(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.