Effects of Ga- and P-modified USY-based NiMoS catalysts on ultra-deep hydrodesulfurization for FCC diesels

USY zeolites have been modified by incorporation of gallium, phosphorus and a combination of gallium and phosphorus by wetness impregnation method using gallium nitrate and ammounium phosphate diabasic, and the corresponding NiMo supported hydrodesulfurization (HDS) catalysts have been prepared for HDS of an inferior FCC diesel. The individual physical-chemical properties of the modified USY zeolites and the series NiMo supported catalysts were characterized using XRD, N-2-adsorption-desorption(BET), NH3-TPD, Py-FTIR, H-2-TPR, HRTEM and XPS methods, and their catalytic performances for an inferior FCC diesel HDS were assessed. The results show that both gallium and phosphorus modification can modulate the acid property of USY zeolite and weaken the interaction between the active metal and the supports, thus enhancing the degree of sulfidation and the dispersion of Mo species that are beneficial for the HDS of highly refractory organosulfur compounds. The highest HDS and HDN efficiencies of 99.7% and 99.6%, respectively, were observed over the catalyst containing the PGaUSY zeolite. More importantly, gallium modification of the USY zeolite promotes the hydrodesulfurization of all organosulfur compounds, and especially 4,6-DMDBT, in the FCC diesel and phosphorus modification of the USY zeolite promotes the hydrodesulfurization of most organosulfur compounds except for 4,6-DMDBT in the FCC diesel.