Determining the Ce\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e2\u3c/sub\u3eS-CeO\u3csub\u3ex\u3c/sub\u3e Phase Boundary for Conditions Relevant to Adsorption and Catalysis

The interaction of sulfur with ceria under highly reducing conditions was investigated. The phase boundary between CeO1.83 and Ce2O2S was determined for temperatures between 873 and 1073 K. This data was used to derive an empirical equation for ΔGfº of Ce2O2S in this temperature range. This equation along with thermodynamic data for cerium oxides and sulfides obtained form the literature was used to predict Ce-O-S phase diagrams at 873 and 973 K. These phase diagrams provide insight into the mechanism of the deactivation of ceria-based catalysts by sulfur under reducing conditions

TPD and XPS Investigation of the Interaction of SO\u3csub\u3e2\u3c/sub\u3e with Model Ceria Catalysts

The interaction of SO2 with model thin film ceria catalysts was studied using temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). During TPD of ceria samples that had been exposed to SO2 at room temperature, SO2 desorbed in peaks centered at 473, 883 and 963 K. The lower temperature peak is associated with molecularly adsorbed SO2, while the higher temperature peaks are due to decomposition of adsorbed sulfates. XPS results show that at room temperature a small fraction of the adsorbed SO2 is oxidized to SO42- using oxygen supplied by the ceria. This reaction also results in partial reduction of the ceria surface. High coverages of surface sulfate species could be produced by exposing the ceria samples to mixtures of SO2 and O2 at 573 K. In addition to producing gaseous SO2, thermal decomposition of surface sulfates at temperatures above 823 K resulted in the formation of an oxy-sulfide (Ce2O2S) on the ceria surface

Structure and Thermal Stability of Ceria Films Supported on YSZ(100) and α-Al\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e(0001)

The morphology and reducibility of vapor-deposited ceria films supported on yttria-stabilized zirconia (100) (YSZ(100)) and α-Al2O3(0001) single crystals were studied using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The results of this study show that the gas environment has a significant effect on the structure of the ceria films on both substrates. CeO2 films on α-Al2O3(0001) were found to be stable in a reducing environment at temperatures up to 1000K, but underwent agglomeration and reaction with the support to form CeAlO3 upon annealing at 1273 K in air. Heating CeO2/YSZ(100) in air at 1273 K caused the ceria thin film to agglomerate into bar-shaped features which were re-dispersed by subsequent annealing in vacuum. Interactions at the CeO2-YSZ interface were also found to dramatically enhance the reducibility of ceria films supported on YSZ(100)

Determining the Ce 2 O 2 S-CeO x Phase Boundary for Conditions Relevant to Adsorption and Catalysis Determining the Ce 2 O 2 S-CeO x Phase Boundary for Conditions Relevant to Adsorption and Catalysis Determining the Ce 2 O 2 S-CeO x Phase Boundary for Con

Abstract The interaction of sulfur with ceria under highly reducing conditions was investigated. The phase boundary between CeO 1.83 and Ce 2 O 2 S was determined for temperatures between 873 and 1073 K. This data was used to derive an empirical equation for ΔG f º of Ce 2 O 2 S in this temperature range. This equation along with thermodynamic data for cerium oxides and sulfides obtained form the literature was used to predict Ce-O-S phase diagrams at 873 and 973 K. These phase diagrams provide insight into the mechanism of the deactivation of ceria-based catalysts by sulfur under reducing conditions