The transesterification of phenol with dimethyl oxalate over Sn-modified TS-1 was conducted to prepare diphenyl oxalate used to produce diphenyl carbonate. The component, structure and phase of TS-1 catalysts with various Sn loadings were studied. The relationship between the catalytic properties and the Sn loading was discussed. The results indicated that although the Sn-modified TS-1 catalyst had fewer Lewis acid sites than the unmodified TS-1, its catalytic activity was increased greatly by the interaction of Sn with Ti-O-SiO3 weak Lewis acid centers. The catalyst of TS-1 with 2% Sn loading based on metal performed best, giving 50.3% conversion of dimethyl oxalate and 99.2% selectivity for target products. By means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and X-ray energy dispersive spectroscopy (EDS), the relationship between the catalytic properties and the structure of Sn dispersed on the surface of TS-1 was studied in detail. At Sn loadings below 2%, Sn was highly dispersed, but at higher loadings it was crystallized into bulk tin dioxide, thus, the interaction between Ti and Sn was not evident, and the catalytic activity decreased. XPS results showed that Ti could not be detected even when 1% Sn was loaded. EDS results indicated that the content of Ti on the surface decreased with increasing Sn loading, but the decrease of Ti content was much less than the increase of Sn content. Moreover, NH3-TPD results showed that there were only weak acid centers on all catalysts and the Sn loading did not have effect on the acid strength of the catalysts.
