Nickel Family Metal Clusters for Catalytic Hydrogenation Processes

作者：Han Bo; Cheng Han-Song^*

来源：Acta Physico - Chimica Sinica, 2017, 33(7): 1310-1323.

DOI：10.3866/PKU.WHXB201704172

• Clusters
• Transition metal
• Catalytic hydrogenation
• Full H saturation
• Charge state
• Density functional theory

Nanoparticles of precious metals play an important role in many heterogeneous catalytic reactions due to their excellent catalytic performance. As an idealized model, gas phase metal clusters have been extensively utilized to understand catalytic mechanisms at a molecular level. Here we provide an overview of our recent studies on H-2 dissociative chemisorption on nickel family clusters. The structure evolution and the stability of the metal clusters were first compared. H-2 dissociation on the clusters was then carefully addressed to understand the capability of metal clusters to break the H-H bond. Two key parameters, the dissociative chemisorption energy (Delta E-CE) and the H sequential desorption energy (Delta E-DE), were employed to characterize the catalytic activity of metal clusters. Our results show that both Delta E-CE and Delta E-DE decline significantly as the H coverage increases. Since the catalyst is in general covered entirely by H atoms and H-2 molecules in a typical hydrogenation process, and maintained at a pre-determined pressure of H2 gas, we can rationally use the calculated Delta E-CE and Delta E-DE values at full H saturation to address the activity of metal clusters. Our results suggest that at full H coverage, each Pt atom is essentially capable of adsorbing 4 H atoms, while each Ni or Pd atom can only accommodate 2 H atoms. Considering the similar values of H desorption energies on Pt and Pd clusters, the higher average H capacity per Pt atom could probably lead to a faster reaction rate because more active H atoms are produced on the Pt catalyst particles in the hydrogenation process. Finally, the charge sensitivity of the key catalytic properties of Pt clusters for hydrogenation was systematically evaluated. The results show that the dissociation of H-2 and H desorption are strongly correlated to the charge state of the Pt clusters at low H coverage. However, at high H-capacities, both Delta E-CE and Delta E-DE fall into a narrow range, suggesting that the charge can be readily dispersed and that the Pt H bonds average the interaction between clusters and H atoms. As a result, the H-capacities on charged clusters were found to be similar as the cluster size increased; in case of sufficiently large clusters, the reactivity of a fully saturated cluster was no longer sensitive to its charge state.

• 出版日期2017-5-31
• 单位中国地质大学（北京）