Shape Selectivity in Hydroisomerization of n-Hexadecane over Pd Supported on Zeolites: ZSM-22, ZSM-12 and Beta

Abstract

The development of bifunctional catalysts with high branched isomers selectivity in hydroisomerization of n-alkanes constantly remains crucial for the manufacture of green biodiesel from vegetable oil. Herein, three bifunctional catalysts (Pd/zeolite) have been prepared by providing 0.5 wt % Pd over the ZSM-12, ZSM-22 and Beta zeolite, respectively. The physicochemical properties of above-prepared zeolites and catalysts were investigated by XRD, SEM, N2 physical adsorption, NH3-TPD, Py-IR measurements and H2 chemisorption methods. The catalytic property for the n-hexadecane hydroisomerization over three bifunctional catalysts was measured which indicate that higher distribution of mono-branched iso-hexadecane is received over Pd/ZSM-22 and Pd/ZSM-12 catalysts based on the zeolites with one dimensional pore channel due to the high shape selectivity. Compared with Pd/ZSM-12, the Pd/ZSM-22 catalyst displays the higher selectivity for iso-hexadecane because of more favorable metal-acid balance caused by the larger CPd/CH+ ratio. Furthermore, the Pd/Beta catalyst shows highest catalytic activity and maximum iso-hexadecane yield of 69.7% when the n-hexadecane conversion is 78.9%, which results from the maximal porosity, Bronsted acid sites density and mild acidity.