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 PdCl 2 under a NH 3 flow at 1000 °C gave a composite with highly crystalline Pd nanoparticles dispersed in an R-Si 3 N 4 matrix. A composite with partially crystallized Pd nanoparticles dispersed in an amorphous Si 3 N 4 matrix was obtained by the hydrogen reduction of the reaction product of silicon nitride with PdCl 2 , whereas hydrogen reduction of an impregnated mixture of Si 3 N 4 with bis(dibenzylideneacetone)palladium (DBA) led to the formation of a composite with amorphous Pd nanoparticles dispersed in an amorphous Si 3 N 4 matrix. Most of these new mesoporous nanocomposites exhibit a high surface area >400 m 2 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 liquidphase chemical reactions.

Solution Phase Preparative Routes to Nitride Morphologies of Interest in Catalysis

“…5). The authors also synthesised these nanocomposites with various morphologies by three different sol-gel routes and tested them on the liquid phase hydrogenation of hex-1-ene and cyclohexanone at 30 and 135°C, respectively [33]. Of the three morphologies crystalline Pd/a-Si 3 N 4 , nanocrystalline Pd/amorphous Si 3 N 4 and amorphous Pd/amorphous Si 3 N 4 , small metal nanoparticles on amorphous Si 3 N 4 showed the highest conversion for hex-1-ene (100%) and cyclohexanone (56%).…”

Catalytic ammonolytic sol–gel preparation of a mesoporous silicon aluminium nitride from a single-source precursor

“…Silicon nitride has been shown to be a very useful support for catalytically active phases, e.g., the oxidation of methane using Pd/Si 3 N 4 and Pt/Si 3 N 4 [31][32][33], the selective hydrogenation of butadiene to butene using Pd/Si 3 N 4 [29] and the dehydrogenation of propane using Pt/Si 3 N 4 [28]. Our recent results show that nitrogen-based porous catalysts can be superior to commercially-available metal oxide catalysts for some gas-phase and liquid phase reactions [34,35].…”

“…Our interest is to develop new micro-and mesoporous non-oxide materials with high-surface-area accessible for applications in heterogenous catalysis, membranes and filters, e.g., for solid-state semiconductor gas sensors with improved performance in terms of sensitivity and selectivity [34][35][36][37][38]. Composite mesoporous ceramics consisting of two or more binary nitrides may be expected to have improved properties compared with single-component nitrides [39].…”

Synthesis and processing of silicon nitride and related materials using preceramic polymer and non-oxide sol-gel approaches

“…Pyrolysis led to mesoporous structures with 5-12 nm or 15-25 nm pores, depending on pyrolysis conditions, and 5-20 nm Pd nanoparticles dispersed throughout the matrix. These were found to more active than crystalline Si3N4 infiltrated with Pd nanoparticles in alkene isomerisation reactions and in the hydrogenation of alkenes and of cyclohexanone [234,235].…”