Crystallite size and morphology of the phases in Au/TiO2 and Au/Ce-TiO2 catalysts

Au/TiO2 and Au/Ce-TiO2 catalysts with 5 wt % An and 12 wt % cerium were prepared with the sol gel technique, and characterized using X-ray powder diffraction and transmission electron microscopy. The crystallography, crystallite size, and morphology of all of the phases in the catalysts, including the metallic gold phase, were obtained by refining the crystalline structures with the Rietveld method. The gold crystallite size and morphology, which was based on truncated cuboctahedra, depended on the titania polymorph used as the support: when the support was anatase the gold crystallites had their smallest dimension (1 nm) perpendicular to the (111) planes of gold's crystalline structure, whereas for brookite and rutile this dimension (1.73 for brookite and 1.54 for rutile) was perpendicular to the (200) planes. The large amount of structural defects of the support served as particle pinning centers of the gold crystallites, hindering the diffusion that produces larger crystallites. From the refinement, the contribution of the metallic gold to the X-ray diffraction pattern of the catalyst was extracted. Cerium doping decreased anatase and brookite crystallite size and increased the number of structural defects because cerium atoms incorporated into their crystalline structures.