Synthesis and characterization of a novel Au nanocatalyst with increased thermal stability.

We report the synthesis of a new Au nanocatalyst with increased thermal stability. This catalyst system consisted of gold nanoparticles attached to functionalized TiO2/SiO2 core-shell nanocomposites, together with the encapsulation of mesoporous silica. The synthesis process mainly involved four steps, which included the synthesis of the TiO2/SiO2 core-shell composites, synthesis of the Au/TiO2/SiO2 particles, coating of Au/TiO2/SiO2 with silica, and etching the outer silica layer. TEM images were used to confirm the success of each of the synthesis steps, and both UV-vis adsorption spectra and the catalytic activity evaluation were employed to investigate the degree of re-exposure of Au nanoparticles after the etching treatment. In our experiments, the obtained mesoSiO2/Au/TiO2/SiO2 catalyst showed a superior thermal stability and higher activity for CO conversion compared to the mesoSiO2/Au/SiO2 one. It resisted sintering during the calcination at 500 °C, whereas the unprotected one was found to sinter. Moreover, it was found that on the mesoSiO2/Au/TiO2/SiO2 sample, the outside silica material could hinder the phase transformation of titania to some extent. Thus, small crystalline particles of TiO2 anchored on the silica beads of the core-shell composites, leading to a better dispersion of small Au nanoparticles and improved catalytic capacity to resist sintering.