Abstract
A vanadium oxide powder catalyst supported on titanium oxide (VO x /TiO 2(anatase)) was investigated with in situ X-ray absorption spectroscopy (XAS). This system is applied in industry for partial oxidation processes. The structural changes of the supported vanadium oxide due to different treatments were determined: during a reduction–oxidation cycle at 623 K after calcination in air and after heating in inert atmosphere. Unsupported crystalline V 2O 5 powder was used as a reference system. After calcination in air of the VO x /TiO 2(anatase) a V 2O 5 bulk crystal structure appears, while an octahedral co-ordination with a V O vanadyl bond is present after heating in inert atmosphere. The redox cycle performed on fully oxidized supported vanadium oxide induces similar structural changes as for unsupported V 2O 5: a reduction to V 4+ with a slightly distorted V O octahedron and a re-oxidation to the initial V 2O 5 structure. However, when the supported vanadium oxide is reduced after heating in inert, a valence lower than V 4+ is obtained and a different structure is found: a symmetrical V O octahedron is present with V O and V V distances identical to the Ti O and Ti Ti distances in TiO 2(anatase or rutile). After re-oxidation the V 2O 5 bulk structure is again obtained for the supported vanadium oxide.
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