Optical properties and electronic interactions of microcrystalline copper/zinc oxide (Cu/ZnO) catalysts

Diffuse reflectance spectra of the microcrystalline Cu/ZnO solids provide evidence for interactions between an x-ray amorphous or solute form of copper and the ZnO wurtzite crystals. These interactions result in the emergence of a new absorption band at 17,500 cm/sup -1/ and the simultaneous spectral disappearance of the 25,800-cm/sup -1/ fundamental absorption edge of zinc oxide. This behavior is most pronounced when the copper concentration in the zinc oxide phase reaches the saturation value of 17 +- 1%. The copper solution in the zinc oxide is a highly degenerate semiconductor with a strong light absorption intensity in the visible region of the spectrum. A comparison with earlier observations of methanol synthesis activity of the Cu/ZnO catalysts shows that specimens containing a maximum amount of copper dissolved in the zinc oxide are also the best catalysts for methanol synthesis.