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.