Highly selective CO₂ photoreduction to CO on MOF-derived TiO₂

Metal–Organic Framework (MOF)-derived TiO₂, synthesised through the calcination of MIL-125-NH₂, is investigated for its potential as a CO₂ photoreduction catalyst. The effect of the reaction parameters: irradiance, temperature and partial pressure of water was investigated. Using a two-level design of experiments, we were able to evaluate the influence of each parameter and their potential interactions on the reaction products, specifically the production of CO and CH₄. It was found that, for the explored range, the only statistically significant parameter is temperature, with an increase in temperature being correlated to enhanced production of both CO and CH₄. Over the range of experimental settings explored, the MOF-derived TiO₂ displays high selectivity towards CO (98%), with only a small amount of CH₄ (2%) being produced. This is notable when compared to other state-of-the-art TiO₂ based CO₂ photoreduction catalysts, which often showcase lower selectivity. The MOF-derived TiO₂ was found to have a peak production rate of 8.9 × 10⁻⁴ μmol cm⁻² h⁻¹ (2.6 μmol g⁻¹ h⁻¹) and 2.6 × 10⁻⁵ μmol cm⁻² h⁻¹ (0.10 μmol g⁻¹ h⁻¹) for CO and CH₄, respectively. A comparison is made to commercial TiO₂, P25 (Degussa), which was shown to have a similar activity towards CO production, 3.4 × 10⁻³ μmol cm⁻² h⁻¹ (5.9 μmol g⁻¹ h⁻¹), but a lower selectivity preference for CO (3 : 1 CH₄ : CO) than the MOF-derived TiO₂ material developed here. This paper showcases the potential for MIL-125-NH₂ derived TiO₂ to be further developed as a highly selective CO₂ photoreduction catalyst for CO production.