Perspectives on the Active Sites and Catalyst Design for the Hydrogenation of Dimethyl Oxalate

What should people do with the huge amount of CO2 captured? CO2 to CO is a promising way for using carbon resources because CO is one component of syngas for the production of many important synthesis intermediates such as dimethyl oxalate (DMO). Hydrogenation of DMO provides an economical and eco-friendly approach for the synthesis of methyl glycolate, ethylene glycol (EG), and ethanol, which is often determined by the reaction conditions and catalysts with different active sites. Thus, DMO or EG is also an important carbon carrier or CO2 utilization product. Also, DMO hydrogenation is a representative reaction for studying the structure–activity relationship in C═O/C–O bond hydrogenation. Therefore, this work provides a comprehensive review of the progress in DMO hydrogenation from the perspective of constructing and stabilizing the active sites. The silver and copper based catalysts with different structures and morphologies used for DMO hydrogenation have been discussed with regard to their catalytic performance and reaction mechanism. The synergy of Cu0 and Cu+ in DMO hydrogenation has been questioned, and new active sites are proposed with more experimental evidence. New reaction routes, hybrid active sites, and the effect of catalyst structure on the active sites for DMO hydrogenation have been achieved and reviewed. Moreover, a strategy of introducing organic additives to improve EG yield and stabilize copper species has been described. This work may help advance the understanding of active sites in DMO hydrogenation and guide the future rational design and fabrication of highly stable and low-cost DMO hydrogenation catalysts.