>spindle>octahedron, which was in line with the trend of the formation energy of oxygen vacancies on the corresponding exposed lattice planes. Combined with the results of chemisorption and in situ FTIR experiments, it is demonstrated that the oxygen vacancies are not the primary active sites for MA hydrogenation, whereas they could significantly affect the electronic state of copper species. Under reduced conditions, the mobile oxygens could be released from the lattice and form lots of oxygen vacancies, which could strongly interact with copper particles and benefit for the generation and stabilization of Cu+ species. Thus, increasing the oxygen mobility of supports could effectively increase the amount of surface Cu+ species and enhance the catalytic activity for MA hydrogenation.