Kinetic studies of zeolite-catalyzed methylation reactions. Part 2. Co-reaction of [12C]propene or [12C]n-butene and [13C]methanol

The co-reaction of propene or n-butene and methanol over an H-ZSM-5 acidic zeolite catalyst has been investigated using isotopically labeled reagents. The main objective has been to obtain kinetic data for the methylation of the propene and n-butene. This study is an extension of our previous investigation of the co-reaction of ethene and methanol [S. Svelle, P.O. Rønning, S. Kolboe, J. Catal. 224 (2004) 115]. At the very high feed rates employed here, the methylation products are dominating, and the isotopic composition is in accord with a methylation formation mechanism. Arrhenius plots have been constructed, and the activation energies, when corrected for the appropriate heats of alkene adsorption, were ∼110 kJ/mol for the methylation of propene and ∼90 kJ/mol for the methylation of n-butene. The results are compared with recent computational studies of the methylation of alkenes. The origin of the products not formed via methylation is briefly discussed. A short survey of the reactivity of propene and n-butene without methanol co-feed is presented. It has been found that alkene interconversion reactions are strongly suppressed by the presence of methanol.