Effect of SiO2 amount on heterogeneous base catalysis of SiO2@Mg–Al layered double hydroxide
| Autor: | Shun Nishimura, Kohki Ebitani, Mahiro Shirotori |
|---|---|
| Rok vydání: | 2018 |
| Předmět: |
chemistry.chemical_classification
Base (chemistry) General Chemical Engineering Layered double hydroxides 02 engineering and technology General Chemistry engineering.material 010402 general chemistry 021001 nanoscience & nanotechnology 01 natural sciences 0104 chemical sciences Catalysis Reaction rate chemistry.chemical_compound chemistry Mole engineering Hydroxide Atomic ratio Crystallite 0210 nano-technology Nuclear chemistry |
| Zdroj: | RSC Advances. 8:28024-28031 |
| ISSN: | 2046-2069 |
| DOI: | 10.1039/c8ra04925d |
| Popis: | The effects of SiO2 amount on the base catalysis of highly active finely crystallized Mg–Al type layered double hydroxides prepared by the co-precipitation method with coexistence of SiO2 spheres, denoted as SiO2@LDHs, were investigated. With the Si/(Mg + Al) atomic ratios of 0–0.50, the highest activity for the Knoevenagel condensation was observed in the case of Si/(Mg + Al) = 0.17, as the reaction rate of 171.1 mmol g(cat)−1 h−1. The base activity increased concomitantly with decreasing LDH crystallite size up to Si/(Mg + Al) atomic ratio of 0.17. However, above the Si/(Mg + Al) atomic ratio of 0.17, the reaction rate and TOFbase were decreased although the total base amount was increased. Results of TEM-EDS and 29Si CP-MAS NMR suggest that the co-existing SiO2 causes advantages for dispersion and reduction of the LDH crystallite to improve the base catalysis of SiO2@Mg–Al LDH, whereas the excess SiO2 species unfortunately poisons the highly active sites on the finely crystallized LDH crystals above a Si/(Mg + Al) atomic ratio of 0.17. According to these results, we inferred that the amount of spherical SiO2 seeds in the co-precipitation method is an important factor to increase the base catalysis of SiO2@LDHs; i.e. the control of Si/(Mg + Al) atomic ratio is necessary to avoid the poisoning of highly active base sites on the LDH crystal. |
| Databáze: | OpenAIRE |
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