改性Y沸石上的氢转移反应

Hydrogen Transfer Reaction on Modified Y Zeolites

本文试图用环己烯和邻二甲苯两典型反应考察改性Y沸石的氢转移反应性能.发现在改性Y沸石上环己烯的氢转移、异构化和聚合反应同时发生.在反应开始时SY沸石的氢转移反应和异构化反应活性与铝含量之间的关系与沸石强酸量和铝含量的关系一致,呈火山形曲线,极大值在Al/(Al+Si)为0.15左右,结焦以后反应总转化率迅速下降,且氢转移活性和异构化活性随铝含量减少而单调下降.USY沸石的氢转移活性低于SY沸石,而裂解活性高于SY沸石.高温水蒸汽处理使两种改性Y沸石的氢转移活性大幅度降低.在改性Y沸石上邻二甲苯异构化和歧化反应同时进行,SY沸石的歧化反应变化规律与环己烯氢转移反应相似.当沸石样品中有大量非质子酸位存在时,两个反应的数据会出现矛盾.

Reactivity of modified Y zeolites towards hydrogen transfer reactions was studied with model reactions such as cyclohexene and o-xylene conversion reactions. It has been found that on modified Y zeolites hydrogen transfer, isomerization and polymerization of cyclohexene take place simultaneously. As the Al content of the SY zeolites decreases the initial activities for cyclohexene hydrogen transfer and isomerization reactions vary similarly with the strong acidity of the zeolites, the activities increase first and then decrease, displaying volcano-like curves with maximum at Al/(A1+Si) =0.15. The zeolites deactivate quickly due to coke deposition, and then the activities decrease monotonously with decreasing Al content. The reactivity of USY zeolite for hydrogen transfer reaction is lower than that of the SY zeolites, but its cracking activity is higher. The activities of both types of modified Y zeolites are lowered considerably after steam treatment at elevated temperature. o-xylene isomerization is accompanied by disproportionation reaction on modified Y zeolites. For SY zeolites the results of the o-xylene disproportionation reaction are consistent with that of the cyclohexene hydrogen transfer reaction. The data of these two reactions may be contradictory when a significant amount of Lewis acid sites exists in the sample.