CONVERSION OF PROPANE USING H-ZSM-5 AND GA H-ZSM-5 IN THE PRESENCE OF CO-FED NITRIC-OXIDE, OXYGEN, AND HYDROGEN

The conversion of propane to propene and aromatic hydrocarbons has been studied using cofed NO, O-2, and H-2 to probe the reaction mechanism with H-ZSM-5 and Ga2O3/H-ZSM-5 physical mixtures as catalysts. NO co-feeding with H-ZSM-5 causes a decrease in the conversion of propane and in the yields of methane and aromatic products. These effects are reversible on the removal of NO, but there is a significant delay that is dependent on the duration of the NO co-feeding, indicating that the effects are due to-poisoning of active sites. Although propane conversion decreases, NO does not affect the yield of propene. Similar effects are observed when NO is co-fed using Ga2O3/H-ZSM-5 as catalyst. O-2 co-feeding with H-ZSM-5 leads to an increase in propane conversion, propene yield, and deactivation rate, whereas, as observed with NO, the yields of methane and aromatic products are decreased. Co-feeding of excess H-2, Which is a major product from the aromatization of propane, has very little effect on the conversion of propane over H-ZSM-5, although the selectivities to alkanes are increased. For Ga2O3/H-ZSM-5 physical mixtures containing 10-90% Ga2O3, H-2 co-feeding leads to a significant decrease in propane conversion and in the yield of aromatic products. For Ga2O3 alone, the co-feeding of H-2 gives a significant increase in propane conversion with only limited effects on the product selectivities. A series of experiments that use a physical mixture of Ga2O3 powder and pelleted H-ZSM-5 with and without co-fed H-2 in which the mixture is separated by sieving after reaction for 3 h at 600 degrees C is described. The results are interpreted in terms of a mechanism in which propane is activated at the interface between the gallium oxide and the zeolite. (C) 1995 Academic Press, Inc.