Small Co₃O₄ nanoparticles uniformly distributed in size were encapsulated within LTA zeolite crystals in a one-step process through hydrothermal self-assembly of crystalline frameworks around ligated Co²⁺ precursors. The use of bifunctional ligands containing a chelating bidentate amine functionality and an alkoxysilane moiety prevented the precipitation of Co²⁺ species as colloidal hydroxides in the highly alkaline synthesis gels, while also allowing the formation of linkages between precursors and the framework during the nucleation and growth of LTA crystals. Oxidative treatments of ligated compounds occluded within zeolite crystals removed ligand residues and formed small Co₃O₄ nanoparticles visible in transmission electron micrographs. These nanoparticles retained their small size (average diameter 1.5 nm) after oxidative treatment at 620–870 K, a reflection of their stabilization by confinement within zeolite voids. The infrared spectra of adsorbed CO on Co-LTA samples confirmed the absence of Co²⁺ as exchanged cations or aluminosilicates, indicating the presence of Co oxide clusters, with dynamics and stoichiometry of reduction in H₂ corresponding to small Co₃O₄ clusters. Ethanol oxidation rates on Co-LTA samples, exchanged with K⁺ or Ca²⁺ cations to vary the diffusive properties of LTA crystals, indicated that more than 97% of the active surfaces on these Co₃O₄ clusters resided within zeolite crystals, where ethanol and O₂ concentrations depend on the diffusive properties of the LTA framework. The Co₃O₄ clusters prepared by these methods, in contrast with Co²⁺ in exchanged or aluminosilicate forms, exhibit reactivity in CO and NO oxidation. Their turnover rates (per exposed Co atom), however, were lower than on bulk Co₃O₄ powders, because of the combined effects of diffusional constraints imposed by the confining framework and the small size of these clusters, which leads to lower intrinsic reactivities as a result of their more difficult reduction during catalytic redox cycles. These clusters would be attractive in catalytic applications requiring stability against sintering during reaction or regeneration, reactant or product shape selectivity, or protection from contact with large molecules that block active surfaces. Such oxide clusters cannot be formed by sequential ion exchange, detachment by reduction to Co⁰, and re-oxidation because the extremely high temperatures required for reduction destroy the aluminosilicate frameworks. The synthesis protocols and their mechanistic interpretations described herein represent a conceptual and practical platform for the encapsulation of nanoparticles of base elements within a broad range of confining crystalline environments through one-step hydrothermal self-assembly.

通过围绕连接的Co ²⁺前体的晶体骨架的水热自组装，一步一步将大小均匀分布的小Co ₃ O ₄纳米颗粒封装在LTA沸石晶体中。使用含有螯合双齿胺官能团和烷氧基硅烷部分的双官能团配体可防止Co ²⁺物种作为胶体氢氧化物在高碱性合成凝胶中沉淀，同时还允许在成核和生长过程中在前体和骨架之间形成键LTA晶体。沸石晶体中封闭的连接化合物的氧化处理去除了配体残基并形成了小的Co ₃ O _4。在透射电子显微照片中可见的纳米颗粒。这些纳米颗粒在620–870 K氧化处理后仍保持其较小的尺寸（平均直径1.5 nm），这反映了它们被限制在沸石空隙中的稳定性。Co-LTA样品上吸附的CO的红外光谱证实不存在作为交换阳离子或铝硅酸盐的Co ²⁺，表明存在Co氧化物簇，并且动力学和化学计量学上的H ₂还原对应于小的Co ₃ O ₄簇。Co-LTA样品上的乙醇氧化速率，与K ⁺或Ca ²⁺交换阳离子改变LTA晶体的扩散性能，表明这些Co ₃ O ₄簇上超过97％的活性表面位于沸石晶体内，其中乙醇和O _2的浓度取决于LTA骨架的扩散性能。通过这些方法制备的Co ₃ O ₄团簇与交换的或硅铝酸盐形式的Co ²⁺相反，在CO和NO氧化中表现出反应活性。但是，它们的周转率（每个暴露的Co原子）要低于散装Co ₃ O _4的周转率由于限制框架施加的扩散约束和这些团簇的尺寸小，这些粉末的综合作用会导致固有反应性降低，这是由于它们在催化氧化还原循环中难以还原而导致的。这些簇在催化应用中将很有吸引力，因为催化应用需要在反应或再生过程中对烧结具有稳定性，对反应物或产物的形状具有选择性，或者需要防止与阻止活性表面的大分子接触。这样的氧化物簇不能通过顺序的离子交换，还原为Co ⁰来分离而形成。以及再氧化，因为还原所需的极高温度会破坏硅铝酸盐骨架。本文所述的合成方案及其机理解释代表了一种概念和实用的平台，用于通过一步水热自组装将基础元素的纳米粒子封装在宽范围的限制结晶环境中。