XPS Study of the Deactivation and Sulfiding of Nitrided Molybdena−Alumina Catalyst during the Hydrodesulfurization of Dibenzothiophene

Abstract

The deactivation and sulfidation processes of nitrided 12.5% Mo/Al2O3 catalysts at the initial stage were studied on the basis of the behavior of sulfur and nitrogen using XPS spectroscopy. The hydrodesulfurization (HDS) of dibenzothiophene was carried out in a fixed-bed microreactor at 573 K and 10.1 MPa of total pressure. The Mo/Al2O3 catalyst was nitrided by a temperature-programmed reaction with pure ammonia at 4 L h-1 at various temperatures. From XPS measurement, the sulfur atoms removed from dibenzothiophene were not exchanged with nitrogen atoms in the nitride catalyst during the first hour but molybdenum was sulfided by 71% of the total sulfur accumulated during the 14-h run. The sulfur deposition followed the Elovich equation. The decreased HDS activity and increased hydrogenation selectivity of the nitride Mo/Al2O3 catalyst were caused by the accumulation of sulfur on the nitride catalyst. At steady state achieved after 14 h, however, the nitrogen achieved after the Mo/Al2O3 catalysts were nitr...