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

Abstract

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 Brønsted acid sites could inhibit the formation of N₂O.