In summary, two series of ZSM-5/SAPO-34 and SAPO-34/ZSM-5
hybrid composites with binary hierarchical structures were
successfully synthesized with hydrothermal methods. A facile
new technique has been proposed for the synthesis of zeolitic
SAPO-34/ZSM-5 bi-phase composite utilized with TPA-exchanged
SAPO-34 crystals. It seems that pre-treatment of SAPO-34 crystals
in organic amine solution containing TPA+ species was a determining
step to preserve SAPO-34 crystals from phase transformation
and dissolution when they were exposed to harsh basic condition
of ZSM-5 pre-crystallized gel mixture. In this case, ZSM-5 layer
was formed without any problem rising from cores dissolution
and considerable detachment phenomenon. Moreover, role of
composites as carrier were evaluated in direct dehydrogenation of
propane reaction and compared with those of physical mixturederived
composite and individual ZSM-5. Results showed that
binary structure of the composites did not only combine reactivity
and dominant sieving property of ZSM-5 and SAPO-34, but also had
influential impacts on the product features to adjust the reaction
towards higher activity and propylene selectivity. Physical mixture
consisted of two separate phases while they were intimately
bonded in the composites by the interfacial effects. Thus their
synergism in acidity, topology, and pore structure were enhanced
which could not be achieved simply by mixing the same single zeolites.
The yield of propylene and the catalytic stability of the Pt–Snbased
composite catalysts were closely relative to the composition
and applied synthesis strategy. PtSn-SAPO-34/ZSM-5 (Si/Al = 60)
novel catalyst represented a high potential as a promising PDH
catalyst to meet a change of market demand for propylene.
In summary, two series of ZSM-5/SAPO-34 and SAPO-34/ZSM-5hybrid composites with binary hierarchical structures weresuccessfully synthesized with hydrothermal methods. A facilenew technique has been proposed for the synthesis of zeoliticSAPO-34/ZSM-5 bi-phase composite utilized with TPA-exchangedSAPO-34 crystals. It seems that pre-treatment of SAPO-34 crystalsin organic amine solution containing TPA+ species was a determiningstep to preserve SAPO-34 crystals from phase transformationand dissolution when they were exposed to harsh basic conditionof ZSM-5 pre-crystallized gel mixture. In this case, ZSM-5 layerwas formed without any problem rising from cores dissolutionand considerable detachment phenomenon. Moreover, role ofcomposites as carrier were evaluated in direct dehydrogenation ofpropane reaction and compared with those of physical mixturederivedcomposite and individual ZSM-5. Results showed thatbinary structure of the composites did not only combine reactivityand dominant sieving property of ZSM-5 and SAPO-34, but also hadinfluential impacts on the product features to adjust the reactiontowards higher activity and propylene selectivity. Physical mixtureconsisted of two separate phases while they were intimatelybonded in the composites by the interfacial effects. Thus theirsynergism in acidity, topology, and pore structure were enhancedwhich could not be achieved simply by mixing the same single zeolites.The yield of propylene and the catalytic stability of the Pt–Snbasedcomposite catalysts were closely relative to the compositionand applied synthesis strategy. PtSn-SAPO-34/ZSM-5 (Si/Al = 60)novel catalyst represented a high potential as a promising PDHcatalyst to meet a change of market demand for propylene.
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