Synergistic Defect and Halide Catalysis for CO₂ Cycloaddition on ZIF-8: Mechanistic and Energetic Insights from...

Area of Science:

• Materials Science
• Catalysis
• Green Chemistry

Background:

• Efficient carbon capture and utilization (CCU) is crucial for mitigating climate change.
• Metal-organic frameworks (MOFs) show promise as catalysts for CO2 conversion.
• Understanding catalytic mechanisms at a molecular level is essential for catalyst design.

Purpose of the Study:

• To investigate the catalytic mechanism of CO2 cycloaddition with propylene oxide using a defective ZIF-8 model.
• To elucidate the synergistic effect of Zn-OH-Zn moieties and bromide ions in promoting the reaction.
• To provide molecular insights into defect-engineering strategies for MOFs in CO2 fixation.

Main Methods:

• Density-functional theory (DFT) calculations were employed to study reaction pathways and energy barriers.
• A defective ZIF-8 model incorporating Zn-OH-Zn sites and bromide ions was utilized.
• Computational results were compared with experimental thermodynamic data.

Main Results:

• The uncatalyzed reaction exhibits high activation barriers (52.02–59.31 kcal mol⁻¹).
• The defective ZIF-8 model with bromide assistance drastically reduces the rate-limiting barrier to 14.45 kcal mol⁻¹.
• Calculated reaction energy (-13.89 kcal mol⁻¹) closely matches experimental values (-12.64 kcal mol⁻¹).

Conclusions:

• A synergistic catalytic mechanism involving Lewis acid/base sites and halide assistance is confirmed.
• Defect engineering in ZIF-8 is an effective strategy for enhancing CO2 cycloaddition.
• This study offers valuable insights for developing advanced MOF catalysts for CO2 capture and utilization.