Khivantsev Konstantin, Vityuk Artem, Aleksandrov Hristiyan A, Vayssilov Georgi N, Alexeev Oleg S, Amiridis Michael D
Department of Chemical Engineering, University of South Carolina, Columbia, South Carolina 29208, USA.
Faculty of Chemistry and Pharmacy, University of Sofia, Blvd. J. Bauchier 1, BG-1126 Sofia, Bulgaria.
J Chem Phys. 2021 May 14;154(18):184706. doi: 10.1063/5.0042322.
Rh(CH) species grafted on the HY zeolite framework significantly enhance the activation of H that reacts with CH ligands to form CH. While in this case, the simultaneous activation of CH and H and the reaction between these species on zeolite-loaded Rh cations is a legitimate hydrogenation pathway yielding CH, the results obtained for Rh(CO)(CH)/HY materials exposed to H convincingly show that the support-assisted CH hydrogenation pathway also exists. This additional and previously unrecognized hydrogenation pathway couples with the conversion of CH ligands on Rh sites and contributes significantly to the overall hydrogenation activity. This pathway does not require simultaneous activation of reactants on the same metal center and, therefore, is mechanistically different from hydrogenation chemistry exhibited by molecular organometallic complexes. We also demonstrate that the conversion of zeolite-supported Rh(CO) complexes into Rh(CO)(CH) species under ambient conditions is not a simple CO/CH ligand exchange reaction on Rh sites, as this process also involves the conversion of CH into C hydrocarbons, among which 1,3-butadiene is the main product formed with the initial selectivity exceeding 98% and the turnover frequency of 8.9 × 10 s. Thus, the primary role of zeolite-supported Rh species is not limited to the activation of H, as these species significantly accelerate the formation of the C hydrocarbons from CH even without the presence of H in the feed. Using periodic density functional theory calculations, we examined several catalytic pathways that can lead to the conversion of CH into 1,3-butadiene over these materials and identified the reaction route via intermediate formation of rhodacyclopentane.
接枝在HY沸石骨架上的Rh(CH)物种显著增强了与CH配体反应形成CH的H的活化。在这种情况下，CH和H的同时活化以及这些物种在负载沸石的Rh阳离子上的反应是产生CH的合理氢化途径，然而，对于暴露于H的Rh(CO)(CH)/HY材料所获得的结果令人信服地表明，载体辅助的CH氢化途径也存在。这种额外的、以前未被认识的氢化途径与Rh位点上CH配体的转化相结合，并对整体氢化活性有显著贡献。该途径不需要在同一金属中心同时活化反应物，因此，在机理上不同于分子有机金属配合物所表现出的氢化化学。我们还证明，在环境条件下，沸石负载的Rh配合物转化为Rh(CO)(CH)物种不是Rh位点上简单的CO/CH配体交换反应，因为这个过程还涉及CH转化为C烃，其中1,3-丁二烯是形成的主要产物，初始选择性超过98%，周转频率为8.9×10 s。因此，沸石负载的Rh物种的主要作用不仅限于H的活化，因为即使进料中不存在H，这些物种也能显著加速CH形成C烃的过程。使用周期性密度泛函理论计算，我们研究了几种能导致这些材料上CH转化为1,3-丁二烯的催化途径，并确定了通过中间形成铑环戊烷的反应路线。
