When preparing gold(Au) supported on NiO catalysts by the coprecipitation method, the chemical state of the coprecipitated Au differed when Na2CO3 and NaOH were used as the coprecipitating reagents. In this preparation using Na2CO3 and NaOH solutions, precursor of support metal was largely NiCO3 and Ni(OH)2, respectively. Therefore, the different chemical states of Au may be controlled by the interaction between the [Au(OH)4]− and precursor of support metal. The aim of this study is to elucidate why the chemical state of Au differs when using NiCO3 and Ni(OH)2. Adsorption experiments of [Au(OH)4]− onto NiCO3 or Ni(OH)2 were performed. The Au concentration in the filtrate was determined by atomic absorption spectrometry (AAS). The chemical state of the adsorbed Au was examined by X-ray absorption(XA) spectroscopy. The adsorption experiments suggested that the change in surface charge on NiCO3 and Ni(OH)2 electrostatically controls the adsorption of [Au(OH)4]−. The XA analysis indicated that the chemical state of [Au(OH)4]− adsorbed on NiCO3 is maintained because of electrostatic interactions, while some of the [Au(OH)4]− adsorbed on Ni(OH)2 may be reduced to Au(0) due to specific adsorption-accompanying distortion of the square planar structure of the adsorbed [Au(OH)4]−.
|ジャーナル||Colloids and Surfaces A: Physicochemical and Engineering Aspects|
|出版ステータス||出版済み - 1月 20 2018|
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