A mechanistic DFT study of low temperature SCR of NO with NH3 on MnCe1−xO2(111)

Abstract

Mn-promoted CeO₂ is a promising catalyst for the low temperature selective catalytic reduction of NO by NH₃. We investigated the mechanism of this reaction for a model in which Mn cations are doped into the CeO₂(111) surface by quantum-chemical DFT+U calculations. NH₃ is preferentially adsorbed on the Lewis acid Mn sites. Dissociation of one of its N–H bonds results in the key NH₂ intermediate that has been experimentally observed. NO adsorption on this NH₂ intermediate results in nitrosamine (NH₂NO) that can then undergo further N–H cleavage reactions to form OH groups. The resulting N₂O product is desorbed into the gas phase and can be re-adsorbed through its O atom on an oxygen vacancy in the ceria surface, resulting from water desorption. Water desorption is the most difficult elementary reaction step. This redox mechanism involves doped Mn as Lewis acid sites for ammonia adsorption and O vacancies in the ceria surface to decompose N₂O into the desired N₂ product.