Classical Keggin Intercalated into Layered Double Hydroxides: Facile Preparation and Catalytic Efficiency in Knoevenagel Condensation Reactions |
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| Authors: | Yueqing Jia Yanjun Fang Prof Yingkui Zhang Dr Haralampos N Miras Prof Yu‐Fei Song |
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| Affiliation: | 1. State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029 (P. R. China), Fax: (+86)?10‐64431832;2. School of Economics and Management, Beijing University of Chemical Technology, Beijing 100029 (P. R. China);3. WestCHEM, School of Chemistry, University of Glasgow, Glasgow, G12 8QQ (UK) |
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| Abstract: | The family of polyoxometalate (POM) intercalated layered double hydroxide (LDH) composite materials has shown great promise for the design of functional materials with numerous applications. It is known that intercalation of the classical Keggin polyoxometalate (POM) of PW12O40]3? (PW12) into layered double hydroxides (LDHs) is very unlikely to take place by conventional ion exchange methods due to spatial and geometrical restrictions. In this paper, such an intercalated compound of Mg0.73Al0.22(OH)2 PW12O40]0.04?0.98 H2O (Mg3Al‐PW12) has been successfully obtained by applying a spontaneous flocculation method. The Mg3Al‐PW12 has been fully characterized by using a wide range of methods (XRD, SEM, TEM, XPS, EDX, XPS, FT‐IR, NMR, BET). XRD patterns of Mg3Al‐PW12 exhibit no impurity phase usually observed next to the (003) diffraction peak. Subsequent application of the Mg3Al‐PW12 as catalyst in Knoevenagel condensation reactions of various aldehydes and ketones with Z‐CH2‐Z′ type substrates (ethyl cyanoacetate and malononitrile) at 60 °C in mixed solvents (V2‐propanol:Vwater=2:1) demonstrated highly efficient catalytic activity. The synergistic effect between the acidic and basic sites of the Mg3Al‐PW12 composite proved to be crucial for the efficiency of the condensation reactions. Additionally, the Mg3Al‐PW12‐catalyzed Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate demonstrated the highest turnover number (TON) of 47 980 reported so far for this reaction. |
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| Keywords: | catalysis Knoevenagel condensation layered double hydroxides polyoxometalates spontaneous flocculation |
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