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Partic. vol. 37 pp. 43-53 (April 2018)
doi: 10.1016/j.partic.2017.06.004

Synthesis and stability evaluation of hierarchical silicoaluminophosphates with different structural frameworks in the methanol to olefins process

Seyed Hesam Mousavi, Shohreh Fatemi*, Marjan Razavian

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shfatemi@ut.ac.ir

Highlights

    • Hierarchical silicoaluminophosphates (SAPO) were synthesized using PEG as mesopores generating agent. • Molecular weight and concentration of PEG had significant influence on pore structure of SAPO. • RHO-based SAPO catalyst was fabricated by PEG with molecular weight of 6000. • Mesoporous SAPO-34 with tuned acidity was fabricated by PEG with molecular weight of 4000. • Stability of the modified SAPO-34 with high olefins selectivity was observed in MTO process.

Abstract

Silicoaluminophosphates (SAPOs) with different pore structures were synthesized through the implementation of polyethylene glycol (PEG) as a mesopores impregnation agent. Using PEGs with different molecular weights (MWs) and concentrations in the synthesis precursor, several samples were synthesized and characterized. Applying a PEG capping agent to the precursors led to the formation of tuned mesopores within the microporous matrix of the SAPO. The effects of the PEG molecular weight and PEG/Al molar ratio were investigated to maximize the efficiency of the catalyst in the methanol-to-olefin (MTO) process. Using PEG with a MW of 6000 resulted in the formation of both Zeolite Rho and chabazite structural frameworks (i.e., DNL-6 and SAPO-34). Pure SAPO-34 samples were successfully prepared using PEG with a MW of 4000. Our results showed that the PEG concentrations affect the porosity and acidity of the synthesized materials. Furthermore, the SAPO-34 sample synthesized with PEG (MW of 4000) and a PEG/Al molar ratio of 0.0125 showed a superior catalytic stability in the MTO reaction owing to the tuned bi-modal porosity and tailored acidity pattern. Finally, through reactivation experiments, it was found that the catalyst is stable even after several regeneration cycles.

Graphical abstract

Keywords

Hierarchical SAPO-34; PEG; Mesoporosity; DNL-6 zeolite; MTO process; Catalytic stability