A highly reactive and enhanced thermal stability nanocomposite catalyst based on Au nanoparticles assembled in the inner surface of SiO₂ hollow nanotubes

A novel hollow tubular SiO₂-Au catalyst with a mesoporous structure (HTMS) was successfully fabricated by a combination of the sol-gel and calcination processes. This method involves the preparation of modified MWCNTs, the sequential deposition of Au and then silica layers through the sol-gel processes, and finally the calcination at the desired temperature to remove the MWCNTs. The obtained samples were characterized by several techniques, such as N₂ adsorption-desorption isotherms, transmission electron microscopy, energy-dispersive X-ray spectroscopy analysis, UV-Vis spectra, X-ray diffraction and Thermogravimetric Analysis (TGA). The results established that a different calcination temperature has an obvious influence on the morphology and structure of the final hollow tubular. When the temperature is 550 °C, the obtained materials exhibit the distinctly tubular structure because of the decomposition of MWCNTs and the preservation of hollow tubes. Furthermore, in the catalyst system, the mesoporous silica layer can act as the physical barrier to resist the agglomeration and sintering of Au nanoparticles even after being subjected to harsh treatments up to 650 °C. In our experiments, the catalytic activities of HTMS SiO₂-Au were investigated by photometrically monitoring the reduction of p-nitrophenol (p-NPh) by an excess of NaBH₄. It was found that the prepared HTMS SiO₂-Au catalysts exhibited a high catalytic activity and this sample could be easily recycled without a decrease of the catalytic activities in the reaction.