MECHANISM OF PARTIAL TOLUENE OXIDATION CA TALYZED BY CR2O3-AL2O3 AEROGELS

Partial oxidation of toluene catalysed by Cr2O3-Al2O3 with atomic perc entage in chromium equal to 5 % essentially produces benzaldehyde with high selectivity in the 250-300 degrees C temperature range. For high temperatures the total oxidation is favoured. The kinetic study of th is reaction performed at 270 degrees C shows that the redox mechanism is compatible with experimental results. The two steps of this mechani sm are the catalyst reduction by the hydrocarbon and its reoxidation b y dissociatively adsorbed oxygen. I.R. and E.S.R. studies of simultane ous or successive adsorption of toluene and oxygen show that the adsor ption of toluene constitutes the reduction step by electron transfer t o form the benzylic species, precursor of benzaldehyde formation. The oxidation step involves the-oxygen dissociative adsorption which reoxi dizes a fraction of the reduced surface and forms the oxygen active sp ecies which react at 270 degrees C with benzylic species to form benza ldehyde.