Lanthanum nanocluster/ZIF-8 for boosting catalytic CO2/glycerol conversion using MgCO3 as a dehydrating agent

Abstract

A lanthanum-modified zeolitic imidazolate framework (La/ZIF-8) was developed to produce glycerol carbonate using CO₂ and glycerol as raw materials. La/ZIF-8 provides a high catalytic glycerol conversion efficiency owing to its surface-attached nanoclusters of La₂O₃, which can be viewed as La³⁺–O²⁻ pairs that strengthen the Lewis basicity and acidity, and the large specific surface area of ZIF-8. The catalytic glycerol conversion and the yield of glycerol carbonate were 46.5% and 35.3%, respectively, using CH₃CN as a dehydrating agent. With increase in the amount of CH₃CN, the water molecules could react with CH₃CN to reduce the selectivity. When an inorganic dehydrating agent, MgCO₃, was used to physically adsorb and remove water molecules in the reaction, the selectivity of the reaction could be increased to over 95%, which is the highest ever reported. Reaction kinetics analysis also revealed that the activation energy of using MgCO₃ (5.4 kJ mol⁻¹) as a dehydrating agent is lower than that using CH₃CN (7.8 kJ mol⁻¹). Moreover, the La/ZIF-8 could be recycled and reused at least three times with high catalytic performance. This study provides an effective material with dual Lewis basicity and acidity for CO₂/glycerol conversion and significantly improves the catalytic performance using an inorganic dehydrating agent.