Structure sensitivity of vibrational spectra of mesoporous silica SBA-15 and Pt/SBA-15

The vibrational properties of mesoporous silica (SBA-15) were investigated by deep ultraviolet (UV) Raman and infrared spectroscopies with and without the presence of platinum nanoparticles in the mesopores that were incorporated by sonication. Raman and IR spectral line assignments were made by comparison to amorphous silicas. This procedure permitted identification of vibrations of longitudinal (LO) and transverse (TO) optical lattice modes, the presence of Si-OH, and vibrational modes associated with the presence of three-, four-, and six-membered siloxane rings. Hydraulic pressing of the mesoporous silica with pressure in the range 3-7 tons cm ^-2 destroys the X-ray diffraction pattern and strongly decreases the Raman peak (D ₂) associated with three-membered rings at the surface. In the presence of platinum nanoparticles in the silica mesopores, a peak attributed to a Pt-O stretching vibration appears at between 530 and 580 cm ^-1 in the UV-Raman spectrum, which can be used to monitor the presence of the platinum particles and their interaction with the support. The D ₂ feature in the UV-Raman spectra also decreases with increasing Pt loading, which is attributed to interactions of the Pt nanoparticles with the silica surface.