Department of Chemical and Biomolecular Engineering, University of California at Berkeley, Berkeley, California 94720, USA.
J Am Chem Soc. 2012 Oct 24;134(42):17688-95. doi: 10.1021/ja307370z. Epub 2012 Oct 16.
The synthesis protocols for encapsulation of metal clusters reported here expand the diversity in catalytic chemistries made possible by the ability of microporous solids to select reactants, transition states, and products on the basis of their molecular size. We report a synthesis strategy for the encapsulation of noble metals and their oxides within SOD (Sodalite, 0.28 nm × 0.28 nm), GIS (Gismondine, 0.45 nm × 0.31 nm), and ANA (Analcime, 0.42 nm × 0.16 nm) zeolites. Encapsulation was achieved via direct hydrothermal synthesis for SOD and GIS using metal precursors stabilized by ammonia or organic amine ligands, which prevent their decomposition or precipitation as colloidal hydroxides at the conditions of hydrothermal synthesis (<380 K) and favor interactions between metal precursors and incipient aluminosilicate nuclei during self-assembly of microporous frameworks. The synthesis of ANA requires higher crystallization temperatures (~415 K) and high pH (>12), thereby causing precipitation of even ligand-stabilized metal precursors as hydroxides. As a result, encapsulation was achieved by the recrystallization of metal clusters containing GIS into ANA, which retained these metal clusters within voids throughout the GIS-ANA transformation.
这里报道的金属团簇包封的合成方案扩展了多微孔固体基于分子尺寸选择反应物、过渡态和产物的能力所实现的催化化学的多样性。我们报告了一种在 SOD（方钠石，0.28nm×0.28nm）、GIS（硅硼钙石，0.45nm×0.31nm）和 ANA（斜发沸石，0.42nm×0.16nm）沸石中包封贵金属及其氧化物的合成策略。通过使用氨或有机胺配体稳定的金属前体制备 SOD 和 GIS 的直接水热合成实现了包封，这可以防止它们在水热合成条件下（<380K）分解或沉淀为胶体氢氧化物，并有利于金属前体与微孔框架自组装过程中初生的硅铝酸盐核之间的相互作用。ANA 的合成需要更高的结晶温度（~415K）和高 pH（>12），从而导致即使是配体稳定的金属前体也会沉淀为氢氧化物。因此，通过将含有 GIS 的金属簇再结晶到 ANA 中实现了包封，在 GIS-ANA 转变过程中，这些金属簇保留在空隙内。
