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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Opportunities for Cerium Valorization in the Rare Earth Supply Chain

Rare earth (RE) elements are co-located in ore deposits and must be treated together during the difficult extraction and separation. Cerium is the majority element in most deposits (> 50 %), and the growing need for Nd, Pr and the heavy lanthanides in permanent magnets and other energy transition technologies results in costly stockpiling of cerium oxide which has low demand. Finding new high-value applications for cerium or its compounds is therefore a sought-after goal to improve the profitability of rare earth mining and processing. Here, this contribution will highlight the use of cerium in high-strength aluminum alloys and the preparation of Ce-based permanent magnets as two emerging technologies for high-value products that have potential to stabilize the fluctuating rare earth market, substitute critical materials, support the nascent domestic rare earth industry and provide technologies for the pending green energy transition.

Energy - Conversion, Materials science↗
DOE OSTI2025

First-principles theory for cerium predicts three distinct face-centered cubic phases

We show results from first-principles calculations for cerium at very high compressions. These reveal a most remarkable behavior in a material; depending on atomic volume, cerium adopts three distinct face-centered cubic (fcc) phases driven by different physical mechanisms. The two well-known a and phases are vigorously debated in the literature, but we focus on the a phase as a metal with delocalized character of the 4f electron. The ultimate high compression fcc phase, here named ω, is driven partly by electrostatics. Our density-functional theory (DFT) study excellently reproduces the experimentally known compression behavior of cerium up to a few Mbar but goes beyond those pressures with structural transitions to tetragonal, hexagonal, and cubic (fcc) phases occurring before 100 Mbar (10000 GPa or 10 TPa). The 4f-electron contribution to the chemical bonding is shown to rule phase transitions and compressibility. The change of 4f occupation nicely explains the pressure dependence of the structural axial ratio in the tetragonal phase. At very high pressure, structures known at low pressures return because of band broadening, electrostatic ion repulsion, and an increase in hybridization between states that under normal conditions can be considered core (atomic like) states and the valence-band states.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Differentiating Ligand Tailoring and Cation Incorporation as Strategies for Tuning Heterobimetallic Cerium Complexes

Tuning of redox-active complexes featuring metals with high coordination numbers by incorporation of secondary redox-inactive cations has received far less attention than it deserves. Here, appending moderate steric bulk to a tripodal ligand framework has been tested for its influence on secondary-cation-driven structural and electrochemical tuning of cerium, a lanthanide that tends to adopt high coordination numbers. A quasi -C 3 -symmetric cerium(III) complex denoted [Ce] has been prepared that features pendant benzyloxy groups, and this work demonstrates that this species offers a site capable of binding single Na + or Ca 2+ ions. Electrochemical and UV-visible spectroscopic studies reveal equilibrium binding affinity of [Ce] for Na + in acetonitrile solvent, contrasting with tight binding of all cations in all other previously studied systems of this type. The modulated cation binding can be attributed to the bulky benzyloxy groups, which impact the thermodynamics of cation binding but do not impede the formation of cerium centers with coordination number 8 upon binding of either Na + or Ca2 + . Finally, the Ce(IV/III) reduction potential was found to be tunable under the equilibrium binding conditions, highlighting the potentially significant role that controlled structural changes can play in modulating the solution properties of heterobimetallic complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Orthorhombic cerium(III) carbonate hydroxide studied by synchrotron powder X-ray diffraction

Cerium(III) carbonate is a precursor material for the synthesis of various Ce-containing compounds. In this work, a synchrotron powder X-ray diffraction study of commercially obtained ‘cerium(III) carbonate hydrate' indicates that multiple Ce-containing phases are present. The majority phase CeCO 3 OH (52.49% wt ) was refined using an orthorhombic Pmcn structure model with a = 5.01019 (2) Å, b = 8.55011 (4) Å and c = 7.31940 (4) Å, which is based on a reported structure for the lanthanoid carbonate mineral ancylite. Additionally, a substantial portion of the precursor material is cubic cerium(IV) oxide (47.12% wt ).

