Adsorption and transformations of ethene on hydrogenated rhodium clusters in faujasite-type zeolite. A computational study

作者：Markova Velina K; Vayssilov Georgi N^*; Genest Alexander; Roesch Notker

来源：Catalysis Science & Technology, 2016, 6(6): 1726-1736.

DOI：10.1039/c5cy01589h

Regarding the heterogeneous catalytic hydrogenation of ethene on small rhodium clusters, anchored in faujasite, we computationally studied C2Hx (x = 2-5) intermediates on zeolite-supported Rh-3 and Rh-4 clusters with pre-loaded hydrogen. According to the calculated Gibbs free energies, at temperatures and hydrogen pressure values representing pertinent experiments, the favored stable species on hydrogen-loaded Rh3 is ethylidyne which apparently prevents further hydrogenation due to its strong CH3-C equivalent to Rh-n interaction. In contrast, on bare and hydrogenated Rh-4 clusters, the partially hydrogenated species C2H5, a locally stable intermediate, is among the most stable adsorption complexes examined. These "pseudo ethyl" C2H5 ligands exhibit a very specific structure, where both carbon atoms and a hydrogen atom of the organic moiety interact with the apical Rh center of Rh-4; previously, such ligand structures have been identified only computationally as transition states in homogeneous catalysis of ethene hydrogenation. According to our analysis based on the thermodynamic phase diagrams, one is led to conclude that only Rh clusters of such specific topology may be appropriate for the catalytic hydrogenation of ethene, in contrast to the zeolite-supported Rh-3 clusters. Suggestions are made for further probing this size-specific catalytic activity of Rh clusters.

• 出版日期2016