Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “CEOS”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Surface Density Dependent Catalytic Activity of Single Palladium Atoms Supported on Ceria

The analogy between single-atom catalysts (SACs) and molecular catalysts predicts that the specific catalytic activity of these systems is constant. Here we provide evidence that this prediction is not necessarily true. As a case in point, we show that the specific activity over ceria-supported single Pd atoms linearly increases with metal atom density, originating from the cumulative enhancement of CeO 2 reducibility. The long-range electrostatic footprints (≈1.5 nm) around each Pd site overlap with each other as surface Pd density increases, resulting in an observed deviation from constant specific activity. These cooperative effects exhaust previously active O atoms above a certain Pd density, leading to their permanent removal and a consequent drop in reaction rate. The findings of our combined experimental and computational study show that the specific catalytic activity of reducible oxide-supported single-atom catalysts can be tuned by varying the surface density of single metal atoms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Tailoring the Local Environment of Platinum in Single-Atom Pt 1 /CeO 2 Catalysts for Robust Low-Temperature CO Oxidation

A single-atom Pt 1 /CeO 2 catalyst formed by atom trapping (AT, 800 degrees C in air) shows excellent thermal stability but is inactive for CO oxidation at low temperatures owing to over-stabilization of Pt 2+ in a highly symmetric square-planar Pt 1 O 4 coordination environment. Reductive activation to form Pt nanoparticles (NPs) results in enhanced activity; however, the NPs are easily oxidized, leading to drastic activity loss. In this work, we show that tailoring the local environment of isolated Pt 2+ by thermal-shock (TS) synthesis leads to a highly active and thermally stable Pt 1 /CeO 2 catalyst. Ultrafast shockwaves (>1200 degrees C) in an inert atmosphere induced surface reconstruction of CeO 2 to generate Pt single atoms in an asymmetric Pt 1 O 4 configuration. Owing to this unique coordination, Pt 1 δ+ in a partially reduced state dynamically evolves during CO oxidation, resulting in exceptional low-temperature performance. CO oxidation reactivity on the Pt 1 /CeO 2 _TS catalyst was retained under oxidizing conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Synergy of Oxygen Vacancies and Base Sites for Transfer Hydrogenation of Nitroarenes on Ceria Nanorods

CeO 2 nanorod based catalysts for the base-free synthesis of azoxy-aromatics via transfer hydrogenation of nitroarenes with ethanol as hydrogen donor have been synthesized and investigated. The oxygen vacancies (O v ) and base sites are critical for their excellent catalytic properties. The O v , i.e., undercoordinated Ce cations, serve as the sites to activate ethanol and nitroarenes by lowering the energy barrier to transfer hydrogen from α–C sp3 –H in ethanol to the nitro group coupling it to the redox reactions between Ce 3+ and Ce 4+ . At the same time, the base sites catalyze the condensation step to selectively produce azoxy-aromatics. Finally, the catalytic route opens a much improved way to use non-noble metal oxides without additives for the selective functional group reduction and coupling reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Alkene Hydrosilylation on Oxide-Supported Pt-Ligand Single–Site Catalysts

Heterogeneous single-site catalysts (SSCs), widely regarded as promising next-generation catalysts, blend the easy recovery of traditional heterogeneous catalysts with desired features of homogeneous catalysts: high fraction of active sites and uniform metal centers. We previously reported the synthesis of Pt-ligand SSCs through a novel metal-ligand self-assembly method on MgO, CeO 2 , and Al 2 O 3 . Here, we present their applications in the industrially-relevant alkene hydrosilylation reaction, with 95 % yield achieved under mild conditions. As expected, they exhibit better metal utilization efficiency than traditional heterogeneous Pt catalysts. The comparison with commercial catalysts (Karstedt and Speier) reveals several advantages of these SSCs: higher selectivity, less colloidal Pt formation, less alkene isomerization/hydrogenation, and better tolerance towards functional groups in substrates. Despite some leaching, our catalysts exhibit satisfactory recyclability and the single-site structure remains intact on oxide supports after reaction. Pt single-sites were proved to be the main active sites rather than colloidal Pt formed during the reaction. An induction period is observed in which Pt sites are activated by Cl detachment and replacement by reactant alkenes. The most active species likely involves temporary detachment of Pt from ligand or support. Catalytic performance of Pt SSCs is sensitive to the ligand and support choices, enabling fine tuning of Pt sites. This work highlights the application of heterogeneous SSCs created by the novel metal-ligand self-assembly strategy in an industrially-relevant reaction. It also offers a potential catalyst for future industrial hydrosilylation applications with several improvements over current commercial catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Highly Active and Stable Single Atom Rh 1 /CeO 2 Catalyst for CO Oxidation during Redox Cycling

