Microporous Silicon Nitride-Based Solid Bases

Abstract

High surface area, microporous, amorphous silicon imidonitride, characterized by infrared spectroscopy, MAS 29Si NMR and surface area and porosity measurements has been prepared by the treatment of co-oligomers of methylsilazane and dimethyl silazanes with gaseous ammonia at temperatures up to 700°C. The material has a narrow pore-size distribution showing a maximum in the range associated with wide- pore zeolites (ca. 0.72 nm mean). Variation of the organic content of the silazane is a means of controlling the surface area of the resulting solid. The Knoevenagel condensation reaction of benzaldehyde with a series of active methylene compounds has been used to probe the basicity and size-selectivity of these microporous solid base catalysts.

Synthesis of mesoporous silicon imido nitride with high surface area and narrow pore size distribution

“…Even though this material has been widely studied as a precurser to obtain Si 3 N 4 for structural applications, 3 sinterability and densification have mainly been stressed, whereas only few attempts have been made to systematically tailor its surface area and pore structure and only recently has its potential in heterogeneous catalysis become apparent. [4][5][6] In order to achieve easy access to highly porous materials we have used SiCl 4 (Arkos, 99.8%) in various solvents (4% solution) such as pentane, toluene, tetrahydrofuran and polyethyleneglycol dimethyl ether and precipitated the diimide with anhydrous ammonia gas (UHP, Messer). † After filtration, the coprecipitated NH 4 Cl was removed by sublimation in a dynamic (40 ml min 21 ) ammonia atmosphere (1 bar) at elevated temperature [eqn.…”