Study of the active phase of NiW hydrocracking sulfided catalysts obtained from an innovative heteropolyanion based preparation

Hydrocracking (HCK) Nickel-Tungsten catalysts, supported on amorphous silica alumina, have been prepared by incipient wetness impregnation with new starting materials based on Keggin or on the derived lacunary Keggin heteropolyanion (HPA) structure and were compared to conventional catalysts. After calcination a polytungstate phase evidenced by Raman spectroscopy was generally observed indicating the destruction of the initial HPA. The sulfided solids were characterized by HRTEM to determine the dispersion of the WS2 active phase. A careful XPS study indicated a better promoting effect for HPA based catalysts compared to their conventional counterparts. Toluene hydrogenation catalytic performances were related to the sulfided solids characterizations. Ni4SiW11O39 nickel salt appeared to be the most efficient precursor that led to high dispersion and higher promoting effect due to the proximity of Ni and W in the heteropolyanion salt with an optimum Ni/W ratio.