A study of the NiSb interaction in a rare-earth Y-zeolite

Abstract

Two series of catalysts were prepared by impregnating nickel and nickel-antimony over a rare-earth-exchanged Y-zeolite. The nickel loadings for the monometallic catalysts were within 0.00–1.00% in weight; for the bimetallic systems the Ni loadings were in the 0.10–0.99% range while the Sb loadings were within 0.042–0.84% in weight. The effect of Sb addition on the structure and chemisorptive properties of Ni was examined using reduction studies, CO and H 2 chemisorption, IR spectroscopy, and cracking of isooctane. Complete reduction to metallic nickel and metallic antimony was found for Ni- and Sb-rich catalysts. The addition of Sb dramatically decreased the chemisorption of H 2 and CO. Infrared results suggest the formation of a single species, probably a Ni(CO) x species, for high-loading (>0.3%) nickel catalysts (even after desorption of the gaseous CO at room temperature). For the NiSb catalysts the bands were much weaker (in the presence of gaseous CO) and practically disappeared after the evacuation procedure. The cracking of isooctane showed a considerable increase in the formation of coke and hydrogen with increasing Ni loadings. The presence of antimony restored the amounts of coke and hydrogen to the original values present in the unsupported zeolite. Site blockage of Ni by Sb and weakening of the NiC bond by the addition of Sb are suggested to explain the results.