Ni is widely used in hydrogenation catalysts for its high activity at low cost compared to noble metals. However, unsaturated hydrocarbons (especially in biomass derived feed gases) are known to promote coking of Ni catalysts. Yet, such catalysts may be oxidatively regenerated at elevated temperatures by burning off carbon. However, during regeneration current Ni catalysts with high metal loadings undergo microstructural changes like sintering, which contribute to catalyst deactivation. Incorporation of Ni in LaFe1-xNixO3±δ (LFNO) allows exploitation of the self-regenerating property of perovskite-type mixed oxides. In the current study, we explore the structural reversibility of Ni in LFNO for CO2 hydrogenation. It was demonstrated that LFNO exhibits the exceptional property of reversible nickel segregation. After reduction in 10 vol% H2/Ar at 600°C Ni, Ni was preferentially reduced and segregated to the mixed oxide surface where it formed catalytically active, metallic Ni particles of few nm in size. These Ni particles were again fully reincorporated into the perovskite lattice after reoxidation in air at 650 °C. Amongst other methods like X-ray diffraction and temperature programmed reduction, the state of nickel was assessed over a redox cycle using X-ray absorption spectroscopy around the Ni K-edge. After reduction 50% of all Ni was reduced and all Ni was reincorporated into the host lattice after reoxidation at 650°C for 2 h from which it could be segregated again at no loss of catalytic activity. The stability could be attributed to the constant particle size due to the Ni incorporation and segregation mechanism. It is shown in this work that the preservation of catalytic activity over redox cycles at high temperatures allows the material to be regenerated after it has suffered from severe coking during operation.

La-Fe-Ni-O CO2 hydrogenation catalysts exploiting the reversible segregation of Ni

256th National Meeting (2018)

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