Separate H2 and CO production from CH4-CO2 cycling of Fe-Ni

CH4-CO2 chemical looping is proposed for separate H-2 and CO production using nanostructured Fe-Ni looping materials. The product streams are obtained by first feeding CH4, which decomposes to H-2 and carbon. The latter acts as reductant for the subsequent CO2 feed, which together with Fe re-oxidation yields CO. After 25 CH4-CO2 cycles, 10Fe5Ni@Zr has a higher H-2 space-time yield than 10Fe0Ni@Zr (20mmols-1kgFe+Ni-1$$ 20\ \mathrm{mmol}\ {\mathrm{s}}<^>{-1}\ {\mathrm{kg}}_{\mathrm{Fe}+\mathrm{Ni}}<^>{-1} $$ vs. 15mmols-1kgFe+Ni-1$$ 15\ \mathrm{mmol}\ {\mathrm{s}}<^>{-1}\ {\mathrm{kg}}_{\mathrm{Fe}+\mathrm{Ni}}<^>{-1} $$), a 2.6 times higher CO yield (57mmols-1kgFe+Ni-1$$ 57\ \mathrm{mmol}\ {\mathrm{s}}<^>{-1}\ {\mathrm{kg}}_{\mathrm{Fe}+\mathrm{Ni}}<^>{-1} $$) and lower deactivation. This improvement has two reasons: (i) CH4 activation over Ni leading to cracking, (ii) product hydrogen causing deeper FeO reduction. Deactivation follows from accumulated carbon, non-reactive for CO2. On Ni and Fe sites, carbon can be removed by lattice oxygen or CO2, yielding more CO compared to the theoretical value for Fe oxidation. However, carbon that migrates away from the metals requires oxygen for removal, which restores the activity of the Ni-containing samples.

Automated summary

In this study, CH4-CO2 chemical looping using nanostructured Fe-Ni looping materials for separate H-2 and CO production is proposed. After 25 cycles, 10Fe5Ni@Zr exhibits higher H-2 space-time yield, higher CO yield, and lower deactivation compared to 10Fe0Ni@Zr. The improved performance is attributed to the activation of CH4 over Ni and the deeper FeO reduction caused by product hydrogen.