The synthesis of pure and uniform nanosized TS-1 crystals with a high titanium content and a high space–time yield

Abstract

Anatase-free titanium silicalite-1 (TS-1) zeolite with a high framework titanium content is highly required for catalysing selective oxidation reactions, however, its synthesis generally suffers from issues relating to cost, efficiency, and environmental friendliness. Herein, a new protocol was proposed for synthesizing a zeolite with the necessary characteristics. It involved dissolving large amounts of S-1 zeolite at 80 °C to prepare liquid seeds, which avoided anatase TiO₂ impurity formation and accelerated the incorporation of titanium into the zeolite framework, and using fumed silica as a silicon source in the zeolite to decrease the amount of wastewater discharge. By using this protocol, uniform anatase-free nanosized hierarchical TS-1 zeolite with a Si/Ti ratio of 41, with very high activity for the cyclohexanone ammoximation reaction, was obtained. ESI-MS and DLS analyses indicate that primary silicon species with four- or five-membered rings in the liquid seeds significantly accelerated the crystallization of TS-1 zeolite and the incorporation of titanium into the zeolite framework.