Effects of H2O and SO2 on Selective Catalytic Reduction of NOx by NH3

Abstract

Experiments have been investigated to study the effects of H₂O and SO₂ contents on NO_x reduction efficiency using ammonia (NH₃) as the reducing agent over the nanometer-class V-W/Ti catalyst under variable temperatures on a steady-flow reactor. The results show that the activity of selective catalytic reduction (SCR) is inhibited by H₂O content at low temperature, but higher NO conversion efficiency should be achieved at high temperature due to the reaction of NH₃ oxidized by O₂ to NO_x would be inhibited by H₂O content. The selective catalytic reduction activity will be promoted by SO₂ content in the range of 150-500 ºC, NO conversion efficiency can be improved to 98 % from 94 % by adding SO₂ content. The activity of selective catalytic reduction will be promoted at 150-240 ºC and 350-500 ºC when H₂O and SO₂ exist at the same time, but ammonium sulfates and other sulfates will be generated at low temperature. Additionally, following the ESC test, the positive influence to the NO_x conversion has been proved in the presence of H₂O and SO₂, but it has considerably negative effect to PM emission for the diesel engine.