Determination of platinum valence state in alumina based catalysts by X-Ray fluorescence spectrometry

Abstract

A novel method for the estimation of the platinum valence state in alumina-based catalysts using the intensities of L- and M-series lines of X-ray fluorescence spectrum is proposed. The measurements of metallic platinum (Pt0) and potassium tetrachloroplatinate K2[PtCl4] (PtII) were carried out using wavelength-dispersive spectrometer. We considered the ratios of the most intense groups of closely spaced platinum X-ray fluorescence spectrum L-series lines (Lα2/Lα1, Lβ2/Lβ1, Lβ4,6/Lβ1), as well as the broadening of PtMα1,2 line as parameters influenced by the chemical bond. After decomposition using a pseudo-Voigt function, the ratio of the Lα1 and Lα2 peaks amplitudes for K2[PtCl4] was 0.118, for Pt0–0.162; the difference in the ratio of peak amplitudes in the group of Lβ lines is much smaller. For the broadening of Mα1,2 line, the largest intensity difference (25 rel.%) between Pt0 and K2[PtCl4] was observed at 2.044 keV. Both studied analytical parameters for set of alumina-based catalysts were closer to values for Pt0 than to values of K2[PtCl4] that indicates that platinum in the studied catalysts is in a state close to metallic, probably with a slight shift towards the ionic state.