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.