Gold Particle Size Determination on Au/TiO_2-CeO_2 Catalysts by Means of Carbon Monoxide, Hydrogen Chemisorption and Transmission Electron Microscopy

摘要

Au/TiO_2 and Au/TiO_2-CeO_2 catalysts were prepared by the sol-gel method and carbon monoxide, hydrogen chemisorption and TEM spectroscopy have been exploited to determine the size of gold particles. The gold nanoparticles (8.1 to 2.1 nm) were deposited by using the deposition-precipitation method. The XRD characterization shows the presence of anatase as the TiO_2 crystalline phase; while by XPS spectroscopy, the presence of Au°, Au_2O_3, Ce~(3+) and Ce~(4+) species co-existing in the Au/TiO_2-CeO_2 catalysts is shown. The characterizations by TPD-CO as well as by TPD-H_2 (temperature programmed desorption) showed that on catalysts containing cerium, the gold particle size can be determined with great accuracy by using these chemisorption methods. The gold particle size calculated from either the CO or H_2 thermodesorption values is in good agreement with that obtained by High Resolution Transmission Electron Microscopy (HRTEM) and Scanning Transmission Electron Microscopy (STEM) analyses. It was proposed that the TPD-CO and/or TPD-H_2 techniques could be helpful for the characterization of the gold particles by TEM; especially when the high contrast in the pictures of the supports containing CeO_2 prevents the particle size from being determined.