Hierarchical mesoporous ZSM-5 zeolite with increased external surface acid sites and high catalytic performance in o-xylene isomerization

Abstract

Surface acid sites of hierarchical mesoporous ZSM-5 zeolite synthesized by steam-assisted crystallization were characterized by NH3 temperature-programmed desorption and in-situ infrared spectroscopy. Compared with the conventional ZSM-5 zeolite, the hierarchical ZSM-5 zeolite had a lower concentration of surface acid sites. However, the hierarchical structure had more Lewis acid sites and, more importantly, much more external active sites as confirmed by 2,6-di-tert-butylpyridine infrared spectroscopy. Such hierarchical structure exposed more acid sites on the external surface, which subsequently lead to higher catalytic activity in reactions involving bulky molecules, such as o-xylene isomerization.