Structural Investigation of Au Catalysts on TiO2−SiO2 Supports: Nature of the Local Structure of Ti and Au Atoms by EXAFS and XANES

X-ray absorption spectroscopy (XAS) was utilized to investigate both the Au particle size on several supports composed by silica and titanium oxide, and the coordination of TiO2 in the support phase. Particularly, we wanted to utilize the technique to probe mixing in the support phase, by using different synthetic methods such as by functionalizing silica or by ALD (atomic layer deposition) techniques as prepared in our laboratories, and the growth and stability of Au nanoparticles deposited on these supports. The study using cosynthesis techniques to dope bulk mesoporous SiO2 with TiO2 resulted in TiO2 being dispersed in the SiO2 matrix; however, a second phase starts forming as the TiO2 content increases as indicated by the EXAFS Ti−O shell shift in position and increase of coordination number. On the supports prepared by cosynthesis, Au particles were smaller and more stable. The study using the surface sol−gel technique for deposition of single monolayers of an oxide such as TiO2 produced Ti environme...