Controlling the competitive growth of zeolite phases without using an organic structure-directing agent. Synthesis of Al-rich *BEA

0554273 - ÚFCH JH 2023 RIV NL eng J - Journal Article
Pilař, Radim - Morávková, Jaroslava - Sádovská, Galina - Sklenák, Štěpán - Brabec, Libor - Pastvová, Jana - Sazama, Petr
Controlling the competitive growth of zeolite phases without using an organic structure-directing agent. Synthesis of Al-rich *BEA.
Microporous and Mesoporous Materials. Roč. 333, MAR 2022 (2022), č. článku 111726. ISSN 1387-1811. E-ISSN 1873-3093
R&D Projects: GA ČR GA18-20303S; GA MŠMT(CZ) LM2018124; GA MŠMT(CZ) EF16_013/0001821; GA MŠMT(CZ) EF18_046/0015586
Grant - others:GA MŠk(CZ) CZ.02.1.01/0.0/0.0/16_013/0001821; ERDF(CZ) CZ.02.1.01/0.0/0.0/18_046/0015586
Institutional support: RVO:61388955
Keywords : Crystallization * Hydrothermal synthesis * Mechanisms * OSDAs-free synthesis * Zeolite beta
OECD category: Physical chemistry
Impact factor: 5.2, year: 2022
Method of publishing: Limited access

The synthesis of zeolites without using an organic structure-directing agent (OSDA) offers great environmental and economic advantages. However, the zeolites being formed are not stabilized by the organic molecules and kinetic control of the synthesis ensuring high yield and purity of the phases is challenging for many zeolites. For OSDA-free synthesis of an Al-rich *BEA zeolite, this study shows that the zeolite is formed as a metastable phase that can undergo transformation immediately after completion of its crystallization to form a thermodynamically more stable MOR zeolite according to Ostwald's rule of stages. The OSDA-free zeolite synthesis is a dynamic process in which crystallization and dissolution occur simultaneously. As soon as a thermodynamically more stable MOR zeolite begins to form in the synthesis mixture, its formation causes depletion of the Al and Si from the synthesis mixture, and, because of the desaturation of the synthesis gel, the original *BEA zeolite begins to dissolve rapidly under hydrothermal conditions. The formation of targeted and parasitic zeolite structures is fundamentally affected by the Al and Si sources. Sources of Al and Si with suitable solubility and the presence of stable zeolite *BEA seeds allow kinetic control to direct the exclusive formation of *BEA zeolite up to a relatively high yields. Then, however, the MOR zeolite phase appears in the product and its formation becomes predominant. This study demonstrates the crucial importance of kinetic control for the selective formation of metastable zeolites in the OSDA-free synthesis.
Permanent Link: http://hdl.handle.net/11104/0328904