Modification effects of B2O3 on the structure and catalytic activity of WO3-UiO-66 catalyst

Abstract

Tungsten oxide (WO3) and boron oxide (B2 O3) were irreversibly encapsulated into the nanocages of the Zr-based metal organic framework UiO-66, affording a hybrid material B2 O3-WO3 /UiO-66 by a simple microwave-assisted deposition method. The novel B2 O3-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 B2 O3 were highly dispersed in the nanocages of UiO-66, and the morphology and crystal structure of UiO-66 were well preserved. The B2 O3 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 B2 O3-WO3 /UiO-66 material has a little weaker acidity, which decreased by 10% upon the B2 O3 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 B2 O3 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.