Hydrodesulfurization of 4,6-DMDBT on multi-metallic bulk catalyst NiAlZnMoW: Effect of Zn

Multi-metallic bulk HDS catalysts NixZnyAlzMoW with different Zn/Al molar ratio were prepared using a NiZnAl-layered hydroxide precursor by co-precipitation method. XRD, HRTEM, and SEM results show that the catalysts possess layered structure, and the layered precursor NixZnyAlz-LDH is a mixture of ZnAl-LDH and NiAl-LDH. Ni(Zn)-promoted Mo(W) active species Ni(Zn)-Mo(W)-S are detected by Raman spectroscopy and HRTEM. Hydrodesulfurization (HDS) result of 4,6-dimethyldibenzothiophene (4,6-DMDBT) shows that catalysts NixZnyAlzMoW exhibit excellent HDS performance and the sulfur content in the model diesel could be reduced from 517 ppm to less than 10 ppm (under mild reaction conditions of 3.0 MPa of H-2 pressure, 300 degrees C, LHSV of 9 h(-1), and H-2/oil ratio of 800 Ncm(3)/cm(3)). Catalysts NixZnyAlzMoW show higher HDS activity than the commercial catalyst CoNiMoW/Al2O3 due to the high active metal content, the layered structure, and the positive promoter effect of Zn. Besides, Zn-doping also reduces the apparent activation energy of catalysts and results in larger pore volume and larger pore size for catalysts. Part of Zn (Ni) acts as a promoter but other part as a support. The promoter effect of Zn is partially responsible for the high HDS activity. It is found that the second promoter Zn decreases the interaction between alumina and active components Ni, Mo, W to form more Ni(Zn)-Mo(W)-S active species. (C) 2015 Elsevier B.V. All rights reserved.