Effect of boron addition on the intrinsic activity of Al2O3-supported cobalt-tungsten and cobalt-molybdenum sulfide catalysts for the hydrodesulfurization of thiophene

The effect of boron addition was studied on the intrinsic activity of Al2O3-supported cobalt-molybdenum and cobalt-tungsten sulfide catalysts prepared by a CVD technique using [Co(CO)(3)NO] as a precursor of Co. The catalysts were characterized by means of NO adsorption and Raman spectroscopy. The intrinsic activity of the catalysts are discussed in terms of the turnover frequency (TOF) of the hydrodesulfurization of thiophene, calculated on the basis of the amount of the Co-Mo(W)-S phase. The intrinsic activity on the Co-Mo-S phase and the Co-W-S phase was increased by the addition of boron in a different way depending on the presulfidation temperature. The addition of a proper amount of boron weakened the interactions between molybdenum (tungsten) oxides and the Al2O3 surface, leading to an increase in the TOF on the Co-Mo-S phase and the Co-W-S phase by a factor of 1.6 and 1.3, respectively, when Mo(W)S-2/Al2O3 was presulfided at 673 K. As for the catalyst presulfided at 773 K, the addition of boron increased the TOF on both CVD-Co/MoS2/B/Al2O3 and CVD-Co/WS2/B/Al2O3 by a factor of 1.9. A reverse correlation was observed between the strength of the molybdenum (tungsten) oxides-Al2O3 interactions and the intrinsic activity on the Co-Mo(W)-S phase.