Ind. Eng. Chem. Res. 2001, 40, 4491-4495
4491
KINETICS, CATALYSIS, AND REACTION ENGINEERING Selective Catalytic Reduction of Nitrogen Oxides with NH3 over Natural Manganese Ore at Low Temperature Tae Sung Park,*,† Soon Kwan Jeong,*,† Sung Ho Hong,‡ and Sung Chang Hong§ Department of Chemical Engineering, Korea University, 1, 5-Ka, Anam-dong, Sungbuk-gu, Seoul 136-701, Korea, KOPEC Ltd., 449-713, Mabuk-li, Gusung-myun, Yongin, Kyonggi-do 449-713, Korea, and Department of Environmental Engineering, Kyonggi University, San 94-6, Yiui-dong, Paldal-gu, Suwon, Kyonggi-do 442-760, Korea
The selective catalytic reduction of NOx (NO + NO2) at low temperature with ammonia has been investigated with natural manganese ore, pure manganese dioxide, and manganese dioxide supported alumina. The catalysts showed high activities for NOx reduction with NH3 in the presence of O2 at temperatures below 250 °C. The decrease of SCR activity without oxygen in the gas phase differed among the three catalysts in accord with their differing amounts of lattice oxygen. The SCR activity of the catalysts, in that case, decreased in the order MnO2 > NMO > MnO2/γ-Al2O3. Small amounts of SO2 deactivated the catalysts in the low-temperature range. An XRD analysis of the sulfated catalysts with differing temperature provides evidence that the formation of ammonium sulfates is the main poisoning route. These results could restrict the practical application of these catalysts to sulfur-free conditions. Introduction Removal of NOx from exhaust gases is crucial for solving the problems of acid rain and air pollution. Selective catalytic reduction (SCR) of nitrogen oxides with ammonia is one of the best prospective processes for cleaning the stack gas from stationary sources.1 Efficient reaction can be achieved by conventional catalysts modified with V2O5/TiO2 and with the addition of ammonia as the reducing agent.2 The most effective reaction temperature for these methods is known to be in the range of 300-400 °C.3,4 Because of this high operating temperature, the catalyst bed must be located upstream of the desulfurizer and/or of the particulate control device to avoid reheating of the flue gas, and thus, it is subject to deactivation from high concentrations of sulfur dioxide and dust. In addition, retrofitting SCR devices into existing systems for flue gas cleaning is costly because space and access in many power plants are extremely limited.5 Thus, there is a great interest in developing active SCR catalysts that work at low temperature (
