Bimetal (CuNi and CuCo) substituted CeO2: An approach for low temperature dry reforming of methane

The solution combustion synthesis method was used to make CuNi substituted CeO<inf>2</inf> (7.5 at.% of Cu+7.5 at.% of Ni), and CuCo substituted CeO<inf>2</inf> (7.5 at.% of Cu+7.5 at.% of Co) catalysts. The catalysts were characterized by x-ray diffraction (XRD),XPS, BET surface area measurements, scanning electron microscopy (SEM), and H<inf>2</inf>-temperature-programmed reduction(H<inf>2</inf>-TPR). Further, these catalysts were tested for endothermic dry reforming of methane (DRM) reaction. The CuNi substituted CeO<inf>2</inf> catalyst started dry reforming of methane (DRM) at around 350 °C, while the CuCo substituted CeO<inf>2</inf> catalyst started DRM at around 450 °C. This indicates that the CuNi catalyst has a lower activation temperature for the DRM reaction compared to the CuCo catalyst. The CuNi substituted CeO<inf>2</inf> catalyst converted CH<inf>4</inf> better than the CuCo substituted CeO<inf>2</inf> at all temperatures reaching 98 % conversion at 800 °C The CuNi substituted CeO<inf>2</inf> showed higher H<inf>2</inf>/CO ratio in comparison to the CuCo substituted CeO<inf>2</inf> but the long-term stability followed the opposite order. Thermal gravimetric analysis (TGA), SEM and O<inf>2</inf>-TPO were used to quantify as well as to understand the nature of carbon that had built up on spent catalysts and it is mostly amorphous. Transient studies have shown that along with the lattice oxygen participation, controlled methane decomposition step is necessary for stability of catalysts. Transient studies also recommended additional reaction steps during DRM where an exothermic methane partial oxidation step reduces the endothermicity of DRM. Also, CO<inf>2</inf> activation also goes via the defect dissociation route, an additional step to the conventional carbon oxidation (CO<inf>2</inf>+C→CO) step. So, novelty of this work is in elucidating the exact role of lattice oxygen in imparting the activity and stability to the DRM catalyst.