New insight from an old concept for zeolites

doi:10.1126/science.abj1834

GSTDTAP > 气候变化

DOI	10.1126/science.abj1834
	New insight from an old concept for zeolites
	Dan Xie
	2021-07-02
发表期刊	Science
出版年	2021
英文摘要	Zeolites are a class of crystalline materials with three-dimensional (3D) framework structures that form uniform micropores. Because the size of the pore windows is comparable to molecular dimensions, they can function as “molecular sieves” by adsorbing molecules that fit inside the pores and excluding larger ones. A small change in the dimension of the pore architecture (channels or cavities in the zeolite) sometimes makes the difference between success and failure in adsorption or catalytic conversion applications. This is why efforts have been made to synthesize zeolites with a variety of different framework structures and compositions. Discovering new zeolites is not trivial, especially for large-pore zeolites with thermal stability and strong acidity under harsh processing conditions. On page 104 of this issue, Lee et al. ([ 1 ][1]) report two thermally stable, large-pore aluminosilicate zeolites. The zeolites, PST-32 and PST-2, were discovered with the “multiple inorganic cation” and the “charge density mismatch” synthetic strategies, respectively. Both zeolites exhibit supercages and wide pore windows comparable to the most used one in the oil industry, zeolite Y. PST-32 and PST-2 are both potential cracking catalysts for hydrocarbon refining applications. Almost all commercial fluidized catalytic cracking and hydrocracking catalysts are based on zeolite Y, which has the most accessible pore system and as large as ∼50% of void space in the structure. Its framework structure, coded as FAU (by the Structure Commission of the International Zeolite Association), has a 3D large-pore system with ∼7.4 Å of circular pore windows interconnecting to spherical supercages with a volume of ∼1.15 nm3 (see the figure). Even so, zeolite Y has diffusion limitations and access problems for molecules in the higher boiling temperature range. Searching for alternatives, either for tuning cracking product distribution or for a better performance in activity and selectivity, is a topic of interest. Promising results have in fact been reported for a few large-pore zeolites—for instance, ITQ-21 and ITQ-33—that were discovered by the Corma group ([ 2 ][2], [ 3 ][3]). Now, this racing club has two new members, PST-32 and PST-2. PST-32 has an SBT framework structure, and PST-2 is a disordered material having an SBS/SBT intergrowth structure. The framework structure codes SBT and SBS originated from two phosphate-based zeolites, UCSB-10 and UCSB-6, respectively ([ 4 ][4]). The thermal instability UCSB-10 and UCSB-6 impedes any catalytic applications. PST-32 and PST-2 were synthesized as aluminosilicates with slightly higher silicon-to-aluminum ratio (SAR) compared with zeolite Y and demonstrate sufficient thermal stability during catalytic cracking. Both the SBT and SBS framework structures have a 3D large-pore system. SBT contains one type of supercage with a volume of ∼1.14 nm3 that is interconnected by two different pore window sizes (7.8 Å by 7.3 Å and 7.4 Å by 6.4 Å), whereas SBS contains two types of supercages (∼1.17 nm3 and ∼0.68 nm3 in volume) interconnected by two different pore window sizes (7.0 Å by 6.9 Å and 6.8 Å by 6.8 Å). These structural features make PST-32 and PST-2 very attractive for catalytic conversion applications. ![Figure][5] Stabilized large-pore zeolites Two new zeolites called PST-32 ( SBT -type) and PST-2 ( SBS/SBT -type intergrowth) have supercage structures, like the commercially used zeolite Y ( FAU -type). These zeolites can be produced in large amounts and may find uses for various catalytic processes. GRAPHIC: N. DESAI/ SCIENCE BASED ON D. XIE Apart from the promising structures, PST-32 and PST-2 can be synthesized at relatively low cost. Most industrially relevant zeolites are synthesized by dissolving silica and alumina sources in a basic aqueous solution, where inorganic cations and/or organic molecules help guide zeolite formation and counterbalance the negative charges introduced by aluminum. For catalytic applications, zeolites with higher SAR tend to offer better tolerance to the high temperatures that occur during the catalytic and regeneration cycles. Rather than using inorganic cations alone, synthesizing zeolites is often done with the assistance of organic molecules called organic structure-directing agents (OSDAs). OSDAs have sizes and shapes that correlate well with the pore configuration of the zeolite. Inorganic cations have less size and shape tunability, so are less robust in directing structures with diversified pore configurations. Although a substantial portion of new zeolite discoveries involve designing and screening a large range of OSDAs, the authors focused on a strategy of using multiple inorganic cations along with a relatively simple and inexpensive OSDA to jointly direct crystallization. Although this concept has existed for more than two decades, systematic investigations on the synergistic effect of structure direction were rarely reported. This old strategy, which the authors termed the “multiple inorganic cation” approach, has allowed a number of new zeolites to be discovered ([ 5 ][6]–[ 7 ][7]), and PST-32 appears to be one of the most exciting examples. This approach may serve as a paradigm for rational synthesis of existing and hypothetical cage-based zeolite structures. However, a better understanding of the exact role of each type of inorganic cations during formation is needed. Moreover, the discovery of PST-32 and PST-2 will likely promote further study of their synthesis, modification, and catalytic performance. This includes both in traditional oil-based cracking processes, but also with biomass conversions to produce renewable chemicals and fuels. Other applications are also possible, such as adsorption, separations, and emerging uses such as drug delivery and gas sensing. 1. [↵][8]1. H. Lee et al ., Science 373, 104 (2021). [OpenUrl][9][Abstract/FREE Full Text][10] 2. [↵][11]1. A. Corma, 2. M. J. Díaz-Cabañas, 3. J. Martínez-Triguero, 4. F. Rey, 5. J. Rius , Nature 418, 514 (2002). [OpenUrl][12][CrossRef][13][PubMed][14] 3. [↵][15]1. A. Corma, 2. M. J. Díaz-Cabañas, 3. J. L. Jordá, 4. C. Martínez, 5. M. Moliner , Nature 443, 842 (2006). [OpenUrl][16][CrossRef][17][PubMed][18] 4. [↵][19]1. X. Bu, 2. P. Feng, 3. G. D. Stucky , Science 278, 2080 (1997). [OpenUrl][20][Abstract/FREE Full Text][21] 5. [↵][22]1. J. Shin, 2. D. Jo, 3. S. B. Hong , Acc. Chem. Res. 52, 1419 (2019). [OpenUrl][23][CrossRef][24][PubMed][25] 6. 1. H. Lee et al ., ACS. Mater. Lett. 2, 981 (2020). [OpenUrl][26] 7. [↵][27]1. H. Lee et al ., ACS. Mater. Lett. 3, 308 (2021). 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领域	气候变化 ; 资源环境
URL	查看原文
引用统计
文献类型	期刊论文
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/334175
专题	气候变化资源环境科学
推荐引用方式 GB/T 7714	Dan Xie. New insight from an old concept for zeolites[J]. Science,2021.
APA	Dan Xie.(2021).New insight from an old concept for zeolites.Science.
MLA	Dan Xie."New insight from an old concept for zeolites".Science (2021).