In situ transmission infrared spectroscopy of plasma-assisted CO2 hydrogenation on ZnO: Role of catalyst support materials
Atsushi Saito1, 2, Zunrong Sheng1, Dae-Yeong Kim1, Yutaka Imamura2, Tomohiro Nozaki1, *
* The author to whom correspondence should be addressed.
1 Department of Mechanical Engineering, Tokyo Institute of Technology, Japan
2 Innovative Technology Laboratories, AGC Inc., Yokohama 230-0045, Japan
Abstract
Nonthermal plasma-assisted catalysis is shown to be capable of reducing carbon dioxide (CO2) in the presence of hydrogen (H2). Dielectric barrier discharge-type plasma-activated CO2 and H2 were irradiated on a zinc oxide (ZnO) catalyst, and the surface species and their reaction pathways were investigated via in situ transmission infrared absorption spectroscopy. In our previous study on in situ Raman spectroscopy of CO2 hydrogenation on Cu/ZnO, we found the various surface species were uniquely identified on ZnO when DBD was irradiated. Therefore, this study aimed particularly to investigate the effects of nonthermal plasma on support materials (ZnO) without copper. The infrared absorption peaks of the surface species were analyzed via density functional theory (DFT) calculations. Formate (HCOO), formyl group (HCO), and formaldehyde (H2CO) were generated as reaction products from the plasma and ZnO catalyst. Moreover, the process simultaneously produced plasma-activated hydrogen that adheres to ZnO and undercoordinated Zn in ZnO. These hydrogen adhesions and undercoordinated Zn sites did not appear in thermal reactions in the absence of plasma, suggesting that the plasma-activated hydrogen site in ZnO functions as an active site for the plasma catalytic reaction.
Keywords - CO2 conversion, carbon recycling, in situ spectroscopy, plasma catalysis, nonthermal plasma.
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