Formation of active sites for selective toluene oxidation during catalyst synthesis via solid-state reaction of V2O5 with TiO2

Interaction of V2O5 with TiO2 during the preparation of V/Ti-oxide catalysts via solid-state reaction has been studied by means of in situ FT-Raman spectroscopy, HRTEM and XPS. This interaction results in the formation of monomeric vanadia species with vanadium in tetrahedral coordination. The bridging oxygen in the V-O-Ti bond is suggested to be responsible for the catalytic activity during the partial oxidation of toluene. The formation of the monomeric vanadia species correlates with the improved catalyst performance, characterized by reaction rate and selectivity to benzaldehyde and benzoic acid. Mechanical activation by intensive grinding of V2O5/TiO2 mixture via ball milling was necessary for the interaction of the oxides during the calcination. The monomeric species formation was observed at a temperature as low as 523 K. The dynamics of V2O5/TiO2 interaction strongly depends on the presence of moisture during the calcination. In dry oxidative atmosphere, a part of the monomeric species is rapidly formed. Then, the process slows down and becomes diffusion-controlled. During the calcination in humid oxidative atmosphere, quick amorphization of bulk crystalline V2O5 was observed followed by slow formation of the monomeric vanadia species. (C) 2000 Academic Press.