SEARCH · Engineering Papers
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.
The CEOS Systems Engineering Office will present a 2007 status report of the CEOS constellation process, present a new systems engineering framework, and analysis results from the GEO Societal Benefit Area (SBA) assessment and the OST constellation requirements assessment.
Abstract not provided
Abstract not provided
Not provided.
We report non-degradable polyolefin plastics pose severe environmental threats, and thus demand efficient upcycling technologies. In this work, we discovered that low-loading (= 0.25 wt%) Ru/CeO 2 exhibits remarkable catalytic performance in the hydrogenolysis of polypropylene (PP), polyethylene (PE), and n-C 16 H 34 that is superior to high-loading (= 0.5 wt%) Ru/CeO 2 . They possess high PP conversion efficiency (7-fold increase over current literature reports), low selectivity towards undesired CH 4 , and good isomerization ability. In the low-loading range, the intrinsic activity of Ru in PP hydrogenolysis increases as the particle size decreases, opposite of the trend in the high-loading range. Detailed characterization revealed that the abrupt changes in catalytic behaviors coincide with Ru species transitioning from well-defined to highly disordered structures in the low-loading domain. The disordered Ru species were shown to be sub-nanometer in size and cationic. Mechanistically, the regioselectivity and the rate dependence on hydrogen pressure of C-C bond cleavage are different on low- and high-loading Ru/CeO 2 , both explained by the higher coverage of adsorbed hydrogen (*H) on low-loading Ru/CeO 2 . This work uncovers the remarkable catalytic performance of highly disordered, sub-nanometer, cationic Ru species in polyolefin hydrogenolysis, opening immense opportunities to develop effective, selective, and versatile catalysts for plastic upcycling.
Abstract not provided
Not provided.
The extended DLVO (XDLVO) theory was applied to elucidate the potential effects of CeO{sub 2} nanoparticles (CeO{sub 2} NPs) on sludge aggregation and the role of extracellular polymeric substances (EPS). In this study, seven different concentrations of CeO{sub 2} NPs were added to activated sludge cultured in sequencing batch reactors (SBRs) and compared with a control test that received no CeO{sub 2} NPs. After exposure to 50 mg/L CeO{sub 2} NPs, a negligible change (p>0.1) occurred in the sludge volume index (SVI), whereas the flocculability and aggregation of the sludge decreased by 18.8% and 11.2%, respectively, resulting in a high effluent turbidity. The XDLVO theory demonstrated that the adverse effects of the CeO{sub 2} NPs on sludge aggregation were due to an enhanced barrier energy. Compared to the van der Waals energies (W{sub A}) and the electric double layer (W{sub R}), the acid-base interaction (W{sub AB}) markedly changed for the various concentrations of CeO{sub 2} NPs. The EPS played a decisive role in the sludge surface characteristics, as the removal of EPS equals to the negative effects induced by 5–10 mg/L CeO{sub 2} NPs on the sludge flocculability and aggregation. The presence of CeO{sub 2} NPs induced negative contributions to the tight boundary EPS (TB-EPS) and core bacteria while positive contributions to the total interaction energy of the loose boundary EPS (LB-EPS). - Highlights: • CeO{sub 2} NPs adversely affected the flocculability and aggregation of the sludge. • The presence of CeO{sub 2} NPs increased the energy barrier and led to a stable suspension. • The removal of EPS equals to the negative effects induced by 5–10 mg/L CeO{sub 2} NPs. • The acid-base interaction was dominate and markedly changed for the CeO{sub 2} NPs. • CeO{sub 2} NPs induced negative contributions to the TB-EPS while positive to the LB-EPS.
The stability of engineered nanoparticles (ENPs) in complex aqueous matrices is a key determinant of their fate and potential toxicity towards the aquatic environment and human health. Metal oxide nanoparticles, such as CeO{sub 2} ENPs, are increasingly being incorporated into a wide range of industrial and commercial applications, which will undoubtedly result in their (unintentional) release into the environment. Hereby, the behaviour and fate of CeO{sub 2} ENPs could potentially serve as model for other nanoparticles that possess similar characteristics. The present study examined the stability and settling of CeO{sub 2} ENPs (7.3±1.4 nm) as well as Ce{sup 3+} ions in 10 distinct natural surface waters during 7 d, under stagnant and isothermal experimental conditions. Natural water samples were collected throughout Flanders (Belgium) and were thoroughly characterized. For the majority of the surface waters, a substantial depletion (>95%) of the initially added CeO{sub 2} ENPs was observed just below the liquid surface of the water samples after 7 d. In all cases, the reduction was considerably higher for CeO{sub 2} ENPs than for Ce{sup 3+} ions (<68%). A first-order kinetics model was able to describe the observed time-dependant removal of both CeO{sub 2} ENPs (R{sup 2}≥0.998) and Ce{sup 3+} ions (R{sup 2}≥0.812) from the water column, at least in case notable sedimentation occurred over time. Solution-pH appeared to be a prime parameter governing nanoparticle colloidal stability. Moreover, the suspended solids (TSS) content also seemed to be an important factor affecting the settling rate and residual fraction of CeO{sub 2} ENPs as well as Ce{sup 3+} ions in natural surface waters. Correlation results also suggest potential association and co-precipitation of CeO{sub 2} ENPs with aluminium- and iron-containing natural colloidal material. The CeO{sub 2} ENPs remained stable in dispersion in surface water characterized by a low pH, ionic strength (IS), and TSS content, indicating the eventual stability and settling behaviour of the nanoparticles was likely determined by a combination of physicochemical parameters. Finally, ionic release from the nanoparticle surface was also examined and appeared to be negligible in all of the tested natural waters. - Highlights: • Solution-pH appeared to be a key factor determining CeO{sub 2} ENPs colloidal stability. • A 1st-order kinetics model could describe the time-dependant settling of CeO{sub 2} ENPs. • Suspended solids content affected the settling rate and residual cerium fraction. • CeO{sub 2} ENPs remained stable in dispersion in water with low pH, IS, and TSS content. • Ionic release from the CeO{sub 2} ENPs appeared negligible in all surface waters.
