| Regulatory issues require new catalysts for the deep hydrodesulfurization (HDS) of refractory polyaromatic sulfur compounds such as 4,6-dimethyldibenzothiophene (4,6-DMDBT) present in diesel and jet fuel. Molybdenum sulfide (MoS2 ) supported on mesoporous molecular sieve MCM-41 and promoted by cobalt was hypothesized to have superior activity for deep HDS because of MCM-41's (1) high surface area and uniform mesopores and (2) superior acidity as compared to conventional supports such as γ-alumina (γ-Al 2O3). This study examines the role of MCM-41 as a support for new cobalt (Co)-molybdenum (Mo) HDS catalysts.; At CoO-MoO3 loadings typical of commercially available HDS catalysts, MCM-41-supported catalysts were only slightly better. At higher loadings—27.0% (by weight) MoO3 and 5.8% CoO—MCM-41-supported catalysts were twice more active than the commercial catalyst. This difference in activities is related to the degree of MoS2 stacking.; Remarkable increase in the conversion of 4,6-DMDBT was observed over MCM-41-supported catalysts with decreasing SiO2/Al2O 3 ratio. More significantly, the SiO2/Al2O 3 ratio of MCM-41 has a profound effect on product distribution and catalyst selectivity. Irrespective of CoO-MoO3 loading, catalysts using MCM-41 with a SiO2/Al2O3 ratio of 50 convert more of 4,6-DMDBT through the highly desirable hydrogenolysis pathway. The acidity of these catalysts was measured and correlated to their selectivities for hydrogenolysis and hydrocracking.; Co-Mo/MCM-41 continued to demonstrate activities twice that of the commercial catalyst for the HDS of 4,6-DMDBT in petroleum-derived feedstocks such as light cycle oil. However, for a blend of coal- and petroleum-derived feedstocks, nitrogen from the coal-derived liquid inhibited both catalysts for the HDS of 4,6-DMDBT. Basic nitrogen, e.g., quinoline, significantly retards the HDS of 4,6-DMDBT over both catalysts. Non-basic carbazole, on the other hand, inhibited the MCM-41-supported catalyst only.; This work has demonstrated the potential of mesoporous aluminosilicate molecular sieve MCM-41 as a promising support for hydroprocessing catalysts where the method of preparation, the SiO2/Al2O 3 ratio, and the CoO-MoO3 loading levels all play important roles. Furthermore, the Co-Mo/MCM-41 catalysts displayed different selectivity patterns. These results coupled with the intrinsically desirable structural features of MCM-41 warrant further study of MCM-41-supported hydroprocessing catalysts. |
