Dual origins of photocatalysis: Light-induced band-gap excitation of zirconium oxide and ambient heat activation of gold to enable 13CO2 photoreduction/conversion

Efficient and Selective Interplay Revealed: CO2 Reduction to CO over ZrO2 by Light with Further Reduction to Methane over Ni0 by Heat Converted from Light

The reaction mechanism of CO₂ photoreduction into methane was elucidated by time-course monitoring of the mass chromatogram, in situ FTIR spectroscopy, and in situ extended X-ray absorption fine structure (EXAFS). Under ¹³ CO₂ , H₂ , and UV/Vis light, ¹³ CH₄ was formed at a rate of 0.98 mmol h^-1  g_cat ^-1 using Ni (10 wt %)-ZrO₂ that was effective at 96 kPa. Under UV/Vis light irradiation, the ¹³ CO₂ exchange reaction and FTIR identified physisorbed/chemisorbed bicarbonate and the reduction because of charge separation in/on ZrO₂ , followed by the transfer of formate and CO onto the Ni surface. EXAFS confirmed exclusive presence of Ni⁰ sites. Then, FTIR spectroscopy detected methyl species on Ni⁰ , which was reversibly heated to 394 K owing to the heat converted from light. With D₂ O and H₂ , the H/D ratio in the formed methane agreed with reactant H/D ratio. This study paves the way for using first row transition metals for solar fuel generation using only UV/Vis light.