Porous NiO nano-sheet as an active and stable catalyst for CH4 deep oxidation

•NiO catalysts with different morphologies were prepared with different precipitants.•Mesoporous NiO-NaOH prepared with NaOH solution shows sheet-like morphology.•NiO-NaOH nano-sheet shows the highest CH4 oxidation activity.•The activity of NiO-NaOH is competitive to that of 0.5 wt.% Pd/Al2O3.•NiO-NaOH shows superior stability in both dry and wet feeds.

A series of polycrystalline NiO catalysts with different morphologies have been prepared in this study with a simple precipitation method by changing the precipitants, and used for CH4 deep oxidation. NiO-NaOH, a sample prepared with NaOH solution, displays the highest CH4 oxidation activity among all the catalysts, which is competitive to that of 0.5 wt.% Pd/Al2O3, especially at high WHSV. SEM demonstrates that it consists of uniform nano-sheets with an average thickness around 23 nm. Compared with other two samples composed of irregular nano-particles, this nano-sheet mesoporous sample possesses higher surface area, larger pore volume and pore size. H2-TPR demonstrates that it also contains less Ni3+ cations, which are found to be harmful to the activity. Furthermore, it is revealed that more active oxygen species has been formed on the surface of this nano-sheet sample. As a result, NiO-NaOH shows the highest CH4 oxidation activity among all the NiO catalysts. Water vapour has no any negative effect on the activity of NiO-NaOH, as testified by the long-term stability test in the presence of water vapour.

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