Computationally Guided Synthesis of SSZ-52: A Zeolite for Engine Exhaust Clean-up
Computationally Guided Synthesis of SSZ-52: A Zeolite for Engine Exhaust Clean-up
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DOI：
10.1021/acs.chemmater.5b04578
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发表时间：
2016-02-09
影响因子：
8.6
通讯作者：
Deem, Michael W.
中科院分区：
文献类型：
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作者：
Davis, Tracy M.;Liu, Albert Tianxiang;Deem, Michael W.
小孔笼型沸石，例如 SSZ-13 (CHA)，可在多种重要反应中用作商业催化剂，包括 NOx 物质 1、2 的选择性催化还原以及甲醇转化为轻质烯烃。 3 Xie 等人最近发表的 SSZ-52 (SFW) 和 CHA 之间的结构相似性。 4 建议 SSZ-52 在这些应用中具有类似的用途。然而，迄今为止，这种独特材料的广泛使用和制造因其合成困难而受到阻碍。具体地，唯一公开的用于制备SSZ-52的方法5需要使用有机结构导向剂(SDA)，其合成时间非常长，因此成本过高。现在，通过从头设计计算和实验工作相结合，已经确定了三种替代的 SDA，它们价格便宜且易于从市售试剂合成。分子筛和沸石尤其用作与炼油、石化过程和有毒气体减排相关的许多化学反应的多相催化剂。 6 根据定义，沸石是微孔材料，其晶体骨架由 TO4 四面体组成（其中 T= Si、Al、Ge、B）。孔隙开口（范围从 3 到 10 Å）、孔隙形状和通道维度的独特组合导致了各种各样的沸石骨架类型（由 3 个字母代码表示）。仔细选择整体孔隙结构以及沸石组成、阳离子取代以及某些情况下的金属负载，使沸石能够用于广泛的应用。尽管200多种已知沸石结构7中只有～20种已用于商业应用，但这些材料作为催化剂的货币价值是巨大的。在新兴的排放控制行业中，沸石的市场价值约为数百亿美元，而在以石油原料生产化学品和燃料时其市场价值则远远超过1000亿美元。众所周知，具有由 8 个 T 原子限定的孔且通向相对较大的笼子的沸石，特别是具有双六环二级结构单元的沸石，在发动机废气中发现的氮氧化物物质的选择性催化还原 (SCR) 中作为催化剂表现良好。 8, 9 此类分子筛被称为笼型小孔沸石，包括 CHA、AFX 和 AEI 骨架类型。此类材料中研究较少的一个成员是 SSZ-52，国际沸石协会结构委员会为它指定了框架代码 SFW。 10 与 CHA 和 AFX 一样，SSZ-52 具有三维通道系统
Small-pore cage-based zeolites such as SSZ-13 (CHA) serve as commercial catalysts in several important reactions including the selective catalytic reduction of NOx-species 1, 2 and in the conversion of methanol to light olefins. 3 Structural similarities between SSZ-52 (SFW) and CHA that were recently published by Xie et al. 4 suggest SSZ-52 will be of similar utility in these applications. However, wide usage and manufacture of this unique material has been hindered to-date by the difficulty of its synthesis. Specifically, the only disclosed method 5 for making SSZ-52 requires use of an organic structure directing agent (SDA) that is highly time intensive to synthesize and therefore cost prohibitive. Now, through a combination of de novo design computations and experimental efforts, three alternative SDAs have been identified that are inexpensive and easily synthesized from commercially available reagents.Molecular sieves and zeolites in particular are used as heterogeneous catalysts for a number of chemical reactions relevant to oil refinement, petrochemical processes and noxious gas mitigation. 6 By definition, zeolites are microporous materials, whose crystalline frameworks are composed of TO4 tetrahedra (where T= Si, Al, Ge, B). Unique combinations of pore openings (ranging from∼ 3 to 10 Å), pore shape and channel dimensionality lead to a wide variety of zeolite framework types (denoted by a 3-letter code). Careful selection of the overall pore architecture along with zeolite composition, cation substitution, and in some cases, metal loading, allow for zeolites to be used over a broad range of applications. Although only∼ 20 of the more than 200 known zeolite structures 7 have been utilized in commercial applications, the monetary value of these materials as catalysts is significant. In the emerging emissions control industry, the market value for zeolites is on the order of tens of billions dollars, and their market value is well in excess of 100 billion dollars in the production of chemicals and fuel from petroleum feedstocks. Zeolites with pores defined by 8 T atoms that open into relatively large cages, and particularly those possessing doublesix ring secondary building units, are known to perform well as catalysts in the selective catalytic reduction (SCR) of the nitrogen oxide species found in engine exhaust. 8, 9 This class of molecular sieves, described as cage-based small-pore zeolites includes CHA, AFX and AEI framework types. A less-studied member of this class of materials is SSZ-52, which has been assigned the framework code SFW by the Structure Commission of the International Zeolite Association. 10 Like CHA and AFX, SSZ-52 has a three-dimensional channel system