Highly Stable and Selective Ni/ZrO₂ Nanofiber Catalysts for Efficient CO₂ Methanation

Ni-based oxides are promising catalysts for CO₂ methanation. However, Ni-based catalysts also have some unresolved issues and drawbacks in practical applications. The activity and selectivity of Ni-based catalysts in CO₂ methanation at low temperatures still need to be improved. Here, Ni/ZrO₂ nanofibers with high surface areas (up to 101.2 m²/g) were prepared by electrospinning methods. The Ni/ZrO₂-ES (also named as 66Ni/ZrO₂) catalyst showed excellent catalytic performance in CO₂ methanation (the CO₂ conversion = 81% and CH₄ selectivity = 99% at 350 °C) and excellent stability for 100 h, which was better than most reported Ni/ZrO₂ catalysts. However, the comparison sample Ni/ZrO₂-CP prepared by the coprecipitation method had poor catalytic performance (the CO₂ conversion = 54% and CH₄ selectivity = 90% at 350 °C). Within 100 h, the CO₂ conversion decreased to 30% and the CH₄ selectivity decreased to 52%. Both EPR and O^1S XPS confirmed that Ni/ZrO₂ nanofibers can form more reactive oxygen species vacancies, and CO₂-TPD confirmed that nanofibers had more CO₂ adsorption sites compared with the control sample Ni/ZrO₂-CP. In situ DRIFTS analysis showed that bidentate carbonate and monodentate carbonate were key intermediates in CO₂ methanation. The catalytic performance of Ni/ZrO₂ nanofiber catalysts would be attributed to higher dispersion of Ni species on the surface of nanofibers, high specific surface area (101.2 m²/g), more oxygen vacancies, more CO₂ adsorption sites, and the synergistic effect between Ni nanoparticles and ZrO₂ nanofibers. This work may inspire the rational design of Ni/ZrO₂ nanofiber catalysts with rich oxygen vacancies for low-temperature CO₂ methanation.