Electrical properties of pure vanadium phosphate phases and of VPO catalysts used in the partial oxidation of n-butane to maleic anhydride
- 1 January 1994
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions
- Vol. 90 (10) , 1441-1448
- https://doi.org/10.1039/ft9949001441
Abstract
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 (αII, β, γ and δ) were found to be extrinsic n-type semiconductors with the presense of substitutional V4+ 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 V5+ phase. These become more conducting as the time of activation increases due to the progressive dissolution of V5+ ions into the bulk of the (VO)2P2O7 matrix by the subsitution with V4+ 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).Keywords
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