硅改性对ZSM-5沸石催化剂择形性的影响

Effect of Silicon Modification on Shape Selectivity of ZSM-5

用硅修饰不同酸性的 HZSM-5、PZSM-5和 BiZSM-5沸石催化剂,发现随硅添加量增加,基质的总酸量减少,B 酸和 L 酸中心同时被覆盖,甲苯的乙基化活性下降,对位选择性升高。当加硅至7.2%时,它们各自提高10%、11%和43%。论述了影响选择性的因素,得出在孔内具有中等酸强度的酸中心是提高对位选择性和稳定性的重要条件之一。

Modification by Si of HZSM-5.PZSM-5 and BiZSM-5 zeolites were studied.The results showed that total acid site of various MZSM-5 and activity of tolu-ene ethylation decreased while selectivity for p-ethyltoluene increased with incre-ase of Si content.When Si content reached 7.2%,the selectivity increased by10%,11%,and 43% respectively.The difference in selectivity was mainly dueto different acid strength of MZSM-5 matrix.The para-selectivity,besides beingdependent on suppression of isomerization on external surface acid sites and onfavorable pore size,also depends on the preferential formation of para-isomer andthe existence of sites with medium acid strength in cavity of channel inter-section.