Highly efficient, selective, and durable photocatalytic system for CO₂ reduction to formic acid

Area of Science:

• Photocatalysis
• Supramolecular Chemistry
• Green Chemistry

Background:

• Selective reduction of carbon dioxide (CO2) to valuable chemicals like formic acid is crucial for sustainable chemistry.
• Developing efficient photocatalysts and suitable sacrificial electron donors is key to advancing CO2 utilization.
• Existing sacrificial electron donors have limitations in terms of efficiency and durability for CO2 reduction.

Purpose of the Study:

• To discover and evaluate a novel sacrificial electron donor for the photocatalytic reduction of CO2 to formic acid.
• To enhance the efficiency, durability, and rate of the photocatalytic process using a Ru(ii)-Ru(ii) supramolecular photocatalyst.
• To compare the performance of the new donor against established alternatives.

Main Methods:

• Synthesis and characterization of a novel sacrificial electron donor: 1,3-dimethyl-2-(o-hydroxyphenyl)-2,3-dihydro-1H-benzo[d]imidazole.
• Photocatalytic reduction of CO2 to formic acid using a Ru(ii)-Ru(ii) supramolecular photocatalyst in the presence of the new donor.
• Quantitative analysis of formic acid yield, photocatalyst efficiency (ΦHCOOH), turnover number (TONHCOOH), and turnover frequency (TOFHCOOH).
• Comparative studies using alternative sacrificial electron donors: 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole and 1-benzyl-1,4-dihydronicotinamide.

Main Results:

• The newly discovered sacrificial electron donor, 1,3-dimethyl-2-(o-hydroxyphenyl)-2,3-dihydro-1H-benzo[d]imidazole, proved highly effective for selective CO2 reduction.
• Significantly enhanced photocatalytic performance was observed, with a quantum yield of formic acid (ΦHCOOH) of 0.46.
• Exceptional durability and rate were achieved, demonstrated by a turnover number (TONHCOOH) of 2766 and a turnover frequency (TOFHCOOH) of 44.9 min⁻¹.
• The performance metrics notably surpassed those obtained with conventional donors like 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole and 1-benzyl-1,4-dihydronicotinamide.

Conclusions:

• 1,3-dimethyl-2-(o-hydroxyphenyl)-2,3-dihydro-1H-benzo[d]imidazole is an exceptionally suitable sacrificial electron donor for CO2 photocatalytic reduction.
• The use of this novel donor in conjunction with a Ru(ii)-Ru(ii) supramolecular photocatalyst dramatically improves the efficiency, durability, and rate of formic acid production.
• This finding represents a significant advancement in the field of CO2 utilization, offering a more effective pathway for sustainable chemical synthesis.