Acta Phys. -Chim. Sin. ›› 2019, Vol. 35 ›› Issue (3): 292-298.doi: 10.3866/PKU.WHXB201803121

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In Situ Study of the Conversion Reaction of CO2 and CO2-H2 Mixtures in Radio Frequency Discharge Plasma

Ruilong YANG1,Diyu ZHANG3,Kangwei ZHU1,Huanlin ZHOU1,Xiaoqiu YE1,Aart W. KLEYN3,Yin HU2,*(),Qiang HUANG3,*()   

  1. 1 Science and Technology on Surface Physics and Chemistry Laboratory, Mianyang 621900, Sichuan Province, P. R. China
    2 China Academy of Engineering Physics, Mianyang 621900, Sichuan Province, P. R. China
    3 Center of Interface Dynamics for Sustainability, Institute of Materials, China Academy of Engineering Physics, Chengdu 610200, P. R. China
  • Received:2018-01-19 Published:2018-08-28
  • Contact: Yin HU,Qiang HUANG;
  • Supported by:
    the National Natural Science Foundation of China(21603202);the National Natural Science Foundation of China(51561135013);(PY2014-7-7, PY2014-7-11)(PY2014-7-7);(PY2014-7-7, PY2014-7-11)(PY2014-7-11)


Currently, worldwide attention is focused on controlling the continually increasing emissions of greenhouse gases, especially carbon dioxide. To this end, a number of investigations have been carried out to convert the carbon dioxide molecules into value-added chemicals. As carbon dioxide is thermodynamically stable, it is necessary to develop an efficient carbon dioxide utilization method for future scaled-up applications. Recently, several approaches, such as electrocatalysis, thermolysis, and non-thermal plasma, have been utilized to achieve carbon dioxide conversion. Among them, non-thermal plasma, which contains chemically active species such as high-energy electrons, ions, atoms, and excited gas molecules, has the potential to achieve high energy efficiency without catalysts near room temperature. Here, we used radio-frequency (RF) discharge plasma, which exhibits the non-thermal feature, to explore the decomposition behavior of carbon dioxide in non-thermal plasma. We studied the ionization and decomposition behaviors of CO2 and CO2-H2 mixtures in plasma at low gas pressure. The non-thermal plasma was realized by our custom-made inductively coupled RF plasma research system. The reaction products were analyzed by on-line quadrupole mass spectrometry (differentially pumped), while the plasma status was monitored using an in situ real-time optical emission spectrometer. Plasma parameters (such as the electron temperature and ion density), which can be tuned by utilizing different discharge conditions, played significant roles in the carbon dioxide dissociation process in non-thermal plasma. In this study, the conversion ratio and energy efficiency of pure carbon dioxide plasma were investigated at different values of power supply and gas flow. Subsequently, the effect of H2 on CO2 decomposition was studied with varying H2 contents. Results showed that the carbon dioxide molecules were rapidly ionized and partially decomposed into CO and oxygen in the RF field. With increasing RF power, the conversion ratio of carbon dioxide increased, while the energy efficiency decreased. A maximum conversion ratio of 77.6% was achieved. It was found that the addition of hydrogen could substantially reduce the time required to attain the equilibrium of the carbon dioxide decomposition reaction. With increasing H2 content, the conversion ratio of CO2 decreased initially and then increased. The ionization state of H2 and the consumption of oxygen owing to CO2 decomposition were the main reasons for the V-shape plot of the CO2 conversion ratio. In summary, this study investigates the influence of power supply, feed gas flow, and added hydrogen gas content, on the carbon dioxide decomposition behavior in non-thermal RF discharge plasma.

Key words: Radio frequency discharge plasma, Carbon dioxide, Hydrogen, Decomposition ratio, Energy efficiency, Reaction equilibrium