08 HYDROGEN↗
DOE OSTI2025

Enhancement of oxidative dehydrogenation over cerium-doped nickel niobium catalysts and analysis of batch-to-batch variability

Nickel based catalysts are inexpensive and efficient for use in the oxidative dehydrogenation of ethane. NiO doped with niobium and cerium shows increased ethylene production. Small amounts of Ce doped onto a NiNb catalyst led to increased Ni activity. The catalyst that had the highest ethylene production rate per g of catalyst had 1 atom% Ce, 86 at% Ni, and 13 at% Nb (1CeNiNb) while, if surface area is incorporated into the calculation, the catalyst that had the highest ethylene production rate per m 2 was the 0.5CeNiNb catalyst. The ethylene production rates of these Ce-containing catalysts are 27 %-127 % higher than those with NiNb alone previously reported in the literature. Here, to fully understand how cerium affects the NiNb catalyst, the Ce content and effect on active sites has been fully characterized over multiple batches. In doing this, light has been shed on batch-to-batch variability. Characterization techniques such as powder X-ray diffraction, hydrogen temperature programmed reduction, X-ray photoelectron spectroscopy, synchrotron X-ray absorption spectroscopy, and methanol adsorption were used.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Stoichiometry dependent properties of cerium hydride: An active learning developed interatomic potential study

Cerium hydride has a variety of interesting properties, including a known lattice contraction and densification with increasing hydrogen content. However, precise stoichiometric control is not experimentally straightforward and ab initio approaches are not computationally feasible for many properties such as melting and low temperature diffusion. Therefore, we develop a machine-learned interatomic potential for cerium hydride that is valid for H to Ce ratios from 2.0 to 3.0. A query-by-committee active learning approach is used to develop the training set. Leveraging classical molecular dynamics simulations, we assess a range of properties and provide fundamental mechanisms for the trends with stoichiometry. Finally, a majority of the properties follow the trend of lattice contraction, being governed by the stronger lattice binding induced by adding octahedral atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Direct observation of oxygen vacancy ordering evolution in cerium oxide at varying concentrations via high-resolution transmission electron microscopy

Under illumination by a 300 keV electron beam, oxygen vacancy ordering structures are induced within cerium oxide grains. Here, our high-resolution transmission electron microscopy (HRTEM) study, supported by image simulation, reveals the evolution of these structures as vacancy concentration increases. The observed fluorite-type superlattice structures are identified as CeO 1.825 , CeO 1.75 , Ce 2 O 3 , displaying a gradient in oxygen vacancy concentration moving away from the grain surface. Correspondingly, the structural sequence transitions from Ce 2 O 3 to CeO 1.75 and then to CeO 1.825 . Without the constraints of surrounding grains, fluorite-type Ce 2 O 3 nanocrystals show a preference for transformation into an A-type trigonal structure. Notably, at temperatures up to 200°C, only the perfect fluorite structure is observed. Structural models were validated through both [110] and [001] projections. Our findings further confirm lattice expansion associated with local oxygen vacancy enrichment, which can be compensated by the formation of stacking faults, where a {111} oxygen plane is lost at defect sites.

Cerium oxide↗
DOE OSTI2025

Electrochemical Behavior of Cerium at an Indium Tin-Doped Oxide Electrode in Acidic Media

The redox behavior and speciation of cerium at mesoporous thin films composed of nanoparticles of indium tin-doped oxide (nITO) electrodes were characterized in pH 4.8, 0.1 M acetate buffer and both 0.1 and 1 M HNO 3 using electrochemical techniques and X-ray photoelectron spectroscopy. Anodic deposition of ceria species from Ce(III) to the nITO electrode was achieved under all solvent conditions via spontaneous condensation of electrochemically generated ceric hydroxide species. In 1 M nitric acid, the rate of CeO 2 dissolution is on the same order as CeO 2 deposition, resulting in negligible amounts of CeO 2 electrodeposited at the nITO surface. The cathodic stripping of CeO 2 from the nITO substrate deposited in 0.1 M nitric acid or pH 4.8 acetate buffer follows a 2-step process where Ce(IV)-oxide is initially reduced to an unstable Ce(III)-oxide species that rapidly undergoes acid catalyzed dissolution to yield soluble Ce(III) (aq) . These findings provide a foundation for the pH and anodic potential controlled deposition of CeO 2 thin films to ITO substrates, which can aid in the development of materials composed of ceria. As a result, they can also be used to infer likely analogous actinide redox behavior and speciation at these electrodes.

