Catalytic Conversion of Methane and Ethylene to Propylene

Methane and ethylene react over several catalysts to form propylene as the principal product, with (LiCl + NaCl)/MgO being the most effective material. At 650 °C, it was possible to achieve 53% selectivity to C 3 H 6 at a C 2 H 4 conversion of 9.2%. Experiments utilizing 13 CH 4 demonstrated that one carbon atom in each C 3 H 6 molecule was derived from methane. Methyl radicals, but not vinyl radicals, were detected over these catalysts using a matrix isolation electron spin resonance system. Moreover, it was found that C 2 H 4 inhibited the formation of CH 3 • radicals. A model calculation, which included both heterogeneous and homogeneous reactions, indicated that most of the propylene was formed neither by the coupling of methyl and vinyl radicals nor via the addition of methyl radicals to ethylene in the gas phase. Rather, it appears that the primary pathway involves the reaction of methyl radicals with adsorbed ethylene to produce propyl radicals, which then lose a hydrogen atom to yield propylene. The instability of the vinyl radical limits the extent to which cross-coupling with methyl radicals can occur.