Irregularly Shaped NiO Nanostructures for Catalytic Lean Methane Combustion

NiO nanomaterials prepared using a solid-liquid NH3 center dot H2O precipitation method (NiO-NSL) were tested in the catalytic combustion of methane. The NiO-NSL presented a characteristic rodlike nanostructure with a length of about a few hundred nanometers except for a part of the nanoparticles. For comparison, the NiO nanomaterials prepared by the traditional liquid-phase NH3 center dot H2O precipitation method (NiO-NLL) were tested in the same reaction conditions. NiO-NSL exhibited significantly higher methane combustion activity than NiO-NLL and achieved the complete combustion of methane at 390 degrees C, which was outstanding in non-noble metal-based catalyst. X-ray photoelectron spectroscopy (XPS) and hydrogen-temperature-programmed reduction (H-2-TPR) results indicate that the surface Ni2+ content of NiO-NSL was higher than that of NiO-NLL, and the presence of more Ni2+ might be responsible for the enhanced activity. DFT calculations prove that the energy barrier for C-H bond activation on Ni2+ was lower than that on Ni3+, which was consistent with the higher methane catalytic combustion activity of NiO-NSL. In addition, when the precipitating agent was replaced with NaOH and (NH4)(2)CO3, the generalization of the solid-liquid precipitation method in the preparation of the NiO catalysts was also tested. The results show that the solid-liquid precipitation method proposed in this work was still applicable when NaOH was used as a precipitant. However, with the use of (NH4)(2)CO3 as a precipitant, the methane catalytic activity of the NiO nanoparticles prepared by the solid-liquid precipitation method was reduced to a certain extent compared with the traditional liquid-phase precipitation method. This research can open up a highly efficient and environmentally friendly method for the synthesis of methane combustion catalysts.