Studies on Cu/CeO₂: a new NO reduction catalyst

Abstract

Fine particle and large surface area Cu/CeO₂ catalysts of crystallite sizes in the range of 100-200 Å synthesized by the solution combustion method have been investigated for NO reduction. Five percent Cu/CeO₂ catalyst shows nearly 100% conversion of NO by NH₃ below 300°C, whereas pure ceria and Zr, Y, and Ca doped ceria show 85-95% NO conversion above 600°C. Similarly NO reduction by CO has been observed over 5% Cu/CeO₂ with nearly 100% conversion below 300°C. Hydrocarbon (n-butane) oxidation by NO to CO₂, N₂, and H₂O has also been demonstrated over this catalyst below 350°C making Cu/CeO₂ a new NO reduction catalyst in the low temperature window of 150-350°C. Kinetics of NO reduction over 5% Cu/CeO₂ have also been investigated. The rate constants are in the range of 1.4×10⁴ to 2.3×10⁴ cm³ g^-1 s^-1 between 170 and 300°C. Cu/CeO₂ catalysts are characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and electron paramagnetic resonance spectroscopy where Cu²⁺ ions are shown to be dispersed on the CeO₂ surface.