The synergistic effect of bimetallic Zn-Ti in MCM-41 support for the improvement of catalytic activity

A series of bimetallic Zn-Ti-MCM-41 materials were synthesized through direct hydrothermal method and characterized by X-ray diffraction (XRD), N₂ adsorption-desorption isotherm, transmission electron microscopy (TEM), inductive coupled plasma (ICP), X-ray photoelectron spectra (XPS), UV-vis spectroscopy, Fourier transform infrared spectra (FT-IR) and ammonia temperature programmed desorption (NH₃-TPD). The catalytic activities of synthesized materials were evaluated in the direct oxidation of phenol using H₂O₂ as the oxidant. The results indicated that all obtained materials possessed ordered two-dimension (2D) hexagonal mesostructure with narrow pore distribution and high specific surface area. Most of Zn and Ti species were incorporated into the silica framework without affecting the mesoscopic nature of matrix. Particularly, a strong interaction was identified between the zinc and titanium species: (1) the presence of zinc promotes more incorporation of titanium atoms into the silica framework; (2) new medium surface acid sites introduced by the adsorption of NH₃ on the surface of zinc species were emerged for bimetallic catalysts, which increase the selectivity to diphenol in the oxidation of phenol.