Enhanced Stability of Cu Clusters of Low Atomicity against Oxidation. Effect on the Catalytic Redox Process

Abstract

By a combination of theoretical modeling and XPS and SERS spectroscopic studies, it has been found that it is possible to stabilize metallic copper species under oxidizing reaction conditions by adjusting the atomicity of subnanometer copper clusters. Small Cu 5 clusters display low reactivity toward O 2 dissociation, being less susceptible to oxidation than larger Cu 8 or Cu 20 systems. However, in the presence of water this reactivity is strongly enhanced, leading to oxidized Cu 5 clusters. In that case, the interaction of Cu 5 with atomic O oxygen is weak, favoring recombination and O 2 desorption, suggesting an easier transfer of O atoms to other reactant molecules. In contrast, copper clusters of higher atomicity or nanoparticles, such as Cu 8 and Cu 20 , are easily oxidized in the presence of O 2 , leading to very stable and less reactive O atoms, resulting in low reactivity and selectivity in many oxidation reactions. Altogether, Cu 5 clusters are proposed as promising catalysts for catalytic applications where stabilization of metallic copper species is strongly required.

Reversing Size‐Dependent Trends in the Oxidation of Copper Clusters through Support Effects

“…Thus, for the gas phase clusters, we see that Cu 4 is less prone to oxidation than Cu 12 or Cu 20 . This finding is in excellent agreement with the trends reported very recently by Concepción et al, who found that in the gas phase, Cu 5 is less easily oxidized than Cu 8 or Cu 13 . Importantly, comparing the left panels in Figure with the right panels, we find that the presence of the support significantly impacts oxidizability.…”

On the Stability of Cu5 Catalysts in Air Using Multireference Perturbation Theory

“…As one illustrative example, a previous study of the O 2 photodesorption from a reduced TiO 2– x surface highlighted the high multiconfigurational character of the wavefunction for the O 2 –TiO 2– x interaction, with TiO 2– x having being modeled as a cluster in a doublet spin state. 15 , 16 The analysis of the open-shell Cu 5 cluster in this work extends these previous DFT studies 10 , 23 by considering the multireference nature of the O 2 –Cu 5 interaction. Similarities, but also qualitative differences will be discussed in the following sections.…”

“…Much more energy can be harvested from sunlight, and the coated titanium dioxide stores this energy temporarily in the form of charge pairs—electrons and holes—which is a perfect prerequisite for follow-up chemistry. Moreover, experimental measurements 10 have indicated a particularly high stability of Cu 5 clusters with respect to oxidation up to a temperature of 423 K. The experiment by Corma’s group 10 was realized for copper clusters, with and without water, considering N-doped graphene as the support in XPS spectroscopic measurements. Our previous work has shown that a Cu 5 cluster is minimally perturbed when supported on graphene due to the dispersion-dominated nature of the Cu 5 –graphene interaction.…”

Computational Design of Clusters for Catalysis

“…As most of the atoms are at the surface of the structure, they rearrange themselves to minimize the number of dangling bonds and the surface energy, giving rise to unexpected structures. Because of these particularities, interesting and high catalytic activities often arise (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). Hence, heterogeneous catalysis has the potential to undergo a renaissance and to make possible many previously inaccessible industrial processes.…”