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 %.

Technologies that facilitate the conversion of CH4 and/or CO2 with concentrated sunlight provide a viable strategy for storing solar energy in the form of liquid fuels and reducing anthropogenic greenhouse gas emissions. Herein, a scalable prototype receiver‐reactor is developed to experimentally demonstrate the chemical‐looping, dry reforming of methane over ceria with simulated concentrated solar radiation. Optimal operating conditions are identified by investigating wide ranges of parameters like temperature, gas flowrate, inlet CH4 concentration, initial oxygen nonstoichiometry, and particle size. Ultimately, a selectivity to H2 and CO of greater than 0.93 is observed at reactant conversions of 0.69 and 0.88 for CH4 and CO2, respectively. As a result, the calorific value of the products relative to the reactants is upgraded, and a solar‐to‐fuel conversion efficiency of 10.06% is attained, higher than the previously reported record of 7%. Near‐perfect selectivity to syngas is achieved by operating with low reactant residence times, and if reactions were initiated over oxygen‐deficient ceria. Reactant conversion is enhanced through a reduction in particle size, which enables more rapid kinetics via an increase in surface oxygen availability. Stable performance is demonstrated over 10 consecutive redox cycles under conditions that maximized efficiency for the system presented herein.

In this response to the rebuttal of Krenzke and Davison, the authors of “Theoretical and Experimental Investigation of Solar Methane Reforming through the Nonstoichiometric Ceria Redox Cycle” clarify that the “simultaneous” and “sequential” approaches proposed by the two groups converge to become mathematically equivalent in the limit when H2 and CO constitute the only reaction products.