Severe deactivation and artificial enrichment of thallium on commercial SCR catalysts installed in cement kiln

Thallium (Tl) poisoning is reported for the first time occurring on selective catalytic reduction (SCR) catalysts running in a certain cement kiln. NOx conversion of the poisoned catalyst is almost lost with 6.4 % Tl loading even at 400 degrees C. Besides the decrease of the BET surface area, Tl significantly decreases the oxidation ability of the active sites due to the coverage effect. Ti is present as both Tl2O3 and Tl2SO4 and covers both the Lewis and Bronsted acid sites of V2O5 and the Ti-(OH)-Ti bridging sites of TiO2, leading to a marked decrease in the quantity and strength of acid sites. Similar to the regeneration of alkali-poisoning catalysts, dilute H2SO4 is also effective to remove partial surface Tl2O3, by which yielded 89% of Tl removal with a 0.4 M H2SO4. However, the SCR performance could not total recover because of the remnant Tl2O3 on the catalyst regenerated only once.