The poisoning mechanism of gaseous HCl on low-temperature SCR catalysts: MnOx-CeO2 as an example

The degradation of catalyst properties, rather than the deposition of NH4Cl, was the main reason for the deactivation of the MnCe low-temperature SCR (selective catalytic reduction) catalyst under HCl atmosphere. Cl ions prefer to be located at the oxygen vacancies around Mn cations on the MnCe surface. The adsorbed Cl ions could further promote the formation of oxygen vacancies. Therefore, the active Mn sites on the surface of MnCe would be quickly covered by Cl ions when HCl was present and thus promote the formation of Bronsted acid sites. However, the ionic NH4+ adsorbed on the Bronsted acid sites of MnCe and MnCe - Cl were not fully utilized in the SCR reaction. Meanwhile, the reactivity of the coordinated NH3 bonded with Lewis acid sites was significantly restrained by HCl due to the significant inhibition of the redox performance. Overall, HCl could obviously restrain the low-temperature SCR activity of MnCe.