Chitac Ruxandra G, Zholobenko Vladimir L, Fletcher Robin S, Softley Emma, Bradley Jonathan, Mayoral Alvaro, Turrina Alessandro, Wright Paul A
EaStCHEM School of Chemistry, University of St Andrews, St Andrews KY16 9ST, U.K.
School of Chemical and Physical Sciences, Keele University, Staffordshire ST5 5BG, U.K.
J Am Chem Soc. 2023 Oct 11;145(40):22097-22114. doi: 10.1021/jacs.3c07873. Epub 2023 Sep 27.
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-C8 (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-C8) possess hierarchical microporosity, consisting of noncrystallographic extra-large micropores (13 Å) that connect with the characteristic and 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 / 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.
通过不同路线合成了SWY型铝硅酸盐沸石STA-30，以了解其缺陷化学和固体酸度。变化的合成参数包括凝胶老化、铝源和有机结构导向剂。所有合成方法都得到了具有相似硅铝比（6-7）的晶体材料，这些材料在活化的K，H形式下稳定，并且通过粉末X射线衍射非常相似。然而，它们在晶体形态、晶内孔隙率和硅醇浓度方面表现出重大差异。以二DABCO-C8（1,1'-（辛烷-1,8-二基）双（1,4-二氮杂双环[2.2.2]辛烷）-1-鎓）为模板的STA-30样品（但以双喹核辛烷二喹-C8为模板的样品除外）具有分级微孔结构，由与SWY结构的特征笼和笼相连的非晶态超大微孔（13 Å）组成。这导致孔体积比活化的二喹-C8_STA-30中测量的孔体积大30%，同时硅醇浓度更高，布朗斯特酸位（BASs）更少。分级孔隙率通过异戊烷吸附和吸附吡啶的FTIR得到证明，结果表明高达77%的BASs是可及的（对于具有小孔晶体结构的沸石来说非常显著）。针对超大微孔提出了单/柱空位的结构模型，这通过高分辨率扫描透射电子显微镜明确揭示。因此，STA-30可以通过直接合成制备成分级多孔沸石。通过选择结晶条件，可以增强或大幅降低沸石中额外的非晶态孔隙率以及随后的SiOHs含量。
