Niobium sulfide as a dopant for hydrotreating NiMo catalysts

Niobium sulfide has been recently found to be an interesting new active phase for hydrodesulfurization. In this work, niobium was used as a dopant for a conventional hydrotreating catalyst. A NiMo hydrotreating catalyst in the oxide form was doped with various contents of Nb precursor salt (0<Nb wt, %<7). After drying, the activation of the catalyst was performed with CS2 sulfiding agent in a high pressure vessel. The use of this new dopant increased the catalytic activity in both HDS and HYD model reactions. Highest activities were obtained with an optimum Nb content of 5 wt,%, The selectivity of the products was also modified since more isomerized compounds where produced. Various techniques were used to determine structural and morphological characteristics of the materials. TEM pictures only showed the presence of lamellar particles similar to MoS2, EDX analysis demonstrated the homogeneous distribution of the transition metal elements (Ni, Mo, Nb) even with small electron probes at high magnification. EXAFS was used to determine the local environment of Nb atoms and showed that Nh was present in the form of "NbS2" entities similar to the bulk phase. (C)2000 Elsevier Science B.V. All rights reserved.