NMR studies of methanol-to-hydrocarbon chemistry Part 1Primary products and mechanistic considerations using a wide-pore catalyst

Abstract

The conversion reactions of methanol over H-ZSM-12 and H-Beta zeolites using a static microreactor and a continuous flow system are compared and contrasted. The surface of both zeolites is methylated prior to the conversion of methanol to hydrocarbon (i.e. ⩽493 K). Methane and ethene, which are observed in the very early stages of conversion over the zeolites, are viewed as primary hydrocarbons. The high selectivity for isobutane is considered to be related to the low reactivity of active sites (in H-Beta) to secondary conversion such as ethene oligomerisation and to the distribution of acid sites and pore geometry (in H-ZSM-12). The reaction of methanol, in the presence of hydrogen and oxygen, over H-Beta provides experimental evidence against the involvement of radical species in the conversion reaction. The high selectivity to isobutane is also found for the conversion of isopropanol over premethylated Beta. This is discussed in terms of a possible mechanism.