Supported Embryonic Zeolites and their Use to Process Bulky Molecules

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 S_BET 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 interesting prospects to process bulky molecules in fields such as oil refining, petrochemistry, and biomass upgrading.