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 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.

129Xe NMR on Porous Materials: Basic Principles and Recent Applications

“…Another approach to increase the accessibility of active sites is to use amorphous zeolite seeds (3–4 nm in size) as so‐called embryonic zeolites. [ 91 ] Embryonic ZSM‐5 zeolites possess larger pore sizes than the corresponding crystalline zeolite as evidenced by a lower 129 Xe chemical shift. The xenon signal in the embryonic zeolites is narrower, pointing toward a more open structure and faster exchange.…”

H-ZSM-5 Materials Embedded in an Amorphous Silica Matrix: Highly Selective Catalysts for Propylene in Methanol-to-Olefin Process

“…Our group also synthesized ZSM-5 materials containing amorphous silica matrix using aluminum nitrate as Al source for the first time without using any organic template [35]. Many research groups have reported on the synthesis and characterization of ZSM-5 materials embedded in amorphous silica, but these materials were not explored for catalytic application in the MTO process [36]. In this research, H-ZSM-5 materials with different Si/Al ratios (40, 45, and 50) embedded in amorphous silica were synthesized; the acid-site density of the H-ZSM-5 materials decreased by intercepting the crystallization process and making use of a unified crystallization time of 16 h. The physico-chemical properties were studied by different methods and the materials were used as catalysts in the MTO process.…”

“…Our group also synthesized ZSM-5 materials containing amorphous silica matrix using aluminum nitrate as Al source for the first time without using any organic template [35]. Many research groups have reported on the synthesis and characterization of ZSM-5 materials embedded in amorphous silica, but these materials were not explored for catalytic application in the MTO process [36].…”

Titanosilicate zeolite precursors for highly efficient oxidation reactions

“…59 Although the secondary amorphous phases demonstrate some spectroscopic and size-exclusive characteristics of zeolites, the lack of long-range periodicity of a crystalline zeolite lattice makes it amorphous and unsuitable for X-ray diffraction (XRD). [22][23][24][25] Therefore, these zeolite precursors are also regarded as X-ray amorphous zeolites or embryonic zeolites.…”

“…26 Recently, Haw et al prepared X-ray amorphous ZSM-5 precursors with tetrapropylammonium hydroxide (TPAOH) as the structure directing agent, which presented superior catalytic performances in the dealkylation of 1,3,5-triisopropylbenzene, which cannot penetrate through the micropores of zeolites. 24 The above demonstrated high catalytic activities of the amorphous titanosilicate zeolites were ascribed to the more open structure of X-ray amorphous zeolites, which dramatically increased the accessibility towards the catalytic active sites and enhanced the mass transport efficiency.…”