Effective Way to Control the Performance of a Ceria-Based DeNOx Catalyst with Improved Alkali Resistance: Acid-Base Adjusting

Compared with V2O5W-O-3/TiO2, the ceria catalyst supported on sulfated zirconia (referred to as CeSZ) shows a superior alkali resistance for selective catalytic reduction of NO in flue gases. It reveals an unexpected result that a moderate amount of potassium (normally considered as SCR poisons) could even enhance the activity of CeSZ catalyst. To investigate this exceptional phenomenon, we studied the surface acid-base properties of CeSZ catalysts with different amounts of K and their influences on SCR performances. Although K resulted in a sharp decrease in Bronsted acid sites, the total acidity, especially strong acidity, barely changed when K/Ce was less than 0.4. It was proposed that a small amount of potassium could initially alter some Bronsted acid sites to Lewis ones, therefore retaining the majority of total acidity. Moreover, increased surface basicity due to K depositing led to an enhancement in NO chemisorption and oxidation, which is beneficial to the SCR process via the reaction of NO2 and NOx ad-species with adsorbed NH3 species. This explains why the SCR catalytic activity was improved at lower temperature for CeSZ catalysts after K depositing. Therefore, the catalytic activity and reaction temperature window of CeSZ catalyst could be controlled by simply tuning the surface acid/base sites, which may give some inspiration to improve the catalytic activity and poisoning tolerance.