Unraveling the Influence of Al Addition and Location on the Catalytic Mechanism and Performance of the TS-1 Catalyst toward Ethylene Glycol Synthesis

In this work, the reaction mechanism of ethylene glycol (EG) synthesis from the oxidation hydration of ethylene catalyzed by Al/TS-1 was studied by density functional theory calculations, based on which the optimal energy pathway, rate-limiting step, and the underlying effect of Al addition and location were identified. The calculation results showed that the introduction of Al increased the catalytic activity of the Ti(IV) site of TS-1. The relative position of Al to Ti had an obvious influence on the reaction properties over the Ti(IV) site but had a minor effect on the catalytic activity of the Al(H) Brønsted acid site toward EG generation. In the optimal energy pathway of ethylene oxidation hydration to EG over Al/TS-1, the H2O2 activation and ethylene epoxidation occurred at the Ti(IV) site with barriers of 0.85 and 0.54 eV, respectively, while the hydration of EO to EG preferentially took place at the Al(H) Brønsted acid site with a barrier of 1.33 eV, exhibiting bifunctional actions of Ti–Al(H) sites. The Al/TS-1 catalyst showed a high selectivity to the EG product with the formation of the diethylene glycol byproduct suppressed by slow kinetics.