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 degrees C while completely removing NO in the 285-420 degrees 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 N-2. A mechanism for the reduction of NO with NH3 on Fe-doped ceria is proposed involving adsorbed O-2. Such adsorbed O-2 species will also contribute to the oxidation of soot.