Exploring the Reactivity of Single Atom Doped MxOy Catalysts for NO reduction in TWC Applications
Konstantin Khivantsev, Pacific Northwest National Laboratory
NO reduction with CO is a way to mitigate harmful nitric oxide emissions in gasoline engines. We recently  found that isolated Rh(I) ions on the ceria surface with low Rh loadings are catalytically active for low-temperature (NO+CO) reaction under dry and industrially relevant (wet) conditions. This provides a direct link between organometallic homogeneous Rh(I) complexes capable of catalyzing dry (CO+NO) reaction and supported Rh single atoms, the latter being much more active than their homogeneous analogues. Decreasing the Rh loading from 0.5 wt% to 0.1 wt% leads to a catalyst with uniform Rh ions on the surface of ceria, which is active (full NO conversion >120 C, TOF per Rh atom at 120 C ~ 330 hr-1) and stable. Because of the uniformity of Rh ions on the support, we are able to clarify the mechanistic aspects of this reaction. More specifically, we show that ammonia formation correlates with the WGS activity of the material and thus, rhodium hydride Rh-H species are believed to be involved in this reaction: we demonstrated that the CO/NO ratio is a parameter that controls ammonia formation rate .
Furthermore, we extend the TWC to other Ceria and Titania single-atom doped catalysts ,  and describe a library of structure-activity relationships for these materials. Our findings provide additional mechanistic understanding for the catalytically active species in TWC catalysis and open up a new avenue for the synthesis of industrially relevant emissions control catalysts with higher atom economy of expensive noble metals.
 (First published on Chemrxiv on April 7th, 2020) Pushing the Limits of Precious Metal Atom Economy for Three-Way-Catalysts (TWC): Thermally Stable and Highly Active Single Rh Atom Catalysts (Rh1/ceria) Under Both Dry and Industrially Relevant Conditions for NO Abatement, DOI: 10.26434/chemrxiv.12086004
 Identification of Ru/Ceria Among Single Atom Ceria Catalysts as a Stable and Superior Material for Abatement of Diesel and Gasoline Engine Pollutants, DOI: 10.26434/chemrxiv.12692264
 Ultra-Low Amounts of Palladium (0.005-0.05 Wt% Pd) Supported on Titania: Remarkable Low-Temperature Activity for NO Reduction with CO and Structure-Function Property Relationships in Methane Oxidation, DOI: 10.26434/chemrxiv.13489380