ZSM-5分子筛酸性质对二甲苯异构化反应的影响

EFFECT OF ZSM-5ACIDITY ON XYLENE ISOMERIZATION REACTION

采用间二甲苯(MX)异构化探针反应,考察热处理和酸处理对ZSM-5分子筛酸性质的影响,对酸中心与二甲苯转化反应的关系进行研究,并用Py-FTIR、NH3-TPD和27Al NMR等对改性分子筛进行表征。结果表明:高温焙烧使部分酸中心的酸性质发生变化,提高了分子筛中L酸的比例;酸处理使分子筛中的部分骨架铝脱除,形成非骨架铝,减少B酸中心的同时,提高了L酸中心的量。将两种方法处理后的ZSM-5分子筛用于MX转化反应,结果表明,在MX异构化活性一致的前提下,L酸比例增大,歧化反应也随之增加,证明歧化反应与L酸中心的催化作用相关。

A series of ZSM-5 zeolites were prepared By modification of thermal or inorganic acid treatment to investigate the effect of acidity on their catalytic performance. The meta-xylene （MX） transformation reaction was used as a probe reaction. The modified ZSM-5 zeolites were characterized by Py-FTIR, NHa TPD and 27A1 NMR. It is found that a part of BrOnsted acid is converted to Lewis acid by thermal treatment, and a part of A1 atom is removed from the framework of the zeolite by acid treat- ment. The catalytic test results show that at the similar conversion of MX isomerization reaction, the disproportionation reaction of MX increases as the Lewis acid proportion increases.