Catalytic activity of lime for N₂O decomposition under coal combustion conditions

To understand the contribution of lime to the abatement of N₂O emission from fluidized coal combustor, the catalytic activity of the lime for the decomposition of N₂O under coal combustion conditions was studied. Lime was active for the catalytic decomposition of N₂O, and its activity was stable in the simulated coal combustion flue gas in the absence of SO₂ at 800 °C. The catalytic activity of lime was depressed by the presence of CO₂, H₂O, and SO₂. The affect of the presence of SO₂ seemed to be most important: the catalytic activity of the lime gradually decreased as the degree of sulfation increased, and the specific surface area decreased with the progression of sulfation. From N₂O pretreatment and temperature-programmed desorption studies on the used lime, it was found that two oxygen species and one species of NO desorbed. A surface character change due to sulfation is expected from these gas desorptions. From the relation of the activity to the surface area or the desorption of the gases or both, it was concluded that a decrease in the surface area contributed to the decay of the activity more effectively than the surface character change caused by the sulfation.