Synthesis and application of ZSM-5/SAPO-34 and SAPO-34/ZSM-5 composite systems for propylene yield enhancement in propane dehydrogenation process

• Synthesis of ZSM-5/SAPO-34 binary composite by sequential crystallization.
• Synthesis of novel SAPO-34/ZSM-5 bi-phase composite using pre-treated SAPO-34 crystals.
• Necessity of pre-treatment step to circumvent structural and chemical incompatibilities.
• Promoted catalytic properties based on the synergism between SAPO-34 and ZSM-5 zeolites.
• High conversion and propylene selectivity of PtSn-SAPO-34/ZSM-5 (Si/Al = 60) in PDH.

Two types of zeolitic composite systems with binary hierarchical structures comprising ZSM-5 and SAPO-34 molecular sieves were synthesized employing different procedures. Obtained products were served as catalytic carriers for propane dehydrogenation reaction so as to promote the physicochemical properties of ZSM-5 support, enhance the propylene yield and reduce the formation of light compounds. ZSM-5/SAPO-34 was fabricated in a series hydrothermal procedure employing pre-heated ZSM-5 suspension followed by secondary growth of SAPO-34 layer whereas SAPO-34/ZSM-5 was synthesized using tetrapropylammonium bromide exchanged-SAPO-34 crystals and pre-reacted ZSM-5 slurry in a hydrothermal one-step process. The products were characterized by XRD, FESEM, EDS, FTIR, NH3-TPD, and N2 adsorption–desorption techniques to investigate the textural and structural properties of composite architectures. The catalytic performance of the bimetallic Pt-Sn-based composites were evaluated in propane dehydrogenation reaction and compared with those of physical mixture and single ZSM-5-derived catalysts. Either of composites represented improved catalytic performance due to the synergetic effect between ZSM-5 and SAPO-34, which promoted the catalytic properties of the samples. Catalytic reactivity of the composite catalysts was strongly dependent on the synthesis method and employed zeolite/zeotype ratio. Best result was acquired for Pt–Sn-based SAPO-34/ZSM-5 (Si/Al = 60) brand-new efficient composite with improved stability, boosted conversion and significant selectivity towards light olefins, propylene in particular.

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