Effects of metal substitution in transition-metal phosphides (Ni(1-xM'(x))(2)P (M' = Cr, Fe, Co) studied by X-ray photoelectron and absorption spectroscopy

• Published in: Journal of materials chemistry 2009-09, Vol.19 (33), p.6015-6022
• Main Authors: Blanchard, P.E.R., Grosvenor, A P, Cavell, R G, Mar, A
• Format: Article
• Language: English
• ISSN: 0959-9428
• DOI: 10.1039/b904250d

Mixed-metal variants (Ni(1-xM'(X))(2)P(M' = Cr, Fe, Co; 0 , x , 1) of the binary phosphide Ni(2)P, a well-known hydrodesulfurization and hydrodenitrogenation catalyst, have been examined by X-ray photoelectron (XPS) and absorption (XANES) spectroscopy. The P 2p(3/2) binding energies and K-edge absorption energies in (Ni(1-x)Cr(x))(2)P, (Ni(1-x)Fe(x))(2)P, and (Ni(1-x)Co(x))(2)P are lower than in Ni(2)P, with the shifts becoming more pronounced with greater difference in electronegativity between P and Ni/M'. These shifts are influenced primarily by intraatomic effects. However, secondary interatomic effects are also implicated in the Ni 2p(3/2) XPS spectra, which show enhanced satellite intensities, and in the Ni K- and L-edge absorption spectra, indicating a charge transfer from M' to the more electronegative Ni atoms. This phenomenon was confirmed in the metal L-edge XANES spectra, which revealed lower Ni and higher M' L-edge absorption energy as the degree of charge transfer increases. The Ni K-edge XANES spectra also show a pre-edge feature whose intensity decreases from Ni(2)P to (Ni(0.8)Cr(0.2))(2)P, supporting the occurrence of charge transfer from Cr to Ni.