Influence of Synthesis Conditions on the Structure of Nickel Nanoparticles and their Reactivity in Selective Asymmetric Hydrogenation
Influence of Synthesis Conditions on the Structure of Nickel Nanoparticles and their Reactivity in Selective Asymmetric Hydrogenation
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DOI：
10.1002/cctc.201901955
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发表时间：
2020-01
期刊：
影响因子：
4.5
通讯作者：
Rosa Arrigo;Simone Gallarati;M. Schuster;Jake M Seymour;D. Gianolio;I. Silva;J. Callison;Hao Feng;J. Proctor;P. Ferrer;F. Venturini;D. Grinter;G. Held
中科院分区：
文献类型：
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作者：
Rosa Arrigo;Simone Gallarati;M. Schuster;Jake M Seymour;D. Gianolio;I. Silva;J. Callison;Hao Feng;J. Proctor;P. Ferrer;F. Venturini;D. Grinter;G. Held
以油胺(OAM)为还原剂，三辛基膦(TOP)为保护剂，采用热注射胶体法制备了无负载和二氧化硅负载的镍纳米粒子(NPs)。通过多尺度结构表征发现，改变OAM和TOP的当量不仅影响了纳米粒子的尺寸，而且影响了镍的电子结构。用(R，R)-酒石酸(TA)对合成的纳米粒子进行了修饰，并对乙酰乙酸甲酯不对称加氢合成手性3-羟基丁酸甲酯进行了研究。通过对合成的催化剂的结构和催化性能的对比分析，我们发现了一种镍金属活性表面，其活性随着金属结构域的大小而增加。相反，对于无载体的NPs，在获得高转化率的情况下，颗粒大小对选择性没有影响。(R)-选择性只有在含有正电的镍物种的催化剂上才有很高的选择性，例如在二氧化硅负载的NiO纳米粒子上。这项工作表明，金属镍纳米粒子的TA手性修饰不足以在长时间内保持对(R)-对映体的高选择性，这为设计长期稳定的对映体选择性催化剂提供了指导。
Unsupported and SiO2‐supported Ni nanoparticles (NPs) were synthesised via hot‐injection colloidal route using oleylamine (OAm) and trioctylphosphine (TOP) as reducing and protective agents, respectively. By adopting a multi‐length scale structural characterization, it was found that by changing equivalents of OAm and TOP not only the size of the nanoparticles is affected but also the Ni electronic structure. The synthetized NPs were modified with (R,R)‐tartaric acid (TA) and investigated in the asymmetric hydrogenation of methyl acetoacetate to chiral methyl‐3‐hydroxy butyrate. The comparative analysis of structure and catalytic performance for the synthetized catalysts has enabled us to identify a Ni metallic active surface, whereby the activity increases with the size of the metallic domains. Conversely, at the high conversion obtained for the unsupported NPs there was no impact of particle size on the selectivity. (R)‐selectivity was very high only on catalysts containing positively charged Ni species such as over the SiO2‐supported NiO NPs. This work shows that the chiral modification of metallic Ni NPs with TA is insufficient to maintain high selectivity towards the (R)‐enantiomer at long reaction times and provides guidance for the engineering of long‐term stable enantioselective catalysts.