The opportunities and challenges of iron-zeolite as NH3-SCR catalyst in purification of vehicle exhaust

Selective catalytic reduction of NOx with NH3 over zeolite catalysts is recognized as the most practical technology used in mobile exhaust gases to transform NOx into N-2. Despite a comprehensive structural-activity insight into Cu-zeolite SCR catalyst, Fe-zeolite, which is also popular in the automotive catalysis community, is necessary to be thoroughly investigated on micro-mechanism. This review summarizes the highlights and challenges in the application of Fe-zeolite, and simultaneously analyzes the reasons of some peculiar properties, such as the NH3 inhibition effect at low temperatures, the low N2O production and the sensitivity to NO2/NOx ratio in the feed. In addition, some feasible strategies are classified and summarized subsequently to provide suggestions for the improvement of low-temperature activity, the enhancement of resistance to hydrothermal aging and sulfur poisoning, the construction of controlled structure and the combination of Fe- and Cu- zeolites. Finally, the reaction mechanisms of NH3-SCR over Fe-zeolites are concluded. After establishing a comprehensive overview of Fe-zeolite SCR catalysts, some directions that remain to be thoroughly explored on Fe-zeolite are put forward to assist the future catalyst design and investigation of NH3-SCR.