A study of the reaction pathway upon propane oxidation over V-K/Al2O3 catalysts

The conversion of propane in the presence of oxygen on V-K/Al2O3 catalysts with different surface area and in different feed conditions has been investigated. The activation energy measured at low conversion is 21 kcal/mol (88 kJ/mol) and the reaction order of propane is 1. In order to propose a reaction pathway, complementary experiments have been performed with a K-free V/Al2O3 catalyst, and propene and 2-propanol oxidation tests have also been done. A reaction scheme for the propane oxidation process is proposed. Two different reaction regimes have been observed. Below 950 K true catalytic reaction occurs with propene, ethene, CO2 and CO as the only detectable products. Both CO, and ethene productions likely occur through a parallel-successive reaction scheme with respect to propene production. The key surface intermediate is thought to be the sec-propoxide species, that can give propene by elimination and either COchi or ethene by oxidation. Above near 950 K a new regime involving gas-phase species is observed. In this range, where consumption of oxygen is already total or nearly total, the cracking of propane to ethene+methane becomes predominant. This reaction can be limited by filling the empty space of the reactor. (C) 2002 Elsevier Science B.V. All rights reserved.