Synthesis, characterization, and catalytic properties of high-surface-area aluminum silicon nitride based materials

A new precursor, [RAl(mu-NHEt)(mu-NEt)(2)Si(NHEt)](2) (R = Et, Me), is proposed for the preparation of high-surface-area silicon aluminum nitride based xerogels. The conversion is carried out using ammonia gas and pentane/ammonia mixtures at low (1 bar) and high (200 bar) pressure. Materials with specific surface areas up to 800 m(2) g(-1) are obtained under high-pressure conditions. The enrichment of aluminum in the materials obtained at low pressure indicates the formation of Si(NHEt)(4) as a side product that is also detected in NMR spectra. In scanning and transmission electron micrographs the materials appear with a flakelike morphology. The presence of NH groups is detected in IR spectra, and the Si-29 MAS NMR signal is detected at -40.5 ppm. The materials are X-ray amorphous. The composition varies with the reaction conditions. After a high-pressure transformation, the Al/Si ratio is close to 1.0 (Al-2-Si1.8N8.7C1.3H11.6) but transformation at low NH3 pressure only produces M-enriched materials. The solid imides are efficient catalysts for the Michael addition of malononitrile to acrylonitrile with a high yield of 96% after 5 h.