The effect of phosphorus addition was studied on the hydrodesulfurization (HDS) of thiophene over CO-MOS2/P/A]203, which was prepared by a chemical vapor deposition (CVD) technique using CO(CO)(3)NO as a precursor of Co. The catalysts were characterized by means of NO adsorption, FIFIR and Raman spectroscopy. The HDS activity OfCO-MOS2/Al2O3 was slightly increased by the addition of 0.2 wt% P, followed by a slight decrease with a further addition of phosphorus. In spite of the activity increase, the amount of NO adsorption on MOS2/P/Al2O3 steadily decreased with increasing phosphorus loading, suggesting that the dispersion Of MOS2 particles is decreased by the addition of phosphorus. The TOF of the HDS over CVD-CO/MOS2/P/AI(2)IO(3) catalysts, defined by the activity per Co atom forming the Co-Mo-S phase, increased as much as 1.3 times by the addition of phosphorus, indicating that the active phase of the catalysts shifts from less active Co-Mo-S Type I to more active Co-Mo-S (pseudo) Type II. FrIR results showed that phosphoric acid reacts with the surface OH groups of Al2O3, resulting in weakened interactions between molybdenum oxides and Al2O3 surface and thus in less abundant Mo-O-AI bonds in MOS2-Al2O3 interactions. (c) 2007 Elsevier B.V. All rights reserved.