Simultaneous NOx and particulate matter removal from diesel exhaust by hierarchical Fe-doped Ce-Zr-oxide

Particulate matter and NOx emissions from diesel exhaust remains one of the most pressing environmental problems. We explore the use of hierarchically ordered mixed Fe–Ce–Zr oxides for the simultaneous capture and oxidation of soot and reduction of NOx by ammonia in a single step. The optimized material can effectively trap the model soot particles in its open macroporous structure and oxidize the soot below 400 °C while completely removing NO in the 285–420 °C range. Surface characterization and DFT calculations emphasize the defective nature of Fe-doped ceria. The isolated Fe ions and associated oxygen vacancies catalyze facile NO reduction to N2. A mechanism for the reduction of NO with NH3 on Fe-doped ceria is proposed involving adsorbed O2. Such adsorbed O2 species will also contribute to the oxidation of soot

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

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