STRUCTURAL TRANSFORMATIONS OF VOHPO4-CENTER-DOT-1 2H(2)O IN THE PRESENCE OF AMMONIA/

The structural transformation of vanadium phosphate hemihydrate, VOHPO 4 . 1/2H(2)O, into ammonium vanadyl pyrophosphate, (NH4)(2)[(VO)(3)(P2 O7)(2)], was studied by XRD and spectroscopic methods such as FTIR and Raman spectroscopy. The reaction was carried out at 673 K in the pres ence of the ammoxidation feed (toluene, oxygen (air), ammonia, and wat er vapor), proceeding through an intermediate crystalline phase. The m ain product of the transformation was alpha-(NH4)(2)[(VO)(3)(P2O7)(2)] , which is isostructural to alpha-K-2[(VO)(3)(P2O7)(2)]. Both material s are characterized by the orthorhombic space group Pna2(1) and an int ersecting tunnel structure. Apart from alpha-(NH4)(2)[(VO)(3)(P2O7)(2) ], a vanadium-rich phase was formed according to the stoichiometry whi ch is probably a mixed valent vanadium oxide. The structural transform ation proceeded also in the same direction without participation of th e aromatic substrate. The reaction of VOHPO4 . 1/2H(2)O carried out on ly under an ammonia/oxygen (air) flow led to the generation of alpha-( NH4)(2)[(VO)(3)(P2O7)(2)] as well, but to a minor degree. An XRD-amorp hous 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 double right arrow V-III proceede d.