Deactivation mechanisms in methanol-to-hydrocarbons chemistry
A precise understanding of chemistries mediating deactivation in methanol to hydrocarbons (MTH) conversion over zeolite/zeotype materials has until recently remained elusive despite extensive research efforts focused on the question of catalyst deactivation. This chapter discusses some key recent developments that have helped elucidate the identity and mechanistic provenance of key intermediates mediating deactivation during MTH conversion, and strategies aimed at mitigating their formation. Emphasis is placed on experimental evidence supporting the role of methanol-transfer dehydrogenation to formaldehyde in effecting catalyst deactivation along with a mechanism for polycyclic aromatic hydrocarbon (coke) formation consistent with reported observations. Ultimately, strategies for enhancing catalyst lifetime based on either inhibiting formaldehyde formation, or scavenging formaldehyde, once formed, are discussed, and key knowledge gaps with reference to MTH deactivation chemistries highlighted.