XPS-SIMS surface characterization of aluminovanadate oxide catalyst precursors: Effect of precipitation pH
(2011) Metallofizika i Noveishie Tekhnologii : an international research journal — Vol. 33, n° 11, p. 1487-1512 (2011)
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- X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF SIMS) are used to study the surface physical and chemical state of aluminovanadate oxide catalyst precursors (V-Al-O) precipitated at different pH within the range from 5.5 to 10. For comparison, the reference V <inf>2</inf>O <inf>5</inf> and Al <inf>2</inf>O <inf>3</inf> oxides are also investigated. Using XPS, the core-level photoelectron spectra, x-ray induced Auger spectra, and the valence- band spectra of the samples are obtained, and the surface concentration of components of the catalyst is quantitatively evaluated. Auger parameters for Al and O in V-Al-O, V <inf>2</inf>O <inf>5</inf> and Al <inf>2</inf>O <inf>3</inf> are measured, and the chemical Wagner diagrams are plotted. The O 2p-2p hole repulsion energy for all the samples is estimated. The binding-energy shifts of the O I <inf>s</inf>, V 2p and Al 2p lines are determined as a function of pH and analysed in terms of the initial-state effect related to the atomic charge as well as the Madelung potential and of the final-state relaxation effect. Increasing of pH is found to result in the monotonic variation of the surface composition with the V/Al ratio decreasing by a factor of ≅ 2.6, in the modification of the valence band, progressive hydration of the surface, and increasing dispersion of vanadium-oxide particles. In V-Al-O catalysts, the fraction of reduced V <sup>4+</sup> ions revealed by XPS is increasing with increasing pH, so, the average vanadium oxidation state is changed from ≅+4.8 to +4.6. The enhancement of catalytic activity for propane oxidative dehydrogenation demonstrated by V-Al-O at high precipitation pH is in a good correlation with decreasing surface V/Al ratio, growing population of the V <sup>4+</sup> states, and increasing nucleophilicity of oxygen atoms.
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Chenakin, S. P., Prada Silvy, R., & Kruse, N. (2011). XPS-SIMS surface characterization of aluminovanadate oxide catalyst precursors: Effect of precipitation pH. Metallofizika i Noveishie Tekhnologii : an international research journal, 33(11), 1487-1512. https://hdl.handle.net/2078.5/188456 (Original work published 2011)