Department of Chemistry, NSF ERC for Extreme Ultraviolet Science and Technology, Colorado State University, Fort Collins, Colorado 80523, USA.
J Chem Phys. 2013 Aug 28;139(8):084307. doi: 10.1063/1.4819059.
Reactions of CO, C2H4, NO2, and O2 with neutral Mn(m)O(n) clusters in a fast flow reactor are investigated both experimentally and theoretically. Single photon ionization at 118 nm is used to detect neutral cluster distributions through time of flight mass spectrometry. Mn(m)O(n) clusters are generated through laser ablation of a manganese target in the presence of 5% O2/He carrier gas. A strong size dependent reactivity of Mn(m)O(n) clusters is characterized. Reactions Mn2O5/Mn3O7 + CO → Mn2O4/Mn3O6 + CO2 are found for CO oxidation by Mn(m)O(n) clusters, while only association products Mn2O(3-5)C2H4 and Mn3O(5-7)C2H4 are observed for reactions of C2H4 with small Mn(m)O(n) clusters. Reactions of Mn(m)O(n) clusters with NO2 and O2 are also investigated, and the small Mn2O(n) clusters are easily oxidized by NO2. This activation suggests that a catalytic cycle can be generated for the Mn2O5 cluster: Mn2O5 + CO + NO2 → Mn2O4 + CO2 + NO2 → Mn2O5 + CO2 + NO. Density functional theory (DFT) calculations are performed to explore the potential energy surfaces for the reactions Mn2O(4,5)/Mn3O7 + CO → Mn2O(3,4)/Mn3O6 + CO2, Mn2O5 + C2H4 → Mn2O4 + CH3CHO, and Mn2O4 + NO2 → Mn2O5 + NO. Barrierless and thermodynamically favorable pathways are obtained for Mn2O5∕Mn3O7 + CO and Mn2O4 + NO2 reactions. A catalytic cycle for CO oxidation by NO2 over a manganese oxide surface is proposed based on our experimental and theoretical investigations. The various atom related reaction mechanisms explored by DFT are in good agreement with the experimental results. Condensed phase manganese oxide is suggested to be a good catalyst for low temperature CO oxidation by NO2, especially for an oxygen rich sample.
在快速流动反应器中，通过实验和理论研究了 CO、C2H4、NO2 和 O2 与中性 Mn(m)O(n) 团簇的反应。通过 118nm 的单光子电离，通过飞行时间质谱法来检测中性团簇的时间分辨分布。通过在 5%O2/He 载气存在下激光烧蚀锰靶来生成 Mn(m)O(n) 团簇。研究了 Mn(m)O(n) 团簇的强烈的尺寸依赖性反应性。发现 CO 氧化反应 Mn2O5/Mn3O7 + CO → Mn2O4/Mn3O6 + CO2 由 Mn(m)O(n) 团簇进行，而 C2H4 与小的 Mn(m)O(n) 团簇的反应仅观察到 Mn2O(3-5)C2H4 和 Mn3O(5-7)C2H4 的缔合产物。还研究了 Mn(m)O(n) 团簇与 NO2 和 O2 的反应，并且小的 Mn2O(n) 团簇很容易被 NO2 氧化。这种活化表明可以为 Mn2O5 团簇生成一个催化循环：Mn2O5 + CO + NO2 → Mn2O4 + CO2 + NO2 → Mn2O5 + CO2 + NO。进行了密度泛函理论（DFT）计算，以探索反应 Mn2O(4,5)/Mn3O7 + CO → Mn2O(3,4)/Mn3O6 + CO2、Mn2O5 + C2H4 → Mn2O4 + CH3CHO 和 Mn2O4 + NO2 → Mn2O5 + NO 的势能面。获得了 Mn2O5∕Mn3O7 + CO 和 Mn2O4 + NO2 反应的无势垒和热力学有利途径。基于我们的实验和理论研究，提出了在氧化锰表面上由 NO2 氧化 CO 的催化循环。DFT 探索的各种原子相关反应机制与实验结果吻合良好。建议凝聚相氧化锰是一种用于由 NO2 低温氧化 CO 的良好催化剂，特别是对于富氧样品。
