Mechanisms study of silicotungstic acid modified CeO2 catalyst for selective catalytic reduction of NO with NH3: Effect of pH values

A series of silicotungstic acid modified CeO2 (SC-x, x represents the pH value of solution that is used for the preparation of catalysts) were prepared for the selective catalytic reduction (SCR) of NOx with NH3. SC-9 showed the best catalytic activity among the samples. The monodentate nitrate, bidentate nitrate, bridging nitrate and NO2 were detected over SC-9 and SC-10. Monodentate nitrate and bridging nitrate disappeared over SC-8. Furthermore, the monodentate nitrate and bridging nitrate could react with NH4+ on Bronsted acid sites to generate NH4NO3, and then was reduced by NO to form NO2, accompanied with the fast reaction between NO2 and coordinated NH3 on Lewis acid sites in the presence of gaseous NO. Besides, the SCR reaction pathway of SC catalysts followed by the Langmuir–Hinshelwood mechanism and the Eley–Rideal mechanism.