RELATIONSHIP BETWEEN HDS ACTIVITY AND MO SITE FINE-STRUCTURE OF VARIOUSLY PRETREATED CO-MO AL2O3 AND MO/AL2O3/

In order to investigate the relationship between the activating effect of presulfiding and Mo site fine structure in Co-Mo/Al2O3 catalysis, variously pretreated Co-Mo/Al2O3 and Mo/Al2O3 were supplied for hydrod esulfurization (HDS) activity test and Mo K-edge EXAFS (Extended X-ray absorption fine structure) measurement. The HDS activities of Co-Mo/A l2O3 and Mo/Al2O3 pretreated by some combinations of sulfidation (by 5 % H2S/H-2) and reduction (by H-2) were examined by HDS reaction of ben zothiophene at 270-300 degrees C and 5 MPa in a flow system. The ethyl benzene yield (HDS activity) on Co-Mo/Al2O3 was strongly dependent on the pretreatments as follows: sulfided-reduced > sulfided > reduced-su lfided > reduced CoMo/Al2O3. On the other hand, the ethylbenzene yield on Mo/Al2O3 was very low and hardly dependent on the kind of combinat ion of pretreatments. Mo K-edge EXAFS revealed that the fine structure s of Mo site of Co-Mo/Al2O3 and Mo/Al2O3 changed strongly depending on the pretreatment. The fine structure changes of the Mo site of Co-Mo/ Al2O3 induced by each pretreatment was almost the same as that of Mo/A l2O3. In both catalysts, MoS2-like structures were formed when the cat alysts were initially sulfided, whereas no discrete structure was form ed even after post-sulfidation when the catalysts were initially reduc ed. The presence of Co strongly affects the sensitivity of the catalys t activity to the pretreatment, but does not affect the fine structure of Mo site.