Polymeric ionic liquid with carboxyl anchored on mesoporous silica for efficient fixation of carbon dioxide

Abstract

The utilization of carbon dioxide (CO2) has drawn much attention because of the increasing serious environmental problems. In order to promote the cycloaddition reaction of CO2 to epoxides, a new synthesis strategy for friendly nonmetal catalyst to combine polymeric ionic liquid (PIL) with mesoporous silica (mSiO2) was proposed. By thorough characterizations, those catalysts (mSiO2-PIL-n, n = 1, 2, 3, 4) were verified that PIL with multiply catalytic active sites such as carboxyl group, imidazole ring and Br–, was mainly anchored in mesoporous SiO2 structures. Therefore, mSiO2-PIL-n exhibited excellent catalytic activity for CO2 cycloaddition reaction to epoxides under solventless and cocatalyst-free conditions. Typically, the appropriate PIL loading and specific surface area guaranteed mSiO2-PIL-2 could efficiently catalyze the cycloaddition reaction with 96% yield and 99% selectivity to the target product of propylene carbonate under the conditions of 120 °C, 2 MPa and 6 h. Additionally, the mSiO2-PIL-2 catalyst showed superior recyclability and there was no catalytic activity decrease for 10 runs of recycling due to the tightly anchored PIL on mesoporous SiO2 by copolymerization. And the catalytic activity to other substituted epoxides over mSiO2-PIL-2 was also expanded. Therefore, PIL anchored on mesoporous SiO2 by copolymerization could be a promising synthetic strategy for the efficient catalyst to combine multiple active components in a single catalyst, meanwhile, mSiO2-PIL-n exhibited an appealing catalyst candidate for the effective fixation and utilization of CO2.