ZnO supported on high silica HZSM-5 as new catalysts for dehydrogenation of propane to propene in the presence of CO2

Dehydrogenation of propane to propene in the presence of CO2 was investigated over zinc oxide supported on HZSM-5 with high Si/Al ratios. The stability of supported ZnO catalysts for the reaction improves with increasing the Si/Al ratio of the HZSM-5 support, while the catalytic activity shows a contrary trend. A highly active and stable catalyst, ZnO supported on HZSM-5 with a Si/Al ratio of 160, was obtained, with a propane conversion of 41.5% and a propene yield of 25.8% at steady state. The results of NH3-TPD and FT-IR spectra of pyridine adsorption reveal that the enhancement of the catalytic stability stems from the decrease in acidity of the catalysts, resulting in the suppression of the side reactions, such as cracking, oligomerization and aromatization. This can be verified by the fact that the amount of coke deposited on the catalyst diminishes with raising the Si/Al ratio of the HZSM-5 support. The promoting effect of CO2 on the dehydrogenation reaction is observed, which can be attributed to the reverse water-gas shift reaction. The catalytic stability is also enhanced by the introduction of CO2 to the feed gas.