The Influence of the TiO2 Structure on the Formation of Gold Nanoparticles

Abstract

Supported gold nanoparticles have been of interest in the catalytic industry for decades since Au particles (< 5 nm) supported on metal oxides exhibit a high catalytic activity under mild or even ambient conditions for catalytic reactions such as CO oxidation. Yet, the exact formation of gold nanoparticles on support material remains unclear. In this thesis the influence of titania supports, with distinctive crystal structures, internal pore-structure and porosity including specific surface areas, on the formation of gold nanoparticles is investigated. Titania structures were successfully synthesized by using modified sol-gel procedures based on methods from literature. First, supports with both a pure rutile and anatase crystal structure, as well as an amorphous phase are investigated. Additionally, the commercially available Degussa P25, containing a mix of the anatase and rutile crystal structure is used as a support. Furthermore, in order to investigate the influence of the support porosity and surface area, three titania aerogels containing a range of low, intermediate and high surface area are used. At last, two mesoporous titania supports with an ordered and disordered internal pore-structure are investigated. The gold loading on these titania supports is carried out with ion-adsorption of a cationic gold precursor. The results indicated that the specific crystal structure of the support is an important factor in the formation of gold nanoparticles. Moreover, gold deposited on titania aerogels containing a low, intermediate and high surface area resulted in a few striking differences, including differently shaped gold particles on the low surface area aerogel, and more similar size distributions on the intermediate and high surface area aerogels. At last, the organization of the internal pore-structure did not significantly influence the gold nanoparticles, since a similar gold particle size distribution was observed on both titania structures. Thus, the crystal structure of titania supports influences the formation of gold nanoparticles, while the organization of the internal pore-structure is not of significant influence. Further, titania aerogels containing a low porosity and surface area contain differently shaped gold nanoparticles compared to aerogels with higher porosities and surface areas.