Effect of chlorine on TPR and TPO behavior of an YSZ/gamma-Al2O3 supported copper oxide catalyst

Yttria-stabilized zirconia (YSZ) was deposited on gamma-alumina using a co-impregnation method and then copper oxide was supported on it. The CuO/YSZ/gamma-alumina catalysts were characterized by TPR (temperature-programmed reduction), TPO (temperature-programmed oxidation) and X-ray diffraction (XRD). The bulk-like copper oxide can exhibit a two-step reduction (i.e., Cu2+ --> Cu+ --> Cu-0), while isolated Cu2+ ions cannot. This has been attributed to a ''long-range'' electronic effect caused by the strong electronegativity of chlorine, which comes from the decomposition of the YSZ precursors. An experiment employing chlorine-containing CuO/gamma-alumina catalysts, of which the chlorine content was controlled by adding HCl to the impregnating solution, has confirmed that the two-step reduction behavior is caused by the chlorine. In addition, it was found that the residual chlorine not only improves the dispersion of supported copper oxide but also enhances the oxidizability of the reduced copper.