CO₂ hydrogenation to formic acid on Pd-Cu nanoclusters: a DFT study

Area of Science:

• Catalysis
• Materials Science
• Computational Chemistry

Background:

• Carbon dioxide (CO2) hydrogenation to formic acid is a key strategy for CO2 utilization and chemical synthesis.
• Palladium-copper (Pd-Cu) alloy clusters are investigated as potential catalysts for this transformation.
• Understanding the catalytic mechanisms at the atomic level is crucial for designing efficient catalysts.

Purpose of the Study:

• To investigate the CO2 hydrogenation reaction mechanism on Pd-Cu clusters using theoretical calculations.
• To identify the most stable Pd-Cu cluster configurations and their catalytic activity for formic acid production.
• To elucidate the electronic structure and bonding interactions governing the CO2 adsorption and hydrogenation process.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to study CO2 and H2 interactions on Pd-Cu clusters.
• The climbing image nudge elastic band (CI-NEB) method was used to determine transition states and minimum energy paths.
• Binding energies, adsorption energies, activation barriers, and reaction enthalpies were calculated.
• Density of States (DOS) and charge density distribution analyses were performed to understand electronic properties and bonding.

Main Results:

• Pd2Cu2, Pd4Cu4, and Pd12Cu clusters were identified as the most stable Pd-Cu configurations.
• CO2 adsorption was observed in an inverted V-shaped manner on the stable clusters.
• The hydrogenation of CO2 to formate proceeds via a unidentate intermediate, rapidly transforming to a bidentate structure.
• Lower activation barriers (0.79 eV for Pd2Cu2, 0.68 eV for Pd4Cu4) were found for formic acid formation on Pd2Cu2 and Pd4Cu4 compared to Pd12Cu (1.77 eV).
• Favorable overall reaction enthalpies were calculated for Pd2Cu2 (0.83 eV) and Pd4Cu4 (0.48 eV).

Conclusions:

• Pd2Cu2 and Pd4Cu4 clusters exhibit superior catalytic performance for CO2 hydrogenation to formic acid compared to Pd12Cu.
• The electronic structure, particularly the interaction between Pd 4d, Cu 3d, and CO2 2p orbitals, plays a significant role in CO2 adsorption and activation.
• These findings highlight the potential of specific Pd-Cu cluster compositions as efficient catalysts for CO2 conversion into valuable chemicals.