Comparative study of MTO conversion over SAPO-34, H-ZSM-5 and H-ZSM-22: Correlating catalytic performance and reaction mechanism to zeolite topology

Conversion of methanol to olefins (MTO) was comparatively studied over three zeolites with different topologies, i.e. SAPO-34, H-ZSM-5 and H-ZSM-22. The correlation between reaction mechanism and the zeolite topology was also investigated. SAPO-34 presented the highest selectivity for light olefins such as ethene and propene, and no aromatics were detected. H-ZSM-5 showed relatively high selectivity for ethene and propene, and large amount of aromatics were detected. Over H-ZSM-22, the selectivity for ethene is very low and a large amount of non-aromatic C6+ olefins generated. With the aid of 12C-methanol/13C-methanol switch technique, the reaction routes followed by methanol conversion over the three catalysts could be distinguished. The reaction mechanisms, which varied with the zeolite topologies, caused the differences in catalytic performances. The co-reaction of 13C-methanol with 12C-olefin or 12C-aromatic, were carried out for further clarification of the operation of the different catalytic cycles in methanol conversion.