Zhang Ke-Xiang, Liu Zhi-Pan
Collaborative Innovation Center of Chemistry for Energy Material, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Key Laboratory of Computational Physical Science, Department of Chemistry, Fudan University, Shanghai 200433, China.
State Key Laboratory of Metal Organic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China.
J Am Chem Soc. 2024 Oct 2;146(39):27138-27151. doi: 10.1021/jacs.4c10052. Epub 2024 Sep 19.
Massive ethanol production has long been a dream of human society. Despite extensive research in past decades, only a few systems have the potential of industrialization: specifically, Mn-promoted Rh (MnRh) binary heterogeneous catalysts were shown to achieve up to 60% C oxygenates selectivity in converting syngas (CO/H) to ethanol. However, the active site of the binary system has remained poorly characterized. Here, large-scale machine-learning global optimization is utilized to identify the most stable Mn phases on Rh metal surfaces under reaction conditions by exploring millions of likely structures. We demonstrate that Mn prefers the subsurface sites of Rh metal surfaces and is able to emerge onto the surface forming MnRh surface alloy once the oxidative O/OH adsorbates are present. Our machine-learning-based transition state exploration further helps to resolve automatedly the whole reaction network, including 74 elementary reactions on various MnRh surface sites, and reveals that the Mn-Mn dimeric site at the monatomic step edge is the true active site for C oxygenate formation. The turnover frequency of the C product on the Mn-Mn dimeric site at MnRh steps is at least 10 higher than that on pure Rh steps from our microkinetic simulations, with the selectivity to the C product being 52% at 523 K. Our results demonstrate the key catalytic role of Mn-Mn dimeric sites in allowing C-O bond cleavage and facilitating the hydrogenation of O-terminating C intermediates, and rule out Rh metal by itself as the active site for CO hydrogenation to C oxygenates.
大规模乙醇生产长期以来一直是人类社会的梦想。尽管在过去几十年中进行了广泛的研究，但只有少数系统具有工业化潜力：具体而言，锰促进的铑（MnRh）二元多相催化剂在将合成气（CO/H）转化为乙醇时，被证明能实现高达60%的含氧化合物选择性。然而，该二元体系的活性位点一直未得到很好的表征。在这里，通过探索数百万种可能的结构，利用大规模机器学习全局优化来确定反应条件下铑金属表面上最稳定的锰相。我们证明，锰倾向于铑金属表面的次表面位点，并且一旦存在氧化性的O/OH吸附质，就能出现在表面形成MnRh表面合金。我们基于机器学习的过渡态探索进一步有助于自动解析整个反应网络，包括各种MnRh表面位点上的74个基元反应，并揭示单原子台阶边缘处的Mn-Mn二聚体位点是形成含氧化合物的真正活性位点。根据我们的微观动力学模拟，在MnRh台阶处的Mn-Mn二聚体位点上C产物的周转频率比纯铑台阶上至少高10倍，在523K时对C产物的选择性为52%。我们的结果证明了Mn-Mn二聚体位点在允许C-O键断裂和促进O端基C中间体氢化方面的关键催化作用，并排除了铑金属本身作为CO加氢生成含氧化合物的活性位点。