We report a single atom Rh 1 /CeO 2 catalyst prepared by the high temperature (800 °C) atom trapping (AT) method which is stable under both oxidative and reductive conditions. Infrared spectroscopic and electron microscopy characterization revealed the presence of exclusively ionic Rh species. These ionic Rh species are stable even under reducing conditions (CO at 300 °C) due to the strong interaction between Rh and CeO 2 achieved by the AT method, leading to high and reproducible CO oxidation activity regardless of whether the catalyst is reduced or oxidized. In contrast, ionic Rh species in catalysts synthesized by a conventional impregnation approach (e. g., calcined at 350 °C) can be readily reduced to form Rh nanoclusters/nanoparticles, which are easily oxidized under oxidative conditions, leading to loss of catalytic performance. The single atom Rh 1 /CeO 2 catalysts synthesized by the AT method do not exhibit changes during redox cycling hence are promising catalysts for emission control where redox cycling is encountered, and severe oxidation (fuel cut) leads to loss of performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

NO Reduction with CO on Low‐loaded Platinum‐group Metals (Rh, Ru, Pd, Pt, and Ir) Atomically Dispersed on Ceria

Abstract Low‐loaded platinum‐group single‐atom catalysts on CeO 2 (M 1 /CeO 2 ) were synthesized via high‐temperature atom trapping (AT) and tested for the NO+CO reaction under dry and wet conditions. The activity of these catalysts for NO+CO reaction follows the order Rh>Pd≈Ru>Pt>Ir. For Rh, Ru, and Pd single‐atom catalysts, the N 2 O byproduct is formed but not clearly observed in Ir and Pt cases, which may result from the higher reaction temperature (>200 °C) required for Pt and Ir catalysts. The presence of water can promote the activity of these M 1 /CeO 2 catalysts for the NO+CO reaction. Under wet conditions, significant NH 3 formation occurred during the reaction, which is due to the co‐existence of water‐gas‐shift reaction on these catalysts. Compared with Pt, Pd and Ir, the Rh and Ru single‐atom catalysts show higher selectivity to NH 3 species, resulting from the hydride species on the surface. Among all tested catalysts, Ru 1 /CeO 2 shows the highest production of ammonia and highest CO conversion due to excellent water‐gas‐shift activity, whereas Pd 1 /CeO 2 shows lowest ammonia production. Rh 1 /CeO 2 shows the best low temperature NO reduction activity among all tested catalysts.

Tian, Jinshu↗
DOE OSTI2019

Understanding the Photocatalytic Properties of Pt/CeO x /TiO 2 : Structural Effects on Electronic and Optical Properties

Ceria-titania interfaces play a crucial role in different chemical processes but are especially promising for the photocatalytic splitting of water using light in the visible wavelength region when Pt is added to the system. Yet, the complexity of this hierarchical structure hampers the study of the origin of its outstanding properties. In this article, the structural, electronic and optoelectronic properties of CeO 2 /TiO 2 systems containing 1D, 2D, and 3D particles of ceria are analyzed by means of density functional calculations. Adsorption sites and vacancy effects have been studied to model Pt adsorption. Density of states calculations and absorption spectra simulations explain the behavior of these systems. Conclusively, these models are used for the screening of other metals that can be combined with this heterostructure to possibly find more efficient water splitting photocatalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Tailored (La 0.2 Pr 0.2 Nd 0.2 Tb 0.2 Dy 0.2 ) 2 Ce 2 O 7 as a Highly Active and Stable Nanocatalyst for the Oxygen Evolution Reaction

