**6. Conclusion and outlook**

The synergistic effect induced by DBD was clearly observed both in the CH4 and CO2 conversion and in the syngas yield. CH4 dehydrogenation was enhanced by the synergistic effect of DBD and catalyst. Plasma-activated CO2 and H2O would promote surface reaction and increase CO and H2 yield. The analysis of overall activation energy is expected to understand the contribution of plasma-generated reactive species.

In plasma catalysis, the fine amorphous carbon filaments, deposited in the external surface of catalyst, prove that the interaction of DBD occurs mainly in the external surface. The DBD generation and plasma-excited species diffusion are inhibited in the internal pores of the catalyst. Moreover, although the interaction between plasma and catalyst is limited in the external surface, the coke deposition was inhibited significantly in the internal pores by DBD, which is the clear evidence of reaction enhancement by DBD.

Oxidation behavior of Ni-based catalyst in nonthermal plasma-enabled catalysis showed that the NiO layer was generated in the external surface with the thickness of ca. 20 μm during plasma oxidation. In the internal pores, Ni oxidation is inhibited due to the negligible interaction with DBD. Contributing to the NiO layer, the surface of catalyst uptakes more oxygen beyond thermal equilibrium, which is known as Langmuir isotherm, creating a new reaction pathway via NiO. In the plasma catalysis of DMR, NiO drives the oxidation-reduction cycle, which promotes CH4 dehydrogenation on the surface. Consequently, carbon deposition is suppressed effectively.

For further improvement of plasma-enhanced DMR, the following issues should be investigated:


**51**

**Author details**

Japan

provided the original work is properly cited.

*Plasma-Enabled Dry Methane Reforming*

*DOI: http://dx.doi.org/110.5772/intechopen.80523*

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Zunrong Sheng, Seigo Kameshima, Kenta Sakata and Tomohiro Nozaki\* Department of Mechanical Engineering, Tokyo Institute of Technology, Tokyo,

\*Address all correspondence to: nozaki.t.ab@m.titech.ac.jp

*Plasma-Enabled Dry Methane Reforming DOI: http://dx.doi.org/110.5772/intechopen.80523*

*Plasma Chemistry and Gas Conversion*

**6. Conclusion and outlook**

of reaction enhancement by DBD.

catalytically functionalized surface.

insight in plasma catalysis.

reactive species.

be investigated:

species.

The synergistic effect induced by DBD was clearly observed both in the CH4 and CO2 conversion and in the syngas yield. CH4 dehydrogenation was enhanced by the synergistic effect of DBD and catalyst. Plasma-activated CO2 and H2O would promote surface reaction and increase CO and H2 yield. The analysis of overall activation energy is expected to understand the contribution of plasma-generated

In plasma catalysis, the fine amorphous carbon filaments, deposited in the external surface of catalyst, prove that the interaction of DBD occurs mainly in the external surface. The DBD generation and plasma-excited species diffusion are inhibited in the internal pores of the catalyst. Moreover, although the interaction between plasma and catalyst is limited in the external surface, the coke deposition was inhibited significantly in the internal pores by DBD, which is the clear evidence

Oxidation behavior of Ni-based catalyst in nonthermal plasma-enabled catalysis showed that the NiO layer was generated in the external surface with the thickness of ca. 20 μm during plasma oxidation. In the internal pores, Ni oxidation is inhibited due to the negligible interaction with DBD. Contributing to the NiO layer, the surface of catalyst uptakes more oxygen beyond thermal equilibrium, which is known as Langmuir isotherm, creating a new reaction pathway via NiO. In the plasma catalysis of DMR, NiO drives the oxidation-reduction cycle, which promotes CH4 dehydrogena-

For further improvement of plasma-enhanced DMR, the following issues should

(1) The effect of radical injection on reaction enhancement should be kinetically analyzed by the Arrhenius plot method, and the analysis of the overall activation energy is expected to understand the contribution of plasma-generated reactive

(2) Exploring new types of catalysts, dedicated to plasma catalysis, is an important subject of research. We have demonstrated that the interaction of DBD and catalyst occurs only at the external surface of the pellets, and the effected thickness is ca. 20 μm, which means a majority of the active sites in pores of catalyst do not interact with any excited species. New catalyst preparation method such as catalytic functionalization of reactor wall and catalyst coating for the reactor may be beneficial to strengthen the synergistic effect of nonthermal plasma and

(3) The catalyst activity of partially oxidized catalyst and the nonthermal plasma heating mechanism have not been demonstrated experimentally yet; moreover, diagnosis of intermediate species on the surface, created by plasma-derived species, as well as their reaction dynamics are expected to be investigated for deep

(4) Although the plasma-induced energy transfer mechanism is commonly accepted in particle growth, it has yet to be investigated within the scope of plasma catalysis. Deep understanding of highly transient and nonequilibrium energy transfer via excited molecules, without macroscopic temperature change, need to be studied. (5) The individual contribution of radical injection and heat generation, as well as combination of those, must be understood. The gap between macroscopic and microscopic understanding, including various time scales covering nanoseconds

to the millisecond, should be bridged by consistent manner.

tion on the surface. Consequently, carbon deposition is suppressed effectively.

**50**
