(596b) Methane Dry Reforming over Ni Catalysts on High Oxygen Conductivity Supports

Dry reforming of methane process (DRM, CH₄ + CO₂ 2CO + 2H₂) converts methane and carbon dioxide, two major greenhouse gases, to syngas with an equimolar H₂/CO ratio. Syngas from DRM is ideal for Fischer-Tropsch synthesis to produce long-chain hydrocarbons and high-value chemicals. DRM is a potential process for the valorization of biogas or natural gas with high CO₂ content. Despite the positive environmental impacts, DRM faces a great challenge due to the rapid catalyst deactivation by the accumulation of carbonaceous species on active sites. Therefore, developing a highly stable catalyst system with strong coke resistance for long-term operation is necessary for the commercialization of DRM.

This research investigates the effect of supports possessing high oxygen conductivity on Ni-catalyzed dry reforming of methane. Ni-based catalysts are promising for DRM because of their relatively high catalytic activity and affordable costs, but they are easily deactivated by carbon deposition. Materials with high oxygen ion conductivity, such as Ceria (CeO₂), Gadolinium Doped Ceria (GDC), and Yttrium Stabilized Zirconia (YSZ) can provide oxygen ions for the metal to oxidize the deposited carbon and improve resistance to carbon deposition. These supports can form and eliminate oxygen vacancies, facilitating the adsorption and dissociation of CO₂, thus improving reforming activity. In this work, four support materials, which are very different oxygen ion conductivities, Al₂O₃<CeO₂ < YSZ < GDC, were evaluated for their activity, stability, and coke resistance. The kinetics of these nickel catalysts are also assessed by evaluating the methane activation energy and turnover frequency (TOF). The catalysts are characterized using various analytical techniques to understand the correlation between the catalyst’s performance and their physicochemical properties. The long-term stability tests at 750^oC in 12 hours show the deactivation in all catalysts but with different rates. The most stable catalyst is one with the highest oxygen mobility (Ni/GDC), while the catalyst lowest in oxygen conductivity (Ni/Al₂O₃) is the least stable. Carbon deposition, low in other cases, but is observed by scanning electron microscopy and temperature-programmed oxidation in the case of Ni/GDC. The structure or nature of carbon accumulated on the catalysts’ surface after the DRM reaction is also clarified by Raman spectrometry. Other factors contributing to carbon formation and affecting the role of oxygen conductivity, such as active metal particle size, surface area, and acidity/basicity of support materials, have been also considered.