On the nature and structure of a new MoVTeO crystalline phase

A new MoVTeO mixed oxide has been obtained during the calcination of the corresponding catalyst precursor mixture at 600 degreesC in N-2. The crystal structure has been studied by means of X-ray diffraction, electron diffraction, high-resolution electron microscopy, and diffuse reflectance spectroscopy. Its XRD pattern, similar to those observed in hexagonal tungsten bronze (HTB) K0.13-0.33WO3, was indexed on the basis of a hexagonal cell of parameters a = 0.727 nm and c = 0.4012 nm. However, the electron microscopy study reveals the crystals as being formed by structural domains of an orthorhombically distorted unit cell derived from the HTB structure. Microstructural details are discussed in terms of tellurium location inside the hexagonal tunnels of the structure. The results obtained constitute the first step for elucidating the role of this new orthorhombic phase in the effectiveness of Mo-V-Te-Nb mixed oxide catalysts.