# Nickel-Based Structured Catalysts for Indirect Internal Reforming of Methane
## 1 Introduction  
Biogas is an attractive renewable energy source, alternative to fossil fuels, produced by the anaerobic fermentation of organic matter, mainly consisting of methane (50-80%) and carbon dioxide (25-50%). The CO\({}_{2}\) reforming of CH\({}_{4}\) reaction Equation (1), called dry reforming of methane (DRM), is an interesting strategy in the context of biogas valorization to syngas. Many research efforts have been focused on catalytic aspects and engineering of DRM process [1; 2; 3; 4]. \[\text{CH}_{4}+\text{ CO}_{2}\rightleftarrows\text{ 2H}_{2}+2\text{CO}\text{ \ \ \ \ }\text{\ \ }\Delta\text{H}^{0}=247\text{ kJmol}^{-1} \tag{1}\]  
The syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide, used as a feedstock in the chemical industry for the synthesis of a wide range of chemicals and fuels but it can be also used to feed solid oxide fuel cells (SOFCs) [5; 6; 7]. DRM is an extremely endothermic reaction and it requires temperatures as high as those of SOFCs' operation to attain reasonable yield of syngas. Thus, SOFCs powered by biogas can act as efficient devices for biogas-electricity conversion [8; 9]. Two approaches to SOFC operation can be considered: One is the external reforming (ER) mode, whenthe endothermic CO\({}_{2}\) reforming of CH\({}_{4}\) (DRM) and the electrochemical reactions are operated in different units, and another is the internal reforming (IR) mode, when DRM reaction and the oxidation reaction are operated together in a single unit. A further distinction can be done for the internal reforming operation: Direct internal reforming (DIR) and indirect internal reforming (IIR). In IIR operation the reformer is in contact with the anode side of a fuel cell, potentially still providing intimate heat transfer between the reformer and the SOFC [10]. The aim of this work is the design of an efficient structured catalyst for the DRM as a biogas pre-reformer in IIR-SOFCs. Structured catalysts for hydrogen production from biogas have received large attention for their specific characteristics such as: High geometric surface area and low pressure drop [11; 12; 13; 14]. Structured systems on different configurations (foams, honeycombs, monoliths) showed several advantages compared to conventional packed bed reactors [15; 16; 17; 18]. For our purpose, a suitable metallic structured support has been chosen as substrate for catalyst deposition. Metal foams are recommended supports for their open-cell structure, high thermal conductivity (fundamental in case of endothermic reactions), high temperature stability, and mechanical strength. Their high porous texture allows a better mass and heat exchange and promotes a high contact efficiency between catalyst particles and gases. Other important requirements are corrosion resistance, low pressure drop, and large surface/volume ratio [19; 20; 21]. The main critical issue for structured catalysts' fabrication is the deposition of uniform catalyst layers, able to withstand reaction conditions. Among different deposition methods, the wash-coating into a dispersion is widely considered the best fabrication technique [8; 22; 23]. Among catalyst powders, nickel-based catalysts are highly active for the DRM reaction, but they are quickly deactivated by coking under certain conditions [8; 24; 25; 26; 27].