Propane Dehydrogenation on Chromium Oxide and Gallium Oxide Catalysts in the Presence of CO2

The catalytic and physicochemical properties of GaOx/SiO2 and CrOx/SiO2 supported onto silica gels as catalysts for propane dehydrogenation were studied with the use of stationary and nonstationary (aresponse method) techniques, TPR-H-2, TPD-NH3, and UV spectroscopy, and the effect of CO2 on the course of dehydrogenation reaction was examined. It was found that the relatively low acidity of silica gels prevents intense coke deposition and has a positive effect on the stability of catalyst operation. At the same time, the acid hydroxyls of these supports play an important role in the formation of a disperse active surface. In the case of the GaOx/SiO2 catalysts, the insufficient dispersity of the active phase is a reason for the low specific activity of these systems. It was found that the appearance and growth of catalytic activity with temperature was accompanied by the formation of the reduced forms of gallium oxide, the fraction of which was limited under the conditions of dehydrogenation (600 degrees C). It was established that CO2 hindered the adsorption of propane on the surface of catalysts to decrease its conversion; at the same time, it prevented the adsorption of propylene and its further conversion into coke. In the case of the chromium systems, the increase in the yield of propylene and in the stability of operation due to the oxidation of coke and hydrogen upon the introduction of CO2 prevailed over a negative effect. This negative effect was more pronounced for the gallium catalysts, and this led to a decrease of the propylene yield.