Preparation And Properties Of Polyoxometalate Intercalated Layered Double Hydroxides Catalytic Materials

Polyoxometalates (POMs) are a class of discrete anionic metal oxides with unique physical and chemical properties; various techniques can be modified and used to develop a catalytic material widely used in industry. In the case of POMs-based heterogeneous catalysts, two strategies including solidification and immobilization have been adopted up to now. One of the efficient ways is the intercalation of POMs into layered double hydroxides (LDHs) to develop the heterogeneous LDHs-POMs catalysts. LDHs-POMs nanocomposites as heterogeneous catalysts for the synthesis of important intermediates, petrochemicals and photocatalytic degradation of dyes resulting in their excellent catalytic performance attracts more and more researchers attention. Traditional preparation method of LDHs-POMs such as co-precipitation, ion-exchange, and two-step ion-exchange method have some disadvantages such as the M2+/M3+cations can leach out of the LDHs under the neutral to slightly acidic reaction conditions; some POMs are hydrolytically unstable at weakley acidic to basic pH and the intercalation reactions are often accompanied by the co-formation of an impurity phase and POMs intercalation limited POMs geometries, charge and size, such as the classic Keggin-type POMs PW12, because the charge is less than 4, the smaller charge density, conventional synthetic methods is difficult to successfully intercalation。 As such, it is significant to develop new methods for the preparation of POMs intercalated LDHs.In this paper, to solve the problems of the traditional preparation methods LDHs-POMs as a key point, taking Weakley type and Keggin-type acid intercalated into Mg3Al-LDHs layers though spontaneous flocculation method successfully overcome the disadvantage of traditional preparation methods, and resrearch LDHs-POMs catalytic properties, the main contents include two aspects as follows:1> A series of new heterogeneous Mg3Al-LnW10 (Ln= Eu, Tb, Dy) have be achieved through spontaneous flocculation method with electrostatic interactions between exflolied Mg3Al-LDHs and Weakley type Na-LnWi0. The heterogeneous Mg3Al-EuW10 exhibits highly efficient catalytic reactivity for cyanosilylation of various aldehydes and ketones under solvent-free conditions. The cyanosilylation of benzaldehyde and hexanal gives the highest TON of 119950 and 119906, respectively.2.By using spontaneous flocculation method to overcome the geometry problems of PW12 intercalated into Mg3Al-LDHs and successfully prepared the Mg3Al-PW12 Without modified LDHs. Application of the heterogeneous catalyst of Mg3Al-PW12 for Knoevenagel condensation of various aldehydes and ketones with methyl compounds (ethyl cyanoacetate and malononitrile) has been carried out at mild conditions, and it shows excellent Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate with the highest TON of 47980.