Nickel-Containing Polyoxotungstates Based on [PW9O34]9? and [PW10O39]13? Keggin Lacunary Anions Supported on Al2O3 for Dibenzothiophene Hydrodesulfurization Application

In the present study, different Al2O3-supported Ni-containing polyoxotungstates (POW) based on Keggin lacunary structures were synthesized in order to establish a correlation between the local conformation of the different Ni/POWs and the final catalytic performance of the corresponding supported NiW hydrodesulfurization (HDS) catalysts. POWs containing various amounts of nickel (3, 4, or 9 Ni atoms per POW) were therefore prepared and supported on an Al2O3 support obtained by a sol?gel method using impregnation techniques in aqueous solutions at two different pH values (7 and 9). The as-obtained supported Ni-containing POWs were characterized after the drying (120 C, 4 h) and calcination steps (400 C, 4 h, air). The different solids were then sulfided using 10 mol % H2S in H2 at 400 C for 4 h and evaluated in the hydrodesulfurization of dibenzothiophene (DBT) at T = 300 C and P = 30 bar H2. Both the Ni localization inside the polyoxotungstate and the pH of the impregnation solution influence the degree of sulfidation and the intrinsic activity of the promoted phase, with Ni3 POW/Al2O3 the most HDS active if impregnation occurs at pH 7. A direct correlation between the structure of the nickel-containing polyoxotungstate and the final HDS activity can be observed, opening the way for a rationalization of the preparation of this type of precursor.