Formation and Stability of μ2-Peroxo on Titanosilicates, Anatase, and Rutile: Implications for Zeotype Catalysts

Extra-framework TiO2 in titanosilicate oxidation catalysts has generally been linked with low selectivity, and great emphasis has been put on developing synthetic protocols that yield anatase-free materials. Here, using 17O solid-state NMR spectroscopy, we investigate the formation and stability of μ2-peroxo groups on titanosilicates containing or not containing extra-framework TiO2 as well as on TiO2 polymorphs. By comparison with TiO2 nanoparticle references, H2O2 activation (e.g., peroxo formation) and decomposition are proposed to be related to the presence of rutile-like extra-framework TiO2. In fact, μ2-peroxo species can form and remain stable on anatase, whereas they decompose quickly on rutile. According to DFT calculations, the high stability of μ2-peroxo surface species on anatase is due to the specific arrangement of μ2-oxo groups on the (101) surface that allows for the stabilization of key intermediates through H-bonding. Notably, the μ2-peroxo species formed on titanosilicates and anatase display distinct 17O NMR spectroscopic signatures, which relate directly to the Ti-coordination environments, and can thus be distinguished.