Ordered mesoporous zirconium oxophosphate supported tungsten oxide solid acid catalysts: the improved Brønsted acidity for benzylation of anisole

Abstract

A series of WO₃ supported on ordered mesoporous zirconium oxophosphate (X wt% WO₃/M-ZrPO) solid acid catalysts with a WO₃ loading from 5 to 30 wt% were successfully synthesized, and their structure properties were characterized by X-ray diffraction (XRD), Raman spectroscopy, N₂-physisorption, transmission electron microscopy (TEM), UV-visible diffuse reflectance spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, H₂ temperature-programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS). The catalytic performance of X wt% WO₃/M-ZrPO in liquid phase benzylation of anisole was studied and the relation between activity and states of tungsten species was investigated detailedly. The maximum catalytic activity was reached at a 20 wt% WO₃ loading, which possessed highly dispersed WO₃ species and the strongest Brønsted acidity. Meanwhile, the well dispersed WO₃ species strongly interacted with M-ZrPO, therefore, both sintering and leaching of WO₃ species were effectively restrained. Moreover, compared with the traditional zirconium phosphate synthesized from the sol–gel method (ZrP_sol–gel), the M-ZrPO with an abundant ordered mesostructure was propitious for improving the dispersion of WO₃ species and catalytic performance. In addition, the 20 wt% WO₃/M-ZrPO showed a markedly higher catalytic activity than H-ZSM5, H-Beta and 20 wt% WO₃/ZrP_sol–gel. Furthermore, the catalyst showed no discernible loss in activity or selectivity after five cycles.