Acid-base bifunctional periodic mesoporous metal phosphonates for synergistically and heterogeneously catalyzing CO₂ conversion

Abstract

Integrating multiple functions into one host for improved catalytic performance is challenging and promising for both catalysis and material science. Herein a new acid–base bifunctional periodic mesoporous titanium phosphonate hybrid material is synthesized by a facile one-pot hydrothermal method, using alendronate sodium trihydrate as a coupling molecule. The new material possesses highly periodic mesopores with a large specific surface area of 540 m2 g–1 and pore volume of 0.43 cm3 g–1, favoring the smooth mass transport of reactants and products during the catalytic reaction. It also has an organic–inorganic hybrid framework with homogeneously incorporated phosphonate groups, in which a large number of accessible acidic P–OH and basic −NH2 sites can, respectively, activate aziridine and CO2, synergistically leading to the high conversion (>99%), yield (98%), and regioselectivity (98:2) for the CO2 cycloaddition reaction. The catalytic activity is better than that of the scarcely reported heterogeneous catalysts for aziridine and CO2 cycloaddition and even comparable to that of the state-of-the-art homogeneous ones. Moreover, being superior to the other catalysts, the metal phosphonate materials can be easily separated and reused repeatedly without activity loss, and no hazardous halogen ions, organic solvents, or cocatalysts are needed for the catalytic process. In comparison with previously reported multifunctional catalysts synthesized by complicated multistep fabrications, the facile one-pot preparation of mesoporous metal phosphonates with dual active sites makes it more practical for high-performance heterogeneous catalysis.