High-silica CHA-type aluminosilicates (Si/Al > 100) were successfully synthesized by seed-assisted aging treatment for starting gel without fluoride media.
Various synthesis methods for zeolites have been developed to date; however, precise control over aluminum (Al) content remains a significant challenge. For instance, in the case of CON‐type zeolites, it is especially difficult to obtain a Si/Al ratio below a value of approximately 100 by direct synthesis, and below approximately 30 by post‐treatment. In this study, we have developed a novel direct synthesis method of the CON‐type zeolite having desired Al content by applying the interzeolite conversion/interzeolite transformation, wherein precursor zeolites that possess common composite building units (CBUs) with the target zeolite are employed as the Al and Si source. Initially, a single zeolite was utilized as a precursor, resulting in the successful synthesis of a high Al CON‐type zeolite (Si/Al=40). Finally, we developed a novel synthesis method of the CON‐type zeolite; blending of two types of zeolites, MFI and Beta, as starting material in the IZC method led to the direct crystallization of the CON‐type aluminosilicate with high Al content (Si/Al = 20).
In our previous work, the control of aluminum distribution on microporous ZSM-5 with and without the addition of sodium (Na) was conducted. In the current research, adjustment of the aluminum distribution on hierarchical ZSM-5 synthesized using a surfactant as a mesoporogen has been carried out. The investigation of aluminum distribution was based on 27Al MAS NMR, constraint index (CI) value, and Co(II) ion-adsorbed UV-vis. The aforementioned characterizations revealed that the hierarchical ZSM-5 with Na exhibited a more concentrated aluminum distribution in the channel intersections than the hierarchical ZSM-5 without Na did. The opposite trend was observed with microporous ZSM-5. Furthermore, the influence of the hydrothermal synthesis time on the formation of the hierarchical structure and the arrangement of aluminum within the framework was also investigated. The prolongation of the hydrothermal synthesis time to 144 h was found to be an optimal period for the formation of a well-hierarchical structure, as demonstrated by the observed increase in the hierarchy factor. Moreover, this process resulted in an increase in the strength of the acid sites and a change in the crystal morphology of the hierarchical ZSM-5 from a coffin-like morphology to a coral reef-like or a flower-like morphology. Additionally, the influence of the alteration in the aluminum distribution on the catalytic performance was also investigated. In the case of the n-hexane cracking and methanol conversion reactions, hierarchical ZSM-5 with Na was observed to produce bulkier molecules (≥C5s) than that without Na. On the other hand, it was observed that the hierarchically structured ZSM-5 exhibited enhanced performance in the production of lower olefins, particularly propene, in comparison to the microporous ZSM-5.
Various synthesis methods for zeolites have been developed to date; however, precise control over aluminum (Al) content remains a significant challenge. For instance, in the case of CON‐type zeolites, it is especially difficult to obtain a Si/Al ratio below a value of approximately 100 by direct synthesis, and below approximately 30 by post‐treatment. In this study, we have developed a novel direct synthesis method of the CON‐type zeolite having desired Al content by applying the interzeolite conversion/interzeolite transformation, wherein precursor zeolites that possess common composite building units (CBUs) with the target zeolite are employed as the Al and Si source. Initially, a single zeolite was utilized as a precursor, resulting in the successful synthesis of a high Al CON‐type zeolite (Si/Al=40). Finally, we developed a novel synthesis method of the CON‐type zeolite; blending of two types of zeolites, MFI and Beta, as starting material in the IZC method led to the direct crystallization of the CON‐type aluminosilicate with high Al content (Si/Al = 20).
Rh ion-exchanged Y zeolite (Rh-Y) and amorphous silica–alumina (Rh-ASA) were prepared by the ion-exchange method. The Rh species were identified by UV–vis and IR spectroscopies, TEM, and H2-TPR measurements. Isolated Rh cations were preferentially formed on the Y zeolite, while Rh oxide mainly existed on ASA. The catalytic activities of the prepared samples for oxidative reforming of methane were evaluated. The Rh oxide on Rh-ASA exhibited slightly higher methane conversion and CO yield than those of the isolated Rh cation on Rh-Y. On the other hand, the catalytic lifetime over Rh-Y was longer than that over Rh-ASA because the isolated Rh cations were protected from aggregation by electrostatic interaction with the zeolite framework. In addition, Rh-Y exhibited a high catalytic activity even at low Rh contents owing to its high dispersibility. On the basis of the experimental facts, we have successfully clarified the active Rh species for this oxidative reforming of methane and demonstrated the effectiveness of the zeolite framework for the stabilization of the active species. This article provides the important concept for the design of highly active catalysts in this catalytic system.
A new class of AEI -type aluminosilicates with sheet-like morphology was synthesized by the CGI-assisted method, which showed a higher iso-butene yield than the cubic particle during the PTB reaction.
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