Study of the isomerization of C6 and C6+ alkanes over molybdenum oxycarbide catalysts

Abstract

The synthesis of high specific surface area molybdenum oxycarbide hydrocarbon isomerization catalysts has been achieved from low surface area molybdenum oxide or high surface area molybdenum carbide. A comparison of the molybdenum oxycarbide catalysts, prepared from both sources, with two classical platinum isomerization catalysts, supported on γ-alumina and on β-zeolite, for the isomerization of n-hexane, n-heptane and n-octane is presented, both at atmospheric pressure and elevated pressure. It is demonstrated that a high selectivity to the isomer products can be obtained for the reaction of n-heptane and n-octane even at very high conversion over the molybdenum catalysts. This is not possible over the platinum catalysts at high conversion due to extensive cracking of the C6+ alkanes and is due to differences in the isomerization mechanism. Further, these molybdenum based catalysts are highly active. Evidence is also presented for the non-bifunctional mechanism operating over the molybdenum oxycarbides: the metallacyclobutane bond shift mechanism.