Microporous layer preparation materials

Other kinds of mesoporous manganese based materials have been also reported by transformation of layered bimessite (18). Finally amorphous microporous manganese oxidic materials prepared by the reaction between KMn04 and oxalic acid and incorporation of hetero-cations like Cu, Cr and Zn in them have been recently prepared and tested as catalysts (19, 20). 

Asymmetric phase-inversion membranes like the membranes employed in reverse osmosis are difficult to prepare as gas permeation is much more sensitive to micropores than RO due to the much higher diffusion coefficients of gases. For the same reason, the composite membrane differs from RO composite membranes in gas permeation, the top layer of the asymmetric support structure is responsible for the separation while it is the sole duty of the coating to plug the micropores. Consequently, the material of the coating chosen (silicone) has a high permeability but a low selectivity while the membrane material (poly-sulfone) has a high selectivity (and a much lower permeability). 

De La Iglesia, O., Irusta, S., Mallada, R., Menendez, M., Coronas, J., Santamaria, J. (2006). Preparation and characterization of two-layered mordenite-ZSM-5 bi-functional membranes. Microporous and Mesoporous Materials, 93, 318—324. 

A novel super-microporous layered material, silica-pillared niobic acid, was prepared by a guest-exchange route. This pillard material was found to be an acid catalyst for the vapor-phase Beckmann rearrangement of 5 to 6 in 1-hexanol, which exhibited a 100% conversion of the oxime with a selectivity of lactam above 85% at 340 °C. ... 

For the detailed study of reaction-transport interactions in the porous catalytic layer, the spatially 3D model computer-reconstructed washcoat section can be employed (Koci et al., 2006, 2007a). The structure of porous catalyst support is controlled in the course of washcoat preparation on two levels (i) the level of macropores, influenced by mixing of wet supporting material particles with different sizes followed by specific thermal treatment and (ii) the level of meso-/ micropores, determined by the internal nanostructure of the used materials (e.g. alumina, zeolites) and sizes of noble metal crystallites. Information about the porous structure (pore size distribution, typical sizes of particles, etc.) on the micro- and nanoscale levels can be obtained from scanning electron microscopy (SEM), transmission electron microscopy ( ), or other high-resolution imaging techniques in combination with mercury porosimetry and BET adsorption isotherm data. This information can be used in computer reconstruction of porous catalytic medium. In the reconstructed catalyst, transport (diffusion, permeation, heat conduction) and combined reaction-transport processes can be simulated on detailed level (Kosek et al., 2005). 

There are essentially three different ways how to prepare nanometer sized silicon particles. The porous silicon is, as already mentioned, prepared by anodic etching of silicon wafers in an HF/ethanol/water solution [6, 7]. The microporous silicon has typically a high porosity of 60-70 vol.%, and it consists of few nm thin wires which preserve the original orientation of the wafer. The thickness of the wires varies within the PS layer and the material is very brittle. Free standing PS films can be prepared by application of a high current density after the usual etching of the desired thickness of the PS. 

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