Several SAPO-11-Al2O3 supports with different amounts of SAPO-11 were used to prepare a series of CoMo/ SAPO-11-Al2O3 catalysts by the impregnation method with or without addition of citric acid. Hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene, hydrodenitrogenation (HDN) of acridine, and hydrodearomatization (HDA) of o-xylene, 1-methylnaphthalene and phenanthrene were carried out to evaluate the catalytic activity of the catalysts. The catalysts were characterized by BET, XRF, NH3-TPD, XPS and TEM. The acidity of the supports strongly affected the active slabs structure and activity of the catalysts. 20 wt% SAPO-11 added catalyst showed lower HDA, HDS and HDN activities compared to CoMo/Al2O3 catalyst. The length and stacking number of CoMoS active slabs on the former increased because of decreased dispersion of Mo species due to the reduction in number of strong acid sites on the support surface in the presence of SAPO-11. Addition of citric acid during active metal impregnation decreased HDA activity but increased HDS and HDN activities due to improvement of Mo species dispersion, resulting in formation of shorter length and higher stacking of CoMoS active slabs.
The catalytic precursors of alumina-supported molybdenum dithiocarbamate (Mo-DTC) and molybdenum dithiophosphate (Mo-DTP) were assessed as catalysts for hydrodesulfurizastion (HDS). The effect of the activation method on catalytic activity was evaluated for the HDS of dibenzothiophene (DBT). Catalysts derived from alumina-supported Mo-DTC or Mo-DTP after activation with H2S or H2 showed HDS activity comparable to that of conventional Mo catalyst prepared with ammonium heptamolybdate. Various activation procedures for the Mo complex precursors were investigated. Mo-DTC and Mo-DTP precursors activated with N2 and H2O showed much higher catalytic activity. Moreover, the selectivity for biphenyl of the Mo-DTC and Mo-DTP catalysts, which indicates the capacity of direct desulfurization, was higher than that of the sulfided conventional Mo catalyst.
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