Sol-gel fabrication of porous ceria microspheres for thermochemical carbon dioxide (CO2) splitting

Abstract

Porous CeO2 has been of great interest recently, due to its great catalytic efficiency in splitting CO2 into CO and O2. Porous CeO2 microspheres are the key to scaling up such reactions in the fluidized-bed solar thermochemical reactors. In this paper, we report the processing and CO2 splitting performance of porous ceria microspheres. To fabricate the porous ceria microspheres, homogenous cerium-based sol-gel precursors were synthesized from cerium acetate. The acrylamide (AM) was used as both solidification and pore-generation agent. The polymerization of acrylamide facilitated the conversion of liquid droplets to solid gel microspheres. The optimal AM content was around 20 wt%, ensuring both sufficient porosity and the integrity of the ceria microspheres after thermal decomposition. After heat treatment at 1500 °C for 1 h, porous CeO2 microspheres were obtained, with an average diameter of ∼800 μm and surface area of 2.9 m2/g. These microspheres had high porosity and good sphericity. The CO2 splitting performances of these microspheres were characterized using thermogravimetric analysis (TGA). During the thermal cycles between 1000 and 1400 °C, the O2 yield of porous ceria microspheres was 49 μmol/g, and the CO yield was 88 μmol/g. Compared with porous ceria granules of particle size of ∼800 μm, the porous ceria microspheres exhibited higher O2 and CO production yields. After thermochemical cycles, the microspheres were not sintered together, and the surface area was slightly reduced to 2.7 m2/g.