Suppression of N2O formation by H2O and SO2 in the selective catalytic reduction of NO with NH3 over a Mn/Ti-Si catalyst

A Mn/Ti-Si catalyst was synthesized and investigated using the NH3 selective catalytic reduction (NH3-SCR) of NO in a dry flow and in the presence of H2O or SO2. In particular, the effect of H2O and SO2 was studied in several model reactions to obtain a deeper insight into the impact of poisoning compounds on N2O formation. The adsorption behavior of NO and NH3 indicated that H2O and SO2 decreased the adsorption capacity for NO and increased the adsorption capacity for NH3. The formation of N2O from the disproportionation of NO was negligible. The increase in the adsorption capacity for NH3 caused by H2O and SO2 did not result in an increase in N2O formation. The formation of N2O from the reaction of NO with NH3 was significantly inhibited by H2O and SO2, which could be attributed to the inhibition of the pathway via the Langmuir-Hinshelwood mechanism. The SCR measurements indicated that the formation of N2O primarily originated from the oxidation of NH3 and was suppressed in the presence of H2O or SO2, with a stronger observable effect in the presence of H2O. The formation of N2O is influenced by both the acid-base properties and the redox properties. A mechanism for N2O formation and the suppression effect of H2O and SO2 over the Mn/Ti-Si catalyst was proposed, which suggested that the NH3 adsorbed on the Bronsted acid sites could inhibit the formation of N2O.