Photocatalytic CO2 Reduction Based on a Re(I)-Integrated Conjugated Microporous Polymer: Role of a Sacrificial Electron Donor in Product Selectivity and Efficiency

One of the major challenges in photocatalytic CO2 reduction is achieving control over the selective formation of a single product while maintaining a high conversion efficiency. Here, we report the synthesis and characterization of a conjugated microporous polymer (TEB-BPY) formed by C-C coupling between 1,3,5-triethynylbenzene and 5,5 '-dibromo-2,2 '-bipyridine. Further, [Re(CO)5Cl] covalently integrated with the polymer, and the resulting metalated Re@TEB-BPY polymer was used as a catalyst for the visible-light-driven CO2 reduction. Re@TEBBPY displays photoconversion of CO2 to CO with a production rate of 91.7 mu mol g-1 h-1 and a selectivity of similar to 68% in the presence of triethylamine (TEA) as the sole sacrificial electron donor. Interestingly, CH4 is produced as a major product instead of CO when CO2 reduction was performed using 1-benzyl-1,4-dihydronicotinamide (BNAH) as a sacrificial electron donor in the presence of TEA as a base. In this reaction, Re@TEB-BPY produces CH4 as the major product with a rate of 2.05 mmol g-1 h-1 (selectivity of similar to 96% and apparent quantum efficiency of 0.22%). From an in situ diffuse reflectance FTIR spectroscopy (DRIFTS) study together with DFT calculations, a possible catalytic cycle for CO2 reduction to CO or CH4 is constructed. Theoretical calculations along with control experiments further reveal that TEA acts mainly as a base in the presence of BNAH to suppress the back electron transfer process, resulting in enhanced photocatalytic activity.

Automated summary

One of the major challenges in photocatalytic CO2 reduction is achieving control over the selective formation of a single product while maintaining a high conversion efficiency. In this study, a conjugated microporous polymer (TEB-BPY) was synthesized and characterized, and it was found that Re@TEB-BPY exhibited high photocatalytic activity for CO2 reduction to CO or CH4. The presence of triethylamine (TEA) or 1-benzyl-1,4-dihydronicotinamide (BNAH) as sacrificial electron donors influenced the selectivity of the products.