One-dimensional 10-member ring zeolites are characteristic of pore-mouth catalysis and commonly used in the hydroisomerization of liner alkanes. Here, we reported a new route to prepare a low silica ZSM-48 zeolite and its use in the deposition of Pt to prepare Pt/ZSM-48 catalyst for reverse hydroisomerization of iso-butane to butane. ZSM-48 (SiO2/Al2O3=120) was synthesized by a two-step hydrothermal crystallization method in which a low temperature (373 K) was applied to generate the crystallization nuclei for ZSM-48 and a high temperature (433 K) was chose for zeolite crystal growth. ~0.5 wt.% Pt metal was deposited by a wetness impregnation method. XRD patterns of ZSM-48 zeolite and its corresponding Pt/ZSM-48 samples show characteristic peak due to MRE zeolite structure without any information for the formation of Pt or PtOx particles. This suggests a high dispersion of Pt species in ZSM-48 zeolite.The relation between conversion of iso-butane and product selectivity over Pt/ZSM-48 zeolite sample was studied. Mainly, n-butane, propane and isopentane were observed at a low iso-butane conversion (＜10%), and C1-C2 species could be obtained at a higher conversion or a high reaction temperature. We proposed the reaction network for hydroisomerization of iso-butane at the open-mouth of ZSM-48 zeolite (Figure 1). Firstly, iso-butane was dehydrogenated to isobutene at the Pt metal site, and then the isobutene was protonated to form isobutyl cation at the acidic site and further oligomerized to C8 hydrocarbons. n-butene can be form by the β-cracking of C8 hydrocarbons at the acidic site.

Synthesis and consequence of Pt/ZSM-48 catalyst for pore-mouth catalysis

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