Current use of the supported V2O5-WO3/TiO2 catalyst in industry for the selective catalytic reduction (SCR) of NOx with NH3 as the reducing agent is extensive. However, the tendency for N2O generation at the high temperatures (T&gt;300°C) required for sufficient activity is an issue that still needs to be resolved. These problems can seemingly be overcome by the integration of redox promoters, such as Ce and Cu, capable of cycling between oxidation states with relative ease, though the source of these promotional effects is unclear. Furthermore, the effect of SO2 typically found in industrial flue gas on the structure-performance relations of the unpromoted and promoted catalysts is still poorly understood. In the present work, in situ Raman and IR spectroscopies are used to investigate the anchoring, interactions and surface structures of the metal oxide surface sites, while the surface acidity was measured by monitoring adsorbed NH3 using IR. The effects of CeOx, CuOx and SOx surface sites on the SCR performance of the catalysts is measured using temperature programmed surface reaction (TPSR) spectroscopy. The results indicate that the redox promoters are fully dispersed on the TiO2 support and create unique surface hydroxyls that serve as the main anchoring sites for the surface VOx sites. Both the redox promoters and the surface sulfates affect the surface acidity, with the basic redox and acidic sulfate surface sites strengthening the Lewis and Brønsted acid characters of the catalysts, respectively. Both redox promoters enhanced the low temperature NO conversion activity of the catalyst, but only the CeOx promoted catalyst exhibited lower N2O generation. While the unpromoted catalyst remained unaffected by sulfation, the NO conversion activity of the redox promoted catalysts was inhibited. Finally, it was found that the SCR reaction can efficiently proceed via both Lewis and Brønsted acid sites, resolving the long-lived debate regarding the superior role of one acid site over another. These results serve to establish currently missing fundamental structure-performance relations for the interactions between CeOx, CuOx and SOx surface sites and the V2O5-WO3/TiO2 catalytic system.

Structure-performance relationships for redox promoted (CeOx and CuOx) and surface sulfated V2O5-WO3/TiO2 catalysts for selective catalytic reduction (SCR) of NO with NH3

ACS Spring Meeting 2021

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