CO₂ and H₂ Activation on Zinc-Doped Copper Clusters

Area of Science:

• Computational Chemistry
• Materials Science
• Surface Science

Background:

• Understanding the activation and dissociation of small molecules like carbon dioxide (CO2) and hydrogen (H2) is crucial for catalysis.
• Copper-zinc (Cu-Zn) clusters are of interest due to their potential catalytic applications, particularly in CO2 hydrogenation.
• The electronic and structural properties of small metal clusters dictate their reactivity.

Purpose of the Study:

• To systematically investigate the CO2 and H2 activation and dissociation on small neutral and cationic Cu-Zn clusters (Cu_n Zn^(0/+), n=3-6).
• To identify specific cluster compositions and charge states that promote or inhibit key reaction steps.
• To explore the potential of these clusters as synthetic targets for CO2 hydrogenation.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to model the interactions of CO2 and H2 with Cu-Zn clusters.
• Analysis of electronic properties, including HOMO-LUMO gaps, was performed.
• Energetics of CO2 and H2 adsorption and dissociation pathways were evaluated.

Main Results:

• Cu6Zn exhibits superatom characteristics with a large HOMO-LUMO gap, rendering it inert to CO2 and H2 activation.
• Neutral clusters weakly activate CO2, while cationic clusters bind CO2 in a non-activated monodentate fashion.
• Cu4Zn uniquely facilitates activated CO2 dissociation; larger clusters destabilize activated CO2 binding.
• H2 dissociation is favored on most clusters, except Cu6Zn.
• Cu3Zn+ and Cu4Zn promote formate formation via H2 dissociation over CO2 dissociation.

Conclusions:

• The reactivity of Cu-Zn clusters towards CO2 and H2 is highly dependent on cluster size and charge state.
• Cu4Zn shows promise for CO2 activation and dissociation, while Cu6Zn is catalytically inactive.
• These findings highlight the potential of specific Cu-Zn clusters as targets for developing catalysts for CO2 hydrogenation.