Unveiling alkali metal poisoning of Cr\\Mn catalyst for selective catalytic reduction of NOx with NH3: An experimental and theoretical study

Alkali metal poisoning has been an intricate and unsolved issue confining the catalytic activity of NH3-SCR catalysts up to now. Herein, the effect of NaCl and KCl on catalytic activity of Cr\\Mn catalyst for NH3-SCR of NOx was systemati-cally investigated to clarify the alkali metal poisoning by combined experiments and theoretical calculations. It un-veiled that NaCl/KCl could deactivate Cr\\Mn catalyst due to the decrease in specific surface area, electron transfer (Cr5++Mn3+<-> Cr3++Mn4+), redox ability and oxygen vacancy and NH3/NO adsorption. In addition, NaCl cut off E-R mechanism reactions by inactivating surface Bronsted/Lewis acid sites. DFT calculations revealed that (1) Na and K could weaken Mn\\O bond, (2) competitive adsorption between Cl and NH3 was a main reason weakening Lewis acid, (3) Cl adsorption was also a major cause diminishing Bronsted acid and oxygen vacancy, (4) Both Na and K seriously impeded NO adsorption/activation, (5) NaCl/KCl increased the reaction heat of H2O desorption (rate-determining step) in E-R mechanism reactions and KCl elevated its energy barrier in L-H mechanism reactions. Thus, this study provides the deep understanding of alkali metal poisoning and a well strategy to synthesize NH3-SCR catalysts with outstanding alkali metal resistance.