Towards the development of advanced hierarchical chabazite materials: Novel micro-mesoporous silicoaluminophosphate SAPO-34 zeolites

Abstract

Conventional microporous and hierarchical SAPO-34 zeolites were synthetized by hydrothermal crystallization method. With that purpose, cetyltrimethylammonium bromide (CTAB) mesoporous template was directly introduced into the conventional gel, containing a microporous template (tetraethylammonium hydroxide, TEAOH), before starting the zeolite crystallization. The presence of both templates in the initial gel solution resulted in a microporous zeolite embedded in a physical mixture containing a mesoporous phase. To solve this issue, a defined aging period was implemented before the incorporation of CTAB to the microporous gel solution. The mesoporosity into the microporous SAPO-34 was successfully introduced by both One-pot and Aging methods. Only in the case of Aged Meso-0.15 material, the crystallinity, BET specific surface area and microporosity was conserved after the creation of mesopores. A previous heat treatment is required to form interconnected, pure and crystalline hierarchical pores structures. In order to get more insights into this original material, a series of new hierarchical zeolites was prepared by the same method, varying the amount of CTAB. A strong influence of this parameter was observed on the physicochemical properties. The formation of mesopores was achieved for all of them. Indeed, as the CTAB amount increased, the volume of mesopores increased. However, the volume of micropores, relative crystallinity and acidity seemed to follow an unexpected inverted-volcano trend.