Modification Effects of B₂O₃ on The Structure and Catalytic Activity of WO₃-UiO-66 Catalyst.

Tungsten oxide (WO₃) and boron oxide (B₂O₃) were irreversibly encapsulated into the nanocages of the Zr-based metal organic framework UiO-66, affording a hybrid material B₂O₃-WO₃/UiO-66 by a simple microwave-assisted deposition method. The novel B₂O₃-WO₃/UiO-66 material was systematically characterized by X-ray diffraction, Fourier transform infrared spectroscopy, N₂ adsorption, ultraviolet⁻visible diffuse reflectance spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray phosphorescence, and Fourier transform infrared (FTIR)-CO adsorption methods. It was found that WO₃ and B₂O₃ were highly dispersed in the nanocages of UiO-66, and the morphology and crystal structure of UiO-66 were well preserved. The B₂O₃ species are wrapped by WO₃ species, thus increasing the polymeric degree of the WO₃ species, which are mainly located in low-condensed oligomeric environments. Moreover, when compared with WO₃/UiO-66, the B₂O₃-WO₃/UiO-66 material has a little weaker acidity, which decreased by 10% upon the B₂O₃ introduction. The as-obtained novel material exhibits higher catalytic performance in the cyclopentene selective oxidation to glutaraldehyde than WO₃/UiO-66. The high catalytic performance was attributed to a proper amount of B₂O₃ and WO₃ with an appropriate acidity, their high dispersion, and the synergistic effects between them. In addition, these oxide species hardly leached in the reaction solution, endowing the catalyst with a good stability. The catalyst could be used for six reaction cycles without an obvious loss of catalytic activity.