Issue 15, 2017

Fine-crystallized LDHs prepared with SiO2 spheres as highly active solid base catalysts

Abstract

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.

Graphical abstract: Fine-crystallized LDHs prepared with SiO2 spheres as highly active solid base catalysts

Supplementary files

Article information

Article type
Paper
Submitted
31 Jan 2017
Accepted
13 Mar 2017
First published
13 Mar 2017

J. Mater. Chem. A, 2017,5, 6947-6957

Fine-crystallized LDHs prepared with SiO2 spheres as highly active solid base catalysts

M. Shirotori, S. Nishimura and K. Ebitani, J. Mater. Chem. A, 2017, 5, 6947 DOI: 10.1039/C7TA00984D

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