| Abstract
| - The influence of potassium on the formation of surface vanadia species on V/Ti oxide catalysts containingfrom 0.2 to 5 monolayers of vanadia (K/V atomic surface ratio ≤1) has been investigated by temperatureprogrammed reduction in hydrogen and by FT-Raman spectroscopy under dehydrated conditions. In thepure catalysts, monomeric and polymeric (metavanadate-like) species, “amorphous” and bulk crystallineV2O5 were detected depending on the surface vanadia loading. In the K-doped catalysts, vanadia speciesformed on the surface depend also on the K/V atomic ratio. Even at small K/V ratios, K inhibits theformation of the polymeric species in favor of the “K-doped” and/or “K-perturbed” monomeric species.These species possess lengthened VO bonds with respect to the monomeric species in the undoped V/Tioxides. At K/V = 1, the “K-doped” monomeric species and “amorphous” KVO3 are mainly present on thesurface. Reduction of vanadia forms in the K-doped catalysts takes place at higher temperatures than inthe catalysts where potassium was absent. The monomeric and polymeric species, which are the activesites in partial catalytic oxidation, have the lowest reduction temperature. Vanadia species formed on thecommercial titania, containing K, were also elucidated. The catalysts were characterized via X-rayphotoelectron spectroscopy, high-resolution transmission electron microscopy, and Brunauer−Emmett−Teller surface area measurements.
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