Preparation and catalytic performance of the supported Ti-MWW zeolites

Abstract

Nano-size titanium silicalites is difficult to be separate from the reaction solution, lamellar and homogeneous Ti-MWW zeolites are successfully formed a dense zeolite layers on α-Al2O3 pellets by secondary hydrothermal synthesis in this study. Seeded crystals concentration and titanium source have significantly influences on the morphology, thickness and titanium active sites of Ti-MWW zeolites. Doping NH4F in the precursor synthesis solution could conducive to prepare macroscopically and anatase-free Ti-MWW zeolites layer on the outside of α-Al2O3 pellets, and the thickness of the Ti-MWW zeolites layer is ca. 1 mm. Besides, catalytic performance of the supported Ti-MWW zeolites are significantly improved by NH4F. A fixed-bed reactor with the supported Ti-MWW zeolites are applied to catalyze phenol hydroxylation with hydrogen peroxide efficiently, and reaction time and temperature, amount of the supported Ti-MWW zeolites have obvious effects on the phenol conversion and dihydroxybenzene selectivity. When the actual mass of Ti-MWW zeolites to volume of reaction solution is only 10 g/L, the relative phenol conversion and dihydroxybenzene selectivity are 46.45% and 92.72% at 65 °C after 3 h, respectively.