INFLUENCES OF OXYGEN-CONTAINING SUBSTANCES ON DEACTIVATION OF SULFIDED MOLYBDATE CATALYSTS

The influences of oxygen-containing compounds on the changes in chemical states of sulfided metals in molybdate catalysts during the hydrotreatment of hydrocarbon feedstocks were investigated. The effect of oxygen-containing model compounds on the deactivation in the hydrodenitrogenation (HDN) activity of Ni-Mo catalyst in hydrotreating a subbituminous coal-derived kerosine oil was in the order of O2 > H2O2 > benzofuran > phenol > H2O. The XPS analyses of the heavily deactivated Ni-Mo catalysts in the presence of oxygen-containing model compounds showed that the amounts of Mo4+ decreased significantly, and almost all of nickel sulfide and sulfidic sulfur were converted into Ni2+ and sulfate sulfur, respectively. The pre-oxidation of the sulfided Ni-Mo catalyst via air, i.e. the formation of metal sulfides into oxides/sulfates, resulted in a decrease in HDN activity. The higher the degree of oxidation was, the lower the HDN activity was. It was suggested that some amounts of metal sulfides were converted into the lower reactive oxides/sulfates via oxygen in the oxygen-containing compounds even under hydrotreating conditions.