摘要
运用吸附吡啶的TPD法考察了焙烧温度和预处理剂对TS 1分子筛表面酸性的影响。结果表明 ,TS 1分子筛表面主要存在两种酸性中心 ,对应的脱附峰温度 (Tm)分别为 4 80～ 5 0 0℃和 6 18～ 6 2 7℃。前者为弱酸中心 ,由分子筛骨架Ti(Ⅳ )形成 ,在苯的羟基化反应中起活化H2 O2 的作用 ;后者为强酸中心 ,由不稳定的Si—OH基团形成 ,是导致反应产物深度氧化的主要原因。随着焙烧温度的升高 ,弱酸中心逐渐增多 ,强酸中心逐渐减少。由于不同的预处理剂具有不同的酸性 ,会不同程度地引起骨架中Ti(OSi) 3 (OH)和Ti(OSi) 4 之间的转化 ,从而改变分子筛表面两种酸中心的相对数量 。
Effects of calcination temperature and the acidity of pretreatment reagents on the surface acidity of TS 1 zeolites were studied by using temperature programmed desorption (TPD) adsorbing pyridine. The TPD profiles showed that there were two main kinds of acid sites on the surface of TS 1 zeolites, namely the weak acid site and the strong acid site, whose desorption peak temperatures were located at 480～500 ℃ and 618～627 ℃, respectively. It is postulated that the weak acid sites originated from the framework Ti(Ⅳ) ions and the strong acid sites from the silanol groups at crystal defects, the former helped activating H 2O 2 and the latter might cause by product formation during the hydroxylation of benzene. With the increase of calcinations temperature, the amount of weak acid sites increased and the amount of strong acids decreased. Pretreatment reagents of different acidity may cause the transformation between Ti(OSi) 3(OH) and Ti(OSi) 4 in zeolite framework, changing the relative amount of the two acid sites thus the catalyst activity in hydroxylation of benzene.
出处
《石油学报（石油加工）》
EI
CAS
CSCD
北大核心
2003年第1期28-33,共6页
Acta Petrolei Sinica(Petroleum Processing Section)
