Ethanol (EtOH), as an attractive end product and a versatile feedstock, can be synthesized from syngas via the hydrogenation of dimethyl oxalate (DMO). Unfortunately, DMO hydrogenation is a consecutive reaction and difficult to achieve selective hydrogenation. Copper-based catalysts have been widely used in DMO hydrogenation. However, a high molar ratio of H2 to DMO (H2/DMO, usually as 150–200) and temperature (above 280 oC) are required to achieve good EtOH selectivity. Metal carbides such as FeCx and MoCx have been proposed as potential catalysts, but still require high temperature (above 240 oC) and produce considerable by-products. Here, a series of ternary Cu-Zn-Fe catalysts (CZF) were fabricated for DMO hydrogenation to EtOH. the optimal catalyst (CZF-10) exhibits an outstanding catalytic activity of 99% DMO conversion and 92.2% EtOH selectivity with an excellent stability for at least 350 h, at an unexpectedly low temperature (210 oC) and H2/DMO (100). To the best of our knowledge, this is the lowest temperature reported so far among the copper-based catalysts. By adjusting the molar ratio of Cu to Fe, the catalytic performance of DMO hydrogenation shows obvious component dependence. DMO is first hydrogenated to methyl glycolate (MG). For the catalyst without adding Fe, the final product is ethylene glycol (EG) hydrogenated from MG. However, after adding Fe, MG tends to be hydrogenated to methyl acetate (MA) and then further hydrogenated to EtOH. Moreover, EtOH selectivity increases with Fe content. Combined with in situ experiments and various characterizations, it is proved that copper species is active sites for H2 dissociation and C=O activation, responsible for DMO to EG. And further hydrogenolysis of EG to EtOH requires higher temperature. While with the addition of Fe, FeOX species could promote the activation of C-OH of MG and is responsible for the hydrogenolysis of MG to MA, which could be easily hydrogenated to EtOH at low temperature. Moreover, with the increase of Fe content, the dissociation capacity of H2 is enhanced and the reaction rates of MG to MA and MA to EtOH are significantly increased. Thus, the prominent catalytic activity for the hydrogenation of DMO to EtOH at low temperature could be attributed to the cascade synergy of Cu-Fe species. This insight into active sites for carbon−oxygen bond hydrogenation may provide guidance for high-performance catalyst design.

FeOx modified Cu nanocatalysts boosting the low-temperature hydrogenation of dimethyl oxalate to ethanol

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