Structure replication and growth development of three-dimensionally ordered mesoporous-imprinted zeolites during confined growth

Abstract

Confined synthesis of three-dimensionally ordered mesoporous-imprinted (3DOm-i) zeolites within three-dimensionally ordered mesoporous (3DOm) carbons prepared from silica colloidal crystals was achieved through multiple hydrothermal (MHT) synthesis and steam-assisted crystallization (SAC). The transition of ordered mesoporous structures, starting from silica colloidal crystal to resulting 3DOm-i zeolites including the intermediate 3DOm carbon templates, and the correlations among the confined synthesis methods, crystal growth nature of different zeolites, and the sintering of the templates were studied. An imperfect replication was found in 3DOm-i zeolite when it compared to silica colloidal crystals regardless the synthesis methods (MHT or SAC), which might be originated from combination effects of sintering of the silica colloidal crystals and partial filling of cavities of the 3DOm carbon template during the confined synthesis, and the degree of the structure replication was notably influenced by microstructures of zeolite as well. A thorough investigation of the growth development of 3DOm-i BEA zeolites with various Si/Al ratios ranging from 14 to 27 through the MHT method confirmed that the crystallization takes place in the carbon template by a cage-to-cage propagation growth process.