(551e) Dry Reforming of Methane over Ni Catalysts on High Oxygen Ion Conductivity Supports

The dry reforming of methane (DRM) is a chemical process that converts two greenhouse gases, methane and carbon dioxide, to syngas (a mixture of hydrogen and carbon monoxide). In an ideal case, each mole of methane and carbon dioxide produces 2 moles of carbon monoxide and hydrogen. This reaction is extremely highly endothermic and requires high operating temperatures. A H2/CO molar ratio of 1 is an ideal feed for synthesizing hydrocarbons via Fischer-Tropsch or oxygenated chemicals. Biogas is an attractive feedstock for DRM. Despite environmental and economic benefits, DRM is still not an industrial process due to the rapid catalyst deactivation caused by coke formation and sintering under severe operating conditions.

This research evaluates the effect of support materials on the performance of Ni-based catalysts, especially supports with high oxygen conductivity. Nickel is used as an active metal because of its competitive catalytic activity and affordable costs. Ceria (CeO2) is an interesting support because of its ability to form and eliminate oxygen vacancies, giving it a high oxygen ion conductivity. The oxygen vacancies on the surface of this oxide facilitate the adsorption and dissociation of CO2, improve reforming activity, and leave mobile oxygens on the catalyst surface. These mobile oxygens will react with carbon formed on the catalyst, release carbon monoxide or other carbonate species, significantly reduce coke formation, and improve the catalyst life. Previous work suggests doping CeO2 with rare earth elements, such as Gadolinium, enhances its oxygen ion conductivity. Besides Gadolinium Doped Ceria (GDC), Yttrium Stabilized Zirconia (YSZ) also possesses high oxygen ion conductivity. So, in this work, we investigate three supports with high oxygen ion conductivity and one with low oxygen ion conductivity (Alumina Al2O3) for their activity and coke resistance. Besides oxygen ion mobility, the active metal particle size and acidity/basicity of support materials have also been found to play a decisive role in the performance of DRM catalysts, especially with respect to coke formation. Carbon formation increases with particle size of nickel, so catalysts with high metal dispersion or small metal particles have strong resistance to coking. Acidic support materials tend to speed up methane cracking by acid sites and lead to the rapid deactivation of the catalysts. Basicity, in contrast, is treated as a desirable material property, allowing enhanced carbon dioxide adsorption, reduced activity of methane decomposition, and decreased carbon deposition. Therefore, during our experiments, these properties of supports and catalysts are characterized along with their catalyst activity, stability, and deactivation.