Commercial SCR catalyst modified with different noble metals (Ag, Pt, Pd) to efficiently remove slip ammonia and NOx in the flue gas

Abstract

BackgroundWith the increasingly strict emission standard of flue gas, ammonia escape has been one of the urgent problems to be solved in the SCR process of coal-fired power plants. Slip ammonia is regarded as the secondary pollution in SCR process. Moreover, slip ammonia cannot only result in the deactivation of SCR catalyst, thus reducing NO removal efficiency, but also form NH4HSO4 and then corrode the equipment, which can do serious harm to the operation safety. Therefore, it is important to find ways to efficiently remove slip ammonia from the coal-fired plants with the complex gas composition. MethodsCommercial SCR (V2O5-WO3-TiO2) catalysts were modified with various noble metals (Ag, Pd, Pt) by improved impregnation methods. The NH3 oxidation performance of them was tested to select the most significant catalyst in selective catalytic oxidation of ammonia (NH3-SCO) and the effect of NO, SO2 and H2O were also investigated. Significant findingsThe experimental results showed that noble metals modification could all markedly improve the oxidation ability to remove slip ammonia from coal-fired plants and Ag/SCR catalyst obtained the best application prospect due to its low price. The NH3 conversion of Ag/SCR catalyst reached 92% at 350 °C. Moreover, 95% NOx could be removed when NO was introduced in the gas. Based on the characterization results, the introduction of noble metals had no visible influence on the structure and specific surface area of commercial SCR catalyst but it could increase the redox properties and the number and intensity of surface acidic sites. In addition, the redox cycles between noble metals and vanadium species on SCR catalyst surface were conducive to generate more active oxygen and promote the oxidation capacity of the catalysts.