A first principles study of water dissociation on small copper clusters

Area of Science:

• Surface Science
• Catalysis
• Computational Chemistry

Background:

• Water dissociation on copper is a rate-limiting step in the water-gas-shift (WGS) reaction.
• Copper catalysts tend to form clusters under WGS conditions, altering their reactivity.

Purpose of the Study:

• To investigate water adsorption and dissociation on the smallest stable 3D copper cluster, Cu(7), using density functional theory.
• To understand the influence of water coverage on dissociation pathways and kinetics.

Main Methods:

• Density Functional Theory (DFT) calculations.
• Simulation of sequential water adsorption and dissociation on a Cu(7) cluster.
• Analysis of reaction energetics and kinetics at varying water coverages.

Main Results:

• Water adsorbs sequentially on Cu(7) until steric hindrance prevents further direct contact.
• Water dissociation into OH and H is exothermic but requires high temperatures at low coverage; it becomes faster and more exothermic at high coverage.
• Direct OH dissociation is endothermic, but OH species can react to form O adatoms and water.

Conclusions:

• Water dissociation on small copper clusters exhibits similar basic chemical properties to those on larger surfaces.
• High water coverage facilitates exothermic dissociation pathways with fast kinetics.
• The Cu(7) cluster model provides insights into the behavior of copper catalysts in the WGS reaction.