Characterization of alkaline earth metal-doped CeO2 nanocatalysts and their catalytic activities in the synthesis of dimethyl carbonate through a reaction between methanol and CO2

Abstract

Alkaline earth metal (Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺)-doped CeO₂ nanocatalysts have been prepared by the successive co-precipitation and calcination method. The basicity and quantities of basic sites of alkaline earth metal-doped CeO₂ nanocatalysts are remarkably influenced by the type and content of doped alkaline earth metal cations. The number of weak basic sites, Ce³⁺ cations, and oxygen vacancies of the doped CeO₂ nanocatalysts are obviously improved when the ionic radii of alkaline earth metal cations are comparable to that of Ce⁴⁺. Catalytic activities of the doped CeO₂ nanocatalysts in the synthesis of dimethyl carbonate through the reaction between methanol and CO₂ increase with the increase in weak basic sites and oxygen vacancies. When the Mg_0.05Ce_0.95O₂ nanocatalyst with larger amounts of both weak basic sites and oxygen vacancies catalyzed the reaction with a catalyst/methanol mass ratio of 1.0 : 50.0 at 4.0 MPa of CO₂ and 140 °C for 4 h, the yield of dimethyl carbonate was 3.95 mmol g_cat⁻¹, which is 1.31 times that obtained on the sole CeO₂ catalyst. The doping of the CeO₂ nanocatalyst with alkaline earth metal obviously reduces the catalytic reaction activation energy.