Abstract Designing highly active and robust catalysts for the oxygen evolution reaction is key to improving the overall efficiency of the water splitting reaction. It has been previously demonstrated that evaporation induced self‐assembly (EISA) can be used to synthesize highly porous and high surface area cerate‐based fluorite nanocatalysts, and that substitution of Ce with 50% rare earth (RE) cations significantly improves electrocatalyst activity. Herein, the defect structure of the best performing nanocatalyst in the series are further explored, Nd 2 Ce 2 O 7 , with a combination of neutron diffraction and neutron pair distribution function analysis. It is found that Nd 3 + cation substitution for Ce in the CeO 2 fluorite lattice introduces higher levels of oxygen Frenkel defects and induces a partially reduced RE 1.5 Ce 1.5 O 5 +x phase with oxygen vacancy ordering. Significantly, it is demonstrated that the concentration of oxygen Frenkel defects and improved electrocatalytic activity can be further enhanced by increasing the compositional complexity (number of RE cations involved) in the substitution. The resulting novel compositionally‐complex fluorite– (La 0.2 Pr 0.2 Nd 0.2 Tb 0.2 Dy 0.2 ) 2 Ce 2 O 7 is shown to display a low OER overpotential of 210 mV at a current density of 10 mAcm −2 in 1M KOH, and excellent cycling stability. It is suggested that increasing the compositional complexity of fluorite nanocatalysts expands the ability to tailor catalyst design.

Chemistry↗
DOE OSTI2016

Aerobic oxidation of cyclic amines to lactams catalyzed by ceria-supported nanogold

Here, the oxidative transformation of cyclic amines to lactams, which are important chemical feedstocks, is efficiently catalyzed by CeO 2 -supported gold nanoparticles (Au/CeO 2 ) and Aerosil 200 in the presence of an atmosphere of O 2 . The complete conversion of pyrrolidine was achieved in 6.5 h at 160 °C, affording a 97 % yield of the lactam product 2-pyrrolidone (γ-butyrolactam), while 2-piperidone (δ-valerolactam) was synthesized from piperidine (83 % yield) in 2.5 h. Caprolactam, the precursor to the commercially important nylon-6, was obtained from hexamethyleneimine in 37 % yield in 3 h. During the oxidation of pyrrolidine, two transient species, 5-(pyrrolidin-1-yl)-3,4-dihydro-2H-pyrrole (amidine-5) and 4-amino-1-(pyrrolidin-1-yl)butan-1-one, were observed. Both of these compounds were oxidized to 2-pyrrolidone under catalytic conditions, indicating their role as intermediates in the reaction pathway. In addition to the reactions of cyclic secondary amines, Au/CeO 2 also efficiently catalyzes the oxidation of N-methyl cyclic tertiary amines to the corresponding lactams at 80 and 100 °C.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Optimization of BaHfO{sub 3} Doping Concentration as Secondary Phase in Y{sub 0.5}Gd{sub 0.5}Ba{sub 2}Cu{sub 3}O{sub 7−x} Thin Film Prepared by Pulsed Laser Deposition

