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

摘要

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 HfS(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 hydro is omerization perforamce of n~C_(16)H_(34)that Pd/Hβ(40)catalysts showed the highest conversion of of 96.9% at 230°C.The selectivity of iso-C_(16)Hβ_(40)reached the highest value at the n-C_(16)H_(34)conversion of 45-50%.Pd/Hβ(40)catalysts exhibited the highest iso-C_(16)H_(34)selectivity of 84.4%,much more multi-branched iso-C_(16)H_(34)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.