Influence of CeO2 and WO3 Addition to Impregnated V2O5/TiO2 Catalysts on the Selective Catalytic Reduction of NOx with NH3

We investigate the effect of cerium and tungsten addition to optimize the deNO(x) activity of V2O5/TiO2 catalysts over a broad temperature range in the catalytic reduction of NOx with NH3 (NH3-SCR) with and without the presence of water. The catalysts were synthesized following co-impregnation of TiO2 with different loadings and varying content of V2O5, CeO2 and WO3 oxides as promoters. Based on surface and bulk characterization, we show that all catalysts undergo different structural changes depending on the chemical nature of the promoters. X-ray photoelectron spectra indicate a tendency for surface reduction after addition of CeO2, surface oxidation after addition of WO3, and after catalytic NH3-SCR. Promotion of V2O5/TiO2 catalysts with CeO2 and/or WO3 broadens the operation temperature window of the catalytic NH3-SCR reaction under both dry and wet conditions and improves the N-2 selectivity at high temperatures. The thermal deactivation resistance of CeO2- and WO3-promoted catalysts improves with increasing amount of WO3. We tentatively relate this to suppression of the sintering of the active VOx component and increasing the amount of CeVO4. The latter, as a consequence of Ce-V interaction, detrimentally changes the surface composition of the catalysts and hides active V in the bulk structure inaccessible for reaction. Water slightly decreases the overall catalytic activity of SCR at low temperatures, while preventing the formation of N2O at elevated temperatures. Addition of CeO2 leads to a slight decrease in overall reducibility of the catalysts, while W causes an enhancement in quantitative H-2 uptake. On the contrary, the sole addition of CeO2 leads to an enhancement of ammonia adsorption and the appearance of new acidic surface sites, which beneficially combine the reduced surface of the catalysts with an enhanced deNO(x) activity at low temperature.