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Reversible Segregation of Ni in LaFe 0.8 Ni 0.2 O 3± δ During Coke Removal
Author(s) -
Steiger Patrick,
Nachtegaal Maarten,
Kröcher Oliver,
Ferri Davide
Publication year - 2018
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201800603
Subject(s) - catalysis , methanation , nickel , raman spectroscopy , materials science , chemical engineering , temperature programmed reduction , coke , inorganic chemistry , crystallography , chemistry , metallurgy , organic chemistry , engineering , physics , optics
The deactivation of supported nickel catalysts by coking is an important technological subject for many chemical processes, especially when high concentrations of unsaturated hydrocarbons are present in the feed gas. Here, the reversible segregation of Ni from a LaFeO 3± δ perovskite‐type host lattice was exploited to completely recover a LaFe 0.8 Ni 0.2 O 3± δ catalyst after it had been deliberately subjected to severe carbon deposition during CO 2 methanation in ethylene rich feed gas for several hours. Temperature programmed reduction, X‐ray diffraction, electron microscopy, X‐ray absorption spectroscopy and catalytic activity tests were used to follow the catalyst structure along the various steps of reduction, reaction, coking and subsequent regeneration, while Raman spectroscopy and electron microscopy were used to characterize the nature of the carbon deposits. It is shown that upon reduction Ni atoms segregate to the surface of the perovskite to form catalytic active Ni particles. Oxidation stimulates Ni atoms to readopt the coordination environment of Fe in the perovskite matrix. This property persisted after severe catalyst deactivation by filamentous, partially graphitic carbon. It is demonstrated that simple catalyst reoxidation can be applied to oxidize all carbon deposits while additionally reverting segregated Ni back into the host lattice, thus protecting Ni from particle growth and resultant long‐term loss of catalyst activity over multiple regeneration cycles.