Synthesis, structure, and acidic properties of MCM-41 functionalized with phosphate and titanium phosphate groups

Area of Science:

• Materials Science
• Catalysis
• Surface Chemistry

Background:

• Mesoporous molecular sieves like MCM-41 offer high surface area and tunable porosity.
• Functionalization of these materials can introduce specific chemical properties for targeted applications.

Purpose of the Study:

• To functionalize purely siliceous Si-MCM-41 and titania-silica Ti-MCM-41 with phosphate groups.
• To characterize the structural and chemical changes upon functionalization.
• To evaluate the potential of these modified materials as solid acid catalysts.

Main Methods:

• Synthesis of Si-MCM-41 and Ti-MCM-41.
• Phosphate functionalization using POCl3.
• Characterization using Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), N2 adsorption, 1H MAS NMR, 31P MAS NMR, and Temperature Programmed Desorption (TPD) of ammonia.

Main Results:

• Phosphate functionalization retained the hexagonal mesoporous structure and porosity of MCM-41 materials, though with slight reductions.
• 1H and 31P MAS NMR confirmed the presence of silicon phosphate and pyrophosphate species on Si-MCM-41(P).
• Ti-MCM-41(P) showed additional titanium phosphate species, with pyrophosphate being dominant.
• TPD of ammonia indicated the creation of moderate and strong acid sites on both functionalized materials.

Conclusions:

• Phosphate functionalization of MCM-41 materials preserves their mesoporous structure.
• The functionalized materials exhibit significant acidity, making them promising solid acid catalysts.
• The combination of mesoporosity and acidity opens avenues for applications in heterogeneous catalysis.