A Working Hypothesis for Broadening Framework Types of Zeolites in Seed-Assisted Synthesis without Organic Structure-Directing Agent

Abstract

Recent research has demonstrated a new synthesis route to useful zeolites such as beta, RUB-13, and ZSM-12 via seed-assisted, organic structure-directing agent (OSDA)-free synthesis, although it had been believed that these zeolites could be essentially synthesized with OSDAs. These zeolites are obtained by adding seeds to the gels that otherwise yield other zeolites; however, the underlying crystallization mechanism has not been fully understood yet. Without any strategy, it is unavoidable to employ a trial-and-error procedure for broadening zeolite types by using this synthesis method. In this study, the effect of zeolite seeds with different framework structures is investigated to understand the crystallization mechanism of zeolites obtained by the seed-assisted, OSDA-free synthesis method. It has been found that the key factor in the successful synthesis of zeolites in the absence of OSDA is the common composite building unit contained both in the seeds and in the zeolite obtained from the gel after heating without seeds. A new working hypothesis for broadening zeolite types by the seed-assisted synthesis without OSDA is proposed on the basis of the findings of the common composite building units in zeolites. This hypothesis enables us to design the synthesis condition of target zeolites. The validity of the hypothesis is experimentally tested and verified by synthesizing several zeolites including ECR-18 in K-aluminosilicate system.

Zeolite membranes – a review and comparison with MOFs

“…Some recent reviews summarize the progress towards synthesis of zeolites by such a procedure. [72][73][74][75] Here, seeds are first synthesized using SDA and further used for zeolite growth from a sol that is devoid of SDA. There are significant advantages to using an SDA-free synthesis procedure.…”

High Potential of Interzeolite Conversion Method for Zeolite Synthesis

“…Table 2 lists the framework structures and composite building units of several zeolites as s u m m a r i z e d i n t h e d a t a b a s e o f t h e S t r u c t u r e Commission of IZA 1) . Recently, common composite building units between the seed zeolite and the finally crystallized zeolite from the seed-free starting gel were proposed to be the crucial precursors for crystal growth in the seed-assisted OSDA-free zeolite synthesis 49) . The starting FAU type zeolite contains the composite building units sod and d6r, the final LEV type zeolite contains d6r (the common building unit with FAU type zeolite), BEA type zeolite contains mor, bea, and mtw, and MAZ type zeolite contains the dsc and gme units.…”

Selective Production of Light Olefins over MSE-type Zeolite Catalyst

“…This hypothesis involves structural consideration of the common composite building units (CBUs) between the seed zeolite and the zeolites obtained from seed-free gels. By applying this hypothesis, seed assisted, OSDA-free syntheses of ZSM-5, ZSM-11, and ZSM-12 were successfully performed 49), 50) . Furthermore, an alternative successful route to the OSDA-free synthesis of ZSM-12 (CBU: bik, jbw, mtw, cas) was accomplished with the aid of beta seeds based on considering the combination of the CBUs in the beta seeds (mtw) and the gel-yielding ZSM-5 (cas) when no seeds were added.…”

“…A working hypothesis was proposed for the seedassisted, OSDA-free synthesis of zeolites on the basis of the results of the OSDA-free syntheses of beta, mordenite, and ferrierite 49) . This hypothesis involves structural consideration of the common composite building units (CBUs) between the seed zeolite and the zeolites obtained from seed-free gels.…”