A heterostructured titanium silicalite-1 catalytic composite for cyclohexanone ammoximation

Abstract

Submicron-sized titanium silicalite-1 is difficult to recover in industrial process because of their fineness and rapid decrease in catalytic activity due to particle agglomeration. To solve these problems, we present a heterostructured titanium silicalite-1 (TS-1) catalytic composite using bentonite clay as the catalyst support. The catalytic composite is synthesized by hydrothermal treatment which directly crystallizes TS-1 on the bentonite clay surface. The synthesized composite has been characterized using scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The TS-1 crystals have been found on and between the layers of the bentonite with strong attachment. Characterizations suggest that crystallization temperature of 175 °C is the optimum hydrothermal temperature to produce TS-1 on the bentonite support with characteristics necessary to promote selective catalytic reactions. It is found that prolonged crystallization duration does not necessarily increase the crystallinity of TS-1 on the bentonite surface. The heterostructured composite is able to maintain high conversion of cyclohexanone (97%) and oxime selectivity (83%) after three reaction cycles which is contrary to the unsupported TS-1 that shows apparent decrease in activity (>10%), especially in the selectivity to oxime. The synthesized composite also has significant improvement in separation efficiency with respect to the unsupported catalytic system. Therefore, we conclude that the heterostructured TS-1 composite is a promising catalytic material for cyclohexanone ammoximation and potentially for other TS-1 related processes where catalyst recovery and reuse are required. © 2008 Elsevier Inc. All rights reserved.