Revealing inherent factors of SAPO-34 zeolites etching towards the fabrication of hierarchical structure

Abstract

Fabrication of hierarchical SAPO-34 zeolites by chemical etching is a facile, economic and efficient route to address their intrinsic diffusion limitation. Various leaching strategies have been developed to prepare hierarchical SAPO-34 zeolites. However, the effect of inherent factors of SAPO-34 crystals on the etching, such as crystal size and Si content, have not been systematically investigated. In the present work, a series of SAPO-34 zeolites with different Si contents and crystal sizes are prepared and leached in the mother liquor. The crystal morphology, textural properties, framework environments, and acidity of the synthesized SAPO-34 samples are comprehensively characterized through transmission electron microscope (TEM), nitrogen adsorption-desorption, solid-state MAS NMR, and NH3-TPD measurements. The formation of hierarchical porosity by etching is dependent on the Si contents and particle sizes of SAPO-34 samples. After etching in the mother liquor, the nanosized SAPO-34 zeolites with low Si content exhibit remarkably prolonged lifetime and higher selectivity to ethylene and propylene than other counterparts in methanol-to-olefin reactions, owing to the more accessible sites and improved mass transport. This work will inspire the more suitable and efficient preparation of hierarchical SAPO-34 catalysts via etching route.