Effect of Water Vapor on NO Reduction by Iron in N₂ Atmosphere

Abstract

The effect of water vapor on NO reduction by iron was experimentally investigated at 300-1100 °C in an electrically heated ceramic tubular flow reactor in N2atmosphere. The component changes of iron samples after reaction were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). Results showed that water vapor reacted as oxidizer and the metallic iron was oxidized by both NO and water vapor. Compared to the result without water, NO reduction efficiency decreased when water vapor was added. NO reduction efficiency reached 88.1%, 91.6%, 94.8% above 900 °C in the presence of 2.5%, 5%, 7% water vapor. NO reduction efficiency decreased as the water vapor increased at lower temperature, e.g., 700°C, while decreased slightly first then increased again at higher temperature, e.g., above 800°C. As water vapor increased, the iron was oxidized to Fe3O4/Fe2O3and the surface of iron became more porous, which benefited the diffusion of NO and/or vapor into the inner of the iron to continue the reaction and resulted in the increased NO reduction. The mechanism was preliminarily analyzed.