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Graham J. Hutchings,
J.Antonio Lopez-Sanchez,
Jonathan K. Bartley,
Jeremy M. Webster,
Andrew Burrows,
Christopher J. Kiely,
Albert F. Carley,
Colin Rhodes,
Michael Hävecker,
Axel Knop-Gericke, Ralf W. Mayer,
Robert Schlögl,
Jean Claude Volta,
Martyn Poliakoff
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ABSTRACT: A new preparative route for vanadium phosphate catalysts is described using supercritical CO2 as an antisolvent. The amorphous microspheroidal VPO produced is shown to be more active than comparable crystalline VPO catalysts for the selective oxidation of n-butane to maleic anhydride and, furthermore, does not require an extensive pretreatment or activation period to establish full catalytic activity. VPO catalysts prepared using supercritical CO2 as an antisolvent maintain their amorphous nature throughout the catalyst test period. In contrast, amorphous VPO catalysts can also be prepared by using liquid CO2 as antisolvent or by solvent evaporation in vacuo; however, these materials are found to partially crystallise during the oxidation of n-butane. The wholly amorphous catalysts are characterised using transmission electron microscopy, X-ray absorption spectroscopy, 31P spin-echo mapping, NMR spectroscopy, and X-ray photoelectron spectroscopy. The role of amorphous material in vanadium phosphate catalysis is discussed in detail.
Journal of Catalysis.
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ABSTRACT: The surface of an activated vanadium phosphorus oxide (VPO) catalyst was investigated by means of in situ X-ray absorption spectroscopy in the total electron yield mode. We observed significant changes of the V L3-near edge X-ray absorption fine structure (NEXAFS) when the material was transferred from room temperature to working conditions at 400°C in the reaction atmosphere. We studied the same VPO material under different gas compositions comprising the reaction mixture of n-butane and oxygen, pure oxygen and vacuum to elucidate the influence of the gas-surface interaction and the effect of the temperature. The results of this extensive study indicate a dynamic response of the catalyst surface to the applied conditions.
Applied Surface Science, v.230, 272-282 (2004).
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Catalysis Letters, v.74, 121-125 (2001).
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Catalysis Letters, v.86, 245-250 (2003).
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BESSY GmbH: BESSY annual report 1999, 251-253 (2000).
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BESSY GmbH: BESSY annual report 1999, 306-307 (2000).
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BESSY GmbH: BESSY Highlights 2001, 10-11 (2002).
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BESSY GmbH: BESSY annual report 2000, 167-168 (2001).
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Catalysis Letters, v.86, 245-250 (2003).
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