Reactivity of TS-1 towards H2O2/H2O solutions

We review the experimental works aimed in understanding the interaction of TS-1 with H2O/H2O2. Attention is devoted to recent results that significantly improved the knowledge of the catalyst in conditions close to the working ones. UV-Vis, Raman (under resonance conditions) and X-ray absorption (both XANES and EXAFS) spectroscopies have been determinant in highlighting the structure of the species formed by adsorption of H2O2 on Ti centers inside TS-1. Main highlights are: (i) the O-O species, responsible to the yellow color of the TS-1/H2O/H2O2 system, is a side-on peroxo complex, generated by the reversible rupture of one Ti-O-Si bridge, with the formation of Ti(O2H) and H-O-Si groups; (ii) the stability of this peroxo complex is low in the absence of an excess of H2O; (iii) the strong enhancement of the acidity of the TS-1/H2O2/H2O system, with respect to that of TS-1/H2O, demonstrates a synergic role between Ti(IV) centers and H2O2.