β沸石对NO_2选择性硝化甲苯的催化性能

Catalytic para-selective nitration of toluene with NO_2 over zeolite beta

用二氧化氮为硝化剂 ,在氧气存在的液相反应中 ,比较了不同类型的分子筛及杂多酸等固体酸对甲苯选择硝化的催化性能。Hβ沸石的硝化催化活性和对位选择硝化的选择性均高于其它催化剂。用Fe3 + ,Mg2 + ,Zn2 + 和B3 + 等进行离子交换、用盐酸和NaAlO2 进行脱铝及补铝等处理对Hβ沸石的催化性能影响不显著。随着离子交换使用的NaAc溶液浓度增加 ,Hβ沸石催化硝化甲苯的性能逐渐降低。Hβ沸石的最佳焙烧温度为 5 5 0℃。增加催化剂用量和延长反应时间有利于提高催化剂的活性和对p MNT的选择性。提高反应温度有利于提高反应速率及对硝基甲苯的选择性 ,但过高温度导致副产物增多 ,降低收率。

A series of solid acid catalysts including zeolites and heteropolyacids were examined for the nitration of toluene with liquid nitrogen dioxide in the presence of oxygen. Zeolite beta was the most noticeable due to the highest catalytic selectivity for para-mononitrotoluene formation as well as a high catalytic activity for the toluene nitration. The cation exchanges with Fe 3+ , Mg 2+ , Zn 2+ and B 3+ , the dealumination or alumination treatment of the zeolite beta had little effect on its catalytic performance. Both of the catalytic activity and the selectivity were decreased with the increase in the Na + exchange degree on the zeolite. Calcination of the catalyst at 550℃ was favorable for the best catalytic performance to the para-selective nitration of toluene. Increases in the amount of the catalyst and the duration of the reaction were of benefit to increases in both the catalytic activity for nitration and the selectivity of p-MNT. At a moderately high reaction temperature, the reaction gave a result with a high conversion of NO 2, a reasonable yield of nitration products and a high para-selectivity.