DETERMINATION OF THE DISTRIBUTION OF MOLYBDENUM OXIDATION-STATES IN REDUCED MO/TIO2 CATALYSTS BY FACTOR-ANALYSIS AND CURVE FITTING

This study shows that principal component analysis (PCA) in conjunction with iterative target transformation factor analysis (ITTFA) is able to provide an independent estimate of the number, position and, to a certain extent, the shape of spectral components required to describe the Mo 3d envelope as monitored by XPS in reduced Mo/TiO2 catalysts. Three components were required to reproduce the original data. Abstract components from PCA were transformed through ITTFA into components which have spectroscopic meaning. ITTFA was able to predict the position and basic shape of the three spectral components and thus give an estimate of their relative contribution to each spectrum. The three spectral components were attributed to Mo6+, Mo5+ and Mo4+. These factor analysis (FA) results were used in conjunction with non-linear least-squares curve fitting (NLLSCF), to provide a detailed description of the Mo 3d envelope during reduction of the Mo/TiO2 catalysts.