Efficient and Selective Photocatalytic Conversion of Low-Concentration CO₂ to CO Using Mn-Complex Catalysts

Area of Science:

• Catalysis
• Materials Science
• Green Chemistry

Background:

• Photocatalytic CO2 reduction is crucial for carbon utilization, but performance at low CO2 concentrations remains a challenge.
• Manganese complexes are Earth-abundant and studied for CO2 electrocatalysis, but their photocatalytic application is hindered by unstable dimer formation.
• Previous photocatalytic studies using manganese complexes have not evaluated performance at low CO2 concentrations.

Purpose of the Study:

• To synthesize and evaluate a novel manganese(I) complex for efficient photocatalytic CO2 reduction.
• To investigate the catalyst's performance, particularly its durability and selectivity, at low CO2 concentrations.
• To overcome limitations of previous manganese-based photocatalysts, such as photochemically unstable dimer formation.

Main Methods:

• Synthesis of a novel Mn(I) complex with a sterically bulky mesityl group on a 4,4'-dimethyl-2,2'-bipyridine ligand.
• Photocatalytic reduction of CO2 using the synthesized Mn complex, trifluoroethanol (TFE), diisopropylethylamine, and an organic photosensitizer (4DPAIPN).
• Characterization of the CO2 capture intermediate (MnMes-CO2TFE) and evaluation of catalytic activity, durability, selectivity, turnover number (TON), and quantum yield.

Main Results:

• The novel Mn complex (MnMes-CO2TFE) effectively catalyzes the selective reduction of CO2 to CO in the presence of a photosensitizer.
• Excellent catalytic durability was achieved by suppressing Mn dimer formation, with a maximum TON of 8770 and a quantum yield of 40% for CO formation.
• High selectivity and catalytic rates for CO production were observed even at low CO2 concentrations (1-10%), attributed to efficient CO2 capture.

Conclusions:

• The developed manganese complex offers a durable and highly selective solution for photocatalytic CO2 reduction to CO.
• The catalyst's ability to function effectively at low CO2 concentrations addresses a key challenge for practical CO2 utilization systems.
• This work demonstrates the potential of sterically hindered manganese complexes in advancing Earth-abundant photocatalyst development for sustainable chemistry.