Preparation of Mesoporous Pd/Si3N4 Nanocomposites as Heterogeneous Catalysts via Three Different Chemical Routes

Abstract

Mesoporous palladium/silicon nitride nanocomposites were prepared via three different chemical routes to generate simultaneous control of the solid-state morphology of the palladium nanoparticles and that of the silicon nitride support at the same time as controlling the pore size and size distribution. Pyrolysis of the reaction product of silicon diimide gel with PdCl2 under a NH3 flow at 1000 °C gave a composite with highly crystalline Pd nanoparticles dispersed in an α-Si3N4 matrix. A composite with partially crystallized Pd nanoparticles dispersed in an amorphous Si3N4 matrix was obtained by the hydrogen reduction of the reaction product of silicon nitride with PdCl2, whereas hydrogen reduction of an impregnated mixture of Si3N4 with bis(dibenzylideneacetone)palladium (DBA) led to the formation of a composite with amorphous Pd nanoparticles dispersed in an amorphous Si3N4 matrix. Most of these new mesoporous nanocomposites exhibit a high surface area >400 m2 g-1 and a narrow pore size distribution of 5−12 nm with a loading of up to 2% Pd nanoparticles 2−20 nm in diameter. Preliminary investigations show that these nanocomposites are potentially useful heterogeneous catalysts for a range of liquid-phase chemical reactions.