Modification of MCM-48-,SBA-15-,MCF-,and MSU-type Mesoporous Silicas with Transition Metal Oxides Using the Molecular Designed Dispersion Method

摘要

Four various mesoporous silicas(MCM-48,SBA-15,MCF,and MSU)were modified by the molecular designed dispersion method using Fe(acac)_3,Cr(acac)_3,and Cu(acac)2 complexes.The deposition was performed at the same concentration of the metal acetylacetonate(acac)complex in a toluene solution.All as-synthesized samples were investigated by diffuse reflectance infrared Fourier transform spectroscopy,Fourier transform infrared photoacoustic spectroscopy,and thermogravimetric analysis.The calcined materials were studied with respect to their textural properties(Brunauer-Emmett-Teller adsorption isotherm)and chemical composition(electron microprobe analysis).It allowed elucidation of the mechanism of interaction between the acac complex and the silanol groups.For the MCM-48,SBA-15,and MCF materials,the formation of hydrogen bonding was found for the chromium-and copper-modified samples,whereas the Fe-containing materials showed the ligand exchange mechanism.The strong interaction of the MSU support and the different acetylacetonate complexes,resulting in a loss of at least one acac ligand,was observed.The mesoporous silicas modified with transition metal oxides were studied by UV-vis-DR spectroscopy.The different metal dispersions were found for the samples containing various transition metal oxides.