On the formation and accessibility of gold nanoparticles confined in SBA-15 mesoporous molecular sieve

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Mesoporous molecular sieves containing metal nanoparticles inside their pores have been lately studied as promising oxidation catalysts. Articles usually claim that confined particles are less prone to sintering and metal leaching. Furthermore, the pores limit nanoparticle growth during the process of preparation of the catalyst. In this work, we addressed some questions that are still to be answered, such as: how are the metal nanoparticles formed within the pores? Are these particles accessible to the organic molecules in catalytic reactions? For this purpose, SBA-15 samples containing Au nanoparticles were prepared and characterized. FTIR, TG/MS, XRD and XPS gave some insights on the formation of Au nanoparticles, while N-2 adsorption and SAXS were useful to address the accessibility question. It was observed that Au-SBA-15, in spite of having a pore size distribution similar of that of SBA-15, has a lower pore volume and half of the surface area. SAXS experimental data was interpreted with the aid of a theoretical model, and it was possible to demonstrate that the presence of metal induced changes on the lattice parameter and pore dimensions of SBA-15. The results strongly indicate that the pores were filled. TEM images reveal the presence of very small Au nanoparticles inside the pores of the material, and also larger particles on its external walls. Au-SBA-15 is thus a material that is very dissimilar from its precursor, pure-silica SBA-15, and so its adsorption properties must be carefully evaluated. (c) 2015 Elsevier Inc. All rights reserved.Mesoporous molecular sieves containing metal nanoparticles inside their pores have been lately studied as promising oxidation catalysts. Articles usually claim that confined particles are less prone to sintering and metal leaching. Furthermore, the pores2108693Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAPESP [2011/12521-0, 2013/11298-0