Mesoporous silica supports for improved thermal stability in supported Au catalysts

In this work, we present a comprehensive review of our research on the role of mesoporous silica pore architecture, composition of the pore walls (addition of Co or Al), and silica surface chemistry (surface modification by TiO2) to improve the hydrothermal stability of Au particles. We have found that mesoporous silica architecture plays an important role in improving Au stability, with three dimensional mesoporous architectures being less effective than one dimensional (1-D) pores. The tortuous 1-D pores in aerosol silica were found to be most effective at controlling Au particle size. Since An particles continue to grow larger than the pore diameter, we conclude that Ostwald ripening must be the dominant sintering pathway for these Au catalysts. These catalysts are active for CO oxidation even after the An particles have grown large enough to block the pores, suggesting that the thin walls of mesoporous silica provide easy access to gas phase molecules. Further improvements in Au stability and reactivity were obtained by surface modification of the aerosol and MCM-41 silica with TiO2. After TiO2 modification of the silica, the An particles remained smaller than the pore size (<3 nm) even after three cycles of CO oxidation at temperatures up to 400 degrees C.