One-Step Synthesis of Hierarchical Zeolite Beta via Network Formation of Uniform Nanocrystals

Abstract

A hierarchical mesoporous network of zeolite beta with very high micropore as well as mesopore volume was synthesized without the need of a porogen at near 100% yield in the form of easily retrievable micrometer-sized particles. This was achieved by a dense-gel synthesis utilizing steam-assisted conversion (SAC) to induce a burst of nucleation. During the first phase of the synthesis, individual, evenly sized zeolite beta nanoparticles are formed that subsequently condense into a porous network displaying uniform mesopores. The final product consists of hierarchical self-sustaining macroscopic zeolite aggregates assembled from 20 nm crystalline domains of zeolite beta. The small size of the zeolite crystals in the resulting materials gives rise to mesopores with dominant pore sizes of about 13 nm. Large surface areas between 630 and 750 m(2)/g and total pore volumes up to 0.9 mL/g were obtained without sacrificing the microporosity (usually larger than 0.20 mL/g). Crystallization conditions were optimized for different Si/Al ratios between 10 and 33. A complete conversion into hierarchical zeolite beta was achieved in only a few hours at 170-180 °C if the amount of water present during the steam-assisted conversion was adequately adjusted. This dense gel steam conversion process proves to be a highly efficient strategy for fabricating hierarchical zeolite beta networks in a single step.

Synthesis of Wool-Ball-Like ZSM-5 with Enlarged External Surfaces and Improved Diffusion: A Potential Highly-Efficient FCC Catalyst Component for Elevating Pre-cracking of Large Molecules and Catalytic Longevity

“…Larger hysteresis loop occurs after p/p 0 & 0.45 in the adsorption-desorption isotherm of NZSM-5, which indicates not only the presence of mesopores but also a broad pore size distribution. Moreover, significant increase in N 2 adsorption is also observed, from p/p 0 & 0.8, for NZSM-5 because of the capillary condensation [3,7,8,25] in open mesopores or macropores obtained by filling the nano-rodlike MFI zeolite interparticles spaces. The pore size distribution derived from the adsorption branch of the isotherms (Fig.…”

“…Consequently, to improve the transport of molecules in microporous crystals is attracting significant research interests [3][4][5][6]. For a given material, the basic strategy to better the diffusion is to broaden the pore diameter or to shorten the diffusion path length [3][4][5][6][7][8][9][10][11]. To zeolites, enhancing the diffusion rate can be attained by decreasing the crystal size [7,8] or by introducing an additional meso-or/and macro-pore system into the individual zeolite crystal [3][4][5][6]9].…”

“…In the past decades, a lot of attempts have been made to alleviate the diffusion limitation of micropore in zeolites by adjusting their crystal sizes to nanoscale ranges [7,8,12,13], which can be achieved by quenching crystallization, by adopting growth inhibitors [12], by increasing the supersaturation, or by controlling the concentration of alkali metal ions system [13]. For example, a series of nano-sized ZSM-5 zeolite samples with intracrystalline mesopores were synthesized by using organosilane functioned fumed silica as silica source and tetrapropylammonium hydroxide as microporous structure directing agent [12], in which the long chain organic groups, which connect to the Si-species, disturbed the normal growth of the zeolites crystals in the manner of the so called ''bond block''.…”

Zeolite with trimodal porosity by desilication of zeolite nanocrystals aggregate

“…More recently, we show that mesoporous zeolite (ZSM-5, ZSM-12 and so on) with intercrystalline mesopore structure can be obtained through crystallization kinetics control, for instance, increasing super-saturation degree [31]. Very recently, Moller et al reported that hierarchical zeolite beta can be synthesized in one-step through network formation of uniform nanocrystals [32]. Such secondary template and post-treatment free mesoporous zeolite synthesis route allows mesoporous zeolites to be synthesized with a cost similar to or even lower than that of conventional zeolites and thus possibly opens a new, cost-effective, and industrially applicable way to the synthesis of mesoporous zeolites.…”

Unraveling the non-classic crystallization of SAPO-34 in a dry gel system towards controlling meso-structure with the assistance of growth inhibitor: Growth mechanism, hierarchical structure control and catalytic properties

“…As mentioned before, DGC has been recognized as an effective way to introduce mesoporosity and reduce the crystal sizes [23,25,26]. Particularly, in the case of SAPO-34, major attention is focused on the understanding of condition-dependent formation mechanism at the molecular level.…”