CO₂ reduction over NaNbO₃ and NaTaO₃ perovskite photocatalysts

The activity of NaNbO₃ and NaTaO₃ perovskites for the photocatalytic reduction of CO₂ is studied in this work. For this purpose, sodium niobate and tantalate have been prepared using solid-state reactions, extensively characterised by means of powder X-ray diffraction, UV-vis, photoluminescence and Raman spectroscopies and N₂ adsorption isotherms, and tested in the gas-phase reduction of CO₂ under UV light in a continuous flow photoreactor. NaNbO₃ is constituted of an orthorhombically distorted perovskite structure, while a ca. 4.5 : 1 combination of the orthorhombic and monoclinic modifications is found in the tantalate. Both catalysts exhibit interesting intrinsic activities, with the tantalate material giving rise to a slightly higher performance. This is attributed to a compromise situation between electron-hole recombination and the reducing potential of conduction band electrons. In addition, a decrease in the competition of water protons for photogenerated electrons is observed with both catalysts with respect to TiO₂.