Identification of single Ru(II) ions on ceria as a highly active catalyst for abatement of NOx pollutants

Atom trapping allows to prepare catalysts with atomically dispersed Ru ions anchored to the ceria support. The resulting catalysts free of expensive noble metals such as Pt, Pd, Rh (whose prices are ~8-60 times higher than Ru on the per-molar basis) with Ru loadings of only 0.25-0.5 wt% show excellent activity in industrially important catalytic NO oxidation reaction, a critical step that requires use of relatively large loadings of expensive noble metals in diesel aftertreatment systems. Ru1/CeO2 catalysts are stable during continuous cycling, ramping and cooling as well as presence of moisture. Furthermore, Ru1/CeO2 shows excellent NOx storage properties during cold start, with improved NO adsorption compared with the best described Pd/Zeolite NO adsorbers with ~2-3 times higher Pd loadings. We clarify the location of Ru(II) ions on the ceria surface and identify mechanism of NO oxidation (as well as reactive storage) using DFT calculations and in-situ DRIFTS/Mass-spectroscopy measurements. Furthermore, we show the possible applications of Ru1/CeO2 in gasoline engines for NO reduction by CO: only 0.1 wt% of atomically dispersed Ru is sufficient to achieve high activity at low temperatures. With the aid of excitation-modulation in-situ infra-red measurements, we uncover the elementary steps of NO reduction by CO on an atomically dispersed ceria-supported catalyst. Our study highlights the potential applicability of single-atom catalysts to industrially relevant NO and CO abatement.