Regeneration of alkali poisoned TiO2-based catalyst by various acids in NO selective catalytic reduction with NH3

Abstract The K2O poisoned CuNbTi as a model catalyst (K-CuNbTi) was regenerated by various type and strength acids, among which H2SO4, C2H2O4 and H6O39SiW12 exhibited higher regeneration efficiencies. In contrast to H2O treatment, most potassium depositing on the surface of K-CuNbTi could be removed successfully for the acids regenerated catalysts. All the regenerated catalysts showed above 90% NOx conversion and 98% N2 selectivity in the temperature range of 300–350 °C under a high GHSV of 177,000 h−1. And the regenerated catalysts were characterized by different analytic techniques. Both of the surface chemical active oxygen species and the Cu+ species were obviously improved while KNbO3 was transformed into Nb = O and Nb–OH after regeneration process. Furthermore, the quantity and strength of surface acidity were enhanced and more acid sites were generated, especially Bronsted acid sites. The main acid sites of K-CuNbTi was Lewis acid sites while Bronsted acid sites became the dominating acid sites for the regenerated K-CuNbTi catalysts. Also, acid regeneration process promoted –NH2 active species formation on the catalyst. All above induced a better catalytic activity of regenerated catalyst, indicating that oxalic acid and silicotungstic acid could be the potential substitutes for sulfuric acid to regenerate alkali poisoning SCR catalysts.