Morphology-Dependent Evolutions of Sizes, Structures, and Catalytic Activity of Au Nanoparticles on Anatase TiO₂ Nanocrystals

Au nanoparticles with different loadings were prepared on anatase TiO₂ nanocrystals with various morphologies predominantly exposing {001} facets (denoted as TiO₂{001}), {100} facets (denoted as TiO₂{100}) and {101} facets (denoted as TiO₂{001}) by the deposition-precipitation method. Sizes, structures, and catalytic activity in lowerature CO oxidation of the resulting Au/TiO₂ catalysts were comprehensively characterized. Nucleation, growth, and agglomeration of Au particles on TiO₂ supports were observed to depend on TiO₂ morphologies due to the morphology-dependent defect structures of TiO₂ nanocrystals and subsequent Au-TiO₂ interactions. Au particles mainly homogeneously nucleate and grow on these three TiO₂ nanocrystals with Au loadings of 0.2-1%. With the increase in Au loadings to 2 and 5%, Au particles mainly agglomerate on TiO₂{001}, mainly homogeneously nucleate and grow on TiO₂{100}, and both nucleate and grow and slightly agglomerate on TiO₂{101}. The electronic effect of supported Au particles on CO adsorption was observed, in which fine Au nanoparticles with electronic structures deviating from that of bulk Au exhibit a decreased adsorption capacity of CO. Meanwhile, fine Au nanoparticles are less able to activate surface lattice oxygen at the Au-TiO₂ perimeters than large Au nanoparticles and exhibit a lowered intrinsic catalytic activity in lowerature CO oxidation. These results nicely exemplify morphology-dependent metal-oxide interactions and catalysis.