Cerium↗
DOE OSTI2025

Defining the Shape Density of Cerium Oxide and Titanium Dioxide Aerosol

The “shape density” of CeO 2 (cerium oxide) powder (American Elements, Los Angeles CA) is estimated to be 0.82 ± 0.02 g cm -3 and the shape density for TiO 2 (titanium dioxide) powder (American Elements, Los Angeles CA) is estimated as 0.54 ± 0.01 g cm -3 . The “shape density” is defined as the measured loose density (ASTM 2018 and ASTM 2021) of a powder divided by the ICRP (International Commission on Radiological Protection) default aerosol shape factor (Valetin 2002). This information is used for experimental measurements of the RRF (respirable release factor) and other respirable source term parameter (US DOE 1994) experiments at the Los Alamos National Laboratory (LANL). The shape density is the input parameter to the TSI Inc (Shoreview MN) AIM (Aerosol Instrument Manager) software for the TSI model 3321 APS (Aerodynamic Particle Sizer) (Figure 1).

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2025

Recent Progress on Cerium Oxide‐Based Nanostructures for Energy and Environmental Applications

Cerium oxide (CeO 2 ) photo/electrocatalysts for energy storage and environmental applications have attracted considerable interest because of stable crystal structure, low toxicity/cost, superior chemical stability, stable redox (Ce 3+ /Ce 4+ ) pairs, abundant oxygen defects, and capablility for intense interaction with other materials. However, the wide bandgap and poor conductivity lower the CeO 2 photo/electrocatalytic and energy storage performances. To overcome these limitations, various modification strategies (tuning morphology, doping or loading of metal nanoparticles, and heterostructures) have been applied for the improvement of photocatalytic (removal of organic contaminants from water/wastewater and H 2 production and CO 2 reduction reactions) efficiency, electrocatalytic (hydrogen/oxygen evolution reactions and CO 2 reduction reactions), and energy storage performances (supercapacitor) of CeO 2 ‐based materials. Herein, the recent progress of CeO 2 ‐based materials for electro(photo)catalysis and energy storage applications has been discussed. The challenges and possible direction of CeO 2 ‐based materials for electro(photo)catalysis and energy storage applications have been emphasized. Furthermore, this comprehensive review is expected to advance the design of CeO 2 ‐based materials and their applications in electro(photo)catalysis and energy.

Ray, Schindra Kumar [Department of Chemistry North↗
DOE OSTI2025

Synthesis and Characterization of Solvated and Base-Free Cerium(III) Mixed-Sandwich Complexes

A series of solvated complexes: [(C8H8)Ln(C5Me4R)(DME)] Ln = La, R = -Me; (La-2) Ln = Ce, R = -Me, -SiMe3, -H; (Ce-2, Ce-3, Ce-4), [(dbCOT)Ln(C5Me5)(DME)] (Ln-6), (dbCOT2- = dibenzocyclooctadienide; Ln = Ce, La), [(dbCOT)Ce(C5Me4H)(DME)] (Ce-7) and [(hdcCOT)Ce(C5Me5)(DME)] (Ce-8) (hdcCOT2- = hexahydrodicyclopentacyclooctatetraenide) and base-free mixed-sandwich complexes [(C8H8)Ce(C5Me5)] (Ce-9), [(C8H8)Ce(C5Me4H) (Ce-10) and [(hdcCOT)Ce(C5Me5)] (Ce-11) of the early lanthanide metals cerium and lanthanum comprising variable cyclopentadienide (Cp-) and cyclooctatetraenide (COT2-) ligands is described. To evaluate the effect of cyclopentadienide and cyclooctatetraenide ligands on the characteristics of these complexes, their solid-state structural, electrochemical, and photophysical properties were studied and accompanied by theoretical calculations. To further evaluate the effect of ligands on the topology of the complexes and the reducing properties of the complexes, syntheses of several base-free congeners were pursued, which led to isolation of the first base-free monomeric and polymeric Ce(III) mixed-sandwich compounds.

