# Electroreduction of CO2 From Flue Gas: Impurity Tolerance and Mechanistic Insights in Molecular Catalysis

## TL;DR

This paper explores how a rhenium-based catalyst efficiently converts CO2 from industrial flue gas into CO, even in the presence of impurities like SO2 and NO2.

## Contribution

The study reveals the impurity tolerance of a molecular Re catalyst during CO2 electroreduction, offering new insights into catalyst design for real-world CO2 sources.

## Key findings

- The Re catalyst maintains high CO selectivity even with 10% CO2 and impurities like O2, NO2, and SO2.
- DFT calculations show low catalyst affinity for impurities due to their reduced forms during CO2RR.
- O2 reduction accounts for most of the charge consumed during CO2 electrolysis.

## Abstract

Direct utilization of diluted CO2 from industrial flue gas containing SO2, NO2 and O2 impurities is economically appealing and circumvents capture and purification prior to conversion. We present experimental data and density functional theory (DFT) calculations for understanding the effect of those impurities during CO2RR catalyzed by a model Re molecular catalyst, [Re(bpy)(CO)3Cl] (bpy = bipyridine). Under both 10% and 1% v/v CO2 gas streams, high selectivity toward CO production was maintained, with faradaic efficiency (FECO) above 90% and 70%, respectively. O2 reduction reaction (ORR) on the electrode surface represents a substantial competitive reaction that accounts for ≈80% of the charge consumed when a realistic CO2 source mimicking an industrial waste‐incinerator stream (10% v/v CO2, 10% v/v O2, 100 ppm NO2, and 50 ppm SO2 in N2 matrix) is used. Neither NO2 nor SO2 incorporated in the diluted CO2 stream provoke a significant decrease in the CO production (FECO ≥ 82%). DFT calculations indicate low affinity of the catalyst for impurities, because they are in their reduced form at the CO2RR potential. This is experimentally proven by cyclic voltammetry and ion chromatography. These findings call for new strategies that enhance the moderate O2‐tolerance exhibited by Re complex on CO2RR from flue gas.

Impurity‐tolerance exhibited by Re molecular complex for CO2 conversion from flue gas containing 10% CO2, 10% O2, 100 ppm NO2 and 50 ppm SO2 in N2 matrix. This tolerance is based on electrochemical reduction of gas impurities on the electrode surface under CO2 electrolysis conditions.© 2026 WILEY‐VCH GmbH