Sn改性TS－1分子筛催化苯酚和草酸二甲酯合成草酸二苯酯

 使用Sn改性的TS－1分子筛催化苯酚和草酸二甲酯的酯交换反应合成草酸二苯酯，深入研究了不同Sn负载量TS－1分子筛的结构及催化性能．实验结果表明，由于Sn和以Ti－O－SiO3为中心的弱Lewis酸的协同催化作用，与未改性的TS－1分子筛催化剂相比，改性后的催化剂虽 然Lewis酸量有明显下降，但催化剂的催化性能明显提高．当Sn的负载量为2％时，草酸二甲酯的转化率达到50．3％，目的产物的选择性为99．2％．利用X射线衍射、X射线光电子能谱和X射线能量分散谱考察了Sn在TS－1分子筛表面的结构和分散状态及其与酯交换反应催化性能的关系．结果表明，当Sn的负载量低于2％时，SnO2以非晶态形式分散在TS－1表面；而当Sn负载量高于2％时，SnO2以微晶的形式存在，此时Sn原子与Ti原子的协同作用已经不明显，催化剂的催化性能反而下降．

Synthesis of Diphenyl Oxalate from Transesterification of Phenol with Dimethyl Oxalate over Sn-Modified TS-1

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 SiO 3 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, NH 3 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.