Rationalizing the role of the anion in CO sub(2) capture and conversion using imidazolium-based ionic liquid modified mesoporous silica

Covalently supported ionic liquids in mesoporous materials were prepared by grafting 1-methyl-3-(3-trimethoxysylilpropyl)imidazolium chloride in MCM-41. Subsequently, the [Cl super(-)] anion was changed to [BF sub(4) super(-)], [PF sub(6) super(-)] or [Tf sub(2)N super(-)]. These materials that present an advantageous combination of the properties of mesoporous solid materials and ionic liquids were evaluated for CO sub(2) sorption as well as catalysts for CO sub(2) conversion into cyclic carbonate using propylene oxide. The material with the [Cl super(-)] anion had the best performance for both CO sub(2) sorption and conversion. A CO sub(2) sorption of 11 w/w% on the adsorbent was achieved and the cycloaddition reaction exhibited a conversion of 67% with 82% selectivity with the catalyst remaining active after 5 cycles, proving that the same sorbent/catalyst setup can be used for both CO sub(2) capture and conversion. Based on the experimental data and electronic-structure numerical simulations, we have hypothesized two major reasons why chloride out performs other anions when adsorbed on MCM-41 unlike unsupported ionic liquids.