Structure and surface characteristics of Cu-based composite metal oxides derived from layered double hydroxides

Abstract

Layered double hydroxides (LDHs) with Cu 2+/Zn 2+/Al 3+ atomic ratios from 1:1:1 to 3:1:1 have been synthesized by coprecipitation method. The physicochemical properties of both the as-synthesized LDHs and their calcined products obtained at 773 K for 3 h have been characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), chemical analysis, transmission electron microscopy (TEM), scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS), N 2 adsorption–desorption experiments and thermogravimetric analysis (TGA). The chemical states of metal species on the surface of the calcined LDHs were also characterized by temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). The results indicate that Cu 2+/Zn 2+/Al 3+ atomic ratio in the synthesis mixtures influences crystallinity, purity, and thermal stability of the LDHs, and hence, the composition of the resulting calcined LDHs. At room temperature and atmospheric pressure, oxidation of aqueous phenol solutions by hydrogen peroxide in the presence of the calcined LDHs was carried out. The results show that the calcined LDHs with the Cu 2+/Zn 2+/Al 3+ atomic ratio of 1:1:1 has the highest catalytic activity for conversion of phenol, which may be related to the formation of a great amount of composite metal oxide containing Cu 2+ ions and to good dispersion property of active Cu 2+ centers present on the surface.