Supported Embryonic Zeolites and their Use to Process Bulky Molecules

Abstract

X-ray amorphous zeolite precursors, embryonic zeolites, are prepared using tetrapropylammonium (TPA+) hydroxide as a structure directing agent. Their physicochemical properties are compared to those of a highly crystalline zeolite ZSM-5. Embryonic zeolites contain fewer acid sites, but their micropore volume and SBET area are higher than crystalline MFI-type material synthesized with TPA+. They can be introduced in the mesopores of a shaped silica-doped alumina matrix by two procedures: (i) impregnation of externally bred embryos and (ii) in situ growth of embryos to prepare composite catalysts. Their catalytic performances in the dealkylation of 1,3,5-triisopropylbenzene, a bulky molecule hardly penetrating the micropores of most zeolites, are superior to their highly crystalline ZSM-5 counterpart and the silica-doped alumina support. This is attributed to the highly accessible active sites of embryonic zeolites, located in an open microporosity leading to shorter diffusion path lengths. They offer inter...