CO 2 -assisted oxidative dehydrogenation of ethane is a sustainable alternative to steam cracking for ethylene production. In this study, a series of CeO 2 on SiO 2 supported NiFe 3 catalysts were synthesized by incipient wetness impregnation and tested for oxidative dehydrogenation performance. The CeO 2 /SiO 2 supported catalysts with high weight loading of CeO 2 (50%–75%) provided higher activity than the lower CeO 2 (0%–25%) loaded catalysts (with ethylene production rates of 0.62–0.98 µmol/g cat /s and 0.19–0.3 µmol/g cat /s, respectively) while maintaining high ethylene selectivity (43%–45%). In contrast, the NiFe 3 supported on only CeO 2 also exhibited high activity (ethylene production rate of 0.71 µmol/g cat /s), but the ethylene selectivity (16%) was greatly decreased compared to the mixed system. Temperature programmed reduction, X-ray diffraction, and Raman spectroscopy all indicate the creation of a solid solution of the Fe and Ni doped into the CeO 2 crystal structure in the catalysts with high CeO 2 loading/bulk CeO 2 support. Here, the high ethylene selectivity in the high CeO 2 loading catalysts indicates that the Fe is preferentially creating the solid solution, with the decrease in selectivity observed in the CeO 2 -only supported catalyst likely resulting from CeO 2 interacting directly with Ni, creating Ni-CeO X interfaces that are known active sites for the unwanted side reaction of dry reforming.
Catalytic oxidation of CH 4 over nonprecious Ni/CeO 2 catalysts has attracted wide attention. Controlling the morphology of a CeO 2 support can enhance the CH 4 oxidation activity without changing the catalyst composition. Here, in this paper, a series of 2 wt % Ni/CeO 2 nanocatalysts with different CeO 2 support morphologies (nanoparticles (P), rods (R), cubes (C)) and synthetic procedures (precipitation, sol-gel (SG)) were evaluated for their CH 4 oxidation performance. The redox properties of CeO 2 supports and corresponding Ni loaded catalysts were characterized by H 2 -temperature-programmed reduction and oxygen storage capacity (OSC) measurements. The relationship among the CeO 2 morphologies, surface areas, redox properties, and CH4 oxidation activity for both CeO 2 supports and Ni/CeO 2 catalysts was established. The findings suggest that CeO 2 -R has a greater amount of surface oxygen vacancies as well as an improved OSC and CH4 oxidation activity compared to CeO 2 -P and CeO 2 -C supports. The same CH 4 oxidation activity pattern was observed for the Ni containing catalysts (Ni/CeO 2 -R > Ni/CeO 2 -P > Ni/CeO 2 -C). Increasing the CeO 2 surface area by using a sol-gel synthesis method (CeO 2 -SG) improved the amount of surface oxygen vacancies and CH 4 oxidation performance of CeO 2 -SG and Ni/CeO 2 -SG compared to CeO 2 -R and Ni/CeO 2 -R, respectively. Finally, all studied Ni/CeO 2 nanocatalysts showed improved hydrothermal stability compared to conventional Pd/Al 2 O 3 .
Graphical abstract: - Highlights: • Monocrystal CeO{sub 2} nanopoles are synthesized by hydrothermal method. • Suitable reaction time is beneficial for the growth CeO{sub 2} nanopoles. • As-synthesized CeO{sub 2} nanopoles show excellent RTFM. • The RTFM can be attributed to the influences of oxygen vacancies and Ce{sup 3+} ions. - Abstract: Monocrystal CeO{sub 2} nanopoles of 15–25 nm in diameter and 300–900 nm or more in length were synthesized within 100 h using hydrothermal method with CeCl{sub 3}·7H{sub 2}O as cerium source, NaOH as mineralizer, and ethylenediamine as complexant. The results of XRD and SADE analysis indicate that the as-synthesized CeO{sub 2} samples have the fluorite structure. The band gaps of CeO{sub 2} samples are 0.08–0.38 eV smaller than that of bulk CeO{sub 2}. X-ray photoelectron spectroscopy shows that the concentration of Ce{sup 3+} is higher than 20% for CeO{sub 2} samples. All the as-synthesized CeO{sub 2} samples exhibit the room temperature ferromagnetism (RTFM), and the saturation magnetization (M{sub s}) gradually increases with the increase of E{sub g} up to 2.92 eV and then decreases with E{sub g} increasing more. The highest M{sub s} of 0.167 emu/g is obtained from the CeO{sub 2} nanopoles synthesized within 100 h. The RTFM mechanism of CeO{sub 2} nanopoles has been proposed which can be mainly attributed to the influence of oxygen vacancies and Ce{sup 3+} ions.
