Catalytic activities of Co(Ni)Mo/TiO2-Al2O3 catalysts in gasoil and thiophene HDS and pyridine HDN: effect of the TiO2-Al2O3 composition

The effect of the TiO2-Al2O3 mixed oxide support composition on the hydrode sulfurization (HDS) of gasoil and the simultaneous I-IDS and hydrodenitroge nation (HDN) of gasoil+pyridine was studied over two series of CoMo and NiM o catalysts. The intrinsic activities for gasoil HDS and pyridine HDN were significantly increased by increasing the amount of TiO2 into the support, and particularly over rich- and pure-TiO2-based catalysts. It is suggested that the increase in activity be due to an improvement in reducing and sulf iding of molybdena over TiO2. The inhibiting effect of pyridine on gasoil H DS was found to be similar for all the catalysts, i.e., was independent of the support composition. The ranking of the catalysts for the gasoil I-IDS test differed from that obtained for the thiophene test at different hydrog en pressures. In the case of gasoil HDS, the activity increases with TiO2 c ontent and large differences are observed between the catalysts supported o n pure Al2O3 and pure TiO2. In contrast, in the case of the thiophene test, the pure Al2O3-based catalyst appeared relatively more active than the cat alysts supported on mixed oxides. Also, in the thiophene test the differenc e in intrinsic activity between the pure Al2O3-based catalyst appeared rela tively more active than the catalysts supported on mixed oxides. Also in th e thiophene test, the difference in intrinsic activity between the pure Al2 O3- and pure TiO2-based catalysts is relatively small and dependent on the H-2 pressure used. Such differences in activity trend among the gasoil and the thiophene tests are due to a different sensitivity of the catalysts (by different support or promoter) to the experimental conditions used. The re sults of the effect of the H-2 partial pressure on the thiophene HDS, and o n the effect of H2S concentration on gasoil HDS demonstrate the importance of these parameters, in addition to the nature of the reactant, to perform an adequate catalyst ranking. (C) 1999 Elsevier Science B.V. All rights res erved.