阳离子改性对HZSM-5沸石芳构化活性中心的影响

Influence of cation modification on aromatizing active sites over HZSM-5 zeolites

以脉冲反应考察了若干阳离子改性HZSM-5沸石的催化性质。结果表明,氢型和Ga改性沸石具有相近的裂解和氢转移芳构化活性,后者还有脱氢芳构化活性。环己烷在Cd、Zn和Cu改性沸石上也有较高的芳烃收率,芳构化主要通过直接脱氢,其活性中心可能是与吡啶吸附红外光谱中1610cm^(-1)附近新出现的吸收峰对应的改性物种。Ga,Gd和Zn改性沸石对链烷烃如正庚烷和3-甲基己烷也有脱氢芳构化活性。2,6-二甲基吡啶中毒实验证明,Zn改性沸石有两种芳构化活性中心。

The catalytic properties of some cationmodified HZSM-5 zeolites were studied in a pulse microreactor. The results show that HZSM - 5 and Ga-modified zeolites have similar activities for cracking and H-transfer aromatization and the latter has that for dehydroaromatization. Over Cd, Zn and Cu-modified zeolites the aromatic yields from cyclohexane are also higher. The aromatization proceeds mainly through direct dehydro-genation and the active sites correspond to those modifying species binding coordinately with pyridine molecules. with Ga, Cd and Zn-modified zeolites, some aliphatics (e. g. heptane and 3-methylhexane) are also easily to convert into aromatics. The poisoning experiment of 2, 6-dimethyl-pyridine has proven that two kinds of aromatizing active sites are present on the Zn-modified zeolite.