Ni/Co in and on CeO2: a comparative study on the dry reforming reaction

Mono metal (Ni, Co)-substituted (in) and supported (on) CeO<inf>2</inf> catalysts were prepared by using solution combustion synthesis and formaldehyde reduction methods. The catalysts were completely characterized by both bulk and surface techniques. Both supported and substituted catalysts show distinct differences in the dry reforming of methane (DRM) activity. Co-substituted CeO<inf>2</inf> showed the highest stability under the DRM reaction conditions at 800 °C. Detailed kinetic investigations were also carried out to estimate the apparent activation energy. Carbon deposition on the spent catalysts was investigated by thermal gravimetric analysis (TGA) and TEM which shows that the deactivation is due to the presence of amorphous and graphitic carbon. Transient studies on a mass spectrometer indicate that the prominence of the reaction CO<inf>2</inf> + C → 2CO is responsible for the catalyst's stability. Surface lattice oxygen reactivity is a vital factor in catalytic stability and its action decides the reaction steps. DFT further verifies that the energy of vacancy formation is significantly lower in Co-substituted CeO<inf>2</inf> as compared to Ni-substituted CeO<inf>2</inf>. This confirms that the Co-substituted catalyst favors oxidation due to higher availability of surface oxygen, while in contrast Ni hinders oxidation by decreasing the availability of surface oxygen for the reaction.