The key role of Ni dimer in CO2 methanation

The conversion of carbon dioxide (CO₂) into methane (CH₄) offers a promising pathway to mitigate greenhouse gas emissions while addressing the global natural gas shortage. Nickel-based catalysts are widely used for this reaction due to their excellent performance and low cost, but conventional catalysts require extremely high nickel loadings—typically 5% to 50%—to achieve satisfactory activity. Lowering nickel loading, while improving dispersion, often shifts the product selectivity from methane to carbon monoxide, because the strong interaction between nickel oxide and the support inhibits its reduction to metallic nickel.

Now, a team led by Professor Weibin Fan at the State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, has identified the smallest active nickel species for CO₂ methanation and developed a catalyst that achieves excellent performance with only ~0.86% nickel loading. The results are published in the Chinese Journal of Catalysis (10.1016/S1872-2067(26)65095-4)

Using a one-step hydrothermal method, the researchers encapsulated nickel and manganese species simultaneously into the channels of silicalite-1 zeolite. The resulting (0.9)Ni-MnOx(2.0)@MFI catalyst achieved ~76% CO₂ conversion, ~98% CH₄ selectivity, and a CH₄ space time yield of ~450 mol·mol Ni^-1·h^-1 at 400°C and 0.5 MPa, far surpassing most reported nickel-based catalysts under similar conditions.The catalyst maintained stable performance for at least 200 hours.

Through in-situ X-ray diffraction, aberration-corrected HAADF-STEM, XANES/EXAFS, density functional theory (DFT) calculations, and ab initio molecular dynamics (AIMD) simulations, the team demonstrated that the nickel dimer play vital role in triggering CO₂ methanation. The methane formation activity increases linearly with the Ni₂ content.

The introduction of manganese oxide (MnOx) plays a dual role: it not only increases the number of Ni₂ active sites by facilitating the reduction of NiO, but also enhances the intrinsic activity of Ni₂ by transferring electrons to the nickel species, increasing their electronic density. The MnOₓ-promoted Ni₂ species exhibits significantly higher H₂ dissociation activity than single-atom Ni (Ni₁), pure Ni₂, and larger nickel nanoparticles. It also shows much stronger CO adsorption and a lower energy barrier for CO* hydrogenation to CH₄.

In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), isotope-labeled experiments, proton transfer reaction time-of-flight mass spectrometry (PTR TOF-MS), and DFT calculations revealed that CO₂ hydrogenation to methane on the MnOx-Ni₂@MFI catalyst proceeds via the HCOO* and CO* intermediate route: CO₂ is first converted to formate (HCOO), then to CO, and finally hydrogenated sequentially to CH₄.

"This work not only identifies the smallest active Ni species for CO₂ methanation and clarifies the structure-performance relationship, but also makes it possible to significantly reduce nickel loading in catalysts to below 1%," said Professor Fan. "The findings provide theoretical guidance for designing high-performance, low-cost catalysts for CO₂ hydrogenation."

About the Journal

Chinese Journal of Catalysis is co-sponsored by Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Chinese Chemical Society, and it is currently published by Elsevier group. This monthly journal publishes in English timely contributions of original and rigorously reviewed manuscripts covering all areas of catalysis. The journal publishes Reviews, Accounts, Communications, Articles, Highlights, Perspectives, and Viewpoints of highly scientific values that help understanding and defining of new concepts in both fundamental issues and practical applications of catalysis. Chinese Journal of Catalysis ranks among the top one journals in Applied Chemistry with a current SCI impact factor of 17.2. The Editors-in-Chief are Profs. Can Li and Tao Zhang.

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