Shirotori Mahiro, Nishimura Shun, Ebitani Kohki
School of Materials Science, Japan Advances Institute of Science and Technology 1-1 Asahidai Nomi Ishikawa 923-1292 Japan
Graduate School of Advanced Science and Technology, Japan Advances Institute of Science and Technology Japan.
RSC Adv. 2018 Aug 6;8(49):28024-28031. doi: 10.1039/c8ra04925d. eCollection 2018 Aug 2.
The effects of SiO 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 SiO spheres, denoted as SiO@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) h. 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 TOF were decreased although the total base amount was increased. Results of TEM-EDS and Si CP-MAS NMR suggest that the co-existing SiO causes advantages for dispersion and reduction of the LDH crystallite to improve the base catalysis of SiO@Mg-Al LDH, whereas the excess SiO 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 SiO seeds in the co-precipitation method is an important factor to increase the base catalysis of SiO@LDHs; the control of Si/(Mg + Al) atomic ratio is necessary to avoid the poisoning of highly active base sites on the LDH crystal.
研究了SiO用量对通过共沉淀法在SiO球共存下制备的高活性微晶Mg-Al型层状双氢氧化物（记为SiO@LDHs）碱催化性能的影响。当Si/(Mg + Al)原子比为0 - 0.50时，在Si/(Mg + Al) = 0.17的情况下，Knoevenagel缩合反应的活性最高，反应速率为171.1 mmol g(cat) h。在Si/(Mg + Al)原子比达到0.17之前，碱活性随LDH微晶尺寸的减小而增加。然而，当Si/(Mg + Al)原子比高于0.17时，尽管总碱量增加，但反应速率和TOF却降低了。TEM-EDS和Si CP-MAS NMR结果表明，共存的SiO有利于LDH微晶的分散和细化，从而提高SiO@Mg-Al LDH的碱催化性能，而过量的SiO物种在Si/(Mg + Al)原子比高于0.17时会使微晶LDH晶体上的高活性位点中毒。根据这些结果，我们推断共沉淀法中球形SiO晶种的用量是提高SiO@LDHs碱催化性能的重要因素；控制Si/(Mg + Al)原子比对于避免LDH晶体上高活性碱位点中毒是必要的。
