Wang Shibin, Zhao Chengcheng, Li Shenggang, Sun Yuhan
CAS Key Laboratory of Low-Carbon Conversion Science and Engineering, Shanghai Advanced Research Institute, Chinese Academy of Sciences, 100 Haike Road, Shanghai 201210, China.
Phys Chem Chem Phys. 2017 Nov 22;19(45):30874-30882. doi: 10.1039/c7cp04516f.
CoO nanocatalysts have been experimentally shown to have excellent performance in catalyzing CH combustion. These nanocatalysts of different morphologies, such as nanoparticle/nanocube, nanorod/nanobelt, and nanoplate/nanosheet, were previously synthesized and characterized to mainly expose the (001), (011), and (112) surfaces, respectively, with distinct reactivities. In this study, rigorous first principles calculations were performed to investigate CH reactivities of the above CoO surfaces of different terminations. CH dissociation was predicted to occur at the Co-O pair site on these surfaces. For each surface, the most reactive Co-O pair site was identified based on calculated energy barriers of the different active sites, which should contribute most significantly to the reactivity of that surface. The lowest energy barriers for the (001), (011), and (112) surfaces were predicted to be 0.96, 0.90, and 0.79 eV, respectively, suggesting CH reactivity to increase in that order for the different CoO surfaces, consistent with the trend found experimentally for CoO nanocatalysts of different morphologies. Direct comparison between the estimated and experimental CH reaction rates per gram of the nanocatalysts at 325 °C further indicate that their relative ratios were well reproduced by considering three main factors: the effective energy barrier for CH dissociation, the surface area of the nanocatalyst, and the number of independent active sites per unit surface area. The important influence of surface area on CH reactivity is also demonstrated by the significant difference in the reactivities of the nanocatalysts when exposing the same facet but with distinct surface areas.
实验表明，氧化钴（CoO）纳米催化剂在催化甲烷（CH）燃烧方面具有优异性能。先前已合成并表征了不同形态的这些纳米催化剂，例如纳米颗粒/纳米立方体、纳米棒/纳米带以及纳米片/纳米薄板，它们分别主要暴露（001）、（011）和（112）晶面，具有不同的反应活性。在本研究中，进行了严格的第一性原理计算，以研究上述不同端接的CoO晶面的CH反应活性。预计CH在这些表面的Co - O对位点处发生解离。对于每个表面，基于不同活性位点的计算能垒确定了最具反应活性的Co - O对位点，该位点对该表面的反应活性贡献最为显著。预计（001）、（011）和（112）表面的最低能垒分别为0.96、0.90和0.79电子伏特，这表明不同CoO表面的CH反应活性按此顺序增加，这与不同形态的CoO纳米催化剂的实验发现趋势一致。在325°C下每克纳米催化剂的估计CH反应速率与实验CH反应速率之间的直接比较进一步表明，通过考虑三个主要因素可以很好地再现它们的相对比率：CH解离的有效能垒、纳米催化剂的表面积以及每单位表面积的独立活性位点数量。当暴露相同晶面但表面积不同时，纳米催化剂反应活性的显著差异也证明了表面积对CH反应活性的重要影响。
