Effect of metal content on the activity and product selectivity of n-decane hydroisomerization over Ni-Pd/HY zeolite

Abstract

Metal-loaded zeolite catalysts were synthesized and examined in the hydroisomerization of n-decane. Specifically, zeolite Y was impregnated with 0.1 wt% Pd and varying amounts of Ni (0.1–0.5 wt%). The crystallinity of the metal-loaded catalysts was characterized by X-ray diffraction, and the average metal particle size was determined by transmission electron microscopy. The states of Pd and Ni were identified by X-ray photoelectron spectroscopy. Ammonia temperature-programmed desorption analysis revealed the occurrence of ion-exchange of some of the catalyst acid sites with Ni2+. The reducibility of the HY zeolite-supported Pd, Ni, and Pd-Ni catalysts was studied by temperature-programmed reduction. The hydroisomerization of n-decane over the prepared catalyst was conducted at 200–450 °C under 1 atm. Ni addition of up to 0.3 wt% over 0.1 wt% Pd/HY enhanced the n-decane conversion and isomerization product selectivity. The improved selectivity of the mono- and dibranched isomers suggested the occurrence of a protonated cyclopropane intermediate mechanism. However, further Ni addition above 0.3 wt% considerably reduced the activity and isomerization selectivity. The bimetallic catalysts were more selective toward the formation of dibranched isomers, i.e., those containing a higher octane number.