Within the context of a "hydrogen economy", it is paramount to guarantee a stable supply of molecular hydrogen to devices such as fuel cells. At the same time, catalytic conversion of the environmentally harmful methane into ethane, with a significantly lower Global Warming Potential, turns into a highly desirable challenge. Herein we propose a first-step novel proof-of-concept mechanism to accomplish both tasks simultaneously. For that purpose we provide transition-state barriers and reaction Helmholtz free energies obtained from first-principles Density Functional Theory by taking account vibrations for 2CH4(g) → C2H6(g) + H2(g) to show that molecular hydrogen can be produced by subnanometer Pt38 and Au38 nanoparticles from natural gas. Interestingly, the active sites for the reaction are located on different planes on the two nanoparticles, effectively differentiating the working principle of the two metals. The analysis shows that the complete cycle to reduce CH4 can be performed on Au and Pt with similar efficiencies, but Au requires only half the working temperature of Pt. This substantial decrease of temperature can be traced back to several intermediate steps, but most crucially to the final one where the catalyst must be cleaned from H(⋆) to be able to restart the catalytic cycle. This simple study case provides useful guidelines to capitalize on finite-size effects in small nanoparticles for the design of new and more efficient catalysts. Interestingly, present results obtained for the intermediate steps of the catalytic cycle show an excellent agreement with previous experimental evidence. Finally, we stress the importance of including the final cleaning steps to start a new fresh catalytic cycle.

中文翻译：

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在甲烷催化还原为乙烷和分子氢方面，Au 如何优于 Pt。

在“氢经济”的背景下，确保向燃料电池等设备稳定供应分子氢至关重要。同时，将对环境有害的甲烷催化转化为乙烷，具有显着降低的全球变暖潜能值，成为一个非常理想的挑战。在这里，我们提出了一种第一步新颖的概念验证机制来同时完成这两项任务。为此，我们通过考虑 2CH4(g) → C2H6(g) + H2(g) 的振动，提供从第一性原理密度泛函理论获得的过渡态势垒和反应亥姆霍兹自由能，以表明分子氢可以通过以下方式产生来自天然气的亚纳米 Pt38 和 Au38 纳米颗粒。有趣的是，反应的活性位点位于两种纳米粒子的不同平面上，有效区分了两种金属的工作原理。分析表明，还原 CH4 的完整循环可以以相似的效率对 Au 和 Pt 执行，但 Au 只需要 Pt 工作温度的一半。温度的这种显着降低可以追溯到几个中间步骤，但最关键的是必须从 H(⋆) 中清除催化剂以重新启动催化循环的最后一个步骤。这个简单的研究案例为利用小纳米粒子的有限尺寸效应设计新的、更高效的催化剂提供了有用的指导。有趣的是，目前在催化循环的中间步骤中获得的结果与之前的实验证据非常吻合。最后，我们强调包括最后清洁步骤以开始新的催化循环的重要性。