Study of Higher Selectivity to Styrene Oxide in the Epoxidation of Styrene with Hydrogen Peroxide over La-Doped MCM-48 Catalyst

The epoxidation of styrene with hydrogen peroxide with higher selectivity to styrene oxide was carried out over lanthanum-doped MCM-48 (La-MCM-48) molecular sieves, in which aqueous NaOH solution was used to adjust the pH value of the reaction solution. The results show that the pH value of the reaction solution has a great influence on the catalytic performance of La-MCM-48 and the product distribution. When the pH value of the reaction solution was 11.5, the conversion of styrene reached 54.5% and the selectivity to styrene oxide was 98.8%. UV−vis and EPR spectroscopy was used to characterize the lanthanum species in the framework of La-MCM-48 and the peroxo-lanthanum species by H 2 O 2 reacting with the lanthanum species. It has been found that the conversion of styrene has a close relationship with the amount of the peroxo-lanthanum species, and the selectivity to styrene oxide has a close relationship with the ratio of La(III)-superoxide species to La(III)-hydroperoxide species, which can be controlled by adjusting the pH value of the reaction solution.