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.

Hydrogenation of carbon−oxygen bonds is extensively used in organic synthesis. However, a high partial pressure of hydrogen or the presence of excess hydrogen is usually essential to achieve favorable conversions. In addition, because most hydrogenations are consecutive reactions, the selectivity is difficult to manipulate, leading to an unsatisfactory distribution of products. Herein, a copper silicate nanoreactor with a nanotube-assembled hollow sphere (NAHS) hierarchical structure is proposed as a solution to these problems. In the case of dimethyl oxalate (DMO) hydrogenation, the NAHS nanoreactor achieves remarkable catalytic activity (the yield of ethylene glycol is 95%) and stability (>300 h) when the H 2 / DMO molar ratio is as low as 20 (in comparison to typical values of 80−200). For further investigation, nanotubes and lamellarshaped Cu/SiO 2 catalysts with similar surface areas of active sites of NAHSs were investigated as contrasts. By a combination of high-pressure hydrogen adsorption and Monte Carlo simulation, it is demonstrated that hydrogen can be enriched on the concave surface of nanotubes and hollow spheres, leading to a favorable activity in such a low H 2 proportion. Furthermore, because of the spatial restriction effect of reactants, adjusting the diffusion path is an effective route for manipulating the selectivity and product distribution of the hydrogenation reactions. By variation in the length of nanotubes on NAHS, the yields of methyl glycolate and ethylene glycol are easily controlled. The NAHS nanoreactor, with insights into the effect of morphology on hydrogen enrichment and spatial restriction of reactant diffusion, offers inspiring possibilities in the rational design of catalysts for hydrogenation reactions.

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.

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Higher alcohol synthesis (HAS) from syngas using highly active CoCu catalysts has attracted extensive interest, but there still exist problems such as the low coordination between Co and Cu phases and poor catalytic stability. Here, a series of highly dispersed bimetallic CoCu catalysts with different Co/Cu ratios (x = 1–4) encapsulated in KIT-6 were proposed and showed high performances in HAS. The best is Co3Cu1/KIT-6 with a space-time yield toward C2+OH of 31.9 mmol gcat –1 h–1 and excellent stability over 200 h. Notably, these catalysts had well-dispersed metal particles and abundant CoCu alloy sites that were maintained during the reaction, which was benefited from the preparation method of ethylene glycol (EG)-assisted impregnation combined with stepwise pyrolysis. The EG-derived glyoxylate dianion could effectively anchor Co and Cu species in the same precursor, enabling them in atomic close interaction, which also favored their synergistic catalysis in HAS. In addition, the stepwise pyrolysis and the confinement of KIT-6 promoted the high dispersion of CoCu species, facilitating the catalytic activity. Meanwhile, the maintenance of highly dispersed and atomic close interacted CoCu bimetallic sites ensured good stability of the catalyst for HAS. These results may provide new ideas for the design and fabrication of high-performance HAS catalysts.