Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 21, Issue 42, Pages 14862-14870Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201501953
Keywords
catalysis; Knoevenagel condensation; layered double hydroxides; polyoxometalates; spontaneous flocculation
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Funding
- National Basic Research Program [2014CB932104]
- National Science Foundation of China [21222104, U1407127]
- Fundamental Research Funds for the Central Universities [RC1302, YS1406]
- Beijing Engineering Center for Hierarchical Catalysts
- University of Glasgow
- Royal Society of Edinburgh
- Marie Curie Foundation
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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)center dot 0.98H(2)O (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 degrees C in mixed solvents (V2-propanol:V-water=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 47980 reported so far for this reaction.
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