Propane conversion in the presence of iron- and manganese-promoted sulfated zirconia: evidence of Olah carbocation chemistry

Abstract

Iron- and manganese-promoted sulfated zirconia was tested for conversion of propane at 1 bar, 200, 250, and 300°C, and propane partial pressures of 0.01, 0.025, and 0.05 bar. Propane was converted to pentanes, butanes, propene, ethane, ethene, and methane at 250°C, but the conversions were low, for example, being only a fraction of a percent at a space velocity of 9.1 × 10⁻⁷ mol/(g s) and a propane partial pressure of 0.05 bar. Carbonaceous deposits formed rapidly. At 250°C, the number of propane molecules converted to gas-phase products was only about 1 per sulfate group after 16 days of operation in a continuous flow reactor. The observation of butanes and pentanes as products is consistent with Olah superacid solution chemistry, whereby propane is first protonated by a very strong acid to form a carbonium ion. The carbonium ion then decomposes into methane and an ethyl cation, which undergoes secondary reactions with propane to form higher-molecular-weight alkanes.