Influence of the structure and surface properties of CeZnxO2 on its catalytic performance in the synthesis of dimethyl carbonate from CO2 and methanol

Abstract

A series of CeZn_xO₂ catalysts with different Zn doping contents were prepared by a reflux method and used in the direct synthesis of dimethyl carbonate (DMC) from CO₂ and methanol; various characterization techniques were employed to investigate the influence of the structure and surface properties on the catalytic performance of CeZn_xO₂ in the DMC synthesis. The results demonstrate that Zn²⁺ is incorporated into the CeO₂ lattice, forming a solid solution. The Zn/Ce molar ratio can significantly modulate the Ce³⁺/Ce⁴⁺ redox equilibrium in CeZn_xO₂; with an increase of the Zn doping content, the oxygen vacancy concentration initially rises and then declines. A moderate Zn doping level (Zn/Ce = 0.5) can promote the redox process of 2Ce⁴⁺ + Zn⁰ = 2Ce³⁺ + Zn²⁺, resulting in the highest Ce³⁺ proportion and a substantial increase of the oxygen vacancy concentration. In contrast, excessive Zn doping (Zn/Ce ≥ 0.75) leads to a reduction in both the Ce³⁺ content and oxygen vacancy concentration. There is a strong positive correlation between the catalytic activity and the number of weak base sites, as well as a linear relationship with the surface oxygen vacancy concentration. In particular, CeZn_0.5O₂ with a Zn/Ce molar ratio of 0.5 exhibits the best catalytic performance in the DMC synthesis, owing to its high oxygen vacancy concentration and well-balanced distribution of basic sites.