High Coverage Carbon Monoxide Adsorption on a ZnAl₂O₄ Surface: A DFT Study

Area of Science:

• Materials Science
• Surface Chemistry
• Computational Chemistry

Background:

• Zinc aluminum oxide (ZnAl2O4) spinel is a thermally stable catalyst support.
• Understanding carbon monoxide (CO) interaction with ZnAl2O4 is crucial for reaction mechanisms.
• Surface oxygen vacancies (Ovac) can influence CO adsorption and reactivity.

Purpose of the Study:

• To investigate CO adsorption on perfect and O-defective ZnAl2O4 surfaces using DFT.
• To determine the effect of Ovac concentration and CO coverage on carbon deposition (CD).
• To establish conditions to suppress CD and enhance catalyst performance.

Main Methods:

• Density Functional Theory (DFT) calculations.
• Ab initio atomistic thermodynamics.
• Simulation of CO adsorption at varying coverages and Ovac concentrations.
• DFT-simulated Infrared (IR) spectroscopy.

Main Results:

• Ovac concentration and CO coverage influence C* species formation and aggregation.
• Carbon deposition (CD) occurs at high CO coverages on ZnAl2O4 surfaces.
• Specific CO partial pressures at 523 K are identified to prevent CD for different Ovac concentrations (e.g., <100 atm for 0% Ovac, <10^-6 atm for 37.5% Ovac).
• Varying Ovac concentrations significantly alter CO adsorption peaks and cause red shifts in vibrational frequencies.

Conclusions:

• Surface Ovac concentration is a critical parameter for controlling CO adsorption and preventing CD.
• Tailoring Ovac concentrations in ZnAl2O4 can mitigate CD and improve catalyst durability.
• Findings provide a pathway for designing efficient and robust ZnAl2O4-based catalysts.