Ammoximation reaction in the gas and liquid phases with silica based catalysts: role of titanium

Abstract

The catalytic behaviour in the liquid phase and in the gas phase ammoximation of cyclohexanone on amorphous silicas containing different amounts of titanium has been investigated. The silicas were prepared by impregnation and the sol-gel method. The behaviour of the silicas with and without titanium was different in the liquid and gas phases. The presence of titanium sites was found to be essential for the development of selectivity to oxime in the liquid phase. In the gas phase the paramount parameters are the textural and structural features of the silica and the introduction of titanium can only enhance the activity in both impregnated and sol-gel catalysts. It is proposed that the role of titanium in the gas phase is to favour the oxidation of imine, an intermediate in the vapour phase reaction, due to its ability to activate molecular oxygen.