The Role of Solvent Polarity on Low-Temperature Methanol Synthesis Catalyzed by Cu Nanoparticles
The Role of Solvent Polarity on Low-Temperature Methanol Synthesis Catalyzed by Cu Nanoparticles
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DOI：
10.3389/fenrg.2017.00015
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发表时间：
2017-07-14
影响因子：
3.4
通讯作者：
Jens, Klaus-Joachim
中科院分区：
文献类型：
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作者：
Ahoba-Sam, Christian;Olsbye, Unni;Jens, Klaus-Joachim
在液体介质中低温合成甲醇提供了单程合成气完全转化的机会。这项工作的目的是研究溶剂极性对使用八种不同的非质子极性溶剂的低温甲醇合成反应的作用。由铜纳米粒子和甲醇钠组成的“一次通过”催化系统用于在 100 摄氏度和 20 巴合成气压力下合成甲醇。所使用的溶剂极性而不是 7-10 nm Cu（和 SiO2 上的 30 nm Cu）催化剂决定了合成气转化的趋势。在所用的八种不同溶剂中，介电常数 (ε) = 7.2 的二甘醇二甲醚的合成气转化率最高。甲醇的形成随着二甘醇二甲醚溶剂ε值的增加或减少而减少(ε=7.2)。为了探究观察到的趋势，研究了该过程中主要中间体甲酸甲酯（MF）可能发生的副反应。观察到 MF 发生两个主要反应： (i) 脱羰形成 CO 和 MeOH，以及 (ii) 亲核取代形成二甲醚和甲酸钠。降低极性有利于脱羰副反应，而增加极性有利于亲核取代反应。总之，我们的结果表明，中等极性溶剂（例如二甘醇二甲醚）有利于 MF 氢解，从而通过延迟其他两种可能的副反应来促进甲醇的形成。
Methanol syntheses at low temperature in a liquid medium present an opportunity for full syngas conversion per pass. The aim of this work was to study the role of solvents polarity on low-temperature methanol synthesis reaction using eight different aprotic polar solvents. A "once through" catalytic system, which is composed of Cu nanoparticles and sodium methoxide, was used for methanol synthesis at 100 degrees C and 20 bar syngas pressure. Solvent polarity rather than the 7-10 nm Cu (and 30 nm Cu on SiO2) catalyst used dictated trend of syngas conversion. Diglyme with a dielectric constant (epsilon) = 7.2 gave the highest syngas conversion among the eight different solvents used. Methanol formation decreased with either increasing or decreasing solvent epsilon value of diglyme (epsilon = 7.2). To probe the observed trend, possible side reactions of methyl formate (MF), the main intermediate in the process, were studied. MF was observed to undergo two main reactions; (i) decarbonylation to form CO and MeOH and (ii) a nucleophilic substitution to form dimethyl ether and sodium formate. Decreasing polarity favored the decarbonylation side reaction while increasing polarity favored the nucleophilic substitution reaction. In conclusion, our results show that moderate polarity solvents, e.g., diglyme, favor MF hydrogenolysis and, hence, methanol formation, by retarding the other two possible side reactions.