(429c) Insight into Carbon Gasification Via TAP

Syngas production from methane has been widely investigated using various reforming technologies. Among the options, DRM has the lowest operating cost and it offers the additional advantage of utilizing CO2. Nickel-based catalysts are commonly used, but they are sensitive to deactivation by carbon accumulation. Eventually, catalyst regeneration is required, removing carbon species by gasification. The rate of gasification depends on the structure of the carbon, its location and on the nature of the catalysts present. In view of the promising results on Fe–Ni/MgAl2O4 regarding reduced carbon accumulation, this material was used for further investigation of carbon formation and removal. The research questions raised are addressed by performing X-ray diffraction (XRD) characterization of used Fe– Ni/MgAl2O4 catalysts, both in situ during as well as operando. Furthermore, Temporal Analysis of Products (TAP) has been used for the first time to investigate the isothermal carbon species gasification process. In the present research, two different types of carbon species, graphitic and amorphous, were formed and accumulated after methane dry reforming over the Fe–Ni catalysts. CO2 as oxidant could remove part of the carbon species, although EDX-STEM mapping still 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 O2 was identified from temperature programmed and isothermal experiments as a process comprising two components: (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.