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Fuel Regeneration from CO2 by Photocatalysis ---Reaction Mechanism of CO2 Photoreduction into Methane was Elucidated---

 On February 5, 2021, Chiba University announced that a research group at the university found the reducibility of Ni photocatalyst from carbon dioxide into methane and elucidated the reaction mecha-nism by real time and in-situ monitoring using multiple analytical measures. Details were published in Angewandte Chemie International Edition by the group with the first author Professor Yasuo Izumi*.

 Countermeasures against global warming are an urgent issue of the modern world. Fuel regeneration from carbon dioxide (CO2) suppresses the increase of warming gas and will be a promising way to at-tain "carbon neutral cycle". However, it is challenging because of the molecular stability of CO2.

 Previously, the research group has reached to the knowledge that a photocatalyst comprising  of sil-ver nanoparticles and zirconia (ZrO2) support is able to reduce CO2 to CO. Based on this knowledge, the group prepared photocatalyst comprising  of nickel (Ni) nanocrystal and ZrO2, and succeeded in reducing CO2 to CH4 at a rate of 0.98mmol h-1 g cat-1 in  96kPa H2/CO2 gas under UV-visible light irra-diation. Key issue was the use of reduced Ni (Ni(0)) in the catalyst.

 The reaction was monitored by real-time mass chromatography, in situ Fourier transform infrared (FTIR) spectroscopy, and in situ extended X-ray absorption fine structure (EXAFS). Monitoring results has led to the following reaction mechanism:(1) CO2 adsorption as HCO3 on ZrO2, (2) CO generation from HCO3 by UV-light excited electron, (3) CH4 generation from CO and H on Ni(0) heated by visible light. This reaction mechanism found in this study will pave the way for using first row transition met-als for fuel regeneration from CO2 by photocatalysis.

*Yasuo Izumi, Hongwei Zhang, Takaomi Itoi, and Takehisa Konishi, "Efficient and Selective Interplay Revealed: CO2 Reduction to CO over ZrO2 by Light with Further Reduction to Methane over NiO by Heat Converted from Light", Angewandte Chemie International Edition, Accepted Article, doi: 10.1002/anie.202016346; first published: 20 January 2021