Mesoporous metal - silica materials: Synthesis, catalytic and thermal properties

Here, we report a simple and scalable synthesis strategy of metal (Ni or Cu) nanoparticles uniformly distributed inside a mesoporous silica matrix. This method involves incorporation of metal nitrates and citric acid in a stable silica gel through controlled hydrolysis of tetraethyl orthosilicate. Combustion of dried gels with ammonium nitrate in an inert gas atmosphere enables preparation of highly porous Ni/SiO2 and Cu/SiO2 nanomaterials with tunable metal content (∼5–30 wt.%). This approach also allows for independent tuning of the metal nanoparticle size (from 2 to 50 nm) and textural parameters, such as surface area (50–600 m2/g), average pore size (3–8 nm), and pore volume (0.05–0.6 cm3/g) of the materials during the one-step combustion. This new approach also enables uniform incorporation of metal nanoparticles within a porous silica matrix. This feature allows for synthesis of encapsulated stable ultra-small metallic nanoparticles with unusual properties. We tested Ni/SiO2 nanoscale materials with different textural parameters as catalysts in the ethanol decomposition reaction. The catalysts exhibited high activity toward hydrogen generation for ∼100 h. The relevant links between the textural parameters and stability of the catalysts are revealed. Characterization of the spent catalysts showed no structural changes, indicating superior stability over long periods of time. We also used spark plasma sintering (SPS) of Ni/SiO2 and Cu/SiO2 nanoscale materials to fabricate porous (70–80%) compact samples. These materials exhibited significantly low thermal diffusivity, which makes them attractive for thermal management applications. We also showed that the simple preparation method allows for production of large batches of final product, such as 10–50 g, in laboratory conditions.