Ce_1−xRu_xO_2−δ (x=0.05, 0.10): A New High Oxygen Storage Material and Pt, Pd-Free Three-Way Catalyst

Nanocrystalline Ce 1− x Ru x O 2−δ ( x =0.05 and 0.10) of 8−10 nm sizes have been synthesized by hydrothermal method using melamine as complexing agent. Compounds have been characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray analysis (EDX) and their structures have been refined by the Rietveld method. The compounds crystallize in fluorite structure and the composition is Ce 1− x Ru x O 2− x /2 where Ru is in +4 state and Ce is in mixed-valence (+3, +4) state. Substitution of Ru 4+ ion in CeO 2 activated the lattice oxygen. Ce 1− x Ru x O 2− x /2 reversibly releases 0.22[O] and 0.42[O] for x =0.05 and 0.10, respectively, which is higher than the maximum possible OSC of 0.22 [O] observed for Ce 0.50 Zr 0.50 O 2 . Utilization of Higher OSC of Ce 1− x Ru x O 2−δ ( x =0.05 and 0.10) is also reflected in terms of low-temperature CO oxidation with these catalysts, both in the presence and absence of feed oxygen. The Ru 4+ ion acts as an active center for reducing molecules (CO, hydrocarbon “HC”) and oxide ion vacancy acts as an active center for O 2 and NO, leading to low-temperature NO conversion to N 2 . Thus due to Ru 4+ ion, Ce 1− x Ru x O 2−δ is not just a high oxygen storage material but also shows high activity toward CO, hydrocarbon “HC” oxidation, and NO reduction by CO at low temperature with high N 2 selectivity for three-way catalysis.