Investigation of process parameters assessment via design of experiments for CO₂ photoreduction in two photoreactors

CO₂ photoreduction with water to obtain solar fuels is one of the most innovative and sustainable processes to harvest light energy and convert it into hydrocarbons. Although photocatalytically active materials and photoreactors have been developed for this purpose, lack of standardisation in testing conditions makes the assessment of process parameters and the comparison of material performance a challenge. Therefore, this paper is aimed at investigating the effect of CO₂ photoreduction parameters irradiance and reaction time on production of methane from two photocatalytic rigs. This was pursued through a design of experiments (DOE) approach, which assessed the influence of experimental conditions between different setups. Using low irradiance (40–60 W m⁻²), reaction time and temperature significantly affected methane production, with a maximum production of 28.50 μmol g_cat⁻¹ (40 W m⁻², 4 h). When using high irradiance (60–2400 W m⁻²), only irradiance was found to significantly affect methane production, with a maximum production of 1.90 ∙ 10⁻¹ μmol g_cat⁻¹ (1240 W m⁻², 2 h). Considering proposed reaction mechanism for CO₂ photoreduction, this paper highlights that experimental results give different yet complementary information on the two most important steps of the process, i.e. photoexcitation and surface chemical reaction.