Pulparayil Mathew Jikson, Seno Carlotta, Jaiswal Mohit, Simms Charlotte, Reichholf Nico, Van den Eynden Dietger, Parac-Vogt Tatjana N, De Roo Jonathan
Department of Chemistry University of Basel Mattenstrasse 22 Basel 4058 Switzerland.
Department of Chemical Sciences Indian Institute of Science Education and Research (IISER)-Mohali Mohali SAS Nagar Punjab 140306 India.
Small Sci. 2024 Sep 23;5(1):2400369. doi: 10.1002/smsc.202400369. eCollection 2025 Jan.
Oxo clusters are a unique link between oxide nanocrystals and Metal-Organic Frameworks (MOFs), representing the limit of downscaling each of the respective crystals. Herein, the superior catalytic activity of clusters, compared to zirconium MOF UiO-66 and nanocrystals is shown. Focus is on esterification reactions given their general importance in consumer products and the challenge of converting large substrates. Oxo clusters have a higher surface-to-volume ratio than nanocrystals, rendering them more active. For large substrates, for example, oleic acid, MOF UiO-66 has negligible catalytic activity while clusters provide almost quantitative conversion, a fact we ascribe to limited diffusion of large substrates through the MOF pores. Clusters do not suffer from limited mass transfer and we also obtain high conversion in solvent-free reactions with sterically hindered alcohols (hexanol, 2-ethyl hexanol, benzyl alcohol, and neopentyl alcohol). The cluster catalyst can be recovered and shows identical activity when reused. The structural integrity of the cluster is confirmed using X-ray total scattering and pair distribution function analysis. Moreover, when homogeneous zirconium alkoxides are used as catalysts, the same oxo cluster is retrieved, showing that oxo clusters are the active catalytic species, even in previously assumed homogeneously catalyzed reactions.
氧簇是氧化物纳米晶体与金属有机框架（MOF）之间独特的连接体，代表了各自晶体尺寸缩小的极限。在此展示了与锆基MOF UiO - 66和纳米晶体相比，氧簇具有卓越的催化活性。鉴于酯化反应在消费品中的普遍重要性以及转化大分子底物的挑战，研究重点是酯化反应。氧簇的表面体积比高于纳米晶体，使其更具活性。例如，对于大分子底物油酸，MOF UiO - 66的催化活性可忽略不计，而氧簇能实现几乎定量的转化，我们将这一事实归因于大分子底物在MOF孔道中的扩散受限。氧簇不存在传质受限问题，并且在与空间位阻醇（己醇、2 - 乙基己醇、苄醇和新戊醇）的无溶剂反应中也能实现高转化率。该簇状催化剂可回收，重复使用时表现出相同的活性。通过X射线全散射和对分布函数分析证实了簇的结构完整性。此外，当使用均相锆醇盐作为催化剂时，会得到相同的氧簇，这表明即使在先前认为是均相催化的反应中，氧簇也是活性催化物种。
