Ca Doping Effect on the Competition of NH3-SCR and NH3 Oxidation Reactions over Vanadium-Based Catalysts

The Ca poisoning effect constrains vanadium-based catalysts from further application in high-calcium content flue gas, and the deactivation effect of CaO on V2O5-WO3/TiO2 (VWT) and V2O5/TiO2 (VT) catalysts has been investigated from a new perspective. As the NH3 selective catalytic reduction (NH3-SCR) results showed, the NO conversion at 400 degrees C declined by 71.7% for VT and by 34.8% for VWT after CaO doping, and the decrease in NO conversion for NH3-SCR at temperatures greater than 300 degrees C was mainly caused by the competition of the NH3 oxidation reaction. The characterization of catalysts by NH3-SCR, XRD, Raman spectroscopy, H-2-TPR, NH3-TPD, and TEM showed that the number of surface acid sites decreased and that the oxidation and reduction properties of the catalysts all deteriorated after CaO doping, which is the primary reason for the decrease in NO conversion. CaO also affected NH3 oxidation, and the L-NH3 adsorbed on CaO favored the NH3 oxidation reaction, as DRIFTS showed. NH3 reaction pathways changed by CaO doping because NH3 oxidation becomes more competitive at temperatures greater than 300 degrees C. Density functional theory (DFT) calculations confirmed the NO formation pathway on CaO, and the competition mechanism of NH3-SCR and NH3 oxidation reactions has been described, which has hardly been reported.

Automated summary

The poisoning effect of Ca limits the further application of vanadium-based catalysts in high-calcium content flue gas. CaO doping deteriorates the surface acid sites and oxidation/reduction properties of V2O5-WO3/TiO2 (VWT) and V2O5/TiO2 (VT) catalysts, leading to a decrease in NO conversion during NH3-SCR, with NH3 oxidation becoming more competitive at higher temperatures.