Lifetime improvement in methanol-to-olefins catalysis over chabazite materials by high-pressure H2 co-feeds

Mitigating catalyst deactivation in the industrially deployed process of methanol-to-olefins conversion over HSAPO-34 is a critical challenge. Here, we demonstrate that lifetime in methanol-to-olefins catalysis over HSAPO-34 at sub-complete methanol conversion, as determined by the cumulative turnover capacity per Bronsted acid site towards hydrocarbon products in the effluent before complete catalyst deactivation (~15% carbon final conversion), can be enhanced with increasing efficacy (~2.8× to >70×) by co-feeding H2 at increasing partial pressures (400–3,000 kPa) in the influent with methanol compared with co-feeding helium at equivalent pressures. The lifetime improvement in the presence of high-pressure H2 co-feeds is observed to be more prominent at complete methanol conversion than at sub-complete conversion. The improvements in catalyst lifetime by co-feeding H2 are rendered without any deleterious effects on C2–C4 olefins selectivity, which remains ~85% carbon irrespective of the inlet H2 pressure. These observations can be rationalized based on the participation of H2 in hydrogen transfer reactions, and in effect, the interception of pathways that promote the formation of deactivation-inducing polycyclic species. Small-pore zeolites that engender high selectivity for light olefins in the conversion of methanol to olefins deactivate rapidly due to the accumulation of unreactive carbonaceous deposits. Now, experiments show that high-pressure hydrogen added to the methanol feed can substantially enhance catalyst lifetime without compromising selectivity.