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多级孔沸石分子筛的结构性质及其催化性能是近年来分子筛研究的热点.本文采用蒸汽辅助晶化的方法制备了多级孔ZSM-5沸石分子筛,采用NH3程序升温脱附和原位吸附红外光谱等方法研究了其表面酸性质,用邻二甲苯异构化反应考察了其催化性能.结果表明,多级孔结构分子筛的结晶度和总酸量有所下降,但Lewis酸中心却有所增加.进一步研究发现,多级孔结构分子筛的外表面酸中心数量远高于常规分子筛,从而证实了多级孔结构可以将更多的酸中心暴露到外表面;而外表面酸中心数量的增多和扩散传质的改善是多级孔ZSM-5分子筛在邻二甲苯异构化反应中具有更高催化活性和对二甲苯产率的重要原因.
The structural properties and catalytic properties of multi-stage zeolites are the hot topics of molecular sieves in recent years.In this paper, multi-stage zeolite ZSM-5 zeolites were prepared by vapor-assisted crystallization and were characterized by NH3 temperature-programmed desorption and in-situ adsorption infrared spectroscopy The results showed that the degree of crystallinity and the total acidity of multi-stage pore structure molecular sieve decreased, but the Lewis acid center increased Further study found that the number of acid sites on the outer surface of multistage pore structure molecular sieve is much higher than that of conventional molecular sieve, thus confirming that multi-stage pore structure can expose more acid sites to the outer surface; while the number of acid sites on the outer surface increases The improvement of diffusion and mass transfer is an important reason for the higher catalytic activity and the para-xylene yield of the multistage pore ZSM-5 molecular sieve in the o-xylene isomerization reaction.