The structural transformation of vanadium phosphate hemihydrate, VOHPO 4 ‚ 1 / 2 H 2 O, into ammonium vanadyl pyrophosphate, (NH 4 ) 2 [(VO) 3 (P 2 O 7 ) 2 ], was studied by XRD and spectroscopic methods such as FTIR and Raman spectroscopy. The reaction was carried out at 673 K in the presence of the ammoxidation feed (toluene, oxygen (air), ammonia, and water vapor), proceeding through an intermediate crystalline phase. The main product of the transformation was R-. Both materials are characterized by the orthorhombic space group Pna2 1 and an intersecting tunnel structure. Apart from R-(NH 4 ) 2 [(VO) 3 (P 2 O 7 ) 2 ], a vanadium-rich phase was formed according to the stoichiometry which is probably a mixed valent vanadium oxide. The structural transformation proceeded also in the same direction without participation of the aromatic substrate. The reaction of VOHPO 4 ‚ 1 / 2 H 2 O carried out only under an ammonia/ oxygen (air) flow led to the generation of R-(NH 4 ) 2 [(VO) 3 (P 2 O 7 ) 2 ] as well, but to a minor degree. An XRD-amorphous material was obtained, being the main phase. The treatment of the hemihydrate with an ammonia/nitrogen flow generated an XRD-amorphous product and a deep reduction of V IV w V III proceeded.
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