Effect of support type on the magnitude of synergism and promotion in CoMo sulphide hydrodesulphurisation catalyst

The Co, Mo and CoMo catalysts in different Co/Mo ratios supported on SiO2, ZrO2, TiO2, Al2O3, active carbon and MgO were prepared. The catalysts were tested in the hydrodesulphurisation of benzothiophene. The order of activity of monometallic Mo catalysts was MoO3/TiO2 > MoO3/C > MoO3/ZrO2 > MoO3/SiO2 > MoO3/Al2O3 > MoO3/MgO. The order of promotion of MoO3/support by Co addition was CoMo/MgO > CoMo/C > CoMo/Al2O3 > CoMo/TiO2 > CoMo/ZrO2 > CoMo/SiO2. The synergism in activity was accompanied with a decrease of hydrogenation/hydrogenolysis selectivity. Hydrogenolysis was promoted more than hydrogenation and thus less dihydrobenzothiophene was formed on CoMo than on Co and Mo catalysts. The TPR patterns were measured, and the degree of reduction correlated with the activity of monometallic catalysts. The TPR patterns of CoMo catalysts were similar to the patterns of Mo catalysts, and no correlation with magnitude of promotion was found.

The magnitude of promotion by Co in the hydrodesulphurisation activity decreased in the order CoMo/MgO > CoMo/C > CoMo/Al2O3 > CoMo/ZrO2 > CoMo/TiO2 > CoMo/SiO2. This order did not correlate with the reduction patterns of the catalysts in TPR. The promotion in the hydrogenolysis activity is higher than in hydrogenation and is thus accompanied by characteristic decrease of the hydrogenation/hydrogenolysis selectivity. Figure optionsDownload as PowerPoint slide