Effect of SBA-15 microporosity on the inserted TiO2 crystal size determined by Raman spectroscopy

The effect of SBA-15 microporosity on the crystal size of TiO2 was investigated employing SBA-15 materials with high (SBA-15-HM) and low (SBA-15-LM) microporosities (14.2% and 4.7% of microporous volume, respectively). TiO2 phase was incorporated inside SBA-15 using internal hydrolysis method over a wide range of loadings (7–63 wt%). At all loadings, TiO2 inside SBA-15 pores was in the form of anatase nanocrystals as found in characteristic Raman spectra. The crystal size of TiO2 anatase phase was determined by Raman spectroscopy using a correlation between Raman peak position and peak width and TiO2 crystal size. The correlation was established based on the set of unsupported TiO2 samples with the crystals size in the range 5–120 nm (BET and XRD). Using this correlation, it was found that the crystal size of TiO2 inside SBA-15 with high microporosity was lower than inside SBA-15 with low microporosity. This is a direct proof of the effect of wall microporosity on the dispersion of TiO2 inside SBA-15. Due to the higher TiO2 dispersion, TiO2/SBA-15-HM adsorbed more vanadia than TiO2/SBA-15-LM at the same TiO2 loadings. As a result, V2O5/TiO2/SBA-15-HM displayed higher activity than V2O5/TiO2/SBA-15-LM in NO SCR with ammonia.