Role of V and W Sites in V2O5−WO3/TiO2 Catalysts and Effect of Formaldehyde during NH3−SCR of NOx. Issue 15 (10th June 2022)

• Record Type: Journal Article
• Authors: Binh Ngo, Anh; Huyen Vuong, Thanh; Atia, Hanan; Weiß, Jana; Rabeah, Jabor; Armbruster, Udo; Brückner, Angelika
• Is Part Of: ChemCatChem. Volume 14:Issue 15(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-06-10
• Subjects: NH3-SCR -- V2O5−WO3/TiO2 catalysts -- formaldehyde -- redox behavior -- operando spectroscopy; Catalysis -- Periodicals; 541.39505
• DOI: 10.1002/cctc.202200175
• Languages: English
• ISSNs: 1867-3880

Abstract

Abstract: WO3 /TiO2, V2 O5 /TiO2 and V2 O5 −WO3 /TiO2 catalysts (1 wt % V, 6 wt % W) were tested in NH3 ‐SCR of NOx with/without formaldehyde and water and analyzed by in situ FTIR and operando EPR spectroscopy. Activity decreased in the order V−W−Ti>V−Ti≫W−Ti. Two VO 3+ /VO 2+ sites with different redox behavior exist in V‐containing catalysts. Sites I were less active with restricted accessibility by reactants while activity is mainly driven by undercoordinated sites II exposed on the surface. In V−W−Ti, sites II can form W 6+ −O(H)−V 5+ bridges, accelerating surface acidity and V reduction rate. HCHO lowers NOx conversion and N2 selectivity by reacting with NH3 to formamide that decomposes to HCN. Formation of formamide is promoted by high surface acidity and redox activity. Water lowers NH3 conversion by creating Brønsted sites that adsorb NH3 and suppress oxidation to N2 O, thereby improving N2 selectivity. Abstract : Operando spectroscopy : Activity in V2 O5 (WO3 )/TiO2 is driven by undercoordinated surface VO 3+ /VO 2+ sites. Intimate mixing of VOx and WOx forms W 6+ −O(H)−V 5+ sites, boosting activity by highest redox rates and surplus Brønsted sites. The presence of HCHO lowers X(NO) and S(N2 ) by forming HCONH2 and HCN. The formation of intermediate HCONH2 is accelerated by high surface acidity and redox activity.