Implications of methanol disproportionation on catalyst lifetime for methanol-to-olefins conversion by HSSZ-13

• Total turnovers increase with decreasing methanol concentrations local to active centers.
• Methanol undergoes dehydrative disproportionation to methane and formaldehyde.
• Increased concentration of methanol dehydrogenation derivatives accelerates catalyst deactivation.

The effects of methanol space velocity and inlet methanol partial pressure on lifetime and selectivity of methanol-to-olefins catalysis are examined and interpreted to elucidate reaction parameters and propose intermediates and reactions relevant to catalyst deactivation. The propensity of active centers in HSSZ-13 to turn over for methanol-to-olefins catalysis increases when the methanol partial pressure local to organic co-catalysts confined within the inorganic chabazite cages is lower either by decreasing methanol space velocity or inlet methanol partial pressure. High initial methane selectivity reveals methanol disproportionation, to methane and formaldehyde, a primary reaction, and continual methane formation implicates persistent participation of methanol in bimolecular hydrogen transfer reactions throughout the catalyst lifetime. Methane selectivity correlates positively with inlet methanol partial pressure reflecting enhanced relative rates of formaldehyde formation with increasing methanol partial pressure. Subsequent alkylation reactions of olefins- and aromatics-based CC chain growth carriers by formaldehyde accelerate the relative rates of hydrogen transfer and proliferate, apparently, the precursors mediating the transformation of active hydrocarbon pool participants to those inducing catalyst deactivation.

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