Department of Chemistry and Applied Biosciences, ETH Zurich , Vladimir Prelog Weg 1-5, CH-8093 Zurich, Switzerland.
Laboratory of Energy Science and Engineering, Department of Mechanical and Process Engineering, ETH Zurich , Leonhardstrasse 21, CH-8092 Zurich, Switzerland.
J Am Chem Soc. 2017 Nov 29;139(47):17128-17139. doi: 10.1021/jacs.7b08984. Epub 2017 Nov 14.
Transition metal nanoparticles (NPs) are typically supported on oxides to ensure their stability, which may result in modification of the original NP catalyst reactivity. In a number of cases, this is related to the formation of NP/support interface sites that play a role in catalysis. The metal/support interface effect verified experimentally is commonly ascribed to stronger reactants adsorption or their facile activation on such sites compared to bare NPs, as indicated by DFT-derived potential energy surfaces (PESs). However, the relevance of specific reaction elementary steps to the overall reaction rate depends on the preferred reaction pathways at reaction conditions, which usually cannot be inferred based solely on PES. Hereby, we use a multiscale (DFT/microkinetic) modeling approach and experiments to investigate the reactivity of the Ni/AlO interface toward water-gas shift (WGS) and dry reforming of methane (DRM), two key industrial reactions with common elementary steps and intermediates, but held at significantly different temperatures: 300 vs 650 °C, respectively. Our model shows that despite the more energetically favorable reaction pathways provided by the Ni/AlO interface, such sites may or may not impact the overall reaction rate depending on reaction conditions: the metal/support interface provides the active site for WGS reaction, acting as a reservoir for oxygenated species, while all Ni surface atoms are active for DRM. This is in contrast to what PESs alone indicate. The different active site requirement for WGS and DRM is confirmed by the experimental evaluation of the activity of a series of AlO-supported Ni NP catalysts with different NP sizes (2-16 nm) toward both reactions.
过渡金属纳米粒子（NPs）通常负载在氧化物上以确保其稳定性，这可能导致原始 NP 催化剂的反应性发生改变。在许多情况下，这与 NP/载体界面位点的形成有关，这些位点在催化中起着作用。实验验证的金属/载体界面效应通常归因于反应物在这些位点上的吸附更强或更容易活化，这可以从基于密度泛函理论（DFT）的势能表面（PES）中得到证实。然而，特定反应基元步骤与总反应速率的相关性取决于反应条件下的优先反应途径，而这些途径通常不能仅基于 PES 推断得出。在这里，我们使用多尺度（DFT/微观动力学）建模方法和实验来研究 Ni/AlO 界面对水煤气变换（WGS）和甲烷干重整（DRM）的反应性，这两种关键的工业反应具有共同的基元步骤和中间体，但在显著不同的温度下进行：分别为 300 和 650°C。我们的模型表明，尽管 Ni/AlO 界面提供了更有利的反应途径，但这些位点是否会影响总反应速率取决于反应条件：金属/载体界面为 WGS 反应提供了活性位，充当含氧物种的储库，而所有 Ni 表面原子都对 DRM 反应具有活性。这与 PES 单独表明的情况相反。实验评估了一系列具有不同 NP 尺寸（2-16nm）的 AlO 负载 Ni NP 催化剂对这两种反应的活性，证实了 WGS 和 DRM 的不同活性位要求。
