CO2 reduction over NaNbO3 and NaTaO3 perovskite photocatalysts

Abstract

The activity of NaNbO and NaTaO perovskites for the photocatalytic reduction of CO 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 N adsorption isotherms, and tested in the gas-phase reduction of CO under UV light in a continuous flow photoreactor. NaNbO 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 TiO.

Recent Progress in Photocatalytic CO2 Reduction Over Perovskite Oxides

“…For example, the conduction band of NaTaO 3 is more negative by 0.7 eV than that of NaNbO 3 , while their O 2p orbital‐valence bands are almost identical due to the similar ionic radius of oxygen anions coordinated to Ta 5+ or Nb 5+ . Recently, O'Shea et al prepared NaNbO 3 and NaTaO 3 with similar surface area and crystal size via high temperature solid‐state reactions . The crystal structures of both samples were predominantly orthorhombic phase, with the NaTaO 3 also containing approximately 18% monoclinic phase.…”

“…Both tantalum and niobium are group VB elements. Thus, perovskite tantalates and niobates share many similar properties, including valence band energy levels and charge transfer properties . Ta 5d orbitals have a more negative potential than Nb 4d orbitals.…”

“…Generally, for B‐site cations, as you go down a group the conduction band will shift to more negative potentials and the bandgap will get larger (c.f. NaNbO 3 E g = 3.3 eV, NaTaO 3 E g = 4.0 eV) . For A‐site cations, the conduction band will shift to more positive potentials and the bandgap narrow on going down a group (c.f.…”

Recent Advances in Niobium-Based Materials for Photocatalytic Solar Fuel Production

“…The authors also investigated the effect of annealing temperature in the CO2 reduction performance, and a deleterious effect with the increase in the temperature was observed. On the basis of previous reports, Fresno et al evaluated the CO2 photoreduction performance of NaNbO3 obtained by solid state reaction at 900 °C and compared it with NaTaO3 photoactivity [87]. Owing to the high annealing temperature, orthorhombic NaNbO3 with low surface area was obtained (~1 m 2 •g −1 ).…”

Highly Active NaTaO3‐Based Photocatalysts for CO2 Reduction to Form CO Using Water as the Electron Donor

“…Therefore, it is expected that the NaTaO 3 :A (A = Mg, Ca, Sr,B a, and La) photocatalysts show high activity for CO 2 reductionu sing water as an electron donor.R ecently,s everal groups reported CO 2 reduction on NaTaO 3 photocatalysts in an aqueous solution. [24][25][26] Small amountso fh ydrocarbons and Doped NaTa O 3 (NaTaO 3 :A,w here A = Mg, Ca, Sr,B a, or La) has arisen as ah ighly active photocatalyst for CO 2 reduction to simultaneously form CO, H 2 ,a nd O 2 using water as the electron donor when used with an Ag cocatalyst, under UV irradiation, and with 1atm (0.1 MPa)o fC O 2 .T he ratio of the number of reactede lectrons/holes was almost unity,i ndicating that water was consumeda st he electrond onor.Al iquid-phaser eduction methodf or loading of the Ag cocatalyst wass uperiort op hotodeposition and impregnationm ethods. The Ag cocatalystloaded NaTaO 3 :Ba wast he most active photocatalyst in water with no required additives.…”