Characterization and reactivity of silica-supported bimetallic molybdenum and stannic oxides for the transesterification of dimethyl oxalate with phenol

Abstract

Abstract A series of bimetallic MoO3-SnO2/SiO2 catalysts with various Mo and Sn contents ranging from 1–16 wt.% were prepared by sequential impregnation with molybdate species and cationic Sn complexes using the wet impregnation method. The performance of these catalysts in the transesterification of dimethyl oxalate (DMO) with phenol was compared with corresponding stannum- and molybdenum-supported catalysts prepared by the same method. The results indicated that the catalyst of MoO3-SnO2/SiO2 with 14 wt.% Mo and Sn contents performed best, giving 74.6% conversion of DMO and 99.5% selectivity to target products, methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO). The component, structure and phase of MoO3-SnO2/SiO2 catalysts with various Mo and Sn contents were investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), BET specific surface area measurement, temperature-programmed desorption of ammonia (NH3-TPD), and FT-IR analysis of adsorbed pyridine. It was observed that interdispersion between MoO3 and SnO2 plays an important role in modifying the catalytic behavior. NH3-TPD and FT-IR analysis of adsorbed pyridine results showed that only weak Lewis acids were present on the catalyst surface and the amounts of Mo and Sn loadings has hardly effected the strength of the surface acid. The weak Lewis acid sites catalyzed transesterification of DMO with phenol and Sn gave a promotional effect.