Journal of the Chemical Society - Faraday Transactions p. 1441 - 1448 (1994)
Update date:2022-08-11
Topics:
Rouvet, Fabienne
Herrmann, Jean-Marie
Volta, Jean-Claude,
This work aims to correlate previously observed catalytic behaviour and electronic conduction properties of various vanadium phosphate phases active in the mild oxidation of n-butane to maleic anhydride.The pure VOPO4 vanadium phosphate phases (α1, β, γ and δ) were found to be extrinsic n-type semiconductors with the presence of substitutional V(4+) ions acting as acceptor centres.Alternate exposure to oxygen and butane indicated redox processes at the surface: the reduction of the surface by n-butane creates anionic vacancies which are subsequently filled by gaseous oxygen.The most active and selective catalysts, denoted 'VPO', resulting from activation of the precursor under the reacting mixture, comprise a (VO)2P2O7 matrix, initially supporting a dispersed V(5+) phase.These become more conducting as the time of activation increases due to the progressive dissolution of V(5+) ions into the bulk of the (VO)2P2O7 matrix by substitution with V(4+) ions.All the results were in agreement with those obtained with other physicochemical techniques (X-ray diffraction, in situ laser Raman spectroscopy, electron paramagnetic resonance).
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