Supercritical CO2 assisted synthesis of SBA-15 supported amino acid ionic liquid for CO2 cycloaddition under cocatalyst/metal/solvent-free conditions

Abstract

Heterogenization of homogeneous catalysts without the loss of activity is still a huge challenge. Herein, homogeneous [HTMG][His][I] amino acid ionic liquid (IL), consisting of 1,1,3,3-tetramethylguanidine cation, histidine anion and iodine anion, were introduced into the pore channels of SBA-15 substrate with the assistance of supercritical CO2 (scCO2) media. Due to its low viscosity, high diffusivity and absence of surface tension, scCO2 enabled [HTMG][His][I] to highly disperse in SBA-15 pore channels. Surprisingly, [HTMG][His][I]/SBA-15 heterogeneous catalyst displayed higher CO2 cycloaddition activity (95% propylene carbonate yield) than equivalent molar pristine [HTMG][His][I] homogeneous catalyst (69% propylene carbonate yield) under the identical conditions. The significantly enhanced activity was resulted from the synergistic effect of [HTMG][His][I] and SBA-15 support. Moreover, [HTMG][His][I]/SBA-15 performed outstanding universality of various epoxides and reusability. This work developed a promising strategy to heterogenization of homogeneous IL catalyst assisted by scCO2 as synthetic media and provided an efficient catalyst for CO2 conversion.