Diversification of RTH-type zeolite and its catalytic application.
Diversification of RTH-type zeolite and its catalytic application.
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DOI：
10.1002/anie.200905214
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发表时间：
2009-12
影响因子：
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通讯作者：
T. Yokoi;M. Yoshioka;H. Imai;T. Tatsumi
中科院分区：
文献类型：
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作者：
T. Yokoi;M. Yoshioka;H. Imai;T. Tatsumi
沸石由于其独特的孔隙率和高比表面积而被广泛应用于气体吸附、离子交换、分离和催化等工业领域。近年来，八元环沸石和沸石型材料受到了广泛关注，因为它们的小孔有望有利于选择性催化。例如，CHA沸石型材料如SSZ-13和SAPO-34显示出优异的甲醇制烯烃（MTO）反应的催化活性，以提供乙烯和丙烯，其是聚合物工业的重要化学品。[1-5]然而，这些催化剂的活性急剧下降，由于沉积的焦炭来自多甲苯和芳香族多环化合物，这是形成在一个空腔中的沸石。[6]1995年发现的RTH型沸石由RTH笼和8 MR开口组成，具有孔径为0.41 ~ 0.38 nm和0.56 ~ 0.25 nm的二维通道，分别平行于a轴和c轴。自发现以来，由于其独特的结构，这种沸石一直被期望在催化和吸附领域显示出独特的性能。注意，用于MTO反应的RTH型沸石的自由体积（408 3）小于CHA型沸石的自由体积（415 3）。[7]考虑到RTH型和CHA型沸石的孔径、尺寸和自由体积的差异，如果将RTH型沸石用作CTO反应的催化剂，可以抑制焦炭的沉积，从而提高催化性能。遗憾的是，迄今为止仅报道了两个关于RTH型沸石的实例。一种是硼硅酸盐沸石，即RUB-13，它是RTH型沸石的第一个例子。该硼硅酸盐（命名为[B]-RU B-13）可以通过使用1，2，2，6，6-五甲基哌啶（PMP）和乙二胺（EDA）的混合物作为有机结构导向剂（SDA）来合成。[7，8]另一种RTH型沸石是SSZ-50，它是一种铝硅酸盐沸石，可用作固体酸催化剂。不幸的是，SSZ-50的合成需要特殊的有机SDA，即N-乙基-N-甲基-5，7，7-三甲基氮鎓双环[4.1. 1]辛烷阳离子，[9]这是不是商业上可获得的，并通过精心设计的多步有机合成。迄今为止，SSZ-50的合成尚未取得显著进展。因此，RTH型沸石的组成变化及其应用受到限制;特别是，杂原子的引入、替代有机SDA的使用和催化应用尚未被研究。因此，我们一直致力于RTH型沸石的多样化。本文中，我们报道了Al原子掺入到用PMP和EDA的混合物作为SDA合成的[B]-RU B-13中。此外，还开发了一种不含有机SDA的RTH型沸石合成路线。首先，我们考察了Al原子直接引入[B]-RUB-13分子筛骨架中的情况。通过向[B]-RU B-13的母凝胶中添加Al 2（SO 4）3来合成[Al，B]-RU B-13的尝试是不成功的。相反，在NaOH和煅烧的[B]-RU B-13晶种存在下，将Al源加入到[B]-RU B-13的母凝胶中。在凝胶中Si/Al比为20时，产物是无定形的（图la）。
Zeolites have been utilized in many industrial technologies, including gas adsorption, ion exchange, separation, and catalysis for their unique porosity and high surface area. Recently, eight-membered-ring (8MR) zeolites and zeolitetype (zeotype) materials have attracted much attention, as their small pores are expected to be beneficial for selective catalysis. For example, CHA-zeotype materials such as SSZ-13 and SAPO-34 showed excellent catalytic activity for the methanol-to-olefins (MTO) reaction to provide ethylene and propylene, which are important chemicals for the polymer industry.[1–5] The activity of these catalysts, however, is drastically decreased owing to the deposition of coke derived from polymethylbenzene and aromatic polycyclic compounds, which are formed in a cavity in the zeolite.[6] The RTH-type zeolite, which was discovered in 1995, consists of RTH cages with 8MR openings and has twodimensional channels with aperture size of 0.41 0.38 nm and 0.56 0.25 nm, which run parallel to the a axis and the c axis, respectively. Since its discovery, this zeolite has been expected to show unique properties in the fields of catalysis and adsorption because of its unique structure. Note that the free volume of RTH-type zeolite for the MTO reaction (408 3) is smaller than that of CHA-type zeolites (415 3).[7] Considering the differences in pore dimension, size, and the free volume between RTH-and CHA-type zeolites, if the RTH-type zeolite is applied as a catalyst for the MTO reaction, the deposition of coke could be suppressed so that the catalytic performances could be improved. Unfortunately, only two examples on the RTH-type zeolites have been reported to date. One is a borosilicate zeolite, RUB-13, which is the first example of the RTH-type zeolite. This borosilicate (designated as [B]-RUB-13) can be synthesized by using a mixture of 1, 2, 2, 6, 6-pentamethylpiperidine (PMP) and ethylenediamine (EDA) as organic structure-directing agents (SDAs).[7, 8] The other RTH-type zeolite is SSZ-50, which is an aluminosilicate zeolite and will be useful as a solid-acid catalyst. Unfortunately, the synthesis of SSZ-50 requires a special organic SDA, N-ethyl-N-methyl-5, 7, 7-trimethylazoniumbicyclo [4.1. 1] octane cation,[9] which is not commercially available and is obtained through an elaborate multistep organic synthesis. The synthesis of SSZ-50 has not been remarkably advanced to date. Thus, the compositional variations in the RTH-type zeolites and their applications have been limited; especially, the incorporation of heteroatoms, the use of alternative organic SDAs, and the catalytic applications have not been investigated. Therefore, we have focused on the diversification of the RTH-type zeolites. Herein, we report the incorporation of Al atoms into [B]-RUB-13 synthesized with a mixture of PMP and EDA as SDAs. Furthermore, an organic-SDA-free synthesis route to the RTH-type zeolites has been developed. Remarkable catalytic activities of newly developed heteroatom-containing RTH-type zeolites for the MTO reaction are also demonstrated.First, the direct incorporation of Al atoms into the framework of [B]-RUB-13 was tested. Attempts to synthesize [Al, B]-RUB-13 by addition of Al2 (SO4) 3 into the mother gel of [B]-RUB-13 were unsuccessful. Instead, the Al source was added to the mother gel of [B]-RUB-13 in the presence of NaOH and a calcined [B]-RUB-13 seed crystal. At a Si/Al ratio of 20 in the gel, the product was amorphous (Figure 1 a).