Insight into the reasons for enhanced NH3-SCR activity and SO2 tolerance of Mn-Co layered oxides

Abstract

Mn-based catalysts have a fatal flaw in selective catalytic reduction (SCR) of NOx with NH3, which is poor SO2 tolerance. In this work, we successfully fabricated Mn-Co layered double oxides (LDOs) by calcining the Mn-Co layered double hydroxides (LDHs) generated by a hydrothermal method using urea solution. The obtained Mn-Co LDO presents excellent catalytic activity and SO2 tolerance in the SCR reaction of NOx with NH3. The enhanced activity can be attributed to the special surface physicochemical properties endowed by its LDO structure, such as large specific surface area, more exposed active sites, relatively high Mn4+ and Oα/(Oα + Oβ) percentage, good reducibility, and abundant acidic sites. The enhanced SO2 tolerance can be ascribed to the weak adsorption energy of SO2 on Mn-Co LDO, which makes it difficult for SO2 to interact with the active sites. Furthermore, the NH3-SCR of NOx reaction that occurs on the surface of the MnCo-LDO follows both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms. This study shines light on the design of Mn-based de-NOx catalysts with excellent SO2 tolerance.