Catalytic abatement of trichloroethylene over Mo and/or W-based bronzes

In this paper we present the results of the synthesis, characterization and catalytic behaviour of Mo(W)-Nb-V-O mixed metal oxides bronzes for the catalytic oxidation of trichloroethylene. The catalysts were prepared hydrothermally with different Mo/W/Nb/V/P atomic ratio and heattreated at 500 and 700oC. They were characterized by several techniques as N2-adsorption, Xray diffraction, FTIR, SEM-EDS, temperature programmed desorption, temperature programmed reduction, UV-vis, Fourier transformed infrared spectroscopy of adsorbed pyridine and O/O isotope exchange. X-ray diffraction patterns (XRD) of samples heat-treated at 500oC suggest the presence of a semi-crystalline material with a diffraction peak at ca. 2θ= 22.2o, while XRD patterns of samples heat-treated at 700oC show the formation of a tetragonal tungsten bronze (TTB) structure. The activity for the catalytic abatement of trichloroethylene strongly depends on the heat-treatment temperature and the catalyst composition. Thus, samples with W/(Mo+W) atomic ratios of 0.25-0.75 and heat-treated at 500oC are the most active ones. The enhanced activity has been related to the remarkable higher surface area of the catalyst and to the catalyst composition which influences the acid characteristics as well as the reducibility and reoxidation of the catalysts. The importance of the oxygen dissociation on the catalyst surface and the diffusion of oxygen species through the catalyst are also discussed.