Photocatalytic conversion of carbon dioxide, methane, and air for green fuels synthesis

Abstract

Green fuels are derived from renewable resources that can replace or reduce the use of fossil fuels, and they can help reduce carbon emissions and dependence on finite resources including oil and natural gas. This review reports the latest investigations and studies on methane and carbon dioxide photocatalysis as well as nitrogen fixation for the production of green fuels. Specifically, methanol, formic acid, and ammonia synthesis were thoroughly reviewed to understand the corresponding chemical processes, experimental setups, and production strategies involved. The photocatalytic production of fuels from carbon dioxide and methane is generally affected by low yield and low selectivity, representing the main challenges of these processes. Whereas, a key issue in nitrogen photofixation is the fast oxidation of ammonia to nitrate during simultaneous redox reactions. Indeed, significant yield values were reported for methanol from the partial oxidation of methane (4500 μmol g⁻¹ h⁻¹, Pd/H–TiO₂), methanol from carbon dioxide photoreduction (2910 μmol g⁻¹ h⁻¹, 3% Cu–C/TiO₂), formic acid from carbon dioxide photoreduction (3500 μmol g⁻¹ h⁻¹, g-C₃N₄/(Cu/TiO₂)), and ammonia from nitrogen fixation (3.81 mM g⁻¹ h⁻¹, In(OH)₃/CN). To address the existing challenges and enhance efficiency, various solutions were introduced. For instance, developing photocatalysts with high surface area, fast separation of charges, large charge lifetime, photocatalyst performance, reaction conditions, efficient light absorption, appropriate band gap, changing reactor design, and the use of electron donors to consume the photogenerated electrons were proposed and adopted as potential solutions. Overall, this review provides insights into the opportunities and challenges associated with photocatalytic green fuel production from methane, carbon dioxide, and nitrogen and suggests potential avenues for future research and development.