A DFT-based microkinetic study on methanol synthesis from CO₂ hydrogenation over the In₂O₃ catalyst

Area of Science:

• Catalysis
• Materials Science
• Chemical Engineering

Background:

• Methanol synthesis from CO2 is crucial for sustainable energy.
• Understanding the reaction mechanism on indium oxide (In2O3) catalysts is key to optimizing this process.
• Previous studies have explored In2O3 but detailed mechanistic insights remain limited.

Purpose of the Study:

• To elucidate the reaction mechanism of methanol synthesis on the (111) and (110) facets of cubic In2O3 (c-In2O3) using density functional theory (DFT) and microkinetic simulations.
• To identify the rate-determining steps and key intermediates in CO2 hydrogenation to methanol.
• To explain discrepancies between theoretical predictions and experimental observations at different temperatures.

Main Methods:

• Density functional theory (DFT) calculations were employed to determine reaction pathways and energy barriers.
• Microkinetic simulations were performed to model the reaction kinetics under steady-state conditions.
• Degree of Rate Control (DRC) analysis was used to identify the rate-determining step.

Main Results:

• DFT calculations indicate high energy barriers for H atom migration and COOH intermediate formation on both (111) and (110) In2O3 surfaces.
• Direct CO2 deoxygenation to CO is kinetically favored over hydrogenation to COOH.
• Microkinetic simulations suggest CO2 deoxygenation to CO is slower than methanol formation under typical conditions, contradicting high-temperature experimental results.
• DRC analysis for the (111) surface points to homolytic H2 dissociation as the rate-controlling step, not evident from DFT energy barriers alone.

Conclusions:

• The reaction mechanism of methanol synthesis on c-In2O3 is complex and facet-dependent.
• Current models may not fully capture the behavior at high temperatures, potentially due to catalyst structural changes.
• Enhancing CO2 conversion and methanol selectivity on the (111) surface could be achieved by accelerating homolytic H2 dissociation, possibly through doping.