Oxygen storage and release behavior of delafossite-type CuFe_1−x Al _x O₂

Delafossite-type solid solution, CuFe_1−x Al _x O₂, was synthesized and its oxygen storage capacity (OSC) was investigated under oxidation/reduction cycle using a pulse injection method. CuFe_1−x Al _x O₂ was synthesized by heating at 1100–1150 °C in N₂ flow. OSC values for x = 0.1 and 0.3 were larger than that for x = 0 above 500 °C, indicating that substitution of Fe³⁺ by Al³⁺ improved OSC. For x = 0.5–1.0, temperature at which OSC increased steeply shifted upward. Results of X-ray diffraction (XRD) after the thermogravimetry and differential thermal analysis (TG–DTA) measurement in air for CuFe_1−x Al _x O₂ (x = 0–0.7) indicated that oxidative decomposition of delafossite phases to CuO and spinel-type phase occurred. In addition, Cu reduction temperature estimated by the temperature programmed reduction using H₂ (H₂-TPR) shifted to higher temperature with increasing Al content. The XRD results of the samples after H₂ and O₂/He pulse injection suggested that the oxygen storage/release behavior was caused by reversible oxidation/reduction process between CuFe_1−x Al _x O₂ delafossite and (Fe_1−x Al _x )₃O₄ spinel phase +Cu.