H3PW12O40 Grafted on CeO2: A High-Performance Catalyst for the Selective Catalytic Reduction of NOx with NH3

CeO2 showed a poor selective catalytic reduction (SCR) activity due to its poor ability to adsorb NH3. To improve the SCR performance of CeO2, tungstophosphoric acid (i.e., HPW, H3PW12O40) with a high acidic strength was grafted on CeO2 by the adsorption of HPW on CeO2 in a HPW solution. The grafting of HPW on the surface of CeO2 was demonstrated with characterizations by XPS, XRF, TG-DSC, and in situ DRIFT spectra. As HPW on HPW/CeO2-500 still retained the Keggin structure, HPW/CeO2-500 exhibited an excellent ability for NH3 adsorption. Both HPW and CeO2 on/in HPW/CeO2-500 played their functions to the greatest limit for the SCR reaction. CeO2 in HPW/CeO2-500 played the role in the activation of adsorbed NH3 and NO, and the grafted HPW on HPW/CeO2-500 acted as the active sites for NH3 adsorption. Therefore, HPW/CeO2-500 showed a superior SCR performance at 200–450 °C and an excellent H2O/SO2 resistance above 300 °C.