Jia Yueqing, Fang Yanjun, Zhang Yingkui, Miras Haralampos N, Song Yu-Fei
State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029 (P. R. China), Fax: (+86) 10-64431832.
School of Economics and Management, Beijing University of Chemical Technology, Beijing 100029 (P. R. China).
Chemistry. 2015 Oct 12;21(42):14862-70. doi: 10.1002/chem.201501953. Epub 2015 Sep 4.
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 PW12 O40 (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 Mg0.73 Al0.22 (OH)2 [PW12 O40 ]0.04 ⋅0.98 H2 O (Mg3 Al-PW12 ) has been successfully obtained by applying a spontaneous flocculation method. The Mg3 Al-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 Mg3 Al-PW12 exhibit no impurity phase usually observed next to the (003) diffraction peak. Subsequent application of the Mg3 Al-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 Mg3 Al-PW12 composite proved to be crucial for the efficiency of the condensation reactions. Additionally, the Mg3 Al-PW12 -catalyzed Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate demonstrated the highest turnover number (TON) of 47 980 reported so far for this reaction.
多金属氧酸盐（POM）插层的层状双氢氧化物（LDH）复合材料家族在设计具有众多应用的功能材料方面显示出巨大的潜力。众所周知，由于空间和几何限制，通过传统离子交换方法将经典的PW12O40（PW12）的Keggin多金属氧酸盐（POM）插入层状双氢氧化物（LDHs）中很难实现。在本文中，通过应用自发絮凝法成功获得了Mg0.73Al0.22(OH)2[PW12O40]0.04·0.98 H2O（Mg3Al-PW12）这种插层化合物。Mg3Al-PW12已通过多种方法（XRD、SEM、TEM、XPS、EDX、XPS、FT-IR、NMR、BET）进行了全面表征。Mg3Al-PW12的XRD图谱在（003）衍射峰附近未显示通常观察到的杂质相。随后，将Mg3Al-PW12作为催化剂应用于各种醛和酮与Z-CH2-Z'型底物（氰基乙酸乙酯和丙二腈）在60°C的混合溶剂（V2-丙醇:V水 = 2:1）中的Knoevenagel缩合反应，结果表明其具有高效的催化活性。Mg3Al-PW12复合材料的酸性和碱性位点之间的协同效应被证明对缩合反应的效率至关重要。此外，Mg3Al-PW12催化的苯甲醛与氰基乙酸乙酯的Knoevenagel缩合反应显示出迄今为止该反应报道的最高周转数（TON）为47980。
