Abstract
Polyoxometalates (POMs) are molecular metal oxide clusters that feature a broad range of structures and functionalities, making them one of the most versatile classes of inorganic molecular materials. They have attracted widespread attention in homogeneous catalysis. Due to the challenges associated with their aggregation, precipitation, and degradation under operational conditions and to extend their scope of applications, various strategies of depositing POMs on heterogeneous substrates have been developed. Recent ground‐breaking developments in the materials chemistry of supported POM composites are summarized and links between molecular‐level understanding of POM‐support interactions and macroscopic effects including new or optimized reactivities, improved stability, and novel function are established. Current limitations and future challenges in studying these complex composite materials are highlighted, and cutting‐edge experimental and theoretical methods that will lead to an improved understanding of synergisms between POM and support material from the molecular through to the nano‐ and micrometer level are discussed. Future development in this fast‐moving field is explored and emerging fields of research in POM heterogenization are identified.
Highlights
Over the last decades, polyoxometalates versatile classes of inorganic molecular materials
BTC, 1,3,5-benzene tricarboxylic acid; COF, covalent-organic framework; DMA, N,N-dimethylacetamide; DSSC, dye-sensitized solar cells; FTO, F-doped SnO2; GO, graphene oxide; HER, hydrogen evolution reaction; ITO, In-doped SnO2; LBL, layer-by-layer; LIB, Li-ion batteries; MO, methyl orange; metal–organic frameworks (MOFs), metal–organic framework; MWCNTs, multi-walled carbon nanotubes; NT, nanotube; OER, oxygen evolution reaction; PPy, polypyrrole; PYI, pyrrolidine-2-yl-imidazole; QD, quantum dot; rGO, reduced graphene oxide; RhB, Rhodamine B; SWCNT, single-walled carbon nanotubes; TBA, tetrabutylammonium hydroxide; ZIF, zeolitic imidazolate framework; in situ synthesis means that the procedure has been accomplished in the presence of the POM
These results show that the substrate composition can modulate the Bronsted acidity of the immobilized POM, promoting either oxidation or acid-catalyzed reactions when both pathways are in competition for a given reactant
Summary
General POM immobilization routes have already been summarized in recent reviews.[12,17] Therefore, we will only briefly discuss the most commonly used synthetic concepts to deposit POMs on various heterogeneous substrates and describe the most important modes of chemical interaction between POM and support as schematically illustrated in Figure 1.
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