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

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.