Photocatalytic reduction of CO₂ over Bi₂WO₆ in a continuous-flow differential photoreactor: investigation of operational parameters

Carbon dioxide (CO₂) photoreduction is a complex process and, despite significant efforts in photocatalyst development, an investigation of the influence of process parameters on photoreduction is still necessary. In this work, a Bi₂WO₆ photocatalyst was used for the photocatalytic reduction of CO₂ in a continuous-flow differential photoreactor and a rotational central composite design (RCCD) was employed for a systematic evaluation and optimization of the operational parameters. The experimental parameters considered were CO₂ flow rate, light intensity, partial pressure of H₂O, and amount of photocatalyst. The synthesized Bi₂WO₆ was characterized by XRD, XPS, Raman, SEM, BET measurements and UV–vis spectroscopy. The results showed that the CO₂ flow rate had an impact on CO₂ photoreduction; the light intensity, partial pressure of H₂O, and amount of photocatalyst significantly influenced the CO cumulative production. At optimum conditions (120 mW cm^-2, 2.7 kPa, and 15 mg), it was possible to obtain a 60% enhancement in photocatalytic efficiency, compared to the results obtained before the experimental design. Characterization studies carried out after the use of the photocatalyst showed that Bi₂WO₆ experienced changes on its surface, which may explain the deactivation observed during the photoreduction under gaseous flow.