Activity and Surface Properties of Titanium Oxide Modified Silica Supported Molybdenum Oxide Catalysts for Transesterification of Dimethyl Oxalate with Phenol

Abstract

In this work, a series of MoO3/TiO2−SiO2 catalysts were tested in the transesterification of dimethyl oxalate (DMO) with phenol to produce methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO). The evaluation results showed that MoO3/TiO2−SiO2 catalysts were more active and selective than both MoO3/SiO2 and TiO2/SiO2 catalysts in the transesterification reaction. Moreover, the catalytic activities of MoO3/TiO2−SiO2 linearly increased with increased TiO2 content up to a dispersion threshold and then decreased. To explore the influence of TiO2 modified silica support on the dispersion and acidic properties of molybdenum oxide species, a series of characterization approaches were performed. The results of XRD, XPS, and BET measurements indicated that the incorporation of dispersed TiO2 could not only enhance the interaction between MoO3 and SiO2 but also promote the dispersion state of MoO3 on the surface of composite support, and further increase the specific surface areas of the catalysts. NH3-TPD measurements demonstrated that the incorporation of amorphous TiO2 generated new weak acid sites on MoO3/TiO2−SiO2 catalysts. In addition, the synergetic effect of MoO3 with TiO2 could be another possible explanation for the increase of DPO selectivity.