Insights into modified red mud for the selective catalytic reduction of NOx: Activation mechanism of targeted leaching

Abstract

Red mud (RM) is a solid waste rich in iron oxide, which has the potential to be utilized as the catalyst for selective catalytic reduction (SCR) of NOx. We pretreated the RM sample with the selective acid leaching method, after which 97.6 % of the alkali was neutralized, and only 8 % of the Fe2O3 were leached out. Once leached, the RM samples were activated for the SCR reaction. It showed NOx conversions above 90 % in 310–430 °C and exhibited high resistance to SO2 and H2O. After leaching, i. the SBET reached twice as before; ii. the sintering caused by alkali was eliminated; iii. the activated RM exhibited improved Fe3+/Fe2+ ratio and enhanced chemisorbed surface oxygen (Oα); iv. the oxygen mobility and the surface acidity were promoted. Overall, the selective acid leaching is an efficient method to activate RM for the SCR reaction. The RM based catalysts can be an alternative for SCR technology.