Amorphous Ti species in titanium silicalite-1: Structural features, chemical properties, and inactivation with sulfosalt

The nature of the amorphous Ti species in titanium silicalite-1 (TS-1) was investigated by UV Raman spectroscopy (UV Raman), UV–vis diffuse reflectance spectroscopy (UVDRS), infrared spectroscopy (IR), and Hammett indicator titration methods. A new Raman feature at 700 cm−1, which is closely related to the UVDRS band at 260–280 nm, is first assigned to a totally symmetric vibration of hexacoordinated Ti–O–Ti linkages of the amorphous Ti species. The amorphous Ti species in TS-1 can be formed easily under the synthesis conditions in the presence of Na+ or after treatment in ammonia solution. The results reveal that the amorphous Ti species is the main factor in the enhanced acidity and H2O2 decomposition ability of TS-1. A sulfosalt impregnation method has been proved effective in reducing the adverse effect of the amorphous Ti species.