Two-step thermochemical cycles using fibrous ceria pellets for H2 production and CO2 reduction in packed-bed solar reactors

Abstract

The thermochemical redox activity and performance of commercial-grade fibrous ceria pellets were determined including fuel production rates and yields from H 2 O and CO 2 dissociation. Two solar reactors integrating the ceria pellets undergoing two-step thermochemical cycling (with temperatureswing between alternating redox steps) were experimentally tested. They consisted of packed-bed tubular and cavity-type solar reactors with direct or indirect heating of the reacting materials. The obtained fuel production rates compared favorably with the performance of other previously considered microstructured ceria materials such as templated foams, sintered felts, bioinspired or ordered macroporous morphologies. H 2 production rates reached 2.3 mL.g -1 .min -1 (with H 2 /O 2 ratios approaching 2) in the indirectly-heated tubular reactor after reduction at 1400°C and oxidation upon free cooling below 950°C in steam atmosphere (57% molar content). The highest fuel production rate (~9.5 mL.g -1 .min -1 ) and peak solar-to-fuel energy efficiency (~9.4%) were reached in the directlyirradiated cavity-type reactor (with a reduction step at 1400°C under reduced pressure, and an oxidation step in pure CO 2 below 950°C). The reduction extent was favored at low p O2 ( up to 0.056) and the fuel yields were thus improved notably (up to 315 µmol/g) by decreasing the total pressure below 0.1 bar during the reduction step. The fuel production rate increased when the oxidation temperature decreased (because the reaction was thermodynamically more favorable). An increase in CO 2 partial pressure further promoted the oxidation kinetics (and decreased the p CO /p CO2 ratio, thus shifting the thermodynamic equilibrium toward CO product). The fibrous ceria structures exhibited stable morphologies with high fuel production performance similar to less scalable porous structures, thus offering the potential for versatile applications in packed-bed solar reactors.

Solar-driven thermochemical conversion of H2O and CO2 into sustainable fuels

“…At present, the ceria-based redox materials are experiencing explosive development, and various recent advances in the field are continuously reported. 128 , 129 , 130 , 131 , 132 However, there are still several aspects that need to be further developed before commercial application. To plainly take profit of the advantages of ceria-based redox cycles, Abanades 20 reviewed the development of ceria-based redox materials and gave some suggestions: (1) the dopant schemes of ceria need to be further optimized including development of new dopants and utilization of composite materials; (2) synthesis method is also an important aspect, especially when the powdered ceria-based material is adopted, synthesis material must be warranted high-temperature resistance; and (3) for porous structure ceria-based material, thermally resistant supports and efficient coating methods are needed, and elaboration of architecture porous structures (such as biomimetics, 3D printing, etc.)…”

“…Abanades et al. 131 adopted parabolic dish concentrator to directly and indirectly provide high-temperature heat for H 2 O and CO 2 dissociation in solar reactors, and they observed highest fuel production rate of ∼9.5 mL g −1 min −1 and peak solar-to-fuel energy efficiency of ∼9.4% from directly irradiation style.…”

Solar Thermochemical Production of Syngas from H2O and CO2─Experimental Parametric Study, Control, and Automation

“…Solar reactor concepts previously investigated for effecting the ceria redox cycle have included moving − and stationary ,, bulk structures, packed beds, − moving beds, − and aerosol flow , of particles. Of special interest is the solar reactor concept based on a cavity receiver containing reticulated porous ceramic (RPC) structures made of ceria, ,, which enhance heat and mass transfer.…”

Innovative Applications of Cerium Oxide-Based Materials in Civil Engineering, Automation, and Energy Sectors

“…Moreover, the Rare Earth (RE) elements are recognized for their low toxicity, posing no harm to health through ingestion or inhalation [4,5]. Consequently, various Cerium compounds are now being explored for prospective applications in diverse sectors, such as electrocatalytic hydrogen generation [6][7][8], thermochemical fuel production [9][10][11], water-splitting devices [12][13][14][15][16][17][18][19][20], biodiesel production catalysts [21,22], sensors [23][24][25][26][27][28], biosensors [29][30][31][32], and more. Recent investigations into the use of ceria nanoparticles for medical applications [33][34][35][36][37][38][39][40][41] underscore the potential of cerium oxide-based nanomaterials.…”