Dresden 2003 – wissenschaftliches Programm
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O: Oberflächenphysik
O 15: Elektronische Struktur III
O 15.7: Vortrag
Dienstag, 25. März 2003, 12:45–13:00, HSZ/02
Mechanism of (VO)2P2O7 to V2O5 Phase Transformation: DFT Cluster Model Studies — •Malgorzata Witko and Alicja Haras — Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 8, 30239 Krakow, Poland
Vanadyl pyrophosphate, (VO)2P2O7, is believed to be the main component of vanadium phosphate (VPO) catalysts for 14-electron transformation of n-butane to maleic anhydride; the only industrial process of light alkanes oxidation. The composition of catalyst surface as well as the reaction mechanism is poorly understood due to the ability of this system to transform into a number of different VOPO4 phases. Recently, a phase transformation of (VO)2P2O7, generating crystallites of V2O5, has been observed by in situ Laser Raman Spectroscopy. It has been associated with the formation of oxygen vacancies in (VO)2P2O7 after a prolonged treatment by water vapor and considered as disadvantageous in terms of catalytic performance.
To account for the experimental observation, a detailed description of the transformation mechanism involving generation of the O-vacancy followed by separation of vanadium oxide and phosphorous oxide species is presented based upon ab initio DFT studies using the cluster model. Discussion of the energy and electronic changes for the subsequent steps of transformation proves that the restructuring is invoked spontaneously through the formation of high-coordinated oxygen vacancies.