Carbon gasification from Fe-Ni catalysts after methane dry reforming

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.