Mesoporous NiO–CeO2 catalysts for CO oxidation: Nickel content effect and mechanism aspect

• Ordered mesoporous NiO–CeO2 catalysts with various nickel contents were prepared.
• Doped Ni2+, interfacial NiOx and free NiO species were discriminated in catalysts.
• CO oxidation activity and interfacial nickel species decreased with nickel content.
• Comparable apparent activation energy (55 kJ/mol) was found for NiO–CeO2 catalysts.
• A cooperative reaction mechanism was proposed.

Mesoporous NiO–CeO2 catalysts with different nickel contents (meso-NixCe, x = 0.05, 0.1, 0.2) were prepared by a KIT-6-templating method and characterized by XRD, N2 physisorption, TEM, Raman, XPS and H2-TPR to understand their catalytic performances in CO oxidation. The introduction of nickel induced an obvious modification of the pore system of ceria, but the pore size and distribution were hardly affected by nickel content. HRTEM, XRD and Raman results clearly depicted free NiO (both clustered and amorphous) and doped nickel species, while XPS suggested the presence of another kind of nickel species (interfacial NiO). Probably owing to the unique mesoporous structures, the interfacial NiO decreased with increasing nickel content, which was coincident with CO oxidation activity. Besides, the comparable apparent activation energy (∼55 kJ/mol) for all samples indicated similar reaction pathway was followed. By correlating the catalytic performances with textural and compositional properties, it was found the latter dominated catalytic performance, and interfacial NiO was deduced to be the main active species for CO oxidation. Lastly, a synergetic interaction between atomically neighboring nickel oxide and ceria on the adsorbed reactants was tentatively proposed to understand the reaction mechanism.

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