Combustion Synthesis of Non-Precious CuO-CeO(2) Nanocrystalline Catalysts with Enhanced Catalytic Activity for Methane Oxidation

In this study, xCuO-CeO(2) mixed oxide catalysts (Cu weight ratio x = 1.5, 3, 4.5, 6 and 15 wt.%) were prepared using solution combustion synthesis (SCS) and their catalytic activities towards the methane (CH(4)) oxidation reaction were studied. The combustion synthesis of the pure CeO(2) and the CuO-CeO(2) solid solution catalysts was performed using copper and/or cerium nitrate salt as an oxidizer and citric acid as a fuel. A variety of standard techniques, including scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were employed to reveal the microstructural, crystal, thermal and electronic properties that may affect the performance of CH(4) oxidation. The CuO subphase was detected in the prepared solid solution and confirmed with XRD and Raman spectroscopy, as indicated by the XRD peaks at diffraction angles of 35.3° and 38.5° and the A(g) Raman mode at 289 cm(−1), which are characteristics of tenorite CuO. A profound influence of Cu content was evident, not only affecting the structural and electronic properties of the catalysts, but also the performance of catalysts in the CH(4) oxidation. The presence of Cu in the CeO(2) lattice obviously promoted its catalytic activity for CH(4) catalytic oxidation. Among the prepared catalysts, the 6% CuO-CeO(2) catalyst demonstrated the highest performance, with T(50) = 502 °C and T(80) = 556 °C, an activity that is associated with the availability of a fine porous structure and the enhanced surface area of this catalyst. The results demonstrate that nanocrystalline copper-ceria mixed oxide catalysts could serve as an inexpensive and active material for CH(4) combustion.