## 1 Introduction  
The preferred use of fossil fuels to meet energy demands has created environmental concerns due to significant emissions of environmentally harmful gases (CO\({}_{2}\) and CH\({}_{4}\)). In addition, the depletion of fossil fuel reserves puts humanity in front of the need for tough energy conservation and the use of new resource-saving technologies [1, 2]. Converting CO\({}_{2}\) into value-added chemicals or fuels is the background of the sustainable development of the chemical industry and contributes to the reduction of CO\({}_{2}\) emissions. CH\({}_{4}\) is contained in significant quantities in associated gas and in renewables. CH\({}_{4}\) can react with a reducing agent, CO\({}_{2}\), a technique known as dry methane reforming (DMR, Equation (1)) [3]. \[\mathrm{CH}_{4}+\mathrm{CO}_{2}\Leftrightarrow 2\mathrm{CO}+2\mathrm{H}_{2} \;\Delta\mathrm{H}=247.3\;\mathrm{kJ/mol} \tag{1}\]  
DMR simultaneously converts two greenhouse gases and the resulting gas mixture of H\({}_{2}\) and CO (synthesis gas can be used as a fuel or feedstock in the Fischer-Tropsch process [4]), for the production of valuable products such as methanol, dimethyl ether, and acetic acid [5, 6] and for the storage of nuclear and solar energy [3]. The well-proven technology for the fabrication of syngas by the DRM reaction in the presence of catalysts has its drawbacks, associated with the easy poisoning of the catalyst by coke (Equations (2) and (3)):  
\[\mathrm{CH}_{4}\Leftrightarrow\mathrm{C}+2\mathrm{H}_{2}\;\Delta\mathrm{H}=+75 \;\mathrm{kJ/mol} \tag{2}\]\[2\text{CO}\Leftrightarrow\text{C}+\text{CO}_{2}\ \Delta\text{H}=-173\ \text{ kJ}/\text{mol} \tag{3}\]  
Adding steam to the DMR process is an effective way to limit soot formation and increase the ratio H\({}_{2}\)/CO [7; 8]. H\({}_{2}\)O is an inexpensive and abundant resource that reacts with CH\({}_{4}\) via steam-methane reforming (SMR--Equation (4)) and combines with the steam-CO reforming reaction (Equation (5)) to produce H\({}_{2}\):  
\[\text{CH}_{4}+\text{H}_{2}\text{O}\Leftrightarrow\text{CO}+3\text{H}_{2}\ \Delta\text{H}=+206\ \text{ kJ}/\text{mol} \tag{4}\]  
\[\text{CO}+\text{H}_{2}\text{O}\Leftrightarrow\text{CO}_{2}+\text{H}_{2}\ \Delta\text{H}=-41\ \text{ kJ}/\text{mol} \tag{5}\]  
Combining DMR with SMR provides two key advantages over single DMR reactions, namely: (i) H\({}_{2}\)O increases the O/C ratio in the feed, which promotes soot oxidation; (ii) H\({}_{2}\)O provides additional H atoms to form H\({}_{2}\), thereby adjusting the H\({}_{2}\)/CO molar ratio in the product stream. Due to the chemical stability of both CO\({}_{2}\) and CH\({}_{4}\), the reaction of DMR and H\({}_{2}\)O/CO\({}_{2}\) reforming of methane (CSMR) is usually performed at 800-1000 \({}^{\circ}\)C in the presence of a catalyst containing platinum group metals (for example, Rh [9], Ru [10; 11], Pd [12; 13] and Pt [14; 15]) or a base-metal catalyst (Fe, Co or Ni) [16; 17; 18; 19]. Low-cost and active Ni-based catalysts have the most potential for wide industrial use. The Ni dispersion, oxygen vacancy (V\({}_{\text{o}}\)) concentration and the interaction between Ni and its support affect the CSMR performance. An increase in dispersion and, as a result, an expansion of the number of active points promote catalytic performance [20]. Reducible oxides, such as CeO\({}_{2}\), have been used as supports or promoters to obtain catalysts with a high content of oxygen defects [21; 22]. It is believed that V\({}_{\text{o}}\) on metal oxides are active centers of CO\({}_{2}\) activation [23; 24]. These vacancies reduce the activation energy of CO\({}_{2}\) by providing electrons. The high oxygen (O\({}_{\text{x}}\)) and vacant mobility of ceria and the Ni-ceria interface are responsible for burning carbon via the following reactions: C + O\({}_{\text{x}}\) = CO + V\({}_{\text{o}}\) + 2e [25].