Active gold-ceria and gold-ceria/titania catalysts for CO oxidation: From single-crystal model catalysts to powder catalysts

CO oxidation was studied on model and powder catalysts of Au-CeO2 and Au-CeOx/TiO2. Phenomena observed in Au-CeO2(1 1 1) and Au-CeO2/TiO2(11 0) provided useful concepts for designing and preparing highly active and stable Au-CeOx/TiO2 powder catalysts for CO oxidation. Small particles of Au dispersed on CeO2(1 1 1) displayed high catalytic activity, making Au-CeO2(1 1 1) a better CO oxidation catalyst than Au-TiO2(11 0) or Au-MgO(1 00). An excellent support for gold was found after depositing nanoparticles of ceria on TiO2(1 1 0). The CeO, nanoparticles act as nucleation centers for gold, improving dispersion of the supported metal and helping in the creation of reaction sites efficient for the adsorption of CO and the dissociation of the O-2 molecule. High-surface area catalysts were prepared by depositing gold on ceria nanorods and CeOx/TiO2 powders. The samples were tested for the low-temperature (10-70 degrees C) oxygenrich (1%CO/4%O-2/He) CO oxidation reaction after pre-oxidation (20%O-2/He, 300 degrees C) and pre-reduction (5%H-2/He, 300 degrees C) treatments. Synchrotron-based operando X-ray diffraction (XRD) and X-ray absorption (XAS) spectroscopy were used to study the Au-CeO2 and Au-CeOx/TiO2 catalysts under reaction conditions. Our operando findings indicate that the most active phase of these catalysts for low-temperature CO oxidation consist of small particles of metallic Au dispersed on CeO2 or CeOx/TiO2. (C) 2014 Elsevier By. All rights reserved.