Abstract
Despite significant progress made in the past decades, there is still lack of insights into the reactivity of H2O on metal catalysts, in particular, the effect of vibrational modes of H2O in reaction. Here, we report, to the best of our knowledge, the first ab initio study on the correlation between the activation of H2O and the shift of infrared vibrational spectra on the Cu(10-n)Ptn (n = 0–10) alloy clusters. The results revealed that the alloying effect plays an important role in promoting H2O dissociation on Cu(10-n)Ptn (n = 7–9) clusters. The interaction between H2O and substrates fundamentally originates from the band of d-states. The red-shift of the center of v1 and v3 modes of H2O adsorbed relative to that of isolated H2O is a good descriptor of H2O activation. The results probably provide a good opportunity to characterize the reactivity of small molecules on catalysts by infrared vibrational spectra.
Highlights
We investigated all kinds of possible H2O dissociative products to obtain the lowest barriers in the H2O dissociation reaction on the Cu(10-n)Ptn clusters
The structures of transition states corresponding to the lowest barriers and structures of the initial states, final states, and the reaction energies are presented in Figs. 2 and 3
The results revealed that the H2Os prefer the top-site adsorption, and all the structures of transition states correspond to H-dissociation pathways, as shown in Figs. 2 and 3
Summary
Friendly hydrogen fuel generation by the water–gas shift reaction (WGS) has become increasingly important with reduction in fossil fuel resources and the increase in healththreatening pollution. The dissociation of H2O on transition-metal surfaces, which produces chemisorbed H and OH species, is often the rate-limiting step and is of fundamental importance in understanding many industrial heterogeneous catalytic processes, such as the water–gas shift reaction (WGS) and steam reforming. The deep insights into thermodynamics and kinetics of water dissociation would be very helpful for the ultimate control and/or enhancement of the process, which could potentially benefit many industrial processes that involve H2O.4 The increasing understanding has been obtained for the adsorption and dissociation of water on various metal surfaces, e.g., enormous progress on mode specificity and bond selectivity in H2O dissociation processes. It was found that excitations in all three vibrational modes are capable of enhancing reactivity of H2O more effectively than increasing translational energy. Recently, Zhang and co-workers verified that vibrational excitation have a large impact on H2O dissociation by challenging the full-dimensional quantum mechanical calculations. They found that the excitations in vibrational modes of H2O are more efficient in promoting the H2O dissociation than increasing the translational energy, and the excitation in the stretching modes shows larger enhancement than that in the bending modes. Zhang and co-workers verified that vibrational excitation have a large impact on H2O dissociation by challenging the full-dimensional quantum mechanical calculations.5 They found that the excitations in vibrational modes of H2O are more efficient in promoting the H2O dissociation than increasing the translational energy, and the excitation in the stretching modes shows larger enhancement than that in the bending modes. This is in good agreement with the results from the quantum-state-resolved molecular beam experiment on dissociation of D2O on Ni(111)..
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