Competition between Eley–Rideal and Langmuir–Hinshelwood Pathways of CO Oxidation on Cu_n and Cu_nO (n = 6, 7) Clusters

Abstract

The competition between the Eley−Rideal (ER) and the Langmuir−Hinshelwood mechanisms of CO oxidation on Cu n and Cu n O (n = 6, 7) clusters was explored by means of spin-polarized density functional theory calculations. The separate and successive adsorptions of CO and O 2 on the clusters were studied. CO and O 2 molecules exhibit different adsorption behaviors, and a cooperative effect was noted for their coadsorption. The reaction pathways of CO oxidization were then investigated by locating the transition-state and intermediate structures. The ER mechanism was more favorable for the reactions on Cu 6,7 and Cu 6 O but was less favorable on Cu 7 O. The ER or LH preference of the CO + O 2 reaction on the clusters was further rationalized. We found that activation of O 2 is the key issue that affects the ER−LH competition. The pathway, either ER or LH, in which O 2 is highly activated is always preferred, while the O 2 activation depends on its adsorption pattern, site, and sequence in the presence of CO.

The 2D or 3D morphology of sub-nanometer Cu5 and Cu8 clusters changes the mechanism of CO oxidation

“…Since the key feature behind the different behaviour of the smallest Cu n clusters was traced to their morphology, both the planar and the 3D isomers of Cu 5 are considered, together with a larger 3D Cu 8 cluster to clarify the effect of both cluster size and shape on this reaction. The present study completes the description of CO oxidation on small Cu n clusters, including the work by Wang et al 31 on Cu 6 and Cu 7 , and other studies featuring icosahedral Cu 13 , 32 Cu 20 33 and Cu 55 . 34,35…”

“…This type of oxidized structure has also been reported for planar Cu 6 . 31 From 24 , the reaction would imply a 40.8 kcal mol −1 barrier and a thermodynamically unfavoured product where the cluster is broken into planar rhombic Cu 4 + Cu 1 , which are bridged by the CO 2 formed (structure 26 ). The Cu 5 cluster can be recovered with a barrier of 15.8 kcal mol −1 (structure 27 ) and produces an unfavourably adsorbed bent CO 2 that readily desorbs (structure 28 ).…”

Trends in the Reactivity of Molecular O2 with Copper Clusters: Influence of Size and Shape

“…Notice that, as discussed before for Cu n clusters with n = 3-8, activation energies at the p-PW91 level are systematically lower than those provided by hybrid methods, although the difference between the computed E act values seems to decrease as particle size increases. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 5 Finally, O 2 dissociation over a cuboctahedral Cu 38 These results indicate that while periodic non-hybrid p-PW91 methods yield systematically larger adsorption energies and lower activation barriers for O 2 dissociation when compared to the reference B3PW91/6-311+G(d,p) computational level, the structures involved in the reaction mechanisms and the trends found as particle size increases are similar, and therefore the same chemical conclusions can be obtained irrespectively of the methodology employed.…”

The DFT+U: Approaches, Accuracy, and Applications

“…Studying surface chemistry is of great significance for enhancing the overall efficiency of many electrochemical applications [78][79][80]. In catalysis, for example, understanding the adsorption mechanism of species on catalytic surfaces-mainly electrodes-is essential in order to formulate a design principle for the prefect catalyst that can reach the optimum efficiency for a desired electrochemical process [81][82][83].…”