BaHfO{sub 3} (BHO)-doped Y{sub 0.5}Gd{sub 0.5}Ba{sub 2}Cu{sub 3}O{sub 7−x} (YGBCO) films with a series of doping concentrations (1, 3, 5, and 10 mol%) were fabricated on CeO{sub 2} buffer layers by pulsed laser deposition (PLD) technique, and a pristine YGBCO film was also deposited at the same conditions for comparison. X-ray diffraction (XRD) results showed that the undoped and doped YGBCO films had a pure c-axis orientation. While the surface morphology and crystal quality of the BHO-doped YGBCO films deteriorated as the BHO content increased, and the critical current density (J{sub c}) at 77 K and self-field (J{sub c}{sup 77,0}) and critical transition temperature (T{sub c}) of the BHO-doped YGBCO films exhibited varying degrees of decline in comparison with the pristine YGBCO film. However, the 5 mol% BHO-doped YGBCO film exhibited greatly enhanced the J{sub c} and the highest pinning force densities (F{sub p}) at both 4.2 and 65 K, which showed the maximum value of 5776 GN/m{sup 3} (4.2 K, H//c) and 117 GN/m{sup 3} (65 K, H//c), about 1.5 times that of the undoped YGBCO film. Based on the results, the 5 mol% BHO-doped YGBCO film had the most effective flux pinning centers, which are responsible for strongly improved critical current densities in magnetic fields.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

The Influence of Substrate Temperature of Seed Layer on the Structure and Superconducting Property of BaHfO{sub 3}-Doped Y{sub 0.5}Gd{sub 0.5}Ba{sub 2}Cu{sub 3}O{sub 7−δ} Film Prepared by Pulsed Laser Deposition

For various practical applications, excellent superconducting properties under magnetic field of REBa{sub 2}Cu{sub 3}O{sub 7−δ} (RE = rare earth elements (REBCO))-coated conductors are required, which can be fabricated by introducing artificial pinning centers, such as second-phase dopant. It is well known that BaMO{sub 3} (M = Zr, Sn, or Hf) can form self-organized nanorods in REBCO matrix and improve the critical current density (J{sub c}) under applied magnetic field. However, with increasing dopant level, the critical temperature T{sub c} and J{sub c} at 77 K in self-field decreased. In order to inhibit the degradation of the J{sub c} in self-field, we fabricated 5 mol% BaHfO{sub 3} (BHO)-doped Y{sub 0.5}Gd{sub 0.5}Ba{sub 2}Cu{sub 3}O{sub 7−δ} (YGBCO) seed layers on CeO{sub 2}-buffered IBAD-MgO tapes by pulse laser deposition (PLD) at a laser repetition of 10 Hz and different substrate temperature T{sub seed}, and subsequently deposited 5-mol% BHO-doped YGBCO upper layers at 160 Hz and higher substrate temperature. The effect of T{sub seed} on the quality of the 5-mol% BHO-doped YGBCO upper layer was investigated. With increasing T{sub seed} from 710 to 820 {sup ∘}C, the Δφ value of YGBCO (103) reflection first decreased and then increased, while the J{sub c} at 77 K increased with increasing T{sub seed} to 790 {sup ∘}C and decreased at higher T{sub seed}. The 5-mol% BHO-doped YGBCO layer with a seed layer deposited at 790 {sup ∘}C had the highest J{sub c} (77 K, self-field) of 4.0 MA/cm{sup 2}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Polymer-assisted deposition of nanoparticle feedstocks for target fabrication

Traditional polymer-assisted deposition has been shown to produce highly uniform thin films of metal oxides, including actinide oxides. Furthermore, while producing thicker films for nuclear targets is possible through repeated coating application, we exchanged the dissolved metal species with nanoparticles to maximize the thickness that can be achieved with an individual layer. Using CeO 2 nanoparticles in a polyethyleneimine matrix, we produced targets with single-layer areal densities of 0.22 ± 0.01 mg·cm −2 (1σ) and thicknesses of 690 ± 80 nm (1σ). A custom 3D-printed spin coating chuck attachment with an inlay improved target homogeneity and will streamline future work with radioactive materials.

and nuclear chemistry↗
DOE OSTI2018

Friction and Wear of Nanoadditive-Based Biolubricants in Steel–Steel Sliding Contacts: A Comparative Study

