Mechanism of the Ethylene Homologation Reaction and Enhancement of the Reaction by Hydrogen on Molybdena Silica Catalyst

The mechanism of the ethylene homologation reaction to form propylene on molybdena silica catalyst was investigated. The homologation reaction is suggested to proceed via dimerization of ethylene, followed by isomerization of 1-butene, and finally metathesis of ethylene and 2-butene. Isomerization of 1-butene to 2-butene occurs slowly on the catalyst, particularly in the initial stage of the homologation. This slow isomerization both determines the overall rate of the homologation reaction and causes an induction period. However, use of hydrogen adsorbed catalyst significantly enhanced the rate of the homologation reaction. This promotion was presumably caused by an increase in the isomerization rate of 1-butene, which may proceed via an associative mechanism enhanced by dissociated hydrogen.