Ce-modified NiO catalysts for catalytic combustion of low-concentration coalbed methane: Oxygen-species regulation...

Developing cost-effective non-noble-metal catalysts that retain high activity under water- and sulfur-containing conditions is important for the utilization of low-concentration coalbed methane. Herein, a series of Ce-modified NiO catalysts were prepared by coprecipitation. X-ray diffraction and Raman analyses revealed CeO₂-related domains together with Ce-induced perturbation of the local NiO environment, while inductively coupled plasma optical emission spectroscopy confirmed the intended Ce-loading sequence. Ni_0.9Ce_0.1O_x exhibited the best dry-feed performance, with temperatures for 50% and 90% methane conversion of 372.7 ± 1.4 and 439.5 ± 5.5 °C, respectively, and a mass-normalized methane-consumption rate of (62.8 ± 1.5) × 10^-5 mol·s^-1·kg^-1 at 350 °C. Quantitative oxygen temperature-programmed desorption showed that Ni_0.8Ce_0.2O_x possessed the largest total oxygen-desorption area, whereas Ni_0.9Ce_0.1O_x exhibited the lowest surface- and lattice‑oxygen-related desorption temperatures and a favorable hydrogen-reduction response. These results demonstrate that the optimum Ce content arises from a balance among defect formation, oxygen lability, reducibility, and surface acid-base properties rather than from the maximum oxygen-associated amount. Density functional theory calculations using a representative local CeONi model showed a decrease in oxygen-vacancy formation energy from 2.12 to 1.24 eV and indicated that a high-valence Ni-related local configuration is more favorable for initial CH cleavage. In situ Fourier-transform infrared spectroscopy further showed that oxygen availability predominantly regulates the subsequent oxidation of hydrocarbon-derived intermediates. Under 3% vol. H₂O, Ni_0.9Ce_0.1O_x maintained high activity with a decrease of only 4.5 percentage points during a 50 h stability test and also retained substantially higher activity than pristine NiO under SO₂ and combined H₂O-SO₂ feeds. These results provide a basis for regulating oxygen and surface redox properties in non-noble-metal methane-combustion catalysts under inhibitory feeds.