AVS 66th International Symposium & Exhibition
    Plasma Science and Technology Division Thursday Sessions
       Session PS+SS-ThA

Paper PS+SS-ThA1
Rate Limiting Factors of Low Pressure Plasma-catalytic CO2 Methanation Process

Thursday, October 24, 2019, 2:20 pm, Room B131

Session: Plasma Conversion and Enhanced Catalysis for Chemical Synthesis
Presenter: Kazunori Koga, Kyushu University, Japan
Authors: K. Koga, Kyushu University, Japan
A. Yamamoto, Kyushu University, Japan
K. Kamataki, Kyushu University, Japan
N. Itagaki, Kyushu University, Japan
M. Shiratani, Kyushu University, Japan
Correspondent: Click to Email
The methanation of CO2 attracts attention as the ways of CO2 reduction and energy storage as well as space exploration. It is expected to produce rocket propellant fuels at Mars and CO2 conversion in space stations. The Sabatier reaction has been employed to generate CH4 from CO2 and H2. Using catalysts realizes a high conversion efficiency. However, the conventional catalytic reaction starts at about 200 oC but thermal runaway occurs above 250 oC. The heat management is an important problem. A method using non-thermal plasma with catalyst allows methanation under low-temperature condition [1, 2]. Here, we studied rate-limiting steps of CO2 methanation and their important parameters in the plasma-catalytic process. Experiments were carried out using a capacitively coupled plasma reactor. The electrode diameter was 50 mm and the distance between the electrodes was 6.1 mm. The Cu electrodes were employed as catalyst. We set a CO2 gas flow rate between 1.0 sccm and 5.0 sccm and an H2 gas flow rate between 1.0 sccm and 30 sccm. The pressure was 750 Pa. The discharge power was set in a range of 10 to 100 W. Gas composition in the discharge plasmas was measured with a quadrupole mass spectrometer. CH4 yield rapidly increases with time after plasma initiation. It tends to be saturated after 200 s. From time dependence of catalyst temperature, the saturation occurs between 350 K and 370 K. The temperature shows the threshold temperature at which the rate-limiting step change from gas-phase reactions in plasma to surface reactions on the catalyst. The CH4 yield increases with increasing the gas residence time. From optical emission spectroscopy, emission intensity related with CO angstrom band increase with the gas residence time but hydrogen-related emission is irrelevant to the residence time. It suggests that CO excited by plasma is responsible to the CH4 yield increase. The results of H2 gas flow rate dependence suggest that electron temperature is an important factor in the rate-limiting step of the gas phase reaction. I will discuss the detail mechanisms at the conference.

Work supported partly by JAXA and JST.

[1] S. Toko, et al., Sci. Adv. Mater. 10 (2018) 655.

[2] S. Toko, et al., Sci. Adv. Mater. 10 (2018) 1087.