重新审视 CO2 加氢对 Ni 的结构敏感性,Journal of the American Chemical Society

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重新审视 CO2 加氢对 Ni 的结构敏感性
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2023-09-07 , DOI: 10.1021/jacs.3c04284
Jérôme F M Simons ₁ , Ton J de Heer ₁ , Rim C J van de Poll ₁ , Valery Muravev ₁ , Nikolay Kosinov ₁ , Emiel J M Hensen ₁

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_{尽管金属纳米粒子催化CO 2}催化加氢生成CO和碳氢化合物已有大量研究，但活性位点的性质和反应机理仍未得到解决。这阻碍了与能量存储相关的有效催化剂的开发。_{通过研究一组二氧化硅负载的Ni纳米颗粒催化剂（2-12 nm）上CO 2}加氢的结构敏感性，我们发现负责将CO ₂转化为CO的活性位点与后续加氢的活性位点不同。 CO转化为CH ₄。虽然前一个反应步骤对纳米颗粒尺寸的依赖性较弱，但后者对结构非常敏感，小于 5 nm 的颗粒会失去甲烷化活性。_{原位X射线衍射和X射线吸收光谱结果表明，不存在显着的氧化或重组，而这可能是观察到的CO 2}氢化速率差异的原因。相反，小纳米粒子上甲烷化活性的降低和相关的较高的 CO 选择性与 CO 解离活跃的阶梯边缘的可用性较低有关。_{Operando红外光谱与（同位素）瞬态实验相结合，揭示了CO 2}加氢过程中Ni表面表面物种的动态，并证明CO ₂直接解离为CO，随后强键合的羰基转化为CH ₄。这些发现为备受争议的CO ₂加氢反应的结构敏感性提供了重要的见解，并且是高活性和选择性催化剂的知识驱动设计的关键。

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Structure Sensitivity of CO2 Hydrogenation on Ni Revisited

Despite the large number of studies on the catalytic hydrogenation of CO₂ to CO and hydrocarbons by metal nanoparticles, the nature of the active sites and the reaction mechanism have remained unresolved. This hampers the development of effective catalysts relevant to energy storage. By investigating the structure sensitivity of CO₂ hydrogenation on a set of silica-supported Ni nanoparticle catalysts (2–12 nm), we found that the active sites responsible for the conversion of CO₂ to CO are different from those for the subsequent hydrogenation of CO to CH₄. While the former reaction step is weakly dependent on the nanoparticle size, the latter is strongly structure sensitive with particles below 5 nm losing their methanation activity. Operando X-ray diffraction and X-ray absorption spectroscopy results showed that significant oxidation or restructuring, which could be responsible for the observed differences in CO₂ hydrogenation rates, was absent. Instead, the decreased methanation activity and the related higher CO selectivity on small nanoparticles was linked to a lower availability of step edges that are active for CO dissociation. Operando infrared spectroscopy coupled with (isotopic) transient experiments revealed the dynamics of surface species on the Ni surface during CO₂ hydrogenation and demonstrated that direct dissociation of CO₂ to CO is followed by the conversion of strongly bonded carbonyls to CH₄. These findings provide essential insights into the much debated structure sensitivity of CO₂ hydrogenation reactions and are key for the knowledge-driven design of highly active and selective catalysts.

更新日期：2023-09-07

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