Title : The effect of redox thermal treatment on copper and cobalt species in the CO2 purification of industrial flue gas
Abstract:
Human and environmental health has become a critical concern due to various pollutants mainly CO2 from industrial flue gases that necessities its carbon capture and purification prior to valorization. For the purification of industrial flue gas (CO2, O2, CO, NO, H2O)1, selective catalytic reduction (SCR) of NO by CO under oxidative and wet conditions is conducted effectively in the presence of transition metal-based catalysts, particularly cobalt and copper. Recent studies highlighted the crucial role of copper species2 and carbonate content within CO2 purification process3. Therefore, the aim is to study the effect of reduction/oxidation thermal treatment on copper and carbonate species for the SCR process of industrial flue gas under oxidative and wet conditions.
Cobalt-Copper-Aluminum layered double hydroxides were synthesized via co-precipitation method and calcined under Air or CO2 gas3 at 400 °C to obtain the respective mixed oxides (Co4Cu2Al2 Air or CO2 samples). Subsequent redox cycles (CO-O2 or CO-CO2) were performed on the mixed oxides to promote the formation of specific Cu active sites denoted as Co4Cu2Al2 Air R CO-O2 for example. All samples were characterized by various techniques (XRD, TGA, FTIR, Raman …) and tested in a continuous-flow reactor under simulated flue gas conditions3 (20.5% CO2, 8.8% O2, 8.2% H2O, 1300 ppm of CO and 500 ppm of NO) at temperatures ranging from 100 to 400 °C.
The redox treatment performed on Co4Cu2Al2 mixed oxides demonstrated lower temperatures of total CO oxidation at 240 and 260 °C (Figure 1). XRD analysis revealed crystallographic phases of CuO and Cu2O species within redox treated samples that are responsible for the enhancement of CO oxidation. The Co4Cu2Al2 Air R CO-O2 sample showed enhanced NO reduction compared to the air-treated sample reaching 31% of N2 yield at 320 °C (Figure 1). When comparing NO reduction temperatures, both redox-treated samples exhibited lower temperature of reduction compared to the air treated sample where TG and FTIR analysis confirmed the presence of mono and polydentate carbonates that play a primary role in NO reduction. Based on further characterization (TPR, Raman …), the relationship between catalytic activity and the role of copper and/or carbonate species will be clearly defined.
