Conversion of Methane Over LaNiZnO₃ Perovskite Catalysts

Abstract

Carbon dioxide reforming of methane reaction (DRM) is an important process to produce synthesis gas at low H₂/CO ratio and to consume the two main greenhouse gases CH₄ and CO₂. Nickel-based catalysts are the most frequently used in dry reforming of methane. However, deactivation of these catalysts is a major problem due to carbon deposition and metal sintering. In order to minimize the deactivation phenomena of the nickel-based catalysts, a great attention is given to the use of the perovskite oxide (ABO₃) catalysts. These oxides have a defined structure that yields small metallic particles highly active and quite stable during DRM reaction. This work deals dry reforming of methane to produce synthesis gas (H₂/CO), using the mixed oxides LaNi_1-xZn_xO₃ (x = 0, 0.2, 0.8 and 1) perovskite-type catalysts. The auto-combustion using glycine as ignition promoter was the method for the synthesis of these catalysts, and then, they were characterized by using XRD, FTIR, and N₂ physisorption. XRD analysis of the solids LaNi_1-xZn_xO₃ (x = 0, 0.2, 0.8) shows the formation of perovskite structure at 2θ between 32° and 33°. At high Zn content (x = 1), the catalyst showed the presence of individual metal oxides ZnO and La₂O₃. These oxides are confirmed by FTIR characterization with observation of bands in the range 450–700 cm⁻¹which are attributed to M–O-M of the perovskite structure and M–O of the simple oxide. The effect of partial substitution of Ni by Zn on the catalytic performance has been studied. LaNi_0.8Zn_0.2O₃ was the most active toward the CH₄ and CO₂ conversions and was selective for synthesis gas products at 750 °C. This activity was attributed to high dispersion of the small metallic nickel particles (19 nm) and the high surface area (27 m²/g).