Lanthanides↗
DOE OSTI2025

Cerium Dimer Anion and the Contribution of 4f Electrons to Lanthanide Metal–Metal Bonds

Direct metal−metal bonding between lanthanide atoms has been challenging to observe. We report on the first spectroscopic characterization of the cerium dimer anion (Ce 2 − ) and its neutral analog (Ce 2 ) in the gas phase, achieved using photoelectron and ultrafast spectroscopy combined with high-level quantum chemistry calculations. The electron affinity of Ce 2 is 0.24 eV, from which a dissociation energy of 2.21 eV is derived for Ce 2 − . The wave-packet dynamics upon photodetachment are studied and yield vibrational frequencies for electronically excited Ce 2 . Ce 2 − exhibits a conventional metal−metal triple bond with minimal contribution from 4f electrons. However, evidence of 4f-electron participation in bonding is identified for the low-energy excited states only 0.1 eV higher. The results challenge the assumption of inert 4f electrons in metal−metal bonding, and we propose a promising strategy for forming stable lanthanide−lanthanide bonds involving significant 4f-electron contributions.

Anions↗
DOE OSTI2026

The impact of metastability on the high-pressure behavior of cerium

The structures adopted by solids under pressure are often assumed to reflect thermodynamic equilibrium, yet in many materials phase selection is strongly influenced by kinetic pathways and microstructural inheritance. Elemental cerium (Ce) exemplifies this challenge, with decades of conflicting reports describing different high-pressure crystal structures emerging under nominally identical conditions. Here we use neutron diffraction from large ( ~ 60 mm 3 ) sample volumes to follow the structural evolution in ultra-high-purity Ce during controlled pressure-temperature cycling between 85 and 295 K and up to 8 GPa. We find that the crystal structure formed at high pressure depends on the compression pathway: slow compression ( ~ 0.25 GPa hr −1 ) at room temperature favors an orthorhombic phase (α'), whereas slow ( ~ 0.25 GPa hr −1 ) and also moderately faster ( ~ 0.5 GPa hr −1 ) compression at low temperature stabilizes a pure monoclinic phase (α"). The low-temperature phase persists metastably over a wide temperature range but transforms irreversibly upon heating above ~ 280 K, or modest pressure cycling. Remarkably, the lower-pressure γ phase remains trapped far beyond the expected stability field, persisting to the highest pressures studied. These observations show that phase selection in Ce is governed by kinetics and microstructural memory rather than equilibrium thermodynamics or sample morphology alone, establishing path dependence as a defining feature of its high-pressure behavior.

Ridley, Christopher J. [Oak Ridge National Laborat↗
DOE OSTI2026

Leveraging the redox activities of cerium and dibenzotetrathiafulvalene to discover a photo-responsive magnetic material

