Ni/Ce0.8Zr0.2O2−x solid solution catalyst: a pathway to coke-resistant CO2 reforming of methane†

The CO₂ reforming of methane effectively produces syngas using two prevalent greenhouse gases: CO₂ and CH₄. This study investigates the performance of three nickel-based catalysts, Ni/ZrO₂, Ni/CeO₂ and Ni/Ce_0.8Zr_0.2O_2−x, in the DRM reaction. Each catalyst was thoroughly examined using a range of techniques, including XRD, TPR, BET, TPD, HR-TEM, Raman, O₂-TPD, XPS, TGA and CO₂-TPD to assess its structural and catalytic properties. The Ni/Ce_0.8Zr_0.2O_2−x catalyst, combining the advantages of both supports to form a solid solution, achieved the best overall performance with enhanced activity and stability. Meanwhile, Ni/ZrO₂ and Ni/CeO₂ catalysts showed a tendency towards deactivation over extended reaction times. Characterization showed that incorporating zirconia into the CeO₂ lattice led to the solid solution synthesis with a solely defective cubic fluorite phase, as confirmed by XRD and Raman analysis. The TPR and CO₂-TPD revealed that the resulting Ni/Ce_0.8Zr_0.2O_2−x catalyst possesses strong metal–support interaction and higher CO₂ adsorption compared to pure CeO₂ and ZrO₂ samples. This composite support facilitated the generation of oxygen vacancies/active oxygen species, which are beneficial for reducing coke deposition. The Ni/Ce_0.8Zr_0.2O_2−x catalyst demonstrated exceptional performance, achieving around 90.8% methane conversion and 91.0% CO₂ conversion at 700 °C, with the resulting H₂/CO ratio precisely equal to one. The stability test revealed remarkable stability against coke deposition for Ni/Ce_0.8Zr_0.2O_2−x; meanwhile, Ni/ZrO₂ and Ni/CeO₂ are more susceptible to coke deposition, with the Ni/ZrO₂ sample showing a greater tendency towards graphitic coke deposition. This study highlights the importance of catalyst supports in optimizing the performance of nickel-based catalysts for CO₂ reforming applications.