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 &gt;120 C, TOF per Rh atom at 120 C ~ 330 hr<sup>-1</sup>) 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.

Exploring the reactivity of single atom doped MxOy catalysts for NO reduction in TWC applications

ACS Fall 2021

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