Effects of CO2 on the low-temperature NH3-SCR performance of CeOx-biochar catalyst

Abstract

Low-temperature NH3-SCR of NOx technology was recognized as a promising way to control NOx emissions from industrial kilns at low temperatures. Except for SO2 and H2O, lots of CO2 exist in the flue gas of industrial kilns. However, there are few researches on the effects of CO2 on the low-temperature NH3-SCR activity. To investigate the effects of CO2 on the low-temperature NH3-SCR performance and mechanism of CeOx-biochar catalyst, a series of experiments employed. The results showed that the presence of CO2 had an obvious inhibitory effect on the NH3-SCR performance of CeOx-biochar0.6 at 150 °C. There was competitive adsorption between CO2 and NO on the surface of CeOx-biochar0.6. CO2 was mainly adsorbed on CeO2, which hindered the oxidation of NO and the adsorption of NOx on the catalyst surface. Meanwhile, although the presence of CO2 could improve NH3 adsorption capacity of CeOx-biochar0.6 due to the formation of NH4HCO3 and (NH4)2CO3, the existence of carbonates and bicarbonates blocked the formation of active intermediates NH4NO2 and NH2NO for NH3-SCR reaction. As a result, the NOx conversion of CeOx-biochar0.6 was dropped from 96.9% to 40.8% at 200 °C. In view of the bicarbonate and carbonate species was unstable at high temperatures, the inhibitory effect of CO2 on NH3-SCR reaction was gradually weakened with the increase of reaction temperature. The NH3-SCR activity of CeOx-biochar0.6 was seldom affected by CO2 at 300 °C. Finally, a CO2 poisoning mechanism for NOx removal by NH3-SCR at low temperature was proposed.