SOLID-STATE C-13 MAS NMR-STUDY OF METHANOL-TO-HYDROCARBON CHEMISTRY OVER H-SAPO-34

C-13 solid-state MAS NMR was used to probe the chemistry of a number o f species involved in the methanol-to-hydrocarbon process over H-SAPO- 34 molecular sieve at both high (573 K) and low (473-563 K) temperatur e ranges and at very low conversion (<0.1%). Isobutane was the only hy drocarbon product observed at 473 and 573 K. Evidence for the operatio n of a stepwise methylation reaction via surface-bound species derives from, first, the treatment of several samples with different loadings of methanol at 523-563 K and, second, when either [C-13]methanol is c oadsorbed with [C-12]ethene over the catalyst or [C-12]ethene is react ed with pre-[C-13]methylated SAPO-34. The hydrocarbon products in thes e experiments were mainly isobutane and isopentane as well as methane, ethene, and propane. Based on these experimental findings, a number o f mechanistic approaches concerning the very first stages of the react ion are discussed. (C) 1996 Academic Press, Inc.