7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Elucidating plasma-surface interaction mechanism for CO2 conversion
toward decentralized low carbon technology
1Tomohiro Nozaki
Department of Mechanical Engineering, Tokyo Institute of Technology
nozaki.t.ab@m.titech.ac.jp

Conversion of carbon dioxide to useful chemicals
using low-carbon energy sources attracts keen attention.
The use of renewable electricity to operate catalytic
conversion of CO2 is being recognized as a promising
decarbonizing technology [1,2]. First, a chemical
reaction is activated electronically thus renewableelectricity
isutilizeddirectly.
Second,anelectron-assisted reaction would decrease the reaction
temperature that eliminates high-temperature processes
with combustion of hydrocarbons. Electrochemistry,
Photochemistry, and a combination of these principles
are studied exclusively for this purpose. In addition,
electrical heating with renewable electricity is considered
as industrially applicable electrification technology forthe decarbonization of chemical processes. However,high temperature is still needed within the scope of
conventional thermal reaction regime: technologicalinnovation may arise via efficient heat transfer andtemperature management technology, such as selective
heating of material, rapid heating, extreme
high-temperature that the combustion can not achieve.
We propose nonthermal plasma-driven heterogeneous
catalysis of CO2 as a new concept of an electricity-driven
chemical reaction control while utilizing renewableenergy [3,4]. The catalytic surface reaction is modified
by the plasma-generated reactive species, most likely
vibrationally excited molecules, leading to much smaller
activation energy than that of thermal catalysis [5,6]. In
this study, DBD (dielectric barrier discharge) combined
catalytic reaction was applied to reverse water gas shift
reaction (CO2 + H2 = CO + H2O ΔH = 41 kJ/mol, ΔG =24 kJ/mol at 400 K). The CO2 conversion exceeded thethermal equilibrium when Pd2Ga/SiO2 (10wt.%) alloy
catalyst was used. The in situ transmission infrared (TIR)
spectroscopy was employed while DBD was generated
during the spectroscopy. The formation of monodentate
formate (m-HCOO) was promoted by direct interaction
between adsorbed hydrogen and vibrationally excited
CO2 via the Eley-Rideal pathway. Because bending
mode vibration of CO2 becomes an excellent electron
acceptor and the reaction between adsorbed hydrogen on
Pd, as an electron donor, is enhanced. Interestingly, thedissociation of m-HCOO, as a rate-determining step, wasalso promoted by DBD under hydrogen-rich conditions.
Such unique reaction behavior was confirmed by thefluidized-bed DBD reactor [6-8], showing the activationenergy of 75 kJ/mol for thermal catalysis and a drastic
reduction to 43 kJ/mol for plasma catalysis. The
individual role of DBD and alloy catalyst over theplasma-promotion effect is discussed comprehensively.
This work is supported by JST CREST (JPMJCR19R3)

Figure 1. Schematic diagram of fluidized-bed DBD
reactorFigure 2. Arrhenius plot for the reverse water gas shift
reaction in the fluidized-bed DBD reactor. ■ 10 wt.%(100 kHz), ▲ 10 wt.% (12 kHz), □ 3 wt.% (100 kHz), ∆3 wt.% (12 kHz), ● 10 wt.% (Thermal), ○ 3 wt.%
(Thermal). Total flow rate = 200 cm3/min (STP), Power= 30 W, H2/CO2 = 3, WHSV = 3000 cm3/g/h (STP), Total
pressure = 15 kPa, SEI = 220 kJ/mol. STP: standard
temperature and pressure (101.3 kPa and 298 K).
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[3] A Bogaerts et al: J. Phy. D: Appl. Phys. 53 (2020)
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15 (2021) e01004[5] Z Sheng et al: Chem. Eng. J. 399 (2020) 125751[6] D-Y Kim et al: J. Am. Chem. Soc. 144 (2022) 14140[7] X Chen et al: J. CO2 Util. 54, (2021) 101771[8] X Chen et al: Plasma Process. Polym. e2200207(2023)