Role of nickel and vanadium over USY and RE-USY coke formation

摘要

The present paper approaches the role of nickel and vanadium oxidation states in the coke formation from cyclohexane model cracking reaction over USY and RE-USY zeolites. The coke yield increased for both zeolites, USY and RE-USY, due to the presence of nickel and/or vanadium contaminant metals. USY loaded with Ni and V presented about the same reducibility of USY loaded distinctly with Ni or V, when steam deactivation is not applied previously. However, coke formation decreased by a factor of 2 for RE-USY or USY loaded with Ni and V when compared to Ni or V loaded distinctly. This factor was affected neither by oxidation/reduction treatments, nor by rare-earths presence. After oxidation treatment vanadium is the principal responsible for coke formation. For V-USY catalyst the coke yield increase by a factor of 2.7 after reduction, while for Ni-USY catalyst coke yield increase by a factor of 13. For the RE-USY catalyst, the coke formation is strongly inhibited on vanadium sites and promoted on nickel sites. These results suggest that the coke formation on the zeolite acidic sites is influenced by multicomponent interaction between Ni-V, Ni-RE and V-RE elements. (c) 2006 Elsevier B.V. All rights reserved.