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Preparation, Characterization, and Surface Modification of Periodic Mesoporous Silicon–Aluminum–Carbon–Nitrogen Frameworks

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journal contribution
posted on 22.10.2013, 00:00 by O. Majoulet, C. Salameh, M. E. Schuster, U. B. Demirci, Y. Sugahara, S. Bernard, P. Miele
Periodic mesoporous silicon–aluminum–carbon–nitrogen (Si/Al/C/N) frameworks with P6mm hexagonal symmetry were synthesized by a solvent nanocasting route using mesoporous carbon (CMK-3) as hard template and preceramic polymers containing both −[R1R2Si–N­(R3)]n– and −[R4Al–N­(R5)]n– backbones (with R1 = R2 = R3 = R4 = H and R5 = CH2CH3) as ceramic precursors. The preceramic polymers are prepared through a simple and cost-effective procedure by blending poly­(perhydropolysilazane) and poly­(ethyliminoalane) as precursors of silicon nitride/silicon (Si3N4/Si) and carbon-containing aluminum nitride (Al/C/N), respectively. The blended polymers with various and controlled Al:Si ratios were infiltrated into the porous structure of CMK-3, followed by a pyrolysis-template removal cycle performed under nitrogen at 1000 °C (2 h, ceramic conversion), then in an ammonia atmosphere at 1000 °C (5 h, template removal). This procedure resulted in the formation of periodic mesoporous Si/Al/C/N frameworks with surface areas of 182–326 m2 g–1, a pore size distribution of 4.1–5.9 nm, and pore volumes in the range of 0.51–0.65 cm3 g–1. The uniformity of the mesopores and periodicity of the obtained amorphous micrometer-size powders, studied by transmission electron microscopy (TEM), small-angle X-ray diffraction (SA-XRD), and N2 sorption, are affected by the Al:Si ratio. Amorphous materials did not exhibit weight change up to 1400–1470 °C in flowing nitrogen, and their behavior in air, up to 1000 °C (with dwelling time of 5 h), is dependent on the proportion of AlN and Si3N4 phases. The as-obtained powders then were decorated with Pt (nano)­particles by impregnation to form supported catalysts. The as-formed catalysts showed attractive reactivity and robustness in our probe reaction, namely, the hydrolysis of an alkaline solution of sodium borohydride at 80 °C. Our main results are reported therein.