Triazole/Triazine-Functionalized Mesoporous Silica As a Hybrid Material Support for Palladium Nanocatalyst

Noble and precious metal catalysts are sought for their remarkable efficiency in catalyzing numerous reactions in heterogeneous phase. However, they are costly and require the development of high-surface-area supports that favor their strong immobilization, dispersion, and stability. Toward this end, mesoporous silica-based materials can be regarded as unique supports for nanometric-sized noble metal catalysts provided they are functionalized with appropriate ligands. In this work, mesoporous silica SBA-15 was prepared and modified with 3-azidopropyltriethoxysilane and then clicked with alkyne derivatives of 1,3,5-triazine complex ligand. The resulting hybrid material contains triazole and triazine moieties covalently bound to the mesoporous silica network. The triazole/triazine minidendron was immobilized through a 1,3-dipolar cycloaddition click reaction, which was monitored by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The heterocyclic ligand-functionalized SBA-15 material served as a hybrid reactive platform for in situ deposition of palladium nanoparticles whose size is 3.154 ± 0.49 nm as assessed by X-ray diffraction and confirmed by transmission electron microscopy. The catalytic performance of the final palladium-decorated hybrid triazole/triazine-functionalized SBA-15 support was evaluated in the model reduction of 4-nitrophenol to 4-aminophenol by catalytic hydrogenation and stoichiometric reduction. Excellent catalytic performances were achieved, with reduction rate constant (K_app) of 16.8 × 10^-3 s^-1 for this model reaction. Moreover, the hybrid catalyst can be produced in high yield and recycled.