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

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% N-2 selectivity in the temperature range of 300-350 degrees 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.

Automated summary

Acid regeneration effectively removed potassium deposits on the surface of the K-CuNbTi catalyst, resulting in excellent catalytic performance at high temperatures. The increase in acidic sites and generation of Bronsted acid sites were crucial factors contributing to the improved catalytic activity of the regenerated catalyst.