InTaO4 was synthesized by a solid-state reaction method using
metal oxide as the starting materials. Co was added by incipient-wetness
impregnation. The sample was pretreated by H2 (200 Torr) reduction
at 500?C for 2 h and subsequent O2 (100
Torr) oxidation at 200?C for 1
h. The core-shell structure of metallic Co and Co3O4 was
formed by this reduction-oxidation
procedure. The catalysts were characterized by powder X-ray diffraction,
scanning electron microscope, and ultraviolet-visible spectroscope. The
photocatalytic reduction was carried out in a Pyrex reactor with KHCO3 or NaOH aqueous solution bubbled with ultra pure CO2 gas under
visible light illumination. SEM micrographs show many small Co3O4 particles on the surface of InTaO4. The band gap of Co3O4-InTaO4 was 2.7 eV, confirming that these catalysts have the ability to reduce CO2 to methanol. The methanol yield increased with the amount of Co3O4 cocatalysts. The catalyst had a higher activity in KHCO3 aqueous
solution than in NaOH solution. The InTaO4 catalyst with 1 wt% Co3O4 cocatalyst had the highest activity among all catalysts. Co3O4 was incorporate into the surface structure of InTaO4 to form CoxInTaO4-x.
It resulted in more defect sites on the surface of InTaO4 and
changed the valence band structure. It formed a Schottky barrier to suppress
the electron-hole recombination.
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