Department of Materials Science and Engineering, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon 34134, Republic of Korea.
Nanoscale. 2017 Aug 24;9(33):12077-12086. doi: 10.1039/c7nr04435f.
When the elements that compose bimetallic catalysts interact asymmetrically with reaction feedstock, the surface concentration of the bimetallic catalysts and the morphology of the reaction center evolve dynamically as a function of environmental factors such as the partial pressure of the triggering molecule. Relevant experimental and theoretical findings of the dynamic structural evolution of bimetallic catalysts under the reaction conditions are emerging, thus enabling the design of more consistent, reliable, and efficient bimetallic catalysts. In an initial attempt to provide an atomic-level understanding of the adsorption-induced structural evolution of bimetallic nanoparticles (NPs) under CO oxidation conditions, we used density functional theory to study the details of CO-adsorption-driven Pd surface segregation in (AuPd) bimetallic NPs. The strong CO affinity of Pd provides a driving force for Pd surface segregation. We found that the vertex site of the NP becomes a gateway for the initial Pd-Au swapping and the subsequent formation of an internal vacancy. This self-generated internal vacancy easily diffuses inside the NP and activates Pd-Au swapping pathways in the (100) NP facet. Our results reveal how the surface and internal concentrations of bimetallic NPs respond immediately to changes in the reaction conditions. Our findings should aid in the rational design of highly active and versatile bimetallic catalysts by considering the environmental factors that systematically affect the structure of bimetallic catalysts under the reaction conditions.
当组成双金属催化剂的元素与反应原料不对称地相互作用时，双金属催化剂的表面浓度和反应中心的形态会随着环境因素（如触发分子的分压）的变化而动态演化。在反应条件下，双金属催化剂的动态结构演化的相关实验和理论研究结果正在出现，从而能够设计出更一致、可靠和高效的双金属催化剂。在试图从原子水平上理解 CO 氧化条件下双金属纳米颗粒（NPs）的吸附诱导结构演化的初步尝试中，我们使用密度泛函理论研究了 CO 吸附驱动下（AuPd）双金属 NPs 中 Pd 表面偏析的细节。Pd 的强 CO 亲和力为 Pd 表面偏析提供了驱动力。我们发现，NP 的顶点位置成为初始 Pd-Au 交换和随后形成内部空位的门户。这种自生成的内部空位容易在 NP 内部扩散，并在（100）NP 面中激活 Pd-Au 交换途径。我们的结果揭示了双金属 NPs 的表面和内部浓度如何立即响应反应条件的变化。我们的发现应该有助于通过考虑系统地影响反应条件下双金属催化剂结构的环境因素，来合理设计高活性和多功能的双金属催化剂。
