A tungsten oxide catalysts supported on yttrium-or ytterbium-doped crystalline zirconium oxide (WO x /Y(Yb)-ZrO 2 ) with different dopant concentrations but the same tungsten loadings and calcination temperatures were prepared to investigate the mechanism responsible for the strong solid acidity of so-called tungstated zirconia. The surface acid−base properties of WO x / Y(Yb)-ZrO 2 and the support were characterized by catalyses of nbutane skeletal isomerization, alkylation of anisole with benzyl alcohol, and 2-butanol decomposition. The structural characterization and quantitative analysis were conducted by XRD, XAFS, and UV−Vis techniques. Crystalline zirconium oxides were effective as the starting material for tungsten−zirconium-based strong solid acid catalysts instead of amorphous Zr(OH) x if the crystalline form was tetragonal. Tetragonal-phase Y(Yb)-ZrO 2 substitutional solid solutions with dopant concentrations of 3−5 mol % was a suitable support for stabilization of active small WO 3 clusters. Tungsten species aggregated to form inactive large WO 3 particles on the monoclinic ZrO 2 polymorph with Y-dopant amount less than 2 mol % even though the surface density of tungsten species and calcination temperature were the same as those for the active catalysts. Inactive yttrium−tungsten binary oxides formed when the yttrium doping level exceeded 10 mol %. Intrinsic role of crystalline phase of tetragonal zirconia on generating the strong solid acidity is confirmed to stabilize WO 3 small clusters without aggregation.
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