Ni based catalysts have been identified as very promising catalysts for CO methanation, because of highly effective catalytic performance and rather low price. Ni particles are always supported on various metallic oxide, e.g. SiO2, MgO, Al2O3, TiO2, CeO2 and ZrO2. Basic oxide ZrO2 has been widely used as the support for methanation due to its rich catalytic active sites, containing surface basic sites (hydroxyl groups, adsorbed oxygen), acid-base Zr4+-O2- pairs and oxygen vacancies. So far, the challenge that Ni catalysts are facing is the high thermodynamic potential for carbon deposition, leading to catalytic instability and even deactivation. A novel Ni/ZrO2 catalyst (denoted as Ni/ZrO2-P) prepared via dielectric barrier discharge (DBD) plasma has been reported in this work. Its improved low-temperature activity and sintering and coke resistance in CO methanation as compared with thermally decomposed catalyst (marked as Ni/ZrO2-C) are mainly attributed to unique geometrical and electronic structure, including higher reducibility and Ni dispersion, smaller Ni particle size with high-coordinate Ni (111) as the principal exposing facet and stronger basic sites derived from higher oxygen vacancy density on ZrO2 surface. At H2/CO ratio of 6, 100 % CO conversion and 98.1 % CH4 yield can be obtained at 513 K over Ni/ZrO2-P, whereas they are only 28.1 % and 12.9 % over Ni/ZrO2-C. When the H2/CO ratio below 6, Ni/ZrO2-C keeps severely deactivated, owing to sintering agglomeration and carbon deposition. In contrary, the higher resistance force caused by the stronger interaction between Ni and ZrO2 in Ni/ZrO2-P effectively suppresses Ni particles’ transfer and further agglomeration. Besides, CO dissociation as one of steps in CO methanation is promoted with more α-carbon in lower graphite crystallinity produced. These more active carbon species can be more quickly removed by H2 gasification, resulting in higher CH4 yield and less carbon deposition. The better balance between CO dissociation and gasification not at the sacrifice of catalytic activity achieves greater coke resistance. The present work demonstrates that the DBD plasma decomposition is capable of serving as an efficient and eco-friendly approach for fabrication of highly reactive Ni catalysts, and can further contribute to the design of structuralized Ni catalysts.

Preparation of Ni/ZrO2 catalyst with enhanced activity and coke resistance for CO methanation

256th National Meeting (2018)

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