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

Currently commercial NO_x removal (DeNO_x) abatement systems for lean-burn engines exceed regulation limits on the road for NO_x emissions. Commercial DeNO_x 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 DeNO_x 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.