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 1023 K, 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 O-2 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 1123 K. 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 O-2 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. (C) 2015 Elsevier B.V. All rights reserved.