Diffuse Reflectance Laser Flash Photolysis Study of Titanium-Containing Zeolites

A series of porous titanosilicates (Ti-preferrierite, Ti-ferrierite, Ti\ITQ-6, Ti\ITQ-2, and silylated Ti\MCM-41), all of them active as alkene epoxidation catalysts, have been submitted to diffuse reflectance laser flash photolysis. The transient spectra in the microsecond time domain exhibit characteristic absorption bands at 350 nm (sharp) and 450-800 nm (featureless) attributable to triplet ligand-to-metal charge-transfer state and ejected electrons, respectively. It is proposed that the relative intensity of these two bands is a reflection of the presence of isolated, tetrahedral Ti atoms versus Ti aggregates, the former being considered the most active titanium sites in olefin epoxidation. Our study shows the applicability of laser flash photolysis to the characterization of titanium atoms in titanosilicates