Methylbenzene Chemistry on Zeolite HBeta: Multiple Insights into Methanol-to-Olefin Catalysis

The reactions of 1,2,4-trimethylbenzene, 1,2,4,5-tetramethylbenzene (durene), pentamethylbenzene, hexamethylbenzene (HMB), ethylbenzene, and cumene were studied on large-pore zeolite HBeta catalysts, either alone or with co-injection of methanol- 13 C . The reactivity of the methylbenzenes alone increased with increasing methyl substitution, as did selectivity for propene over ethylene. Disproportionation occurred for all methylbenzenes studied; in the case of HMB, pentamethylbenzene was a major volatile product, and we inferred that the heptamethylbenzenium cation also formed and remained in the catalyst. Substantially higher yields of olefins were obtained when methylbenzenes were co-reacted with methanol- 13 C. Ethylbenzene alone was unreactive at 350 °C, but when injected with five equivalents of methanol- 13 C, ethylbenzene formed ethylene- 12 C 2 with very high selectivity. These and other experiments led to a detailed description of the hydrocarbon pool mechanism for MTO chemistry with side-chain methylation as the predominant route to olefins and the paring reaction as a possible minor pathway.