Organic sulphonate salts tethered to mesoporous silicas as catalysts for CO2 fixation into cyclic carbonates

Abstract

A series of mesoporous silica materials tethered with the sulphonate salts of organic bases were synthesized and their catalytic activity for CO₂–epoxide cycloaddition was investigated. The sulphonate group was supported on silica through the functionalization and subsequent oxidation of 3-mercaptopropyltrimethoxysilane (3-MPS) by a post-grafting method. All the synthesized materials have been characterized using various physicochemical techniques such as SAXS, BET, SEM, TEM, FTIR and XPS. The as-formed SBA-15(SO₃H) was neutralized with different organic bases such as 4-dimethylaminopyridine, triethanolamine and triethylamine, such that the SO₃H group ionizes to become the SO₃⁻ ion. These materials along with KI displayed promising CO₂ conversion yields with excellent selectivity towards the desired product, cyclic carbonates, with a turnover frequency (TOF) as high as 1900 h⁻¹. The catalysts were thermally stable and their reusability studies were also performed. The synergistic play between SO₃⁻ and KI is supposed to be the reason behind the good catalytic rates exhibited by this catalytic system. All the parameter studies have also been carried out.