Studies Of Methanol Conversion Over One-dimensional 10-membered HZSM-22 And SAPO-11 Zeolites

Methanol-to-Olefins (MTO) is an important non-petrochemical pathway for hydrocarbons production. Therefore, studies of methanol conversion is of great significance for catalyst design and products selectivity control. This dissertation focuses on the methanol conversion over two one-dimensional 10-ring HZSM-22 and SAPO-11. The MTO performance, deactivation and mechanism of olefins generation over both zeolites have been investigated in detail. Based on these results, an efficient modification approach has been proposed and applied for HZSM-22 zeolite.Different catalytic performances of methanol to olefins have been observed over HZSM-22 and SAPO-11 due to the diversity of acid strength of these two zeoltes, even though HZSM-22 and SAPO-11 possess similar pore architecture. HZSM-22 with strong acidity exhibited high reactivity for methanol conversion and yet rapid deactivating feature. SAPO-11 with lower acidity showed inferior reactivity but deactivated slowly. The effect of temperature on products distribution was significant for HZSM-22. The higher hydrocarbons were mainly formed at lower temperature (?400?), while C2-C4 olefins were dominant products at higher temperature (?450?). For SAPO-11, the effect of temperature on products distribution was marginal and the majority of the products were C5+ higher hydrocarbons. The deactivation at lower temperatures over both zeolites was mainly due to the formation of polycyclic compounds resulting in the blockage of pores. In contrast with SAPO-11, the coke species prefer to be formed near the pore openings of HZSM-22, while the deposition of insoluble, bulky coke on their outer surface was the primary reasons for deactivation at high temperatures.Methanol conversion over HZSM-22 and SAPO-11 mainly via alkene methylation-cracking mechanism, which is substantialized by means of 12C/13C-methanol switch experiments. However, the diversity of acid strength led to the differences in cracking reactivity. Large amounts of light olefins was formed over HZSM-22 with strong acidity, while heavy hydrocarbons was the main products over SAPO-11 with weak acidity. Even though alkene methylation-cracking mechanism was the main route for methanol conversion over HZSM-22, for the first time to our knowledge, an induction period of methanol conversion at lower temperature and dimethylcyclopentadiene cation (DMCP+) and trimethylcyclopentadiene cation (TMCP+) as active intermediates have been observed directly by MAS NMR technology, confirming the possibility of the formation of initial ethene through a hydrocarbon pool mechanism. Possible complete catalytic cycle of MTO over HZSM-22 was successfully established by the aid of theoretical calculation.HZSM-22 with high degree of crystallinity, small particle size and high dispersion has been successfully prepared using ball milling method combined with alkaline and acid post-treatment for the parent HZSM-22 with large size. The small-sized HZSM-22 greatly improved the catalyst life span of HZSM-22 in methanol conversion and did not change the products distribution concurrently.