Fe-Modified CuNi Alloy Catalyst as a Nonprecious Metal Catalyst for Three-Way Catalysis

In this study, we explored the feasibility of using base metal catalysts for three-way catalysis. The catalysts contain up to three base metals that were chosen to replace or reduce use of platinum group metals (Rh, Pd, and Pt). The aim was to develop catalysts with high activities at low temperatures having robustness against oxygen concentration fluctuations. Various base metal catalysts supported on alumina [10 wt % X/Al₂O₃ (X = Fe, Co, Ni, or Cu), 10 wt % CuY/Al₂O₃ (Y = Mn, Fe, Co, or Ni; Cu/Y = 1:1 in atomic ratio), and 10 wt % CuNi–5 wt % Z/Al₂O₃ (Z = Mn, Fe, or Co; Cu/Ni = 1:1 in atomic ratio)] were tested by temperature-programmed reaction in NO–CO–C₃H₆–O₂ flow and under fluctuating oxygen concentration conditions. We found that the rate of reduction of NO over the 10 wt % CuNi–5 wt % Fe/Al₂O₃ catalyst in the low-temperature region was comparable to that of 1 wt % Pt/Al₂O₃, and this catalyst was also tolerant to oxidative conditions to some extent. Ex situ characterization of the catalysts before and after the three-way catalytic reaction was carried out via powder X-ray diffraction, X-ray absorption spectroscopy, scanning transmission electron microscopy with an energy-dispersive X-ray spectrometer, and in situ diffuse reflectance infrared Fourier transform measurements and revealed that the presence of Fe species resulted in the significantly improved oxidation of C₃H₆ and, thus, an increased rate of reduction of NO.