Pushing the limits of precious metal atom economy for three-way-catalysts (TWC): thermally stable and highly active single Rh atom catalysts (Rh1/ceria)
Konstantin Khivantsev, Pacific Northwest National Laboratory
We show for the first time 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 (CO+NO) reaction but without the stability concern. In particular, thermally stable Rh cations in 0.1wt% Rh1/CeO2 achieve full NO conversion with a TOF of >300 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. 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. These findings provide new mechanistic understanding for the catalytically active species in TWC catalysis and open up a new avenue for the synthesis of novel emissions control catalysts.