The different poisoning behaviors of various alkali metal containing compounds on SCR catalyst

Abstract

Alkali metals are poisonous to the metal oxide catalyst for NO removal. The chemical configuration of alkali containing substance and interacting temperature can affect the poisoning profile. A computational method based on Frontier Molecular Orbital analysis was proposed to determine the reacting behavior of various alkali-containing substances with SCR catalyst. The results reveal that the poisoning reactivities of various substances can be ranked as: E (MOH)>E (M2SO4)>E(MCl)>E(MNO3)>E(MHSO4). The experimental activity tests of the catalysts calcined at stepped temperatures show that NaOH can react with the catalyst below 200°C. NaCl and NaNO3 start to react with the catalyst at a temperature between 300 and 400°C. Unlike MOH, MCl and MNO3, which can produce volatile or decomposable species for the anions after reacting with the catalyst, M2SO4 and MHSO4 will leave both cations and anions on the catalyst surface. The sulfate ions left on the catalyst can generate active acid sites for NH3 adsorption. The experimental results also show that Na2SO4 and NaHSO4 will not lower the NO conversion. The after-reaction influences of various alkali metals were studied using theoretical and experimental methods. The theoretical results show that the acidity decreases with doping of alkali metal. Experiments show a consistent result that the NO conversion decreases as undoped >LiCl>NaCl>KCl.