The specific activity of the Co-W-S phase, formed on WS2/ SiO2 (presulfided above 973 K) by a CVD technique using Co(CO)(3)NO, was 1.6 times as high as that of the Co-Mo-S phase formed on MoS2/SiO2 (above 873 K) for the hydro desulfurization of thiophene, demonstrating, for the first time, that in sharp contrast to general belief, CO-WS2 is a much more favorable combination for the generation of catalytic synergy than Co-MoS2, which has been widely used in industry.