Oxygen Vacancies in Reduced Rh/ and Pt/Ceria for Highly Selective and Reactive Reduction of NO into N2 in excess of O2

Abstract

Currently commercial NOx removal (DeNOx) abatement systems for lean-burn engines exceed regulation limits on the road for NOx emissions. Commercial DeNOx catalysts exhibit poor performance in the selective conversion of NO to N2, especially at high temperature and high gas hourly space velocities (GHSV). In this study, oxygen vacancies of reduced ceria and Pt/ or Rh/ceria are found to be the efficient and selective catalytic sites for NO reduction to N2. Even at low concentrations, NO can compete with an excess of O2 at 600 °C and a high GHSV of 170 000 L L−1 h−1, conditions in which SCR and NSR DeNOx system are not able to function well. N2O is not detected over the whole range of conditions, whereas NO2 is only formed upon oxidation of the catalyst, after both NO and O2 start to appear. For consideration of the fuel economy, the working temperature should be between 250 and 600 °C. Above 600 °C, most of the injected fuel was combusted with O2. Below 250 °C, ceria support will not be reduced by fuel and the oxidation rate of the deposited carbon through oxygen from ceria lattice will be too low.