Identification of Single Atom Ru/Ceria As a Stable and Superior Catalyst for Abatement of Diesel and Gasoline Engine Pollutants

Atomically dispersed transition metals (Ru, Pd and Pt) have been prepared on CeO₂ and evaluated for NOx/CO abatement applications for diesel and gasoline engines. Remarkably, atom trapping method allows to solve the previous issues of volatility with ruthenium atoms tightly anchored on ceria surface. 0.25-0.5 wt% Ru/CeO₂ catalysts (Ru is ~35 and ~7 times cheaper than commonly used Rh and Pd) show remarkable PNA performance, with 0.5 wt% Ru performing better than 1 wt% Pd/Zeolite and achieving 100% removal of NOx during vehicle cold start.

DFT calculations coupled with IR spectroscopy measurements precisely identify location of active isolated Ru⁺² cations on ceria. Upon NO adsorption, NO donates an electron to a Ce⁴⁺ center, thus NO⁺ ligand and a Ce³⁺ center are formed, while the formal charge of the Ru remains +2. FTIR measurements reveal the formation of remarkably stable Ru(II)(NO) complexes as well as spill-over of NO to CeO₂ surface via the Ru-O-Ce shuttle, explaining high NO storage. Notably, Ru/ceria survives hydrothermal aging in air/water vapor at 750 ⁰C without evaporation of atomically dispersed ruthenium, and as a consequence shows no loss of PNA capacity. NOx related applications of this new material are not constrained by it being a stable NOx storage materials: Ru/ceria is also a robust NO oxidation catalyst, considerably more active than Pt or Pd/CeO₂ and comparable to the best industrial catalysts based on more expensive Pd and Pt. Expanding the repertoire of Ru/CeO₂ catalytic applications, we further find 0.1 and 0.5 wt% Ru/CeO₂ to be excellent TWC catalysts, rivaling best single-atom Rh-containing uber-expensive supported materials. Our study pushes the frontier of precious metal atom economy for environmental catalysis from ultra-expensive Rh/Pd/Pt to more sustainable cheaper Ru and highlights the utility of single-atom catalysts for identifying previously unknown materials for industrially relevant applications.