(20i) Low-Temperature Catalytic Reduction of NO By NH3 Over Vanadia-Based Nanoparticles Prepared By Flame-Assisted Spray Pyrolysis: Influence of Various Supports
A series of V/CeO2, V/TiO2, V/Al2O3, V/ZrO2, V/CeO2−ZrO2, V/TiO2−Al2O3, and V/CeO2−Al2O3 metal oxide nanoparticles were synthesized by a one-step rapid Flame Spray Pyrolysis (FSP) synthesis technique. Benefiting from the short residence time and high quenching rate during the single-step flame spray process, V4+, V3+ ions are successfully incorporated into the crystal lattice of various metal oxide supports. As can be envisaged from XPS spectra, as-synthesized V/ZrO2 sample primarily consists of V5+ species due to the formation of ZrV2O7 solid solution as a result of zirconia migration into the V2O5 crystallites. Our XPS results imply that the formation of surface V2O3 species is improved enormously by the addition of Al2O3 (V3+/Vn+= 0.36, 0.38, and 0.41 for V/TiO2−Al2O3, V/Al2O3, V/CeO2−Al2O3, respectively), whereas, the addition of TiO2 led to the formation of surface VO2 species (V4+/V5+= 0.88, 1.57 for V/TiO2, V/TiO2−AlO3, respectively). Among all the catalysts, high surface (V3++V4+)/Vn+, and V4+/ Vn+ concentrations were observed for the V/TiO2-Al2O3, V/Al2O3, V/CeO2-Al2O3, respectively. Our in-situ FT-IR studies of NO+NH3 co-adsorption demonstrate that the strong signals at 1435 and 1714 cm-1 (bending vibration of NH4+) decrease with respect to temperature. This observation reveals that the NH4+ species bound to Brönsted acid sites are responsible for the enhancement in the SCR reaction over the vanadia-zirconia surfaces. The introduction of Zr (seven fold coordination) into V2O5 is leading to the reduction of elemental number in crystal grain and deviation of adjacent oxygen atoms. The catalytic performance of various V/M' (M'=Ce, Al, Ti, Zr, Ce-Zr, Ti-Al, and Ce-Al) flame-made catalysts (with consistent V content V/M' = 0.17) was studied for the low-temperature SCR reaction at a range of temperatures (140-360°C). The intrinsic activity of V/Ti-Al, V/Al, V/Ce-Al catalysts with V/M' = 0.17 atomic ratio measured under differential reaction conditions will be discussed in the presentation.