Preparation of La0.75Sr0.25Mn1-xNixO3+delta Materials and Their Catalytic Performance for Methane Partial Oxidation

A series of perovskites La0.75Sr0.25Mn1-xNixO3+delta (x = 0, 0.4, 0.5, and 0.6) were prepared by the citric chelating method. Methane partial oxidation was used to investigate the catalytic performance of the samples. The crystal structures were characterized by X-ray diffraction (XRD) and temperature-programmed reduction (H-2-TPR), temperature-programmed desorption of oxygen (O-2-TPD), and temperature-programmed oxidation (TPO). XRD results showed that the unit cells of the samples with x < 0.6 were perovskite structures, and perovskites and spinel structure were detected with x = 0.6. The results of H-2-TPR indicated that most of the reducible species were in La0.75Sr0.25Mn0.5Ni0.5O3+delta. O-2-TPD results showed that most of the movable oxygen species existed on the surface and in the lattice of La0.75Sr0.25Mn0.5Ni0.5O3+delta; in combination with TPO results it can be concluded that La0.75Sr0.25Mn0.5Ni0.5O3+delta had the best performance of resisting carbon deposition among the samples. The catalytic activity tests showed that with Ni doped in the B-sites of LaSrMnO3 perovskite, the methane conversion increased, and the highest selectivity for H-2 and CO and good stability were found on the La0.75Sr0.25Mn0.5Ni0.5O3+delta sample. In addition, this catalyst yielded a H-2/CO molar ratio close to 2 at 700 degrees C and showed good resistance to carbon deposition.