Au/Rutile Catalysts: Gold Crystallites Transformation in Time at Room Temperature

ABSTRACT

Quantitative analysis of Au/Rutile catalysts with X-ray powder diffraction showed that gold crystallites got transformed, in time, at room temperature. In this experiment, after aging the catalysts for two days, the morphology of the gold crystallites changed from a cubotahedron into a cube. This diminished the activity of the catalysts for catalyzing the oxidation of CO at temperatures below 200 ºC. On the other hand, after 5 days, the catalysts got inactivated at these temperatures. The catalyst activity correlated strongly with the gold crystallite morphology as well as its dimensions and its lattice deformations. The quantitative analysis of the catalysts suggested that the most active catalysts in the present work had gold crystallites with the morphology of a cuboctahedron with the magic number 309, and that the observed changes in the catalytic activity could be caused by defects at the boundary between the Au(100) and the Au(111) surfaces of the gold crystallites. These defects could be caused by the atomic reconstruction of the surfaces, produced by the relativistic effects on the 6s and the 5d electrons in gold atoms.

Keywords:

Gold catalyst, Rutile, aging with time, Rietveld refinement, crystallite growing, Oxidation of CO, gold crystallite magic number, crystallite surface reconstruction.