Effect of iron and calcium over USY coke formation

Although several studies discuss the effect of metals on the FCC process, very few focus on those caused specifically by Fe and Ca. Within this work, different zeolite samples were prepared by impregnating nickel and vanadium on an ultra stable Y zeolite (USY), previously exchanged with iron and calcium. The samples were used in three model reactions: cyclohexane transformation at 300 degrees C, n-hexane cracking (500 degrees C) and ethane hydrogenolysis. The first reaction aimed at studying coke formation tendencies. The second reaction allowed an indirect measure of catalyst acidities and ethane hydrogenolysis (which was used to discuss nickel particle formation). Bifunctional catalysts presented a higher tendency to form coke compared to pure USY. This effect was much more pronounced in the presence of Ni and V. Bimetallic catalyst NiVUSY forms relatively low amounts of coke when compared to monometallic catalysts, and exhibits a higher olefin to paraffin ratio. The addition of Fe or Ca to the bimetallic catalyst largely reduces coke formation and increases the olefin to paraffin ratio. When compared to the NiVUSY catalyst, the reduction temperature decreases 20 and 50 degrees C for FeNiVUSY and CaNiVUSY catalyst, respectively. In addition ethane hydrogenolysis reveals nickel activity only for FeNiVUSY catalyst. These results support that Fe and Ca affect nickel and vanadium chemical environment and probably their distribution on the catalyst surface. (c) 2008 Elsevier B.V. All rights reserved.