Steering Interzeolite Conversion with Alkali Metal Cations: Lithium Maximizes Al Proximity in SSZ-13 Zeolite Genesis

Abstract

Zeolites have long been regarded as difficult to modify during synthesis, as their synthesis is governed by kinetic processes. Recent breakthroughs have made it possible to exert a certain degree of control over zeolite properties with more performant materials as a result. Here, we investigate the effects alkali cations have on high-silica FAU-to-CHA interzeolite conversion (IZC) and on the resulting aluminum distributions. In this way, by using Li-cations in conjunction with an organic structure directing agent, the first route to a "fully paired" (divalent cation capacity, Co 2+ /Al = 0.48) high-silica SSZ-13 zeolite is demonstrated. Lithium shows great potential in steering IZC synthesis as it speeds up crystallization, and evidence was gathered in favor of a more elaborate mechanism of IZC in which dissolved Al-rich oligomers crash out of solution first and possibly spark nucleation. These findings help in gaining insights into a more general theory on zeolite nucleation in heterogeneous environments such as IZC. Furthermore, the "fully paired" sample has great potential for ion-exchanged zeolite catalysis or in adsorbents.

Studies on the Conversion of FAU Zeolites to SSZ-13: The Rate Advantage of Having Both Si and Al in the FAU Reagent

“…The Dusselier group recently reported an intriguing study of conversion to SSZ-13 and differential crystallization times with the greatest enhancement coming from lithium. 28 In our current study we have shown that there is a much faster reaction for the use of CBV-720 as Si and Al sources in the reaction than the intermediate system of NaY and sodium silicate, or sodium silicate and a soluble Al source at the start of the reaction mixing like aluminum sulfate or a hydrated alumina trihydroxide. We showed that even the degraded CBV-720 converts quickly.…”

“…It is also important to note that, in the OSDA-free syntheses, the solvated alkali metal cations become important. The Dusselier group recently reported an intriguing study of conversion to SSZ-13 and differential crystallization times with the greatest enhancement coming from lithium …”

“…A recent study by Dusselier and co-workers showed an impressively fast conversion of CBV-780 (SAR = 80) to SSZ-13 at 160 °C. 28 Dissolution of silica is the first step. 29 Very nice studies from the Corma group demonstrated in the synthesis of AEI that the precursor FAU, in the early stages of the synthesis, could be shown to have a diminished unit cell, indicative of Al enrichment as Si dissolved away.…”

“…This would indicate that much of the reaction is the dissolution of silica and a product obtained as SSZ-13 would have an SAR much less than that of the starting reagent. A recent study by Dusselier and co-workers showed an impressively fast conversion of CBV-780 (SAR = 80) to SSZ-13 at 160 °C . Dissolution of silica is the first step .…”

Direct Detection of Paired Aluminum Heteroatoms in Chabazite Zeolite Catalysts and Their Significance for Methanol Dehydration Reactivity

“…For example, previous modeling and indirect measurements inferred from Co 2+ titration have indicated that the rate of methanol dehydration over H + -chabazite may be faster over catalysts in which framework Al heteroatoms are near one another, compared to when they are isolated. − Here, two H + -chabazite catalysts were tested for the rates at which methanol was converted to dimethyl ether under identical conditions (Figure ). The two zeolites were both synthesized using trimethyladamantylammonium hydroxide as the organic structure-directing agent, although H + -CHA-1 was synthesized via interzeolite conversion using FAU zeolite as a precursor, while H + -CHA-2 was synthesized by conventional methods using molecular precursors. − The resulting products had very similar bulk compositions (Si/Al ∼ 10) and were indistinguishable by conventional scattering or NMR characterization techniques (Figures S1–S4) or their 2D 1 H– 1 H NMR spectra (Figure S5). Notably, standard Co 2+ exchange analyses resulted in low Co 2+ /Al ratios of <0.02 for both catalysts (Table S1).…”