Stimuli-responsive changes in lanthanide-based materials are a promising research direction. In this study, [DBTTF] 4 [Ce 2 Cl 10 ] DBTTF = dibenzotetrathiafulvalene (1) was synthesized by a light-induced crystallization, where photo-oxidation of DBTTF enables formation of the cerium dimer [Ce 2 Cl 10 ] 4− . Intermolecular interactions between the stacked organic units of the crystal result in charge transfer bands in the visible-NIR (near-infrared) region, evident in the solid-state absorption spectrum upon comparison with the solution spectrum. The assignments of the sublattice oxidation states were made with single-crystal X-ray diffraction (SC-XRD) structural characterization, Raman spectroscopy, X-ray absorption spectroscopy, and magnetometry. Continuous 532 nm laser irradiation of the microcrystalline solid modulates the redox states in 1, leading to ∼40% reduction in the observed magnetization at 2 K. Density functional theory PBE+U/HSE06 band structure calculations predict Mott insulating behavior in 1, with a bandgap of 0.54/0.81 eV, and further support the conjecture that the observed photo-induced change in magnetization results from electron transfer from the [Ce 2 Cl 10 ] 4− anions to the π-stacked [DBTTF] 2 2+ organic dimer subunits. An enhancement in conductivity is similarly observed upon 532 nm irradiation, determined by single-crystal transport measurements. The findings reveal that photo-responsive lanthanide-based materials can be achieved by integration of redox-active organic moieties with redox-active lanthanide cations for the realization of switchable, photo-magnetic materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Electron–electrophile coupled dinitrogen reduction in a cerium– meta -tetraphenolate system: a computational study

The use of lanthanide complexes for catalytic dinitrogen reduction is a new development in homogeneous catalysis. Density functional theory calculations on our recently reported cerium phenolate catalyst [K 2 Ce 2 (sol) 4 (mTP) 2 ] (mTP = {(OC 6 H 2 - 2- t Bu-4-Me) 2 CH} 2 - 1,3-C 6 H 4 ; sol = OMe 2 here; THF in the experiment) have been undertaken to elucidate the reduction, activation and silylation steps at the bound dinitrogen molecule, in the presence of the reductant, potassium metal (K 0 ) and the electrophile Me 3 SiCl (TMSCl). Out of the total of six electron reductions required to cleave the N 2 , the first two-electron reduction step was found to be highly disfavoured unless potassium cations (K + ) are included, upon which the step is rendered strongly exergonic; N–Si bond formation at the two-electron stage is predicted to be unfavourable. The three-electron-reduced N 2 -adduct is found to be at the reductive activation limit in the absence of added electrophiles, which can form N-element bonds and lower the overall charge. Added electron density beyond three-electron reduction no longer localises on N 2 , preventing formal N 2 4− formation. A pathway in which both K 0 and Me 3 SiCl work in concert was modelled, and six sequential reduction–silylation steps were calculated, showing how the N–N bond is cleaved after the third reduction, eventually releasing two equivalents of N(SiMe 3 ) 3 , and regenerating the starting complex with the highest barrier of any step being 22 kcal mol −1 . We establish alkali metal coordination and coupled electron–electrophile transfer as key factors in the design of rare-earth-mediated dinitrogen functionalisation.

Ahmad, Shahbaz [Univ. of Manchester (United Kingdo↗
DOE OSTI2026

Nanocluster Rearrangement Forms a Family of Ordered Cerium–Titanium Bimetallic Metal–Organic Frameworks with Three Different Nodes, Nanocavities, and Thermal Stabilities

Metal–organic frameworks (MOFs) provide a versatile platform for incorporating multiple metal ions within a single crystalline framework, yet achieving spatial and stoichiometric order in heterometallic nodes remains a synthetic challenge. Building on our previously reported, highly thermally stable Ce/Ti bimetallic MOF NU-3000, we identified and isolated two additional crystalline phases, NU-2998 and NU-2999, that arise from the same Ce/Ti nanocluster precursor under modified solvothermal conditions. Systematic variation of reaction temperature, time, solvent ratio, and modulator concentration directs the assembly of these distinct frameworks. Structural analysis and comprehensive characterization studies reveal that these MOFs each feature an unreported nodal geometry with nanocavities of different sizes. NU-2998 even adopts an unreported topology, denoted nui , that features an elongated pore spanning 4 nm. Together, these findings establish a synthesis route that starts with a nanocluster and ends with a set of bimetallic MOFs, offering a glimpse into the pathway-dependent assembly of multimetallic porous materials. Finally, we evaluated the thermal stability of each additional analogue and compared them to NU-3000, providing further insight into material stability. NU-3000 maintained the highest thermal stability and was evaluated as a catalyst for CO oxidation at elevated temperatures.

bimetallic MOFs↗