Deactivation of oxidation and SCR catalysts used in flue gas cleaning by exposure to aerosols of high- and low melting point salts, potassium salts and zinc chloride

For the purpose of this deactivation study, Pt- and vanadia supported catalysts were used. The catalysts have been exposed to aerosol particles of inorganic salts, with high- or low melting points. The average diameter of the generated salt particle was kept constant at around 70 nm. The aerosol particle penetration depth for the samples exposed to potassium salt, was 1 μm as measured by scanning electron microscopy (SEM). The corresponding depth for zinc chloride salt (ZnCl2) was 5 μm. In order to validate the dependency of the catalytic decay rate to exposure temperature, Pt/wire-mesh catalyst was treated with potassium chloride at two temperatures, namely 300 and 500 °C. Pt/supported catalyst was also treated with ZnCl2 salt at 190 and 300 °C. The extent of decay was tested in the oxidation of CO for particle treated Pt/wire-mesh samples. The degree of the deactivation for the aerosol particle deactivated vanadia supported catalysts were also examined in the reduction of NOx. When the Pt/wire-mesh catalyst have been exposed to the poisons aerosol particles at higher temperature lead to the strongest deactivation in the CO oxidation. The Pt-supported catalysts that were treated with aerosol particles from potassium carbonate and potassium sulphate revealed a minor deactivation in the CO oxidation reaction. No significant deactivation was observed for the salt treated vanadia supported monolith samples used in selective catalytic reduction (SCR). A slight pronunced deactivation effect appeared when the vanadia supported wire-mesh catalysts were salt treated. Generally, the obtained results in this study do not indicate any correlation between the salt melting point and the degree of catalytic decay. The obtained results indicate that the exposure temperature during the deactivation procedure is the most critical parameter. Also, the higher the exposing temperature the stronger deactivated sample is produced.