Catalysis at Metal/Oxide Interfaces: Density Functional Theory and Microkinetic Modeling of Water Gas Shift at Pt/MgO Boundaries
Catalysis at Metal/Oxide Interfaces: Density Functional Theory and Microkinetic Modeling of Water Gas Shift at Pt/MgO Boundaries
复制标题
金属/氧化物界面催化作用：密度泛函理论和铂/氧化镁界面水煤气转移的微观动力学模拟
DOI：
10.1007/s11244-020-01257-4
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发表时间：
2020-04-03
影响因子：
3.6
通讯作者：
Greeley, Jeffrey
中科院分区：
文献类型：
--
作者：
Ghanekar, Pushkar;Kubal, Joseph;Greeley, Jeffrey
金属/氧化物界面对氧化物负载的金属纳米颗粒的催化性能的影响是多相催化领域中长期感兴趣的话题。金属/氧化物相互作用的重要性已被证明根据金属纳米颗粒的固有反应性和氧化物载体的性质而变化，其影响例如金属d带中心、纳米颗粒形状和氧化物的还原性被认为有助于整体系统反应性。近年来，水煤气变换（WGS）反应，其中一氧化碳和水转化为二氧化碳和氢气，已成为一种模式化学，以探索如何在这种环境中促进催化的分子水平的细节，这个反应是本贡献的重点。使用周期性的密度泛函理论计算和微观动力学建模相结合，我们提出了一个全面的分析在准一维铂纳米线和不可还原的MgO支持之间的界面处的WGS机制。纳米线晶格匹配的MgO支持，以消除寄生应变在金属/氧化物界面，和反应的纳米线和三相边界本身被认为是在机械分析。此外，为了阐明吸附物-吸附物相互作用对WGS化学的后果，进行CO覆盖度的从头算热力学分析，并明确评估较高覆盖度的CO状态对反应化学的影响。这些结果相结合的详细计算的吸附质熵和双网站的微观动力学建模，以确定动力学上的显着特点的WGS反应网络，随后，通过实验测量的表观反应级数和活化势垒进行验证。分析表明，金属/氧化物界面在反应中起着重要的作用，与水的解离步骤相比，纯金属或氧化物表面是容易在界面处。此外，明确考虑CO与其他吸附物在金属/氧化物界面的相互作用被发现是正确确定反应机制，速率决定步骤，反应顺序，和有效的活化障碍的核心。这些结果被捕获在一个封闭的形式的朗缪尔-欣谢尔伍德模型，来自一个简化版本的完整的微动力学分析，其中揭示了，除其他结果外，著名的羧基机制Mavrikakis和同事是占反应相关的CO覆盖率时的管理途径。
The impact of metal/oxide interfaces on the catalytic properties of oxide-supported metal nanoparticles is a topic of longstanding interest in the field of heterogeneous catalysis. The significance of the metal/oxide interaction has been shown to vary according to both the inherent reactivity of the metal nanoparticle and the properties of the oxide support, with effects such as the metal d-band center, the nanoparticle shape, and the reducibility of the oxide believed to contribute to the overall system reactivity. In recent years, the water gas shift (WGS) reaction, wherein carbon monoxide and water are converted to carbon dioxide and hydrogen, has emerged as a model chemistry to probe the molecular-level details of how catalysis can be promoted in such environments, and this reaction is the focus of the present contribution. Using a combination of periodic Density Functional Theory calculations and microkinetic modeling, we present a comprehensive analysis of the WGS mechanism at the interface between a quasi-one dimensional platinum nanowire and an irreducible MgO support. The nanowire is lattice matched to the MgO support to remove spurious strain at the metal/oxide interface, and reactions both on the nanowire and at the three-phase boundary itself are considered in the mechanistic analysis. Additionally, to elucidate the consequences of adsorbate-adsorbate interactions on the WGS chemistry, an ab-initio thermodynamic analysis of CO coverage is performed, and the impact of the higher coverage CO states on the reaction chemistry is explicitly evaluated. These results are combined with detailed calculations of adsorbate entropies and dual-site microkinetic modeling to determine the kinetically significant features of the WGS reaction network which are subsequently, validated through experimental measurements of apparent reaction orders and activation barrier. The analysis demonstrates the important role that the metal/oxide interface plays in the reaction, with the water dissociation step being facile at the interface compared to the pure metal or oxide surfaces. Further, explicit consideration of CO interactions with other adsorbates at the metal/oxide interface is found to be central to correctly determining reaction mechanisms, rate determining steps, reaction orders, and effective activation barriers. These results are captured in a closed-form Langmuir-Hinshelwood model, derived from a simplified version of the complete microkinetic analysis, which reveals, among other results, that the celebrated carboxyl mechanism of Mavrikakis and coworkers is the governing pathway when accounting for reaction-relevant CO coverages.