HYDRODEMETALLISATION OF NICKEL-5,10,15,20-TETRAPHENYLPORPHYRIN OVER SULFIDED MO AL2O3 - INITIAL CATALYST DEACTIVATION/

Hydrodemetallisation (HDM) of Ni-TPP was studied in a fixed-bed reacto r at temperatures ranging from 550-615 K in the presence of a sulphide d Mo/Al2O3 catalyst, The kinetic network of Ni-TPP HDM comprises hydro genation steps and a lumped hydrogenolysis step. It appears that these two types of reactions occur on sites with different characteristics. Initial catalyst deactivation takes place in two distinct stages. The first deactivation stage is the result of nickel deposition and its e nd is marked by a relatively constant molar ratio of deposited nickel to molybdenum. Hydrogenolysis is affected to a larger extent by nickel deposition than hydrogenation. In the second stage deactivation is mu ch slower. Deactivation follows first order kinetics in both stages. F inally, a quasi steady-state activity is reached. Despite a continuing deposition of nickel, the catalyst remains remarkably active. It is c oncluded that nickel is not deposited on active sites. A variety of ad sorbed species was found to exist on the working catalyst. Kinetic ana lysis of data sets obtained from experiments at steadystate conditions revealed that product inhibition of the hydrogenation reactions is ne gligible.