Intrinsic potential of alumina-supported CoMo catalysts in HDS: Comparison between γc, γT, and δ-alumina

MoS2 catalysts were firstly prepared over three different alumina supports γc-Al2O3, γT-Al2O3, and δ-Al2O3 with the same Mo loading per nm2. Then, using various deposition methods and different Co-precursors as Co(NO3)2, Co(acac)2 and Co(CO)3NO, Co-promoted MoS2 catalysts were obtained. The different catalytic systems were tested in hydrodesulfurization (HDS) reactions of thiophene and 4.6-dimethyldibenzothiophene (4,6-DMDBT) under atmospheric and high pressure (4 MPa), respectively. For the non-promoted catalysts, we observed for δ-alumina supported system a higher intrinsic catalytic activity than for γc-Al2O3 and γT-Al2O3. For the Co-promoted systems, the use of cobalt organometallic complex allowed obtaining catalysts which exhibit higher intrinsic activity than the catalysts prepared by impregnation of Co inorganic salts on supported Mo sulfide. Furthermore, the intrinsic catalytic activities of promoted systems obtained with δ-alumina support were always higher than for the classical γ-alumina. This support effect can be partially explained and supported by physicochemical characterization results of XPS and IR of adsorbed CO at low temperature (77 K).