AMMOXIMATION REACTION IN THE GAS AND LIQUID-PHASES WITH SILICA-BASED CATALYSTS - ROLE OF TITANIUM

The catalytic behaviour in the liquid phase and in the gas phase ammox imation of cyclohexanone on amorphous silicas containing different amo unts of titanium has been investigated The silicas were prepared by im pregnation and the sol-gel method. The behaviour of the silicas with a nd without titanium was different in the liquid and gas phases. Tile p resence of titanium sites was found to be essential for the developmen t of selectivity to oxime in the liquid phase. In the gas phase the pa ramount parameters are the textural and structural features of the sil ica and the introduction of titanium can only enhance the activity in both impregnated and sol-gel catalysts. It is proposed thar the role o f titanium in the gas phase is to favour the oxidation of imine, an in termediate in the vapour phase reaction, due to its ability to activat e molecular oxygen.