HYDRODEMETALIZATION KINETICS OF NICKEL TETRAPHENYLPORPHYRIN OVER MO AL2O3 CATALYSTS/

The hydrodemetalization (HDM) kinetics of nickel 5,10,15,20-tetrapheny lporphyrin (Ni-TPP) has been studied at 613 K in the presence of sulfi ded Mo/Al2O3 catalysts. The reversible sequential mechanism, in which the intermediate compounds nickel 5,10,15,20-tetraphenylchlorin (Ni-TP C) and nickel 5,10,15,20-tetraphenylisobacteriochlorin (Ni-TPiB) are f ormed, is in good agreement with earlier findings that the kinetic net work is governed by the type of porphyrin and independent of the type of catalyst applied or its chemical state. The current study focuses o n the influence of the H-2 and H2S concentrations on the various react ion-steps in the kinetic mechanism. H2S promotes the hydrogenolysis st ep in the HDM of Ni-TPP. Through evaluation of kinetic models in which porphyrins, H-2, and H2S adsorb on various types of sites it is shown that a two-site model, with small inhibition by H-2 and negligible in hibition by H2S, provides a satisfactory description of the HDM of Ni- TPP over Mo/Al2O3.