Phase development and morphology during the thermal treatment of VOHPO4.0.5H2O

The thermal activation of VOHPO4.0.5H(2)O in O-2, air, N-2 or n-butane-air was studied using in situ X-ray diffraction and ex situ X-ray photoelectron spectroscopy and focussed ion beam microscopy with cross sectioning. In O-2 or air, an amorphous solid forms when VOHPO4.0.5H(2)O is heated above 270 degrees C and a crystalline V5+ phase develops on heating above 350 degrees C. By contrast, during activation in n-butane-air or in N-2, (VO)(2)P2O7 is formed at 300 degrees C without any intermediate amorphous phase. The interiors of VOHPO4.0.5H(2)O and (VO)(2)P2O7 particles were identical, with the platelet like morphology of the precursor preserved during activation. By contrast the interiors of particles from the air or O-2 activation procedures had become dense and sintered like in appearance. Some oxidation of surface regions was observed during activation in n-butane-air. These results are discussed in terms of platelet type morphology of (VO)(2)P2O7 generating a resistance to overoxidation during activation and catalytic work. (c) 2005 Elsevier B.V. All rights reserved.