On the nature of active sites in MoVTeO and MoVTeNbO catalysts: The influence of catalyst activation temperature Original Research Article

MoVTeO and MoVTeNbO catalysts have been prepared, characterized (by XRD, Raman, IR, XPS, oxygen isotopic-exchange and IR of adsorbed methanol) and tested in the partial oxidation of propane to acrylic acid. The catalysts have been prepared hydrothermally and heat-treated at 500, 550 or 600 °C in a N2 atmosphere. The heat-treatment has different influence on the formation and stability of M1, the surface characteristics of catalysts and the catalytic behavior of MoVTeO and MoVTeNbO catalysts. The more selective catalyst was the MoVTeNbO sample heat-treated at 600 °C, which present relatively high oxygen isotopic-exchange, the lower onset temperature of 18O2-consumption and a very low number of acid sites. In addition, it is characterized by the presence of only a type of Mo6+ species and the absence of Te6+ species (only Te4+ is observed) on the catalyst surface. The characteristics of active and selective catalysts are also discussed.