Mechanism of the Decomposition of Aqueous Hydrogen Peroxide over Heterogeneous TiSBA15 and TS-1 Selective Oxidation Catalysts: Insights from Spectroscopic and Density Functional Theory Studies

The Ti-based heterogeneous catalysts TiSBA15, Bu cap TiSBA15, TS-1, and [Ti,Al]-MFI were investigated with respect to controlling factors for the competitive decomposition of aqueous H 2 O 2 during selective catalytic oxidations. DRUV–vis spectroscopy revealed that the titanium species in these materials exist mainly in isolated, tetrahedral coordination environments. The observed rates of H 2 O 2 decomposition at 65 °C in acetonitrile decreased in the following order: Bu cap TiSBA15 > TiSBA15 and TS-1 > [Ti,Al]-MFI . The decompositions of H 2 O 2 were also monitored in the presence of inorganic additives and Brønsted acids and bases, in benzene/aqueous biphasic solutions. Significant retardation of the decomposition rates with the KH 2 PO 4 additive was found with TiSBA15, which suggests that the KH 2 PO 4 stabilizer may be useful for optimization of hydrogen peroxide efficiency in catalytic oxidations. DRUV–vis spectroscopy was employed to identify possible catalytically active intermediates, proposed to be Ti(IV)(OOH) species that are produced upon reaction of the Ti-based materials and H 2 O 2 . Density Functional Theory (DFT) studies starting from a molecular model, (HO)Ti[OSi(OH) 3 ] 3, suggest that three Ti(IV)(OOH) intermediates are in equilibrium, and the formation of Ti–O • and HOO • radical species may be involved in the H 2 O 2 decomposition. In addition, the potential role of KH 2 PO 4 in the H 2 O 2 decomposition process, as a proton acceptor in a [Ti(OO)(HOP(O)(OH) 2 )] complex, has been investigated.