Zhang Hao-Tian, Liu Cheng, Liu Ping, Hu Yun Hang
Department of Materials Science and Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, Michigan 49931-1295, USA.
Mechanical Engineering College, Yangzhou University, 196 Huayang West Road, Yangzhou, Jiangsu 225127, People's Republic of China.
J Chem Phys. 2019 Jul 14;151(2):024304. doi: 10.1063/1.5110875.
The single atom catalysts have been attracting much attention for catalysis. In this work, the significant influence of single-metal-atom (M = K, Ti, Fe, Co, Ni, Cu, Rh) doping on a MoS cluster was revealed for the direct methane to methanol conversion in water stream using density functional theory calculations. It was found that all single atom dopants help to facilitate the conversion via the steam reforming of methane (SRM). The single Fe atom on MoS (Fe-MoS) exhibits the most significant promoting effect, which is followed by Ni, Co, Rh-MoS > K, Ti, Cu-MoS > MoS in a decreasing sequence. The enhanced activity by single atom doping on MoS is mainly associated with the interplay between the ensemble effect via the direct participation of an active M dopant and the site confinement imposed by doping of a single M atom, in tuning the methane conversion and methanol selectivity. It generates the new active center, M, which confines the SRM to occur at the M-Mo bridge sites and facilitates the selective production of methanol. A good single-atom promoter should not only bind OH or O moderately, being strongly enough to help water dissociation and weakly enough to allow the oxidation of methane, but also impose the confinement effect to facilitate the C-O bond association and production of methanol. Our results highlight the importance of the interplay among ligand, ensemble, and confinement effects in promoting the complex SRM over single atom catalysts.
单原子催化剂在催化领域一直备受关注。在这项工作中，利用密度泛函理论计算揭示了单金属原子（M = K、Ti、Fe、Co、Ni、Cu、Rh）掺杂对MoS团簇在水流中直接将甲烷转化为甲醇的显著影响。研究发现，所有单原子掺杂剂都有助于通过甲烷蒸汽重整（SRM）促进转化。MoS上的单Fe原子（Fe-MoS）表现出最显著的促进作用，其次是Ni、Co、Rh-MoS > K、Ti、Cu-MoS > MoS，呈递减顺序。单原子掺杂到MoS上增强的活性主要与活性M掺杂剂直接参与产生的集合效应和单M原子掺杂施加的位点限制之间的相互作用有关，这在调节甲烷转化和甲醇选择性方面发挥作用。它产生了新的活性中心M，将SRM限制在M-Mo桥位发生，并促进甲醇的选择性生成。一个好的单原子促进剂不仅应适度结合OH或O，强到足以帮助水离解，弱到足以允许甲烷氧化，还应施加限制效应以促进C-O键结合和甲醇生成。我们的结果突出了配体、集合和限制效应之间的相互作用在促进单原子催化剂上复杂的SRM中的重要性。
