Boosting the catalytic activity via an acid–base synergistic effect for direct conversion of CO2 and methanol to dimethyl carbonate

Abstract

Direct synthesis of dimethyl carbonate (DMC) from CO₂ and CH₃OH holds significant economic and environmental value. Numerous catalysts have been employed for this reaction, yet further enhancement of its activity requires a deeper understanding of the catalyst's structure–activity relationship and catalytic mechanism. In this study, we utilized structurally well-defined and highly tunable MOF-808 as a research platform. Functionalizing MOF-808 with ethylenediamine (MOF-808-ED) boosted the space time yield of DMC from 3.25 mmol g⁻¹ h⁻¹ to 7.23 mmol g⁻¹ h⁻¹. The experimental results demonstrate that the reaction involves acid–base synergistic catalysis, where an appropriate balance of acid–base site content is crucial for CO₂ and CH₃OH to produce DMC, as it facilitates the formation of the key intermediates (CH₃OCOO*). Additionally, the nucleophilicity of N is stronger than that of O, further promoting the catalyst's enrichment and activation of CO₂. Finally, employing in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) testing, we elucidated the mechanism by which the MOF-808-ED catalyst, with –NH₂ as base sites and Zr as acid sites, facilitates the synergistic catalysis of the reaction. This study provides insights into the synergistic effects of acid–base sites on the synthesis of DMC from CO₂ and methanol, offering valuable guidance for the development of high-performance catalysts.