Synthetic Control of the Defect Structure and Hierarchical Extra-Large-/Small-Pore Microporosity in Aluminosilicate Zeolite SWY.
Synthetic Control of the Defect Structure and Hierarchical Extra-Large-/Small-Pore Microporosity in Aluminosilicate Zeolite SWY.
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DOI：
10.1021/jacs.3c07873
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发表时间：
2023-10-11
影响因子：
15
通讯作者：
Wright, Paul A.
中科院分区：
文献类型：
--
作者：
Chitac, Ruxandra G.;Zholobenko, Vladimir L.;Fletcher, Robin S.;Softley, Emma;Bradley, Jonathan;Mayoral, Alvaro;Turrina, Alessandro;Wright, Paul A.
SWY 型铝硅酸盐沸石 STA-30 通过不同的途径合成，以了解其缺陷化学和固体酸性。不同的合成参数是凝胶老化、铝源和有机结构导向剂。所有合成都会产生具有相似 Si/Al 比 (6-7) 的晶体材料，这些材料在活化的 K,H 形式下是稳定的，并且粉末 X 射线衍射结果非常相似。然而，它们在晶体形态、晶内孔隙率和硅烷醇浓度方面表现出重大差异。 diDABCO-C82+（1,1′-（辛烷-1,8-二基）双（1,4-二氮杂双环[2.2.2]辛烷）-1-ium）模板化的 STA-30 样品（但不包括双奎宁鎓辛烷 diQuin-C82+ 模板化的样品）具有分级微孔性，由非晶体超大微孔 (13 Å) 组成，与SWY结构的特征swy和gme笼连接。这导致孔体积比活化的 diQuin-C8_STA-30 中测量的孔体积高出 30%，并且硅烷醇浓度更高，布朗斯台德酸位点 (BAS) 更少。异戊烷吸附和吸附吡啶的 FTIR 证明了分级孔隙率，这表明高达 77% 的 BAS 是可接近的（对于具有小孔晶体结构的沸石来说非常显着）。针对超大微孔提出了单can/d6r柱空位的结构模型，高分辨率扫描透射电子显微镜明确地揭示了这一点。因此，STA-30 可以通过直接合成制备为分级多孔沸石。通过选择结晶条件，可以提高或强烈降低沸石中额外的非结晶孔隙率以及随后的SiOH含量。
The SWY-type aluminosilicate zeolite, STA-30, has been synthesized via different routes to understand its defect chemistry and solid acidity. The synthetic parameters varied were the gel aging, the Al source, and the organic structure directing agent. All syntheses give crystalline materials with similar Si/Al ratios (6–7) that are stable in the activated K,H-form and closely similar by powder X-ray diffraction. However, they exhibit major differences in the crystal morphology and in their intracrystalline porosity and silanol concentrations. The diDABCO-C82+ (1,1′-(octane-1,8-diyl)bis(1,4-diazabicyclo[2.2.2]octan)-1-ium)-templated STA-30 samples (but not those templated by bisquinuclidinium octane, diQuin-C82+) possess hierarchical microporosity, consisting of noncrystallographic extra-large micropores (13 Å) that connect with the characteristic swy and gme cages of the SWY structure. This results in pore volumes up to 30% greater than those measured in activated diQuin-C8_STA-30 as well as higher concentrations of silanols and fewer Brønsted acid sites (BASs). The hierarchical porosity is demonstrated by isopentane adsorption and the FTIR of adsorbed pyridine, which shows that up to 77% of the BASs are accessible (remarkable for a zeolite that has a small-pore crystal structure). A structural model of single can/d6r column vacancies is proposed for the extra-large micropores, which is revealed unambiguously by high-resolution scanning transmission electron microscopy. STA-30 can therefore be prepared as a hierarchically porous zeolite via direct synthesis. The additional noncrystallographic porosity and, subsequently, the amount of SiOHs in the zeolites can be enhanced or strongly reduced by the choice of crystallization conditions.
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