Polyoxometalate (POM)-Layered Double Hydroxides (LDH) Composite Materials: Design and Catalytic Applications

Abstract

Layered double hydroxides (LDHs) are an important large class of two-dimensional (2D) anionic lamellar materials that possess flexible modular structure, facile exchangeability of inter-lamellar guest anions and uniform distribution of metal cations in the layer. Owing to the modular accessible gallery and unique inter-lamellar chemical environment, polyoxometalates (POMs) intercalated with LDHs has shown a vast array of physical properties with applications in environment, energy, catalysis, etc. Here we describe how polyoxometalate clusters can be used as building components for the construction of systems with important catalytic properties. This review article mainly focuses on the discussion of new synthetic approaches developed recently that allow the incorporation of the element of design in the construction of a fundamentally new class of materials with pre-defined functionalities in catalytic applications. Introducing the element of design and taking control over the finally observed functionality we demonstrate the unique opportunity for engineering materials with modular properties for specific catalytic applications.Keywords: layered double hydroxides; polyoxometalates; intercalated materials Layered Double Hydroxides (LDHs)-Intro BackgroundLayered double hydroxides (LDHs) or hydrotalcite-like compounds are a large family of two-dimensional (2D) anionic clay materials made up of positively charged brucite-like layers with an interlayer region containing charge compensating anions and solvation molecules, which can be represented by the general formula -4]. As shown in Figure 1 and generally in the range of 0.20-0.33, which occupy the space between the layers compensating for the positive charge and inducing stability in the overall structure [5,6]. The M II /M III -based edge shared octahedra are used to construct 2D infinite sheets, whereas hydroxyl groups are organized on the vertices of the octahedra with the hydrogen atoms pointing toward the interlayer region, as a consequence forming a complex network of hydrogen bonds with the interlayer anions and water molecules [1,[7][8][9][10]. LDH-based materials are very attractive systems due to their robust structure,

Boosting the cycling stability of transition metal compounds-based supercapacitors

“…An important type of hydroxide that should be discussed in particular is the binary metal cation based layered double hydroxide (LDH) materials. As shown in Figure 4a, the LDH has a hydrotalcite-like crystalline structure with a general [92,[96][97][98] In addition, transition metal oxyhydroxides including CoOOH and NiOOH also have the potential of delivering high cycling lifetime in SCs. This type of material has a nonstoichiometric composition with a layered structure and a good electric conductivity due to the high oxidation states of transition metal cations, which are beneficial for fast electron and electrolyte ion transportation.…”

Jenseits von Ladungsausgleich: Gegenkationen in der Polyoxometallat‐Chemie

“…Dies führt zur Bildung einer kationischen Überschussladung innerhalb der Schichten, die durch Interkalation mobiler Anionen und Wasser zwischen den Schichten kompensiert wird. Da dieser Bereich chemisch zugänglich ist, kann ein Ionenaustausch der Originalionen mit POMs erfolgen; dies wurde genutzt, um eine Reihe industriell relevanter Katalysatoren herzustellen und komplexe katalytische Kaskaden durchzuführen . In Zukunft könnten diese Materialkonzepte für neue Anwendungen in der multifunktionalen (Elektro‐)Katalyse oder in Batterieelektroden genutzt werden.…”

“…Die Autoren verwendeten ein kovalent durch zwei Terpyridin-Metallkoordinationsstellen kovalent funktionalisiertes Dawson-Anion, das eine Y-artige Struktur aufweist. [153] [162] und komplexe katalytische Kaskaden durchzuführen. [163] In Zukunft kçnnten diese Materialkonzepte für neue Anwendungen in der multifunktionalen (Elektro-)Katalyse oder in Batterieelektroden genutzt werden.…”

Self-Assembly in Polyoxometalate and Metal Coordination-Based Systems: Synthetic Approaches and Developments

“…The formation of LDH-based materials is driven by weak interlayer interactions, and as a consequence, they offer an excellent opportunity for the development of composite compounds by exchanging the anionic and solvent content of the interlayer cavities with the desirable components. For example, exploitation of supramolecular interactions between the LDH layers and POM clusters, have given a wide range of materials with interesting catalytic properties tailored for applications in epoxidations, N-oxidations and desulfurisations [88][89][90][91][92]. …”

“…Figure 16. Schematic representation of the classical LDHs structure [88]. Adapted from Catalysts 2017, 7, 260.…”