Large crystalline particles of ZSM-5 zeolites (S-ZSM-5) have been successfully synthesized by adjusting crystallization time and Si/Al ratios in the starting solid mixtures in the absence of water solvent. Catalytic tests in the methanol-to-olefins (MTO) reaction show that these S-ZSM-5 zeolites obtained from the solvent-free route exhibit superior catalytic properties including excellent propylene selectivity and extraordinarily long life in the MTO reaction. Particularly, when the crystallization time is 30 h and the Si/Al ratio in the starting solid mixture is adjusted at 150 under the solvent-free conditions, the S-ZSM-5-30h-150 catalyst with the large particle sizes (10−20 μm) gives propylene selectivity as high as 50.0% and catalyst life as long as 9 h, which are much better than those (propylene selectivity at 38.9% and catalyst life of 3 h) of the conventional ZSM-5 zeolite with smaller crystals (ca. 5 μm) synthesized from the hydrothermal route. High-resolution TEM images of these S-ZSM-5 zeolites demonstrate that there is mesoporosity in the samples. More interestingly, these mesopore size distributions could be adjusted by the crystallization time during the solvent-free synthesis. Obviously, the presence of mesoporosity is very favorable for the mass transfer, and an appropriate Si/Al ratio in the zeolite framework could offer suitable acidic density for the catalytic conversion, which should be responsible for the superior catalytic properties in the MTO over the S-ZSM-5-30h-150 catalyst. The features of mesoporosity in the S-ZSM-5 crystals and sustainability for the solvent-free synthesis could be potentially important for wide applications of these S-ZSM-5 zeolites in the future.
Aluminosilicate SSZ-39 zeolite has been prepared by transformation from ZSM-5 and beta zeolite in the presence of N,N-diethyl-cis-2,6-dimethylpiperidinium hydroxide.
There are a large number of zeolites, such as ITH, that cannot be prepared in the aluminosilicate form. Now, the successful synthesis of aluminosilicate ITH zeolite using a simple cationic oligomer as an organic template is presented. Key to the success is that the cationic oligomer has a strong complexation ability with aluminum species combined with a structural directing ability for the ITH structure similar to that of the conventional organic template. The aluminosilicate ITH zeolite has very high crystallinity, nanosheet‐like crystal morphology, large surface area, fully four‐coordinated Al species, and abundant acidic sites. Methanol‐to‐propylene (MTP) tests reveal that the Al‐ITH zeolite shows much higher selectivity for propylene and longer lifetime than commercial ZSM‐5. FCC tests show that Al‐ITH zeolite is a good candidate as a shape‐selective FCC additive for enhancing propylene and butylene selectivity.
A large amount of
zeolite structures are still not synthetically
available or not available in the form of aluminosilicate currently.
Despite significant progress in the development of predictive concepts
for zeolite synthesis, accessing some of these new materials is still
challenging. One example is the IWR structure as well. Despite successful
synthesis of Ge-based IWR zeolites, direct synthesis of aluminosilicate
IWR zeolite is still not successful. In this report we show how a
suitable organic structure directing agent (OSDA), through modeling
of an OSDA/zeolite cage interaction, could access directly the aluminum-containing
IWR structure (denoted as COE-6), which might allow access to new
classes of materials and thus open opportunities in valuable chemical
applications. The experimental results reveal that the COE-6 zeolites
with a SiO2/Al2O3 ratio as low as
30 could be obtained. Very interestingly, the COE-6 zeolite has much
higher hydrothermal and thermal stabilities than those of the conventional
Ge–Al–IWR zeolite. In methanol-to-propylene (MTP) reaction,
the COE-6 zeolite exhibits excellent selectivity for propylene, offering
a potential catalyst for MTP reaction in the future.
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