Catalytic Performance of Novel Hierarchical Porous Flower-Like NiCo2O4 Supported Pd in Lean Methane Oxidation

In this work, NiCo2O4 with a hierarchical porous flower-like structure was fabricated and used as catalyst support for Pd nanoparticles. The NiCo2O4 was composed of porous nanoplates without overlapping, and the Pd nanoparticles were uniformly distributed on these nanoplates. Pd–NiCo2O4 with the Pd loading of 2.0 wt% showed extremely high activity and stability, methane (1.0% CH4/Air) can be totally oxidized at 330 °C and the T90 is 309 °C, which is much lower than that of pure NiCo2O4 (T90 = 405 °C). At wet condition with the presence of 10 vol% water vapor, the catalytic activity was still acceptable with the T90 of 366 °C, and no activity decrease or permanent damage for the catalyst was observed after 35 h reaction, showing high stability. A series of techniques including TEM, SEM, XRD, H2-TPR, BET and especially quasi in situ XPS combined with in situ MS were used to characterize the catalysts and investigate the catalysis mechanism. Two pathways of CHO evolution were proved by the quasi in situ XPS and in situ MS results: OCHO intermediate dehydrogenation pathway at lower temperature and CO oxidation pathway of CHO at higher temperature.