Site-specific scaling relations observed during methanol-to-olefin conversion over ZSM-5 catalysts

The conversion of methanol over ZSM-5 catalysts was studied using step response and temperature-programmed desorption and surface reaction analyses in a temporal analysis of products reactor, as well as quasi-elastic neutron scattering and Fourier transform infrared investigations, buttressed by archived ¹³C magic angle spinning nuclear magnetic resonance studies. The results were combined with micro-kinetic models that simulated the formation of the first C–C bond and primary olefin(s) from methanol. Dimethyl ether was the major surface oxygenate and a source of surface methoxy species. Propylene, the major olefin produced from dimethyl ether, was formed with a reaction barrier of ∼ 200 kJ mol⁻¹, in agreement with archived density functional theory calculations. Propylene could form from dimethyl ether via a methoxymethyl mechanism under intrinsic kinetic conditions. Site-specific scaling relations between the barriers to methyl propenyl ether and methoxy methyl species formation and dimethyl ether desorption were observed. The active sites of the ZSM-5 catalysts can be locally optimised and selectively tuned to improve their activity during the conversion of methanol to olefin(s).