ROLE OF MOLECULAR-OXYGEN IN THE CATALYTIC BEHAVIOR OF ZSM-5 ZEOLITE IN HYDROCARBON TRANSFORMATION

The reactivity of 1-butene over H-ZSM-5 was studied in the absence and in the presence of molecular oxygen. Two ZSM-5 samples were compared: a highly crystalline sample (A) with homogeneous size distribution, and a less crystalline sample (B), of non-homogeneous size distribution. The alkene gives rise to aliphatics, aromatics and carbon oxides; the nature of the prevailing product depends on the reaction temperature. In the presence of oxygen, catalyst deactivation gives rise to a change in the distribution of the products within the first hours of time-on-stream. The rate of deactivation is influenced by the zeolite crystallinity. The addition of small amounts of Fe, Cu or Co into sample B does not substantially modify the catalytic performance, thus suggesting that the ability in oxygen activation is a property of the zeolitic matrix itself, and not of possible traces of metal impurities present in the original material. For comparison the conversion of n-butane and benzene was tested, too. The oxidation of benzene gives rise only to carbon oxides; butane also is converted mainly to carbon oxides, with some formation of aromatics.