Hydrodesulfurization of 4,6-dimethyldibenzothiophene over high surface area metal phosphides

Unsupported monometallic phosphides (MoP and Ni2P), as well as a series of bimetallic nickel molybdenum phosphides (NixMoP), were synthesized with high surface area by adding citric acid (CA) to precursor metal salt solutions prior to drying, calcination and temperature-programmed reduction (TPR). The resulting MoP and Ni2P catalysts had surface areas of 139 and 216 m2/g, respectively. The surface areas of the NixMoP catalysts decreased with increased Ni content and ranged from 121 to 16 m2/g. In all cases, the catalyst surface area was greater than that obtained when a conventional preparation procedure was followed that did not use CA. The activity of the catalysts for the hydrodesulfurization (HDS) of a feed containing 3000 ppm 4,6-dimethyldibenzothiophene (4,6-DMDBT) in toluene was measured at 583 K and 3.0 MPa. The resulting catalysts were highly active and among the studied phosphides, Ni2P exhibited the highest HDS activity with a conversion of 87.7% at a WHSV of 26 h−1 and a H2/liquid feed ratio of 625 (v/v). The HDS TOF decreased in the order Ni2P > NixMoP > MoP and for the NixMoP catalyst, the observed TOF increased with Ni content.