Ruthenium-based catalysts for NOx reduction in the EGR leg of a D-EGR engine
A Ru/Al₂O₃ coated cordierite monolith was investigated for selective catalytic reduction (SCR) of NOx to N₂ using various synthetic exhaust gas mixtures. It was found that Ru is an ineffective SCR catalyst in lean mixtures due to a propensity to promote oxidation reactions upon conversion to RuO₂, but is capable of SCR under appropriate rich conditions. A potential application of Ru-based SCR was identified and investigated. By implementation in the exhaust gas recirculation (EGR) leg of a dedicated-EGR (D-EGR) engine, a ruthenium catalyst can eliminate recirculated NOx, thereby reducing the knock propensity of the engine. The D-EGR cylinder is operated rich of stoichiometry to produce H₂ and CO, which can then serve as the reductant for SCR. A detailed investigation was conducted to determine Ru/Al₂O₃ activity when exposed to conditions found in the EGR leg. Light-off inhibitors and promoters present in the gas mixture were identified. Also, the use of alternate support materials was investigated to assist in further reducing light-off temperatures. The ruthenium catalysts were prepared using two different methods to determine if the catalyst synthesis method influenced light-off temperatures. It was found that the conditions present in the EGR leg are amenable to Ru-based SCR with a high selectivity and conversion efficiency. Additionally, ruthenium based SCR may find applications in other fuel-rich applications.