Solid-state NMR study of methanol conversion over ZSM-23, SAPO-11 and SAPO-5 molecular sieves. Part 2

The chemistry of methanol-to-hydrocarbon conversion over H-ZSM-23, H-SAPO-11 and H-SAPO-5 was studied using solid-state NMR and gas chromatography. The first hydrocarbons observed in the very early stages of the reaction were either C-1 and C-2 or C-1-C-4, depending upon loading. The various selectivities of SAPO-5 for hydrocarbon products are considered to be related to the stability of isobutyl cation intermediate and the loadings of the catalyst. The formation of higher carbon number products for SAPO-11 is caused by the lower reactivity of the active centres for cracking reactions. To gain a better understanding of the intermediates involved in the conversion reaction, premethylated samples were treated with hydrogen and dimethyl sulfide.