Resolving the Reaction Mechanism for Oxidative Hydration of Ethylene toward Ethylene Glycol by Titanosilicate Catalysts

Due to the complex internal structure of titanium silicalite-1, the reaction mechanism for oxidative hydration of ethylene toward ethylene glycol on the titanium silicalite-1 (TS-1) catalyst is still disputable and inconclusive. In this work, density functional theory calculations, microkinetic modeling, and experiments are combined to provide unique insights into the reaction mechanism. With consideration of perfect titanium sites (including isolated and dinuclear titanium sites) and hydrolyzed titanium sites, the results demonstrate that oxidative hydration of ethylene prefers a catalysis mechanism completed by the coupling of two types of active centers, where the isolated titanium site participates in ethylene epoxidation and the hydrolyzed titanium site is responsible for the hydration of ethylene oxide. The ethylene glycol generation rate, reaction order, and apparent activation energy calculated by microkinetic modeling are highly consistent with our experimental kinetics. This study provides a decisive description of the reaction mechanism for oxidative hydration of ethylene over TS-1 catalysts, which may enable further optimization of TS-1 by targeted modification on specific active centers.