Effect of surface hydroxyl group of ultra-small silica on the chemical states of copper catalyst for dimethyl oxalate hydrogenation

Abstract

Abstract Cu/SiO2 catalyst prepared by ammonia evaporation method was reported to perform a great catalytic activity and selectivity in dimethyl oxalate (DMO) hydrogenation, which is one of the key steps in ethylene glycol (EG) synthesis from syngas. In recent years, significant advances have achieved on the nature of active sites and catalytic mechanism. However, the fabrication of Cu/SiO2 catalyst with controllable copper species remains challenging. Here, we reported a facile and effective approach to manipulate the surface hydroxyls of silica, which was revealed to be important factor for the formation of active species. An excellent linear correlation between surface hydroxyl groups of silica and the amount of Cu+ species was demonstrated, indicating that the formation of copper phyllosilicate can be kinetically favoured with increasing surface hydroxyls during preparation. Furthermore, as the copper phyllosilicate formation is enhanced, the specific surface area is significantly increased and the polymerization of copper hydroxide may be slow down, resulting in a highly improved dispersion of metallic copper as well. The enlarged surface areas of Cu0 and Cu+ species greatly enhanced the catalytic performance of Cu/SiO2 in DMO hydrogenation to EG. These understandings on the relationship between surface hydroxyl groups and chemical states of copper catalyst may lead to new possibilities in rational design of catalysts.