Structural and Kinetic Study of the Reduction of CuO–CeO2/Al2O3 by Time-Resolved X-ray Diffraction

Abstract

The crystallographic structure of (11 wt.%)CuO–(6 wt.%)CeO2/γ-Al2O3 has been studied and compared with (11 wt.%)CuO/γ-Al2O3 under reducing conditions, using time-resolved in situ X-ray diffraction in the temperature range 25–800 °C. In CuO–CeO2/Al2O3, H2-TPR reduces the CuO phase to Cu, while in C3H8-TPR reduction follows a two-step pathway via Cu2O. A thermal treatment in He also induces reduction for CuO, albeit at higher temperature. In addition to CuO reduction, the CeO2 promoter in CuO–CeO2/Al2O3 is also partially reduced, without crystallographic transition, regardless of the atmosphere and at similar temperature where reduction of CuO occurs. Supported CuO as in CuO–CeO2/Al2O3 or CuO/Al2O3, is more readily reduced by thermal treatment in He than unsupported CuO and Cu2O. Moreover, the addition of CeO2 to the CuO–CeO2/Al2O3 catalyst allows for enhanced reducibility of CuO, compared to CuO/Al2O3. The CuO phase in CuO–CeO2/Al2O3 is reduced to Cu2O and partly to Cu at 700 °C and mainly to Cu at 800 °C in He flow. The thermal reduction of CuO–CeO2/Al2O3 requires an apparent activation energy of 216 kJ/mol. An isothermal reduction treatment at 800 oC in He reduces CuO–CeO2/Al2O3, as demonstrated by time-resolved in situ X-ray diffraction. Supported CuO are more easily reduced by thermal treatment compared to unsupported CuO and Cu2O. The CuO phase in CuO–CeO2/Al2O3 is reduced to Cu2O and partly to Cu at 700 °C and mainly to Cu at 800 °C in He flow (see figure)