Hydroisomerization of n-hexadecane over Hβ molecular sieve loading palladium bifunctional catalyst: effect of SiO2/Al2O3 molar ratios

Abstract

Hβ molecular sieves with different SiO2/Al2O3 ratios (Hβ(x))and Hβ(x) loading Pd(0.5 wt%) bifunctional catalysts(Pd/Hβ(x)) were prepared by hydrothermal synthesis and incipient wetness impregnation, respectively. The structure, morphology, pore and acid properties of Hβ(x) and Pd dispersion of Pd/Hβ (x) were characterized using XRD, SEM, N2 physical adsorption, NH3-TPD and H2 chemical absorption. Hβ (x) samples were highly crystalline microporous materials. With the increase of SiO2/Al2O3 ratios, BET surface area, micro-pore surface area and volume of Hβ (x) gradually decreased, and the external surface area and mesoporous volume gradually increased, and the number and acid strength of weak acid sites for Hβ(x) and Pd dispersion for Pd/Hβ(x) decreased. It was known from hydroisomerization perforamce of n-C16H34 that Pd/Hβ(40) catalysts showed the highest conversion of of 96.9% at 230°C. The select ivity of iso-C16H34 reached the highest value at the n-C16H34 conversion of 45~50%. Pd/Hβ(40) cata lysts exhib ited the highest iso-C16H34 selectivity of 84.4%, much more multi-branched iso-C16H34 and C4+C5 cracking components. The decrease of SiO2/Al2O3 molar ratios can increase the number of acid sites and dispersion of Pd/Hβ(x) bifunctional catalysts, thus not only aggravating the secondary heterogeneous reaction, but also accelerating the serious secondary cracking reaction.