Preparation and catalytic performance of the supported Ti-MWW zeolites

Nano-size titanium silicalites is difficult to be separate from the reaction solution, lamellar and homogeneous TiMWW zeolites are successfully formed a dense zeolite layers on alpha-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 alpha-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.

Automated summary

In this study, nano-sized titanium silicalites were successfully synthesized on alpha-Al2O3 pellets by secondary hydrothermal synthesis, with NH4F doping improving the catalytic performance of supported Ti-MWW zeolites. Reaction conditions and the amount of Ti-MWW zeolites have significant effects on the phenol hydroxylation efficiency.