H2 production from a plasma-assisted chemical looping system from the partial oxidation of CH4 at mild temperatures

A plasma-assisted chemical looping system for the production of H-2 (PCLH) was investigated in this study. This system allows the partial oxidation of CH4 at mild temperatures (573-773 K). Four active oxygen carriers: Fe2O3, NiO-impregnated Fe2O3 (NiO/Fe2O3), SrFeO3-delta and NiO-impregnated SrFeO3-delta (NiO/SrFeO3-delta) were compared, each working both as a packed material for the plasma reactor and an oxygen source for the partial oxidation of CH4. Similar conversions of CH4, and low yields of H-2 were obtained in Fe2O3 and SrFeO3-delta. It was concluded that in these cases, H-2 was mainly produced from direct cracking of CH4 by plasma. In contrast, when using NiO/Fe2O3 and NiO/SrFeO3-delta, substantial production of H-2 was achieved. It is proposed that there is a synergistic effect between the catalyst and the oxygen carrier; the presence of the metallic Ni phase was responsible for catalysing the production of H-2, and the oxygen from the support helped prevent the build-up of coke. As a result, the activity of Ni was continuously maintained for H-2 production. The chemical loop is closed with the oxygen carriers being regenerated in air with plasma and then used in the next looping cycle. The high H-2 production capability in NiO/Fe2O3 was repeatable; whilst, NiO/SrFeO3-delta deactivated in the second and third cycles. Amongst the temperatures studied, NiO/Fe2O3 at 673 K resulted in the best performance for H-2-rich gas production. A further increase in the operating temperature led to a total combustion of CH4.