Ionothermal synthesis, physicochemical characterization and catalytic performance of extra-large-pore silicoaluminophosphate zeotype with -CLO structure

摘要

Silicoaluminophosphate zeotypes with -CLO structure (SAPO-CLO) were ionothermally synthesized in 1-ethyl-3-methyl imidazolium ([emim](+)) ionic liquid in the presence of tetrapropylammonium hydroxide. The physicochemical properties of SAPO-CLO with different silicon content were comparatively studied using several characterization techniques including XRD, SEM, XRF, NMR, BET, NH3-TPD, in situ DRIFTS etc. Notably, Si-29 MAS NMR results revealed the incorporation of Si in the structure that was mainly in the form of SMII and SMIII combination. NH3-TPD and in situ DRIFTS results demonstrated that SAPO-CLO exhibited higher acid amount than AlPO-CLO as a result of the formation of new Bronsted acid sites Si-OH-Al in addition to structural P-OH in the framework. N-2 physisorption results showed SAPO-CLO compared with AlPO-CLO exhibited higher BET surface area and microporous volume with the presence of extra-large-pore of about 1.2 nm. Finally, the catalytic performance of SAPO-CLO was evaluated in both methanol-to-olefin and propene oligomerization reactions to elucidate its activity, shape-selectivity and hydrothermal stability. SAPO-CLO showed improved catalytic activity in comparison to AlPO-CLO in both reactions, and lower selectivity of light olefins in the former reaction and higher selectivity of C-3n oligomers in the latter reaction in comparison to small-pore SAPO-LTA. The deactivated catalyst was unrecoverable in MTO reaction due to structure degradation by water produced during the reaction, whereas recoverable in oligomerization reaction after the removal of coke by high temperature calcination.