Au/CeO2 觸媒的鑑定及水氣轉移反應上的應用

Abstract

The effect of Au/CeO2 pretreatment in CO, H2 or H2O atmosphere on the catalytic activity for water gas shift reaction (WGSR, a critical step in producing H2 from hydrocarbons) has been investigated. It was discovered that gold particle size is an essential property for gold catalytic activity. In order to determine the size of nano-particles of gold metal, the particle sizes were predicted by using plasmon band around 550 nm in UV-Vis spectra and by using the theoretical calculations in this research. The correlations of lmax (wavelength of maximum Plasmon band) and particle size were established. It is concluded that the higher lmax is measured, the larger gold particle size on the CeO2 surface should be. In addition, the higher absorbance is from the more reduced gold on the surface. The activities of catalysts were examined by using WGSR tests at 200 ℃, and by HRTEM for observing gold particles, diffuse reflectance UV-Vis spectroscopy for measuring nano-gold plasmon bands and average particle sizes, and diffuse reflectance infrared Fourier Transform spectroscopy (DRIFTS) for detecting surface adsorbates. It was found that different pretreatments caused considerable different reaction activity for WGSR, and the lowest activity was from the pretreatment in H2O at 200 ℃. The study of diffuse reflectance UV-Vis spectroscopy indicated that the reaction activities for WGS were strongly correlated to the wavelength of plasmon bands. The highest wavelength (red shift) from Au/CeO2 after pretreatment under H2O and after WGSR suggests that the lowest catalytic activity was due to the largest gold nano-particles on CeO2 surface. However, the particle growing of nano-gold was not at H2O pretreatment step; rather, it was after the injection of CO into the reactor for WGSR. DRIFTS studies indicated that the particle growing of gold species was induced by the formate species on CeO2. The most active Au/CeO2 was from the pretreatment in CO atmosphere before WGSR at 200℃.