FT-IR AND FLOW REACTOR STUDIES ON HETEROGENEOUSLY CATALYZED GAS-PHASE AMMOXIMATION OF CYCLOHEXANONE

IR spectroscopic measurements, with adsorption of cyclohexanone and cyclohexylamine, in the presence and in the absence of ammonia and oxygen, over amorphous silica calcined at different temperatures, were used in this study directed towards obtaining a. better understanding of the gas-phase ammoximation of cyclohexanone with molecular oxygen, amorphous silica being the catalyst. The results obtained substantially confirm the reaction network previously suggested on the basis of flow-reactor experiments. The catalyst was found to have unusual Bronsted acidity due to free and H-bonded silanols with a distribution of different acid strengths. The surface silanols were found to react with cyclohexanone and ammonia to produce the tautomeric forms of the cor-responding imine, these forms being thought to be bonded to the surface by Si-N bonds and to be intermediates for the production of the oxime and the tars. The dehydrogenating capability of this amorphous silica, hypothesized in previous work, was also confirmed here.