**1. Introduction**

Utilization of carbon dioxide is imperative and there is urgent demand for effective carbon dioxide reducing techniques. Reforming of carbon with methane, which is also called dry reforming of methane (DRM, the term "dry" is to distinguish from steam reforming which is to reform methane with water vapor) can be a feasible process to convert CO2 and CH4 into syngas (mixture of H2 /CO). Currently, catalysis and nonthermal plasma are two essential techniques for DRM to generate syngas and to reduce the anthropogenic emissions of greenhouse gases (GHGs). Catalytic reforming of CH4 /CO2 is a high-selectivity, high production rate and well developed technique to generate syngas. Up to date, several types of catalysts have been investigated for their catalytic activity toward DRM, including noble metal catalysts [1], nickel-based catalysts [2], cobalt-based catalysts [3], spinels [4] and perovskites [5].

© 2016 The Author(s). Licensee InTech. 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, provided the original work is properly cited. © 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, provided the original work is properly cited.

### However, high operating temperature is required for effective conversion. Moreover, coke deposition leads to subsequent catalyst deactivation. Thus, how to effectively reduce operating temperature and coke deposition remains the big challenge for catalytic reforming [6, 7]. On the other hand, nonthermal plasma stands for an energy-saving reforming for GHGs reduction and many kinds of nonthermal plasma reactor have been designed and developed to enhance CO2 /CH4 conversion efficiency. Nonthermal plasma can generate syngas at a lower operating temperature since the driving force of nonthermal plasma is electric energy instead of thermal energy [8]. Even so, nonthermal plasma has some limitations including low GHGs conversions, low syngas selectivity and byproduct formation, e.g. carbon soot. The above disadvantages reduce the applicability of nonthermal plasma for DRM [9]. To overcome the shortcomings of catalytic reforming and nonthermal plasma reforming, combining catalyst and nonthermal plasma as a hybrid reactor can be a solution since various interactions can be induced between catalyst and nonthermal, including the change of physicochemical properties of catalyst, enhancement of electric field and activation of catalysis [10]. Based on the interactions between catalysis and nonthermal plasma, limitations of catalytic reforming and nonthermal plasma reforming including catalyst deactivation and byproduct formation can be resolved due to enhancement of reforming performance toward DRM [11–13].

In this chapter, application of three types of DRM system, i.e. catalysis, nonthermal plasma and hybrid plasma catalysis will be introduced and discussed for their fundamental concepts, including reaction mechanism, state-of-the-art development, opportunities and shortcomings. Some important features for various reactors will also be highlighted in this chapter as a reference.

activity order of the above metal catalysts also depends on support and preparation method. Generally, Rh and Ru catalysts are good candidates since they have better catalytic activities and durabilities than other noble metals [15, 16]. However, their costs are also high which limits their industrial applicability. Hence, transition metal-based catalysts such as nickel, cobalt-based catalysts are frequently developed and investigated. Ni-based catalysts are most

Assuming no carbon formation occurs, (b) assuming carbon formation occurs. These plots were created by using Gibbs

**Figure 1.** Thermodynamic equilibrium plots for DRM at 1 atm, from 0–1000oC and at inlet feed ratio of CO2

researches have been conducted for the purpose of increasing selectivity of syngas and stabil-

Generally, pathways of catalytic reactions can be divided into three categories: Langmuir-Hinshelwood (L-H), Eley-Rideal (E-R) and Mars-van Krevelen (MVK), as described in **Table 1** [19]. Kinetic studies point out that DRM follows the reaction route of L-H mechanism. The reaction mechanism of DRM can be described as **Figure 2**, density functional theory (DFT) simu-

firstly adsorbed on Pd and MgO surface and then dissociated into CO, O, C and H atoms [20]. It

and CH4

CO2 Reforming with CH4 via Plasma Catalysis System http://dx.doi.org/10.5772/intechopen.73579

and many

/CH4 =1 (a) 87

and CO2

are

applied for DRM since they have high adsorption capacities toward CO2

lation results of DRM kinetics achieved with Pd/MgO catalyst indicate that CH4

**Carbon structure Designation Temperature range (°C)**

Surface carbide C<sup>α</sup> 200–400 Amorphous carbon films C<sup>β</sup> 250–500 Bulk Ni carbide C<sup>γ</sup> 150–250 Vermicular filaments/whiskers Cv 300–1000 Graphite platelet films Cc 500–550

**Table 1.** Details of different carbon species formed on the catalyst surface [21].

ity of catalyst in terms of resistivity of coke deposition [17,18].

free energy minimization algorithm on HSC Chemistry 7.1 software [14].
