Post-synthesis of MSE-type titanosilicates by interzeolite transformation for selective anisole hydroxylation

Abstract

The practical application of MSE-type titanosilicate (Ti-MSE) catalysts in liquid-phase oxidation processes is facing the problem of inefficient and complex synthesis. A novel and efficient strategy is developed to post-synthesize Ti-MSE by the combination of interzeolite transformation, dealumination and isomorphous substitution of Ti. With the assistance of MCM-68 seeds and tetraethylammonium hydroxide (TEAOH) as an organic structure-directing agent, the MSE aluminosilicate was rapidly crystallized in only 1 day with a high solid yield of 88.3% via the dissolution–recrystallization of siliceous Beta zeolite. The structural similarity between the parent Beta and target MSE was revealed to play a vital role in realizing the efficient interzeolite transformation. After dealumination and solid–gas treatment with TiCl₄ vapor, the Ti-MSE-trans catalyst was readily obtained, which exhibited high catalytic activity in anisole hydroxylation with a methoxyphenol yield of 54.9% and a particularly high para-selectivity of 96.2%. Electrostatic potential (ESP) and density functional theory (DFT) calculations revealed that the framework hydroxyls in Ti-MSE strongly interact with the oxygen-containing substituent groups in aromatic substrates, responsible for the high para-selectivity.