A new synthesis scheme for the formation of porous CeO2/Pt-polycarbosilane composites using inverse microemulsions is presented. Aqueous hexachloroplatinic acid was used as a hydrosilylation catalyst causing crosslinking of allyl groups in a liquid polycarbosilane (PCS). The resulting polymers are temperature stable and highly porous. The Pt catalyst content and post-treatment of the polymer can be used to adjust the porosity. For the first time hydrophobic polymers with specific surface areas up to 896 m(2)/g were obtained by catalytic crosslinking of polycarbosilanes. Ceria nanoparticles 2-3 nm in diameter are well dispersed in the PCS matrix as proven using high resolution electron microscopy. Porosity of the hydrophobic materials could be increased up to 992 m(2)/g by adding divinylbenzene in the oil phase. Pyrolyses at 1200-1500 degrees C and post-oxidative treatment at various temperatures produce porous ceramic structures with surface areas up to 423 m(2)/g. X-Ray diffration investigations show that the crystallinity of the SiC matrix can be controlled by the pyrolysis temperature. Post-oxidative treatments cause silicon oxycarbide formation. Structure and morphology of the polymeric and ceramic composites were investigated using Si-29 MAS NMR, FESEM, FT-IR and EDX techniques. The temperature programmed oxidation (TPO) of methane shows a high catalytic activity of CeO2/Pt-SiC(O) composites lowering the onset in the TPO to 400-500 degrees C

A tutorial review on cellular as well as nanoporous carbides covering their structure, synthesis and potential applications. Especially new carbide materials with a hierarchical pore structure are in focus. As a central theme silicon carbide based materials are picked out, but also titanium, tungsten and boron carbides, as well as carbide-derived carbons, are part of this review.

Reverse microemulsions consisting of aqueous cerium nitrate solution as the internal phase and polycarbosilane dissolved in heptane as the continuous phase were used as a precursor for the controlled synthesis of dispersed cerium oxide particles inside a porous SiC matrix. According to dynamic light scattering experiments, the effective diameter of the cerium hydroxide particles obtained after ammonia addition is effectively controlled in a range of 2-10 nm with the molar water/surfactant ratio (R w ) 6-16). Pyrolysis at 1200 to 1500 °C produces materials with specific surface areas up to 240 m 2 g -1 . Whereas crystallization of the matrix is achieved only at higher temperature, cerium oxide particles form agglomerates composed of smaller nanoparticles that tend to dissolve into the ceramic matrix at 1500 °C leaving macropores behind. The high specific surface area is attributed to the presence of mesopores with a broad size distribution. Excess carbon present after pyrolysis is removed by oxidation at 900 °C causing a significant decrease of the surface area for high surface area materials, whereas intermediate surface area materials (50-100 m 2 g -1 ) show a high textural stability.

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In this study, the possibility of enhancing permeability of porous Si 3 N 4 ceramics was studied by using pore former additive (potato starch; 0-30 vol.%). The open porosity of samples changed between 52 and 66% as the mean pore channel size values ranged from 0.9 to 4 m. Increasing starch addition provides bimodal distribution of pore size channels by accompanying abrupt increment in non-Darcian permeability. k 2 value rised from 8.7 × 10 −10 m to 30.1 × 10 −10 m.