Synthesis of lamellar PtZn@Silicalite-1 zeolite and its catalytic properties for propane dehydrogenation
The lamellar Silicalite-1 zeolite(PtZn@Silicalite-1)encapsulated PtZn nano-alloy was synthesized in one step by hydrothermal crystallization method with tetramethylguanidine(TMG)as morphology regulator.The catalysts were characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),and X-ray photoelectron spectroscopy(XPS),and their catalytic performance for propane dehydrogenation was investigated.The results show that the addition of TMG can effectively regulate the growth orientation of Silicalite-1 zeolite crystals,and the crystal size along the b-axis is inversely proportional to the ratio of TMG/SiO2.At 550℃ and in pure propane atmosphere,the lamellar PtZn@Silicalite-1 catalyst showed excellent propane dehydrogenation performance.After 20 h of continuous reaction,its deactivation constant was only 0.007 h-1,while that of the conventional PtZn@Silicalite-1 catalyst was 0.013 h-1.Combined with the characterization data,the lamellar zeolite catalyst has larger external specific surface area and shorter b-axis through channel,which improves the accessibility of the dehydrogenation active site and shortens the diffusion path of gas molecules in the pore,thus improving the activity and stability of the catalyst.
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