Effect of Cu loading on the structural evolution and catalytic activity of Cu–Mg/ZnO catalysts for dimethyl oxalate hydrogenation

Abstract

The influence of Cu loading on the structural evolution and catalytic behavior in selective hydrogenation of dimethyl oxalate (DMO) by Mg²⁺ doped nanoscaled Cu–Mg/ZnO catalysts has been investigated. It is found that the accessible Cu⁰ surface area and ZnO dispersion increased gradually with the Cu loading increasing from 10.0 wt% to 40.0 wt%, and that the Cu and ZnO NP size distribution has a great effect on the chemical interaction between the Cu and ZnO phase, further determining the surface chemical properties of the catalysts. On the other hand, the catalytic behavior of the Cu–Mg/ZnO catalyst in DMO hydrogenation is closely related to the Cu loading introduced into the system. Most of all, the 30Cu–Mg/ZnO catalyst with 30 wt% Cu loading exhibits 100.0% DMO conversion and 98.0% ethylene glycol (EG) yield even under LHSV = 3.5 h⁻¹, superior to those of the other catalysts. This excellent catalytic behavior should be attributed to the strengthened Cu–Zn synergistic effect and suppressed strong surface basic sites, originating from the enhanced Cu–ZnO interface area. Additionally, the correlation between catalytic activity and Cu species distribution suggests that the DMO dissociation on the Cu⁺ sites generated on the Cu–ZnO interface is the rate-determining step in the presence of enough exposed Cu⁰ sites over the Cu–Mg/ZnO catalysts.