Generally, the performance of such materials can be maximized by keeping the lengths of the diffusion paths, which lead substances from the outer surface of the material to such active sites, as short as possible. As porous materials are generally synthesized in the form of particles, the lengths of the diffusion paths in them can be shortened by simply reducing the size of the particle itself. However, small particles cause a severe resistance to flows, therefore this method does not always lead to the improvement of the performance of the material. In fact, particles with fairly large sizes are usually used in industrial applications only to avoid significant resistance to flows. This indicates that there are many cases that the performance of such materials can be further improved, if such materials can be synthesized to have a structure in which short diffusion paths and low resistance to flows are compatible.
A monolithic microhoneycomb which has straight and axially aligned micrometer-sized channels within it may be an ideal structure, if the walls which form the channels are thin enough. It was thought to be quite difficult to obtain porous materials with such a structure through conventional synthesis methods, but recently we found that porous materials attainable through the sol-gel method can be molded into a monolithic microhoneycomb just by freezing their parent hydrosol or hydrogel unidirectionally. As ice crystals which grow within the precursor during freezing act as the template, we named this method the “Ice Template Method.”
We also found that this method can also be applied to hydrogels including fine particles. The materials obtained through this process have a monolithic microhoneycomb structure and can be regarded as a monolithic column of the fine particles, in which the gel acts as the binder.
In this presentation, results of the attempt to synthesize a zeolite column with a monolithic microhoneycomb structure by applying the newly developed ice template method to silica hydrogels including zeolite fine particles will be reported.