(6e) Thermally Stable and Highly Active Single Rh Atom Catalysts (Rh1/ceria) for NO Reduction

We found that atomically dispersed Rh cations on ceria, prepared via high-temperature atom trapping synthesis, are the active species for (CO+NO) reaction. This provides a direct link with the organometallic homogeneous Rh(I) complexes capable of catalyzing dry (CO+NO) reaction but without the stability concern. In particular, thermally stable Rh cations in 0.1wt% Rh₁/CeO₂ achieve full NO conversion at ~120 ⁰C with a TOF of ~ 330 hr^-1 per Rh atom at 120 ⁰C. Under dry conditions, the main product above 100 ⁰C is N₂ with N₂O being the minor product. The presence of water promotes low-temperature activity of 0.1wt% Rh₁/CeO₂ starting at 50 ⁰C with full NO conversion at ~120 ⁰C. In the case with the wet stream, however, ammonia and nitrogen are the main products with only minor N₂O amounts. We further 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.