A Hierarchical Multifunctional Catalyst for the One-Pot Synthesis of Cyclic Carbonates: Synergistic Catalytic Effects

Tandem catalytic processes present a cost-effective and energy-efficient route for the generation of fine chemicals. In this work, a hierarchical multifunctional MOF (mesoAg+@Al-bpydc) was successfully synthesized using a simple impregnation method, with AgBF4 serving as both the functional sites and etching agents. The incorporated Ag+ ions and N-based ligands are accountable for the selective epoxidation and cycloaddition reaction, respectively. Moreover, the hierarchical pore structures within the mesoAg+@Al-bpydc are anticipated to optimize the mass transfer rate and enhance accessibility of active sites. These advantages synergistically contribute to superior catalytic performance of mesoAg+@Al-bpydc for the one-pot oxidative carboxylation of olefins (conversion ∼99.68%, selectivity ∼50.83%), where the yield of the target product over mesoAg+@Al-bpydc is at least 37% higher than that of microporous counterparts. Moreover, based on the kinetic results and the comparison between single-step reaction and tandem reaction, it was found that the intermediate styrene oxide (SO) is unstable and is easily converted to benzaldehyde (BA) with the extension of reaction time in the individual epoxidation reaction (78.22% selectivity of BA), while generated SO can immediately couple with CO2 to produce SC in the tandem reaction (6.81% selectivity of BA). Consequently, more SC is accessible by rapidly consuming SO and impeding the overoxidation reaction, which supports the preponderance of the direct oxidative carboxylation of styrene and the synergistic effect of varied active sites in the tandem reaction. Besides, the composite mesoAg+@Al-bpydc allows easy separation and recycling at least five times with a negligible loss of activity.