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 work, we investigate YMnO3 perovskites with Sr2+ and Al3+ doping, Y1–x Sr x Mn1–y Al y O3, for use in thermochemical H2O or CO2 splitting for the first time. Oxygen nonstoichiometries (δ) with x = 0.1 or 0.2 and y = 0.4 or 0.6 were measured over a wide range of temperatures and oxygen partial pressures (pO2). Experiments were performed from 973 to 1173 K and pO2 from 1.24 × 10–20 to 2.26 × 10–13 atm in a high-temperature tubular reactor coupled with residual gas analysis by delivering controlled mixtures of H2 and H2O. Higher temperature and pO2 experiments, from 1173 to 1473 K and 1.61 × 10–4 to 3.23 × 10–2 atm, respectively, were performed via thermogravimetric analysis by delivering controlled mixtures of O2 and Ar. In the low-temperature and pO2 region, each material showed low sensitivity to changes in pO2; thus, the slopes of the equilibrium δ isotherms were small. These experiments, under precisely controlled reaction conditions, help to explain some of the discrepancies in the literature regarding Y0.5Sr0.5MnO3 that, in some cases, highlight its superior behavior compared to ceria and other perovskite compositions. Defect models considering oxygen vacancy formation accompanied by either reduction of Mn4+ to Mn3+ or Mn4+ to Mn2+ along with the formation of extended defects were formulated and tested to describe the chemical equilibria of the synthesized perovskites. Y0.8Sr0.2Mn0.4Al0.6O3 could be well described by Mn4+ to Mn3+, but other compositions showed mixed results because of phase transformations, as confirmed by powder X-ray diffraction.

Leveraging solar thermal energy to drive the chemical looping reforming of methane (CLRM) is a promising method of efficiently and selectively reforming methane to produce syngas using renewable energy. In...

Zr‐doped ceria and Sr‐doped lanthanum manganese perovskites are investigated as candidate redox materials for the chemical‐looping reforming of methane to produce syngas. Herein, the effect that these compositions have on syngas selectivity, partial oxidation of methane (POM) rate, and yield in the temperature range of 800−1000 °C is probed. POM reaction rates increase when using 10% Zr‐doped ceria (CZO10) compared with pure ceria at all conditions, but the yields are generally less except at 800 °C. In the case of (La0.65Sr0.35)0.95MnO3 (LSM35), POM yields are equal to or greater than ceria under all conditions investigated. For all materials, selectivity to syngas during POM is relatively high and typically above 85%. However, selectivity of CZO10 and LSM35 is lower than ceria, likely because of their lower reduction enthalpies and more accessible surface oxygen. This is validated by demonstrating improvements in POM selectivity by suppressing the oxidation extent; in this case, there is no observable H2O or CO2 formation. POM rates increase and activation energy (Ea) decreases for all materials following oxidation with O2 versus CO2. Ceria and CZO10 Ea decrease from about 225 to <50 kJ mol−1 and LSM35 from 150 to 100 kJ mol−1.

Ceria–zirconia solid solutions can facilitate the carbon-neutral conversion of CH4 into separate streams of sequestrable CO2 and pure H2.