The promoting mechanism of SO42− on CeO2 for selective catalytic reduction of NO by NH3: A DFT study

Ceria catalysts have attracted considerable interest in the NH3-SCR reaction. The modification of SO42− into CeO2 promotes the NH3-SCR reaction. NH3 adsorption property and four possible reaction paths are further design over CeO2 (111) and SO42−–CeO2 (111) surface. The results reveal that NH3 adsorption of the Lewis acid site is stronger than the Brønsted acid site, and the adsorption energies of the Lewis acid site range from − 0.397 to − 0.963 eV with the modification of SO42−. Thus, the introduction of SO42− into CeO2 increases the adsorption site stability of NH3. NH3 adsorption is the first step in NH3-SCR reaction, and then, the key intermediates such as NH2, NH2NO, NNOH, NH3NO2 species are found. Standard SCR reaction and fast SCR reaction constitute a catalytic cycle in CeO2 catalyst. The different paths of NH3NO2 and NH2NO formation are different, and it led to NNOH only emerge in the fast SCR reaction. Lewis acid site is main reaction site for the standard SCR reaction. Energy barriers of Lewis acid site range from 15.82 to 15.68 kcal/mol by the introduction of SO42−, which makes the NH3-SCR reaction easily occur.