This paper describes an emerging synthetic route for the production of ethanol (with a yield of ~83%) via syngas using Cu/SiO(2) catalysts. The remarkable stability and efficiency of the catalysts are ascribed to the unique lamellar structure and the cooperative effect between surface Cu(0) and Cu(+) obtained by an ammonia evaporation hydrothermal method. Characterization results indicated that the Cu(0) and Cu(+) were formed during the reduction process, originating from well-dispersed CuO and copper phyllosilicate, respectively. A correlation between the catalytic activity and the Cu(0) and Cu(+) site densities suggested that Cu(0) could be the sole active site and primarily responsible for the activity of the catalyst. Moreover, we have shown that the selectivity for ethanol or ethylene glycol can be tuned simply by regulating the reaction temperature.

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Hydrogenation of carbon–oxygen (C–O) bonds plays a significant role in organic synthesis. Cu-based catalysts have been extensively investigated because of their high selectivity in C–O hydrogenation. However, no consensus has been reached on the precise roles of Cu0 and Cu+ species for C–O hydrogenation reactions. Here we resolve this long-term dispute with a series of highly comparable Cu/SiO2 catalysts. All catalysts represent the full-range distribution of the Cu species and have similar general morphologies, which are detected and mutually corroborated by multiple characterizations. The results demonstrate that, when the accessible metallic Cu surface area is below a certain value, the catalytic activity of hydrogenation linearly increases with increasing Cu0 surface area, whereas it is primarily affected by the Cu+ surface area. Furthermore, the balancing effect of these two active Cu sites on enhancing the catalytic performance is demonstrated: the Cu+ sites adsorb the methoxy and acyl species, while the Cu0 facilitates the H2 decomposition. This insight into the precise roles of active species can lead to new possibilities in the rational design of catalysts for hydrogenation of C–O bonds.

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in Wiley Online Library (wileyonlinelibrary.com).The design and application of a Cu/SiO 2 -based monolithic catalyst for hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG) is presented. The catalyst was dip-coated on cordierite with highly dispersed Cu/SiO 2 slurry prepared by ammonia evaporation method. This structure guarantees high dispersion of copper species within the mesopores of silica matrix in the form of copper phyllosilicate. The catalyst is low cost, stable, and exhibits high activity in the reaction of hydrogenation of DMO, achieving a 100% conversion of DMO and more than 95% selectivity to EG. Notably, STY EG over the monolith is significantly enhanced compared to the packed bed Cu/SiO 2 catalysts in both forms of pellet and cylinder. It is primarily due to the relatively short diffusive pathway of the thin wash-coat layer and high efficiency of the active phase derived from the monolithic catalyst. Theoretical results indicated that the internal mass transfer is dominated on the catalysts of pellet and cylinders. Moreover, the monolithic catalyst possessed excellent thermal stability compared to the pellet catalyst, which is attributed to the regular channel structure, uniform distribution of flow. Catalytic activity testsOur catalytic reactivity system (monolithic fixed-bed MRCS8004B System) (shown in Figure 1) consists of a continuous-flow stainless steel reactor (15 mm i.d. and 350 mm length) inside a horizontal furnace with a temperature controller. The gas distributor has been equipped at the entrance of the reactor to ensure a uniform gas distribution. The monolithic Cu/SiO 2 catalysts were placed in the middle of the (a) scheme of monolith catalyst, (b) SEM images of a monolith channel, and (c) cross-sectional cordierite monolith wash-coated with Cu/SiO2 catalyst, and (d) TEM image of calcined wash-coat layer.

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.

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