Monolayer binary active phase (Mo-V) and (Cr-V) supported on titania catalysts for the selective catalytic reduction (SCR) of NO by NH3

Monolayer catalysts containing binary active phases (VOx-CrOx, VOx-MoOx,) were prepared by simultaneous deposition of the corresponding transition metal-oxo species on the TiO2 (anatase) surface using the equilibrium deposition filtration technique. The prepared samples contained various amounts of each transition metal but almost the same total metal loading. They were characterized by atomic absorption spectroscopy, N-2 adsorption, UV-vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and tested for the selective catalytic reduction of NO by NH3 in the temperature range 250-450 degreesC. It was found that the transition-metal ionic species used for the preparation of these catalysts compete for the same surface sites of the TiO2 carrier upon co-deposition. Small amounts of the second phase (Mo- or Cr-oxo phase) are sufficient in order to promote the catalytic activity at relatively high temperatures, in contrast to what happens in the corresponding industrial catalysts prepared by conventional methods. An electronic interaction between V- and Cr-oxo species favored at a V/Cr atomic ratio around 3 is probably responsible for the relatively high catalytic performance of the corresponding TiCrV catalyst. The activity of the studied catalysts is well correlated with the intensity of a DRS absorption band that appeared at ca. 400 nm, which is considered as a measure of the magnitude of interactions exerted between the monolayer transition metal-oxo species and the TiO2 carrier. This correlation is independent of the transition metals combination used and follows the same linear relationship found previously for single-active-phase catalysts.