Lindqvist isopolyanions [NbxW6–xO19](2+x)– (x = 0–4 and 6) were prepared and their spectroscopic and thermal properties were determined by Raman and IR spectroscopy as well as TGA/DSC. The structure of the [NbW5O19]3– anion obtained as single crystal was determined. Ni‐promoted alumina‐supported hydrodesulfurization (HDS) catalysts were prepared from the best soluble NbW polyoxometalates. In the calcined catalysts, better dispersion of the metallic species is observed when using NbW isopolyanions instead of the conventional ammonium metatungstate. The presence of niobium was expected to introduce acidity leading to isomerization property in classical NiW HDS catalysts. In HDS reaction conditions (under hydrogen pressure and sulfided environment) the cyclohexane isomerization into methylcyclopentane activity of niobium‐based catalysts was found up to 5 times superior to that of conventional NiW catalyst, showing the beneficial effect of niobium for this reaction.

Alumina‐supported NiW catalysts doped with Nb were prepared with different W contents and different Ni/W ratios. Studies of the sulfide state by TEM and X‐ray photoelectron spectroscopy (XPS) demonstrated the influence of Nb on the sulfidation of W and Ni. The catalytic performance of the solids was evaluated in toluene hydrogenation and cyclohexane isomerization and was compared to that of Nb‐free catalysts. The presence of Nb resulted in a decrease of the hydrogenation activity at low W content and low Ni/W ratio, in agreement with XPS and TEM characterizations. However, increasing the W content and the Ni/W ratio increased the hydrogenation activity. Regardless of the W and Ni content, cyclohexane conversion was significantly improved by the presence of Nb. The most efficient catalyst of the series, with a W content of 15 wt % WO3 and a Ni/W ratio of 0.9, showed slightly higher activity for hydrogenation than that of a Nb‐free NiW catalyst. Also, the isomerization activity was greatly enhanced, demonstrating the potential of these Nb‐based catalyst formulations.