(605b) NiCe@SiO2 Multi-Yolk-Shell Nanotube Catalyst for Tri-Reforming of Methane

Greenhouse gas emissions have been continuously increasing over the decades, with carbon dioxide (CO₂) being the primary greenhouse gas making up about 80%, followed by methane (CH₄), composing of 10%. Technologies such as tri-reforming of methane (TRM) can mitigate CO₂ emissions with generating syngas for the production of valuable chemicals. The TRM combines dry reforming, steam reforming, and partial oxidation of methane, thereby can directly utilize flue gas from a combustion source without requiring any gas separation. Nickel-based catalysts are widely studied for TRM, as they can show high activity with equilibrium CO₂ and CH₄ conversions reaching up to 80% and 97% at 750 ºC, respectively. Despite the high activity of Ni-based catalysts, different morphologies of the catalyst such as yolk-shell structure have been proposed, since they can maintain high resistance to coke deposition and sintering due to the confinement effect, and provide long term stability.

In this work, NiCe@SiO₂ multi-yolk-shell nanotube catalysts have been prepared at different yolk and tube sizes, and their TRM activity has been evaluated at different oxidizer (CO₂ + H₂O + O₂) to methane (O/M) feed ratios. At high O/M ratio, NiCe@SiO₂ consisting of small yolk particles lost its activity, possibly due to the re-oxidation of active Ni components. On the other hand, the catalyst with bigger yolk particles showed stable activity without deactivation by re-oxidation. At low O/M ratio condition, an opposite behavior was observed for the small and big yolk particles. The catalyst with small yolk particles maintained its initial activity with high resistance to carbon deposition whereas NiCe@SiO₂ with big yolk particles deactivated fast under the low O/M ratio. The stable activity observed on the small yolk particles could be explained by the fast oxidation ability of the small yolk particles, which can enhance oxidation of carbon deposits on the catalyst. A detailed analysis of the fresh and spent samples characterized through STEM, XRD, H₂-TPR, TGA and Raman will be discussed in the presentation. These results confirm that the morphology of the NiCe@SiO₂ yolk-shell nanotube catalyst can be engineered for maintaining a high TRM activity at different gas feed concentrations.