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

Abstract

The solution combustion synthesis method was used to make CuNi substituted CeO2 (7.5 at.% of Cu+7.5 at.% of Ni), and CuCo substituted CeO2 (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 H2-temperature-programmed reduction(H2-TPR). Further, these catalysts were tested for endothermic dry reforming of methane (DRM) reaction. The CuNi substituted CeO2 catalyst started dry reforming of methane (DRM) at around 350 °C, while the CuCo substituted CeO2 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 CeO2 catalyst converted CH4 better than the CuCo substituted CeO2 at all temperatures reaching 98 % conversion at 800 °C The CuNi substituted CeO2 showed higher H2/CO ratio in comparison to the CuCo substituted CeO2 but the long-term stability followed the opposite order. Thermal gravimetric analysis (TGA), SEM and O2-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, CO2 activation also goes via the defect dissociation route, an additional step to the conventional carbon oxidation (CO2+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.