Hierarchically organized pore architectures

As already mentioned, first attempts have been made to prepare binary oxide zeolitic structures with a combination of pore sizes, for example, micro- and mesopores to enhance diffusion within the material. In addition to the templating approaches in which hard or soft objects/molecules/aggregates are applied, phase separation as already seen in the Vycor process plays an important role, especially in the formation of the macroporous structure. In this section, we will 

Open macroporus network, with pores 50 nm diameter 

IR-ATR, UV/vis, XPS, and XAFS measurements led to the conclusion that up to a Si Ti ratio of 35 1, well-dispersed titanium centers in a macro/mesoporous Si02 network with a specific surface area up to 582 m and mainly fourfold coordinated Ti centers have been obtained. An increase of the Ti content resulted in a decrease of the specific surface area, as well as a loss of the cellular character of the macroporous network and an increasing content of Ti in octahedral coordination. With the Si Ti ratio of 1 1, silica-titania powders with 100 m g and anatase domains within the Si02 matrix were obtained. 

9 Rodriguez Avendafio, R., De Los Reyes, J., Viveros, T and Montoya De La Fuente, J. 

18 Bordlga, S., Bonlno, F., Damin, A., and Lamberti, C. (2007) Phys. Chem. Chem. Phys., 9,4854. 

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