Ice TemplatingAn Alternative Technology to Produce Micromonoliths

Hierarchical ceramics with porosities defined at multiple length scales are of particular interest as catalyst support materials. In fixed-bed reactors, catalytically active particles or porous pellets are packed in the reactor. A combination of high specific surface area, accessibility to the active sites and mechanical strength is therefore required and yet difficult to achieve. This problem is tackled using the ice templating process. Two approaches are investigated to obtain micromonoliths combining macro- and mesoporosities. Ice templating of boehmite suspensions provides materials with macropores ranging from 10 to 26?mu m and mesopores from 3.6 to 6.2?nm throughout the entire volume of the sample. Total porosity of the samples ranges from 70 to 98%, and specific surface areas from 170 to 300?m2?g-1 can be reached. The mesopore characteristics can be adapted by modifying the particle size and the freezing rate. However the mechanical properties are not sufficient for application as catalyst carriers. An alternative method based on wash-coating a mechanically resistant ice templated monolith is described. These monoliths have 64% porosity and straight, continuous, 4.5?mu m diameter channels. Uniform 100 to 200?nm thick coatings, with a 360?m?g-1 specific surface are deposited without altering the initial mechanical strength of the monolith: 134?+/-?30?MPa. We expect such architectures, combining high specific surface area, low pressure drop, and high mechanical strength, to be of special interest as catalyst carriers.