Fine-crystallized LDHs prepared with SiO2 spheres as highly active solid base catalysts
Fine-crystallized LDHs prepared with SiO2 spheres as highly active solid base catalysts
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DOI：
10.1039/c7ta00984d
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发表时间：
2017-04
影响因子：
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通讯作者：
Mahiro Shirotori;S. Nishimura;K. Ebitani
中科院分区：
文献类型：
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作者：
Mahiro Shirotori;S. Nishimura;K. Ebitani
采用共沉淀法制备了SiO2微球（SiO2@LDH）层状双金属氢氧化物，并对其碱催化性能和结构性能进行了研究。所制备的SiO2@LDHs表现出更高的碱催化的Knoevenagel缩合比常规的LDHs通过共沉淀法制备的SiO2球的情况下。在具有不同金属组成（M2+：Mg 2+或Ni 2+，M3+：Al 3+或Ga 3+，以及M2+/M3+：1或3）的各种类型的SiO2@LDH中也观察到碱催化活性的这种增加。X射线衍射（XRD）测量表明，添加SiO2诱导LDH晶粒尺寸减小。对SiO2@Mg-Al LDH的透射电子显微镜-能量色散X射线能谱（TEM-EDS）和29 Si交叉极化魔角自旋核磁共振（29 Si CP-MAS NMR）分析表明，Mg-Al LDH晶体通过Si-O-Al和Si-O-Mg共价键固定在SiO2表面。根据这些结果，我们得出结论，在胶体球形SiO2种子的存在下，特别是具有40 nm的直径的共沉淀法，导致LDH晶体生长在SiO2表面上的高度分散的点，这导致细结晶的高活性LDH纳米晶体的产生。
Fine-crystallized layered double hydroxides are prepared via the co-precipitation method with the coexistence of SiO2 spheres (SiO2@LDH), and their base catalysis and structural properties are investigated. The as-prepared SiO2@LDHs exhibit higher base catalysis for the Knoevenagel condensation than conventional LDHs prepared via the co-precipitation method in the absence of SiO2 spheres. Such an increase in the activity for base catalysis is also observed in various types of SiO2@LDHs with different metal compositions (M2+: Mg2+ or Ni2+, M3+: Al3+ or Ga3+, and M2+/M3+: 1 or 3). X-ray diffraction (XRD) measurement suggests that the addition of SiO2 induces decreases in the LDH crystallite size. The results of transmission electron microscopy – energy dispersive X-ray spectroscopy (TEM-EDS) and 29Si cross polarization magic angle spinning nuclear magnetic resonance (29Si CP-MAS NMR) on SiO2@Mg–Al LDH suggest that the crystals of Mg–Al LDH are immobilized on the SiO2 surface through Si–O–Al and Si–O–Mg covalent bonds. According to these results, we conclude that the co-precipitation method in the presence of colloidal spherical SiO2 seeds, particularly possessing a 40 nm diameter, result in highly-dispersed points of LDH crystal growth on the SiO2 surface, which lead to the generation of fine-crystallized highly active LDH nanocrystals.