The effect of potassium addition on the state of the components in the oxide precursor of the (Ni)(Mo)/γ-Al 2O 3 water-gas shift catalysts: FT-IR, diffuse reflectance and Raman spectroscopic studies

Abstract

One-component samples containing K, Ni, and various concentrations of Mo were prepared by incipient wetness impregnation technique. Bi- and tri- component samples have been prepared from the calcined one- and bi-component samples following the same procedure. The samples were characterized by SSA, FT-IR, DRS and Raman measurements. The decrease of the ratio Ni 2+(Td)/Ni 2+(Oh) with the increase of Mo loading and the re-dispersion of Mo phase after the Ni addition on the one-component Mo containing samples proved the occurrence of interactions between these components in the bi-component NiMo-containing samples. Most probably Ni–Mo–O surface species with different number of Mo-oxo and Ni-oxo entities are formed, depending on the Ni/Mo atomic ratio. It may be accepted, that the Ni 2+ ions are partially localized into the molybdate layer without forming well-defined phases. Two kinds of K + ions have been determined in the corresponding samples, interacting (“ bounded” K + ions) and not interacting (“ free” K + ions) with the rest of the supported phases. The potassium deposition increased the dispersion of Mo phase and influenced the coordination state of the Mo 6+ and Ni 2+ ions in the bi-component KMo-, KNi-containing samples and the tri-component KNiMo-containing samples. It provoked partial transformation of the polymeric Mo 6+(Oh) species into monomeric Mo 6+(Td) ones and Ni 2+(Td) species predomination over Ni 2+(Oh) ones. Most probably, new complex K–Ni–Mo–O species were formed on the support surface in the case of the tri-component samples.