Reaction Pathways in the Chemical Transformation of CO₂ with β,γ -Unsaturated Alcohols into Cyclic Carbonates Catalyzed by Methylated Nitrogen-substituted SBA-15

Abstract

Methylated nitrogen-substituted SBA-15 (MeNSBA-15) was demonstrated to catalyze cyclic carbonate synthesis using β,γ -unsaturated alcohol and CO₂. The methylated nitrogen in the framework acts as the catalytic active site. The turnover frequency (TOF) as function of CO₂ partial pressure and β,γ -unsaturated alcohol concentration reflected the major active surface species. The CO₂ dependence could be explained by the adsorption equilibrium of CO₂ over the active site. The formation of carbamate species is the key to this reaction. Less β,γ -unsaturated alcohol is adsorbed on the catalytic site than CO₂. The reaction could involve the following five steps; carbamate formation, interaction of β,γ -unsaturated alcohol with the carbamate species, deprotonation and associated C–O bond formation, intramolecular cyclization, and desorption of the unsaturated cyclic carbonate. Compared with cyclic carbonate synthesis from cyclic ether, the difference in pressure dependence of the cyclic carbonate syntheses could be explained by the competing adsorption (or activation) of the counter reactants with CO₂. The adsorption of β,γ -unsaturated alcohol on the methylated nitrogen is much less than that of cyclic ether.