THE EFFECT OF NI LOADING AND THE SULFIDATION TEMPERATURE ON THE STRUCTURE AND CATALYTIC ACTIVITY OF NI-W HYDRODESULFURIZATION CATALYSTS

The effect of nickel concentration and sulfiding temperature on the ty pe and distribution of the surface species and on the dispersion in a series of alumina-supported Ni-W hydrodesulfurization (HDS) catalysts were investigated by temperature programmed reduction (TPR), diffuse r eflectance spectroscopy (DRS), dynamic O-2 and NO chemisorption (DOG, DNOC), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) , sulfur content analysis and thiophene HDS reaction. In the thiophene HDS reaction, the Ni-W/gamma-Al2O3 system showed a strong synergistic behavior. The maximum activity was achieved at about Ni/(Ni + W) = 0. 6. When sulfiding temperature increased from 673 K to 1073 K, the acti vity monotonously decreased with the S-shaped curve. TPR results revea led three different nickel species, a highly dispersed NiO surface spe cies, a mixed Ni-W oxide phase, and a subsurface NiAl2O4-like phase. T he nature and the amount of these species depended on nickel loading. DRS results provided complementary support for the presence of these s pecies. The results of XRD, sulfur content analysis, DOG, DNOC, and XP S indicated that the sulfidability and the crystallinity of WS2 increa sed with the increase in sulfidation temperature. The surface nickel s pecies diffused into the bulk at high sulfidation temperature.