Experimental Demonstration of the Thermochemical Reduction of Ceria in a Solar Aerosol Reactor

We report on the experimental demonstration of an aerosol solar reactor for the thermal reduction of ceria, as part of a thermochemical redox cycle for splitting H₂O and CO₂. The concept utilizes a cavity-receiver enclosing an array of alumina tubes, each containing a downward gravity-driven aerosol flow of ceria particles countercurrent to an inert sweep gas flow for intrinsic separation of reduced ceria and oxygen. A 2 kW_th lab-scale prototype with a single tube was tested under radiative fluxes approaching 4000 suns, yielding reaction extents of up to 53% of the thermodynamic equilibrium at 1919 K within residence times below 1 s. Upon thermal redox cycling, fresh primary particles of 2.44 microm mean size initially formed large agglomerates of 1000 microm mean size, then sintered into stable particles of 150 microm mean size. The reaction extent was primarily limited by heat transfer for large particles/agglomerates (mean size > 200 microm) and by the gas phase advection of product O₂ for smaller particles.