Kinetics and Mechanism of Olefin Methylation Reactions On Zeolites

The effect of zeolite topology on steady-state dimethyl ether (DME) methylation of ethylene and propylene has been studied for zeolites H-FER, H-MOR, H-MFI, and H-BEA.  Reactant pressure dependence studies over these materials at low conversions (<0.5%) and high DME:olefin ratios (30:1) show a first-order rate dependence on olefin pressure and a zero order rate dependence on DME pressure in accordance with a zeolite surface predominantly consisting of activated DME-derived species reacting with olefins.  Temperature dependence studies in low temperature regimes (<430K) yield elementary-step activation energies and rate constants.  Systematically lower activation barriers and higher rate constants were observed for propylene methylation in comparison with ethylene methlyation on all frameworks studied.  Kinetic and isotopic studies probing the involvement of surface methyl groups in olefin methylation cycles and the relative rates of propagation of olefin methylation cycles in methanol to hydrocarbons catalysis on different zeolites will be presented.