Carbon-supported tungsten and nickel catalysts for hydrodesulfurization and hydrogenation reactions

Sulfided W/C catalysts prepared from different tungsten precursors (silicotungstic (HSiW), phosphotungstic (HPW), and tungstic (HW) acids) and their Ni-promoted counterparts were used in the simultaneous hydrodesulfurization (HDS) and hydrogenation (HYD) of thiophene and l-pentene, respectively, at a pressure of 1 MPa, at temperatures ranging from 498 to 548 K and a weight hourly space velocity of 2.5 h(-1). The activity results showed that W/C catalysts were active in hydrogenation but not in hydrodesulfurization at 498 K. The most active monometallic catalyst obtained from HSiW precursor was five times less active in HDS than in HYD at 548 K. However, when Ni was incorporated to the base W/C system, a large enhancement in catalyst performance was observed irrespective of the W precursor. Surface analysis of decomposed impregnates revealed that nickel incorporation into W/C catalysts led to a substantial improvement in surface exposure of the tungsten species. For the most active catalyst (from HSiW precursor and promoted with Ni) Ni-SiW the W exposed on the carbon surface did not change after on-stream operation. On the basis of catalyst structure-activity relationships. it is inferred that this large activity is a direct consequence of the optimum ratio of Ni to W, a large exposure of the active phase of tungsten on the carbon surface, and promotion of WS2 phase by nickel. (C) 2001 Elsevier Science B.V. All rights reserved.