Effect of calcination temperature on the Cu–ZrO2 interfacial structure and its catalytic behavior in the hydrogenation of dimethyl oxalate

Abstract

Copper–zirconium catalysts have been extensively applied in the hydrogenation of carbon–oxygen bonds such as in CO₂ and esters. However, high-performance Cu/ZrO₂ catalysts with low copper loading for dimethyl oxalate (DMO) hydrogenation to ethylene glycol (EG) are seldom reported. Herein, we fabricated 5 wt% Cu/ZrO₂ catalysts by a co-precipitation method and investigated the effect of calcination temperature on the catalyst structure and the corresponding catalytic performance. The crystallization and migration of zirconium and copper species are not simultaneous when increasing the calcination temperature, so the elemental composition of Cu and Zr species is different on the surface and in the bulk CuZrO₂ solid solution. The crystalline morphology of ZrO₂ is transformed from a-ZrO₂ to t-ZrO₂ and m-ZrO₂ and copper dispersion is also changed. The CZ-600 catalyst has the largest copper dispersion, surface area of Cu⁰ and Cu⁺ and strongest H₂ adsorption ability, which endow this catalyst with the best catalytic performance. However, TOF values are the largest for the CZ-550 catalyst with a larger ratio of Cu⁺, oxygen vacancies and Zr³⁺, which suggests the interfacial synergy between Cu and ZrO₂ in DMO hydrogenation. And further increasing the calcination temperature to above 700 °C will cause the aggregation and sintering of copper nanoparticles and deteriorate the hydrogenation reactivity.