摘要
ZSM-5沸石的择形能力与其独特的孔道结构有关,硼酸改性的HZSM-5的孔道结构比ZSM-5有进一步改善,但改性后沸石的催化活性明显下降.近年来,有专利报导,用BF3处理HZSM-5,不仅可以提高择形能力,催化活性也明显增强;但也有改性后活性降低的专利报导。
The surface composition and channel structure of BF3 OEt2 modified HZSM-5 zeolite were studied by XPS, TGA of p-xylene adsorption, XRD and electron probe X-ray microanalysis.The results showed that there was obvious dealumination on the surface of modified HZSM-5 zeolite, and also the inorganic silicon filler and aluminium impurity blocking partly the channel were cleared out after modification and subsequent calcinaton.However, the modification had no effect on framework silicon.The surface framework Si/Al ratio of BF3 OEt2 modified HZSM-5 zeolite was obviously increased.After calcination, the boron atoms incorporated into the vacancy of dislodged lattice Al, the channel radius was contracted and the shape-selectivity was improved.As compared with the unmodified HZSM-5 zeolite, the activity for toluene dispropor-tionation and the selectivity for p-xylene of the modified catalyst were enhanced.
关键词
HZSM-5
沸石
改性
脱铝
择形催化
HZSM-5 zeolite,modification,BF_3 OEt_2,dealumination,shape selective catalysis
