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  gcat -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.