Despite the intensive development of heterogeneous catalysts with transition metal for the Guerbet reaction, a detailed understanding of the metal species and reaction mechanism (rate-determining step and active sites) is still deficient. Herein, we have developed a series of Ni/Ca_xMg_yO catalysts to upgrade n-butanol into branched 2-ethyl-1-hexanol and establish the structure–activity correlation. Given the formation of solid solution between NiO and MgO, the addition of Mg element contributes to the formation of highly dispersed Ni nanoparticles with a small mean size. After optimization in reaction conditions, the highest conversion and selectivity of 80.2 and 79.1%, respectively, were achieved at 240 °C. The pivotal role of Ni⁰ sites and base sites during the Guerbet reaction, as confirmed by the selective poison experiments could be attributed to their synergistic catalysis during the dehydrogenation of n-butanol, which is the rate-determining step of the whole process. Moreover, a possible reaction mechanism for this rate-determining step over Ni/Ca_xMg_yO catalysts was proposed based on experimental results. Overall, this work pushes forward the understanding of the reaction mechanism of the Guerbet reaction over transition-metal-decorated catalysts, which would be constructive for the rational design of heterogeneous catalysts.

中文翻译：

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在Ni / Ca _x Mg _y O上将正丁醇升级为支链醇

尽管在Guerbet反应中大力开发了带有过渡金属的非均相催化剂，但对金属种类和反应机理（决定速率的步骤和活性位点）的详细了解仍然不足。本文中，我们开发了一系列Ni / Ca _x Mg _y O催化剂，将正丁醇升级为支链的2-乙基-1-己醇，并建立了结构-活性相关性。考虑到在NiO和MgO之间形成固溶体，添加Mg元素有助于形成平均粒径较小的高度分散的Ni纳米颗粒。在优化反应条件后，在240°C时，最高转化率和选择性分别达到80.2和79.1％。Ni ⁰的关键作用选择性毒物实验证实，Guerbet反应中的两个位点和碱基可能归因于它们在正丁醇脱氢过程中的协同催化作用，这是整个过程的速率决定步骤。此外，根据实验结果，提出了在Ni / Ca _x Mg _y O催化剂上进行此速率确定步骤的可能反应机理。总体而言，这项工作推动了人们对过渡金属修饰催化剂上的Guerbet反应反应机理的理解，这对合理设计多相催化剂具有建设性。