Gold Nanoparticles on Yttrium Modified Titania: Support Properties and Catalytic Activity

Abstract

A series of titanium oxide catalysts modified with yttrium has been prepared by sol-gel method and their structural properties have been studied. The incorporation of yttrium in the titania lattice favors the formation of oxygen vacancies while at low Y loadings the anatase structure is preserved. The catalytic activity of these solids for CO oxidation is found to be significantly dependent on their physical properties. In particular the amount of dopant controls the number of surface oxygen vacancies created as well as the gold particle size, which directly affects the catalytic activity. Also, a linear relationship between the catalytic activity and the band gap values, which depend on the Y loading, is observed. Density functional theory based calculations show that Y atoms are incorporated at the TiO 2 surface at substitutional positions only, while the preferred oxygen vacancies arise by removing the bridge surface oxygen atoms. These O-vacancies are the preferential adsorption sites for Au atoms and nanoparticles, acting as nucleation centers that favor the dispersion of the catalyst active phase over the support surface. In agreement with experiment, Y doping is found to decrease the band gap of the support due to a destabilization of the valence band of the oxide.

Oxidation of CO over gold supported on Zn-modified ceria catalysts

“…Therefore, oxygen vacancies, as demonstrated for other systems [15,18,40,41], act as preferential structural positions for the nucleation of gold nanoparticles on CeO 2 and CeZn10 oxides. The number of surface oxygen vacancies is higher in the Zn-modified support as stated above, accordingly, FESEM micrographs of the gold catalysts ( figure 8) show that the number of gold nanoparticles with diameters between 4 and 19 nm is smaller for the Au/CeZn10 catalyst.…”

Au/CeO2 Catalysts: Structure and CO Oxidation Activity

“…Moreover, this reversible transformation is strongly affected by the hydroxylation of the reducible oxide surface that, at high temperatures, is involved in the re-oxidation of the cerium sites in a mechanism that implies the competition of hydroxyl groups and gold atoms for oxygen surface vacancies [25]. DFT calculations of the role of water on CO oxidation over Au/TiO2 catalysts support this H2O-Au competition for surface oxygen vacancies [12,18]. Consequently, the catalytic performance of this sort of material during the oxidation reactions is closely related to the interaction between gold and these punctual defects.…”

Tuning the charge state of Ag and Au atoms and clusters deposited on oxide surfaces by doping: a DFT study of the adsorption properties of nitrogen- and niobium-doped TiO2and ZrO2

“…Also the magnetic moment on the substrates is always 0.00 µ B , except for the subsurface vacancies in titania, Table 3. 79 This difference is most likely due to the slightly different model and the different treatment of vdW-forces. 9 (a-c), the tetramers take less flat configurations on titania than the silver tetramers.…”