An aerosol reactor was tested for the thermal reduction of ceria as part of a solar thermochemical redox cycle for producing H-2 and CO from H2O and CO2. The design is based on the downward aerosol flow of ceria particles, counter to an argon sweep gas, which are rapidly heated and thermally reduced within residence times of less than 1 s. When operating in the temperature range of 1723-1873 K and at oxygen partial pressures between 5 x 10(-5) and 1.2 x 10(-4) atm, reduction extents of small particles (D-v50 = 12 mu m) approached those predicted by thermodynamics. However, heat- and mass-transfer effects were found to limit their conversion when the ceria mass flow rate was increased above 100 mg s(-1). This reactor concept inherently results in separation of the reduced ceria and evolved O-2(g), operates isothermally throughout the day, and decouples the reduction and oxidation steps in both space and time for potential 24-h syngas generation.