Department of Chemical Engineering, Stanford University, Stanford, CA 94305.
SUNCAT Center for Interface Science and Catalysis, Stanford University, Stanford, CA 94305.
Proc Natl Acad Sci U S A. 2020 Jun 30;117(26):14721-14729. doi: 10.1073/pnas.2002342117. Epub 2020 Jun 17.
Supported metal catalysts are extensively used in industrial and environmental applications. To improve their performance, it is crucial to identify the most active sites. This identification is, however, made challenging by the presence of a large number of potential surface structures that complicate such an assignment. Often, the active site is formed by an ensemble of atoms, thus introducing further complications in its identification. Being able to produce uniform structures and identify the ones that are responsible for the catalyst performance is a crucial goal. In this work, we utilize a combination of uniform Pd/Pt nanocrystal catalysts and theory to reveal the catalytic active-site ensemble in highly active propene combustion materials. Using colloidal chemistry to exquisitely control nanoparticle size, we find that intrinsic rates for propene combustion in the presence of water increase monotonically with particle size on Pt-rich catalysts, suggesting that the reaction is structure dependent. We also reveal that water has a near-zero or mildly positive reaction rate order over Pd/Pt catalysts. Theory insights allow us to determine that the interaction of water with extended terraces present in large particles leads to the formation of step sites on metallic surfaces. These specific step-edge sites are responsible for the efficient combustion of propene at low temperature. This work reveals an elusive geometric ensemble, thus clearly identifying the active site in alkene combustion catalysts. These insights demonstrate how the combination of uniform catalysts and theory can provide a much deeper understanding of active-site geometry for many applications.
负载型金属催化剂在工业和环境应用中得到了广泛的应用。为了提高它们的性能，确定最活跃的反应位点至关重要。然而，由于存在大量潜在的表面结构，使得这种鉴定变得具有挑战性，从而使这种鉴定变得复杂。通常，活性位点是由一组原子形成的，因此在鉴定它时会引入更多的复杂性。能够生成均匀的结构并确定那些对催化剂性能负责的结构是一个关键目标。在这项工作中，我们结合使用均匀的 Pd/Pt 纳米晶催化剂和理论来揭示在高活性丙烯燃烧材料中催化活性位的集合体。通过胶体化学来精确控制纳米颗粒的尺寸，我们发现富 Pt 催化剂上存在水时丙烯燃烧的本征速率随颗粒尺寸单调增加，这表明反应是依赖于结构的。我们还揭示了水在 Pd/Pt 催化剂上的反应速率阶数接近零或略微为正。理论上的见解使我们能够确定水与大颗粒中存在的扩展平台之间的相互作用导致了金属表面台阶位点的形成。这些特定的台阶边缘位点负责在低温下高效燃烧丙烯。这项工作揭示了一个难以捉摸的几何集合体，从而明确地确定了烯属化合物燃烧催化剂中的活性位点。这些见解表明，均匀催化剂和理论的结合如何为许多应用提供对活性位几何形状的更深入理解。
