High Turnover Frequency CO-NO Reactions over Rh Overlayer Catalysts: A Comparative Study Using Rh Nanoparticles
High Turnover Frequency CO-NO Reactions over Rh Overlayer Catalysts: A Comparative Study Using Rh Nanoparticles
复制标题
Rh 覆盖层催化剂上的高周转频率 CO-NO 反应：使用 Rh 纳米粒子的比较研究
DOI：
10.1021/acs.jpcc.9b00383
复制
发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Machida Masato
中科院分区：
文献类型：
--
作者：
Yoshida Hiroshi;Koizumi Kenichi;Boero Mauro;Ehara Masahiro;Misumi Satoshi;Matsumoto Akinori;Kuzuhara Yusuke;Sato Tetsuya;Ohyama Junya;Machida Masato
采用实验和理论相结合的方法，对薄膜催化剂和纳米Rh催化剂之间的结构敏感CO-NO反应进行了比较周转频率研究。制备了两种蜂窝催化剂：一种是在20-μm Fe-Cr-Al金属箔上电弧等离子体沉积具有(111)择优取向的3 nm Rh覆盖层；另一种是在蜂窝陶瓷上湿法包覆含Rh纳米颗粒的Rh/ZrO2粉末。尽管比表面积较小，但覆盖层的反应速度比纳米颗粒更快，因为覆盖层上的TOF是纳米颗粒上的14倍。在情况下，红外光谱表明，与纳米颗粒上的桥式和顶部的NO吸附相反，覆盖层上形成了中空的NO中心。采用基于密度泛函理论的分子动力学方法，以Rh(111)晶片和Rh55团簇为模型，对吸附NO分子的表面反应能垒进行了分析。尽管纳米粒子需要克服更大的N-N复合势垒，但与覆盖层上的中空NO相比，更有利于桥式NO的解离，这表明纳米粒子表面主要覆盖着N和O原子，其中N-N复合是速率限制步骤。相反，Rh(111)覆盖层不仅为无解离和N-N复合提供了中等或相当的能垒，而且使N原子在表面的迁移能垒更低，从而实现了高TOF反应。将计算结果与CO-NO反应的经验动力学进行了比较，验证了该反应机理的合理性。
A comparative turnover frequency (TOF) study for structure-sensitive CO–NO reactions between overlayer (thin-film) and nanoparticle Rh catalysts was performed using a combined experimental and theoretical approach. Two types of honeycomb catalysts were prepared: one by the arc-plasma deposition of a 3 nm Rh overlayer having a (111) preferential orientation atop a 20-μm Fe–Cr–Al metal foil and the other by a conventional wet coating of Rh/ZrO2powders comprised of Rh nanoparticles onto a cordierite honeycomb. The reaction rate of the overlayer was found to be more superior to the nanoparticles, despite a smaller surface area, as the TOF was 14-fold greater on the overlayer than on the nanoparticle.In situinfrared spectroscopy suggested that a hollow-site NO formed onto the overlayer in contrast to the bridge- and on-top-NO adsorptions on the nanoparticles. The energy barriers for surface reactions of adsorbed NO molecules were analyzed using a density functional theory based molecular dynamics approach for a Rh(111) slab and a Rh55cluster to model the overlayer and the nanoparticle. The nanoparticle was more favorable to the dissociation of bridge NO compared with the hollow NO on the overlayer despite needing to overcome much greater barriers for N–N recombination, suggesting that the surface of the nanoparticles was predominately covered by N and O atoms, where N–N recombination was the rate-limiting step. Conversely, the Rh(111) overlayer, which offered not only moderate or comparable energy barriers for NO dissociation and N–N recombination but also a lower energy barrier migration for N atoms on the surface, enabled a high-TOF reaction. The proposed mechanism was rationalized by comparing the results with the empirical kinetics of CO–NO reactions.