gamma-Al2O3-supported CoMo catalysts doped with phosphate and prepared in the presence of triethylene glycol (TEG), ethylene glycol (EG), and triethylene dimethyl ether (TEG-DME) were tested in the hydrodesulfurization (HDS) of thiophene. The catalyst containing TEG showed a higher catalytic activity than the catalyst prepared without TEG. Laser Raman spectroscopy and EXAFS demonstrated that the impregnation solution containing the metal salts and phosphoric acid contained HP2Mo5O235- diphosphopentamolybdate and that this anion was not affected by the presence of TEG. P-31 NMR measurements of the impregnation solution showed a paramagnetic effect of cobalt, which proved that cobalt is complexed by the diphosphopentamolybdate, both in the presence and absence of TEG. DRIFT experiments with a gamma-Al2O3 support treated with TEG proved that glycol interacts with the basic OHs groups and coordinatively unsaturated Al3+ sites. The diphosphopentamolybdate complexes are decomposed by these sites on the gamma-Al2O3 support, but EXAFS of the dried catalyst precursor showed that in the presence of glycol this decomposition was partially prevented. This favored the precipitation in the alumina pores of clusters in which Co and Mo are in close proximity. Because of their high Co/Mo atomic ratio, these complexes lead to an efficient decoration of the MoS2 slabs by the promoter atoms during the sulfiding treatment, thus increasing the catalytic performance of the supported CoMo catalyst. (C) 2004 Elsevier Inc. All rights reserved.