On the origin of initial hydrocarbons in methanol-to-hydrocarbons reaction

Abstract

Providing a complete scheme to describe the methanol-to-hydrocarbons (MTH) reaction network is impeded by insufficient understanding of the chemistry occurring incipiently. Using a temperature-dependent reaction strategy, combined with operando photoelectron photoion coincidence (PEPICO) spectroscopic diagnosis of intermediate species and theory, we provide a comprehensive understanding on initial hydrocarbons formation, including the first C–C bond, olefins, and aromatics. Surface acetyl groups attached to zeolite and gaseous ethenone (ketene) contain the first C–C bonds. Their generation is associated with surface methoxy species (SMS) formed over Brønsted acid sites and formaldehyde. Ketene methylation by SMS followed by decarbonylation leads to the first olefins, ethylene and propylene. Prins reaction between formaldehyde and propylene results in butadiene, which subsequently reacts with propylene via Diels–Alder reaction to yield methylcyclohexene. Successive hydrogen transfer steps produce the first aromatic compound, toluene. These mechanistic insights will inspire targeted catalyst design and process optimization for MTH technology.