Multipollutant Control (MPC) of Flue Gas from Stationary Sources Using SCR Technology: A Critical Review

The emission of gaseous pollutants from the combustion of fossil fuels is believed to be one of the most serious environmental challenges in the 21st century. Given the increasing demands of multipollutant control (MPC) via adsorption or catalysis technologies, such as NOx, volatile organic compounds (VOCs), heavy metals (Hg etc.), and ammonia, and considering investment costs and site space, the use of existing equipment, especially the selective catalytic reduction (SCR) system to convert pollutants into harmless or readily adsorbed substances, is one of the most practical approaches. Consequently, many efforts have been directed at achieving the simultaneous elimination of multipollutants in a SCR convertor, and this method has been widely used to mitigate the stationary emission of NOx. However, the development of active, selective, stable, and multifunctional catalysts/adsorbents suitable for large-scale commercialization remains challenging. Herein, we summarize recent works on the applications of SCR in MPC, describing the approaches of (i) SCR + VOCs oxidation, (ii) SCR + heavy metal control, and (iii) SCR + NH3 reduction to reveal that the efficiency of simultaneous elimination depends on catalyst composition and flue gas parameters. Furthermore, the synergistic promotional/inhibitory effects between SCR and VOCs/ammonia/heavy metal oxidations are shown to be the key to the feasibility of the reactions.