Encapsulating phosphotungstic acid within metal-organic framework for direct synthesis of dimethyl carbonate from CO2 and methanol

Abstract

Direct synthesis of dimethyl carbonate (DMC) from CO2 and methanol is a sustainable pathway for DMC production and CO2 utilization simultaneously. Herein, metal-organic framework MOF-808 with phosphotungstic acid (HPW) encapsulated into the micropore (HPW@MOF-808) prepared by a simple one-pot synthesis method was demonstrated to be an active heterogeneous catalyst for the direct synthesis of DMC with 1,1,1-trimethoxymethane as dehydrate agent. While HPW/MOF-808 sample prepared using impregnation method with HPW mainly aggregated on the surface of MOF-808 matrix was less active. The superior activity of HPW@MOF-808 was attributed to the encapsulation of HPW in the micropore of HPW@MOF-808 enabled more HPW interacting with Zr6 node to generate more additional HPW induced Bronsted acid sites (Zr-OH) and Lewis acid sites (W+) than HPW/MOF-808, which promoted the formation of methyl cation (rate-determine step in DMC synthesis) and subsequently accelerated the formation of DMC. Additionally, HPW@MOF-808 exhibited better reusability than HPW/MOF-808 since the interaction between the encapsulated HPW and Zr6 node inhibited the leaching of HPW during reaction. This work provided a promising strategy for the designing of efficient MOF based catalyst for direct synthesis of organic carbonate from CO2 and alcohol.