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Classical Keggin Intercalated into Layered Double Hydroxides: Facile Preparation and Catalytic Efficiency in Knoevenagel Condensation Reactions
Author(s) -
Jia Yueqing,
Fang Yanjun,
Zhang Yingkui,
Miras Haralampos N.,
Song YuFei
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201501953
Subject(s) - knoevenagel condensation , malononitrile , catalysis , polyoxometalate , layered double hydroxides , chemistry , benzaldehyde , condensation reaction , keggin structure , inorganic chemistry , organic chemistry
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 [PW 12 O 40 ] 3− (PW 12 ) 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 Mg 0.73 Al 0.22 (OH) 2 [PW 12 O 40 ] 0.04 ⋅0.98 H 2 O (Mg 3 Al‐PW 12 ) has been successfully obtained by applying a spontaneous flocculation method. The Mg 3 Al‐PW 12 has been fully characterized by using a wide range of methods (XRD, SEM, TEM, XPS, EDX, XPS, FT‐IR, NMR, BET). XRD patterns of Mg 3 Al‐PW 12 exhibit no impurity phase usually observed next to the (003) diffraction peak. Subsequent application of the Mg 3 Al‐PW 12 as catalyst in Knoevenagel condensation reactions of various aldehydes and ketones with Z‐CH 2 ‐Z′ type substrates (ethyl cyanoacetate and malononitrile) at 60 °C in mixed solvents ( V 2‐propanol : V water =2:1) demonstrated highly efficient catalytic activity. The synergistic effect between the acidic and basic sites of the Mg 3 Al‐PW 12 composite proved to be crucial for the efficiency of the condensation reactions. Additionally, the Mg 3 Al‐PW 12 ‐catalyzed Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate demonstrated the highest turnover number (TON) of 47 980 reported so far for this reaction.