Investigation of the features of zinc oxide-based catalysts for propylene dehydroaromatization

Abstract

As a followup to a previous work [R. Spinicci and A. Tofanari, Appl. Catal., 1 (1981) 397], propylene dehydroaromatization runs were performed on various types of zinc oxide, including undoped catalysts and catalysts doped with monovalent (Na +, Ag +) and trivalent (Fe 3+) cations, to ascertain whether the doping-induced electron excess concentration can modify catalytic activity. Catalytic activity was tested at the same temperatures and flow conditions as examined in the previous work. Results showed that, with the exception of Ag 2O-doped catalysts, no significant alteration is brought about by doping. This can be explained on the basis of similar behavior of the Ag + and Zn 2+ ions (demonstrated in electron spin resonance experiments) and on the basis of the different types of surface-adsorbed propylene [demonstrated in temperature-programmed desorption (TPD) experiments]; in fact, at the temperature used for the dehydroaromatization tests, only one of the types of propylene still remains adsorbed on the surface, desorbing at about 800°C. From an examination of the TPD peaks, doping appears not to have a significant effect on the adsorptive properties of these catalysts at higher temperatures, and hence, it does not substantially influence dehydroaromatization. This means that dehydroaromatization can be performed at temperatures of up to 800°C - as has already been accomplished in this work. Lastly, it was found that high activity and selectivity towards benzene formation resulted from increased reactivity of the Zn O bonds.