Catalytic reduction of NO with H₂ over redox-cycling Fe on CeO₂

Removal of NO_x species from automotive emissions continues to be a challenge, particularly using replacements for Pt-group metals. Here, we demonstrate the synthesis of FeO_x domains on CeO₂ from the precursor Fe ethylenediaminetetraacetate (NaFeEDTA) and its utility in the reduction of NO with H₂ as a model reaction for tailpipe emissions. Diffuse-reflectance UV-visible and X-ray absorption near-edge spectroscopies indicate the formation of small, non-crystalline FeO_x domains. Using the EDTA precursor, TPR and in situ XANES show that up to 45% of the FeO_x centers were capable of undergoing redox cycles in H₂ up to 550°C, whereas only 23% of FeO_x centers derived from Fe(NO₃)₃ were redox active. Similarly, at comparable Fe surface densities, the FeEDTA-derived catalysts were more active than the nitrate-derived materials in the reduction of NO to N₂ (85-95% selectivity) with H₂ at 450°C. The presence of both the bulky organic ligand and the alkali is essential for the observed enhancements in fraction redox active and to achieve high NO reduction rates. Rates over all materials were fit to a single correlation against the number of redox-active FeO_x centers, suggesting that these are the catalytic active sites. The new materials describe here may offer new avenues for emissions control without Pt-group metals or substituted zeolites.