The present work deals with the study of tribo-pair interaction in lubricated sliding contacts. By considering the environmental issues, the sunflower oil was extracted from the sunflower seeds and used as a base lubricant. The two types of the nanoadditives, i.e., CuO and CeO{sub 2}, varying concentrations from 0.10 to 0.50% w/v were used to formulate the nanolubricants. The compatibility/synergism of the nanoadditives was examined from antifriction and antiwear behavior study with four-ball tester. Also, sunflower oil was modified by the chemical method to improve its fatty acid structure. A comparative tribological and compatibility study was also done in modified oil at similar concentration levels with both types of nanoparticles. The tribological test result exhibits 0.10% w/v concentration of the nanoadditive as optimum due to lowest wear scar and coefficient of friction. Higher concentration of the nanoparticles impaired the base oil performance. Different analytical tools were used to characterize the oil modification and worn surfaces. Moreover, the role of subsurface of the contacting material with the tribological performance has been reported.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Direct Microbial Conversion of Biomass to Advanced Biofuels

'Direct Microbial Conversion of Biomass to Advanced Biofuels' is a stylized text that is rich in both the basic and applied sciences. It provides a higher level summary of the most important aspects of the topic, addressing critical problems solved by deep science. Expert users will find new, critical methods that can be applied to their work, detailed experimental plans, important outcomes given for illustrative problems, and conclusions drawn for specific studies that address broad based issues. A broad range of readers will find this to be a comprehensive, informational text on the subject matter, including experimentalists and even CEOs deciding on new business directions.

09 BIOMASS FUELS↗
DOE OSTI2017

Hydrogen enhances the radiation resistance of amorphous silicon oxycarbides

Here, we use first principles molecular dynamics to investigate unit displacement processes in amorphoussilicon oxycarbides (SiOC) and demonstrate that the introduction of hydrogen (H) into these materialsenhances their radiation resistance. Our simulations show that 100 eV knock-ons in H-free SiOC redistribute C through the formation of CeO and CeC bonds. H counteracts this trend by passivating dangling O bonds and preventing C from coming out of solution. This effect arises from the exceptionally high mobility of H, which leads to the saturation of radiation-induced O and C radicals even before the thermal-spike induced by a high-energy knock-on dies down. Our work suggests that fully hydrogenated SiOC is a promising radiation-resistant material for future nuclear energy applications.

08 HYDROGEN↗
DOE OSTI2022

Enhanced mobility of cations and anions in the redox state: The polaronium mechanism

Hugely enhanced slow-ion diffusivity has been widely observed under extreme redox conditions and for unclear reasons. Aided by first-principles calculations on model systems of ZrO 2 , CeO 2 , BaTiO 3 and Li 4/3 Mn 2/3 O 2 , here we successfully explained the intriguing phenomenon by a polaronium mechanism. We found a polaronium, defined as a transitory complex of a polaronic electron or hole and a migrating counterion, becomes highly mobile when the counterion comes from a d 0 or f 0 cation (e.g., Zr 4+ , Ti 4+ and Ce 4 ) or a p 6 anion (e.g., O 2- ) in the host compound. Upon a redox reaction, the complex attains a d 1 /f 1 or p 5 configuration, which spontaneously forms because it is favored by an electron-phonon interaction (manifest as the Jahn-Teller effect in high symmetry systems) that enables local relaxation and lowers the system energy. Here our calculations found such interaction reaching its peak at the saddle point where the local environment is softest, so soft that it allows a reorientation of the anisotropic d/f/p orbital to minimize the electron repulsion locally. Since the complex may dissolve after a successful ion-migration event, the redox electron/hole can be recycled to form another free-radical-like polaronium elsewhere, thereby enhancing ion migration repeatedly. The proposed polaronium mechanism, which also operates in ceramics doped with mixed-valence cations, is most relevant under dynamic and extreme thermal/field/irradiation conditions where extra electrons/holes are abundantly generated by non-equilibrium redox reactions. For such operations, some with emerging applications, our diffusion-enhancing mechanism may provide new theoretical insight to help understand their material/microstructure stability and performance.

36 MATERIALS SCIENCE↗