Structural Reversibility and Nickel Particle stability in Lanthanum Iron Nickel Perovskite-Type Catalysts

Perovskite-type oxides have shown the ability to reversibly segregate precious metals from their structure. This reversible segregation behavior was explored for a commonly used catalyst metal, Ni, to prevent Ni sintering, which is observed on most catalyst support materials. Temperature-programmed reduction, X-ray diffraction, X-ray absorption spectroscopy, electron microscopy, and catalytic activity tests were used to follow the extent of reversible Ni segregation. LaFe_1-x Ni_x O_3±δ (0≤x≤0.2) was synthesized using a citrate-based solution process. After reduction at 600 °C, metallic Ni particles were displayed on the perovskite surfaces, which were active towards the hydrogenation of CO₂ . The overall Ni reducibility was proportional to the Ni content and increased from 35 % for x=0.05 to 50 % for x=0.2. Furthermore, Ni could be reincorporated reversibly into the perovskite lattice during reoxidation at 650 °C. This could be exploited for catalyst regeneration under conditions under which impregnated materials such as Ni/LaFeO_3±δ and Ni/Al₂ O₃ suffer from sintering.