Beijing National Laboratory for Molecular Sciences (BNLMS), College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, China.
Department of Chemical Physics, College of Chemistry and Materials Science, iChEM, CAS Center for Excellence in Nanoscience, Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China , Hefei 230026, China.
J Am Chem Soc. 2017 Feb 15;139(6):2267-2276. doi: 10.1021/jacs.6b10375. Epub 2017 Feb 2.
Ruthenium is a promising low-temperature catalyst for Fischer-Tropsch synthesis (FTS). However, its scarcity and modest specific activity limit its widespread industrialization. We demonstrate here a strategy for tuning the crystal phase of catalysts to expose denser and active sites for a higher mass-specific activity. Density functional theory calculations show that upon CO dissociation there are a number of open facets with modest barrier available on the face-centered cubic (fcc) Ru but only a few step edges with a lower barrier on conventional hexagonal-closest packed (hcp) Ru. Guided by theoretical calculations, water-dispersible fcc Ru catalysts containing abundant open facets were synthesized and showed an unprecedented mass-specific activity in the aqueous-phase FTS, 37.8 mol·mol·h at 433 K. The mass-specific activity of the fcc Ru catalysts with an average size of 6.8 nm is about three times larger than the previous best hcp catalyst with a smaller size of 1.9 nm and a higher specific surface area. The origin of the higher mass-specific activity of the fcc Ru catalysts is identified experimentally from the 2 orders of magnitude higher density of the active sites, despite its slightly higher apparent barrier. Experimental results are in excellent agreement with prediction of theory. The great influence of the crystal phases on site distribution and their intrinsic activities revealed here provides a rationale design of catalysts for higher mass-specific activity without decrease of the particle size.
钌是一种很有前途的低温费托合成（Fischer-Tropsch synthesis，FTS）催化剂。然而，其稀缺性和适中的比活性限制了它的广泛工业化应用。在这里，我们展示了一种调整催化剂晶体相的策略，以暴露更密集和更活跃的位点，从而提高质量比活性。密度泛函理论计算表明，在 CO 解离后，面心立方（fcc）钌上有许多具有适中势垒的开放面，而在传统的六方最密堆积（hexagonal-closest packed，hcp）钌上只有几个具有较低势垒的台阶边缘。受理论计算的指导，合成了具有丰富开放面的水散 fcc Ru 催化剂，并在水相 FTS 中表现出了前所未有的质量比活性，在 433 K 时为 37.8 mol·mol·h。平均尺寸为 6.8 nm 的 fcc Ru 催化剂的质量比活性约为尺寸更小（1.9 nm）、比表面积更高的最佳 hcp 催化剂的三倍。尽管 fcc Ru 催化剂的表观势垒略高，但实验确定了其具有更高质量比活性的原因是活性位点的密度高了 2 个数量级。实验结果与理论预测非常吻合。这里揭示的晶体相在活性位分布和本征活性方面的巨大影响，为不降低颗粒尺寸而提高质量比活性的催化剂设计提供了依据。
