The dry reforming of methane through the nonstoichiometric ceria (CeO2–CeO2−δ) redox cycle was examined theoretically and experimentally for converting high-temperature, solar process heat to syngas. The aforementioned cycle is composed of: (1) endothermic reduction of ceria and simultaneous partial oxidation of methane and (2) exothermic oxidation of the reduced ceria and simultaneous reduction of CO2. In both steps, chemical equilibrium calculations indicate that isothermal operation is thermodynamically favorable under a wide range of conditions. The influence of the total amount of reactive gas, the operating temperature, and the inclusion of gas- or solid-phase heat exchangers on the cycle performance was determined through a holistic process model. A theoretical solar-to-fuel conversion efficiency, defined as the ratio of the difference between the calorific value of syngas (H2 and CO) produced and methane converted to the total solar radiative input energy, of more than 45 % was predicted with no heat recuperation. Experimental validation was subsequently demonstrated in a packed-bed-type solar reactor using the high-flux solar simulator at the University of Florida at three discrete isothermal temperatures, namely, 950, 1035, and 1120 °C. Upon the completion of the reduction at each temperature, the bed-averaged oxygen nonstoichiometry equaled 0.07, 0.21, and 0.24, which yielded methane conversions of 9, 41, and 51 %, respectively. At 1120 °C, the extrapolated solar-to-fuel conversion efficiency was 9.82 %.
- redox chemistry
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