EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Utilization of excess CO2 and H2 from industrial production plants to produce methane appears a suitable route to store energy in chemicals. Nickel is a typical active metal for this reaction due to its price and availability but suffers from volatility, particle growth and carbon deposition especially in industrial feeds. Nickel can be stabilized by incorporation at the octahedral Fe-site of the LaFeo3 perovskite-type oxide and can be exsolved under reducing conditions to generate metallic Ni nanoparticles that become active for CH4 production. The unreduced mixed metal oxide produces CO.
We show that Ni is effectively incorporated within LaFeO3 to form LaFe0.8Ni0.2O3 and that it can reversibly exsolve and dissolve under appropriately selected reducing and oxidising conditions, respectively. Temperature programmed reduction and oxidation cycles were used to establish the optimal conditions of temperature for this reversible process. Re-oxidation at the appropriate temperature can be used to recover Ni into LaFeO3 to avoid particle growth but especially to recover the catalyst from carbon deposition during reaction in the presence of ethylene that simulates chemical agents present in industrial feeds. Oxidation at a lower temperature produces supported NiO that is active upon reduction but does not allow to take advantage of the perovskite-type structure to avoid particle growth over the cycles of reduction and oxidation at elevated temperature. After recovery from carbon deposition, the catalyst can be reduced to generate cyclically the metal nanoparticles required for catalysis. Beside various characterization methods, X-ray absorption spectroscopy was exploited to determine the structure of Ni in every single step of this process.