Carbon gasification from Fe–Ni catalysts after methane dry reforming

• Published in: Applied catalysis. B, Environmental Vol. 185; pp. 42 - 55
• Main Authors: Theofanidis, Stavros Alexandros, Batchu, Rakesh, Galvita, Vladimir V., Poelman, Hilde, Marin, Guy B.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.05.2016
• Subjects: Carbon; Carbon dioxide; Carbon gasification mechanism; Catalysis; Catalyst regeneration; Catalysts; Fe–Ni catalyst; Gasification; In situ XRD; Iron; Methane dry reforming; Oxidation; Oxygen; TAP reactor; Fe–Ni catalyst; Catalyst regeneration; Methane dry reforming; TAP reactor; Carbon gasification mechanism; In situ XRD
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2015.12.006

[Display omitted] •A mechanism of carbon gasification by CO2 over Fe–Ni catalyst is proposed.•CO2 oxidation could remove only part of the carbon species deposited on the catalyst.•Temporal analysis of products (TAP) study for carbon gasification.•A mechanism of carbon gasification by O2 over Fe–Ni catalyst is proposed.•Particles migration to the carbon species that are deposited far from active metals. Carbon species removal was studied from a Fe–Ni catalyst supported on MgAl2O4 after methane dry reforming at 1023K, atmospheric pressure and a CH4/CO2 molar ratio of 1:1. The deactivated and regenerated catalysts were characterized using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and energy-dispersive X-ray spectroscopy (EDX)-STEM mapping. The catalyst regeneration was studied by CO2 and O2 temperature programmed oxidation (TPO) and by operando time-resolved X-ray diffraction (XRD). A transient response technique, Temporal analysis of products (TAP), was applied to investigate the isothermal carbon species gasification. Two different types of carbon species, graphitic and amorphous, were present after reaction. CO2 oxidation could remove part of the carbon species, although EDX-STEM mapping showed the presence of carbon species located far from active metals phase even after CO2–TPO at 1123K. Carbon species removal by CO2 involves two contributions: (1) the dissociation of CO2 over Ni followed by the oxidation of carbon species by surface oxygen; (2) Fe oxidation by CO2 and subsequent carbon species oxidation by Fe oxide lattice oxygen. The oxidation of carbon species by O2 was identified from temperature programmed and isothermal experiments as a process including two processes: (1) oxidation of surface carbon by lattice oxygen and (2) particles migration to carbon species deposited far from active metals and subsequent oxidation through lattice oxygen of the iron and/or nickel oxides. The contribution of oxygen spillover in carbon gasification was considered to be negligible.