High Capacity Iron-Poor Ferrites for Syngas Generation from Carbon Dioxide and Methane

CO2 and methane are the two major greenhouse gasses that contribute to global warming. Dry reforming of methane converts CO2 and methane into syngas (CO + H2), an important building block for synthesizing organic compounds such as liquid fuels, utilizing the established energy industry technology. However, there is no commercial process for dry reforming of methane mainly because of catalyst deactivation by solid carbon deposition and the high cost of noble metal based catalysts.

Chemical looping technology decouples the dry reforming of methane into two steps: methane reduction of a metal oxide, and CO2 splitting by the reduced metal oxide. Ferrites are a common type of oxide material in chemical looping for their high oxygen exchange capacity and low material cost. Iron is usually the (major) active redox element in ferrite materials such as NiFe2O4, but recent thermodynamic modeling results have predicted that iron-poor ferrite materials have greater oxygen exchange capacities than traditional iron-rich ferrites for dry reforming of methane.

Here we present the first experimental demonstration of this counterintuitive oxygen exchange capacity dependence on ferrite iron ratio in chemical looping dry reforming of methane. Thermogravimetric and fixed-bed tests were conducted on supported Co-, Ni-, and Mg-ferrites of various Fe ratios for isothermal dry reforming of methane at 500~700 °C. As predicted by the theoretical models, iron-poor ferrites exhibited greater oxygen exchange capacities than iron-rich ferrites. Additionally, a specific type of ZrO2 as the support material was found to maximize the chemical reaction kinetics without inducing carbon deposition. The supported iron-poor ferrite has also been able to maintain less than 10% redox capacity decay in 20 cycles. The mechanistic understanding of the support material has been illustrated by x-ray diffraction and x-ray photoemission spectroscopy. To become a technology for syngas generation in remote areas with limited energy resources, the chemical looping dry reforming, which is endothermic, can also be adjusted to be autothermal by introducing a controlled amount of additional oxidant like O2. These findings contribute to future materials design and scale-up for high capacity and energy efficient chemical looping dry reforming processes.