Late in fiscal year 2011, the Crew Earth Observations (CEO) team was tasked to upgrade its science site database management tool, which at the time was integrated with the Automated Mission Planning System (AMPS) originally developed for Earth Observations mission planning in the 1980s. Although AMPS had been adapted and was reliably used by CEO for International Space Station (ISS) payload operations support, the database structure was dated, and the compiler required for modifications would not be supported in the Windows 7 64-bit operating system scheduled for implementation the following year. The Sites Mission Management System (SMMS) is now the tool used by CEO to manage a heritage Structured Query Language (SQL) database of more than 2,000 records for Earth science sites. SMMS is a carefully designed and crafted in-house software package with complete and detailed help files available for the user and meticulous internal documentation for future modifications. It was delivered in February 2012 for test and evaluation. Following acceptance, it was implemented for CEO mission operations support in April 2012. The database spans the period from the earliest systematic requests for astronaut photography during the shuttle era to current ISS mission support of the CEO science payload. Besides logging basic image information (site names, locations, broad application categories, and mission requests), the upgraded database management tool now tracks dates of creation, modification, and activation; imagery acquired in response to requests; the status and location of ancillary site information; and affiliations with studies, their sponsors, and collaborators. SMMS was designed to facilitate overall mission planning in terms of site selection and activation and provide the necessary site parameters for the Satellite Tool Kit (STK) Integrated Message Production List Editor (SIMPLE), which is used by CEO operations to perform daily ISS mission planning. The CEO team uses the SMMS for three general functions - database queries of content and status, individual site creation and updates, and mission planning. The CEO administrator of the science site database is able to create or modify the content of sites and activate or deactivate them based on the requirements of the sponsors. The administrator supports and implements ISS mission planning by assembling, reporting, and activating mission-specific site selections for management; deactivating sites as requirements are met; and creating new sites, such as International Charter sites for disasters, as circumstances warrant. In addition to the above CEO internal uses, when site planning for a specific ISS mission is complete and approved, the SMMS can produce and export those essential site database elements for the mission into XML format for use by onboard Earth-location systems, such as Worldmap. The design, development, and implementation of the SMMS resulted in a superior database management system for CEO science sites by focusing on the functions and applications of the database alone instead of integrating the database with the multipurpose configuration of the AMPS. Unlike the AMPS, it can function and be modified within the existing Windows 7 environment. The functions and applications of the SMMS were expanded to accommodate more database elements, report products, and a streamlined interface for data entry and review. A particularly elegant enhancement in data entry was the integration of the Google Earth application for the visual display and definition of site coordinates for site areas defined by multiple coordinates. Transfer between the SMMS and Google Earth is accomplished with a Keyhole Markup Language (KML) expression of geographic data (see figures 3 and 4). Site coordinates may be entered into the SMMS panel directly for display in Google Earth, or the coordinates may be defined on the Google Earth display as a mouse-controlled polygonal definition and transferred back into the SMMS as KML input. This significantly reduces the possibility of errors in coordinate entries and provides visualization of the scale of the site being defined. CEO now has a powerful tool for managing and defining sites on the Earth's surface for both targets of astronaut photography or other onboard remote sensing systems. It can also record and track results by sponsor, collaborator, or type of study.
Acid gases including CO 2 , SO 2 , and NO x are ubiquitous in large-scale energy applications including heterogeneous catalysis. The adverse environmental and health effects of these acid gases have resulted in high interest in the research and development of technologies to remove or convert these acid gases. The main challenge for the development of these technologies is to develop catalysts that are highly efficient, stable, and cost-effective, and many catalysts have been reported in this regard. CeO 2 and CeO 2 -based catalysts have gained prominence in the removal and conversion of CO 2 , SO 2 , and NO x because of their structural robustness and redox and acid–base properties. In this article, we provide a brief overview of the application of CeO 2 and CeO 2 -based catalysts for the removal of CO 2 , SO 2 , and NO x gases with an emphasis on the fundamental understanding of the interactions of these acid gases with CeO 2 . The studies summarized in this review range from surface science using single crystals and thin films with precise crystallographic planes to practical catalysis applications of nanocrystalline and polycrystalline CeO 2 materials with defects and dopants. After an introduction to the properties of CeO 2 surfaces, their catalytic properties for conversions of different acid gases are reviewed and discussed. Lastly, we find that the surface atomic structure, oxygen vacancies, and surface acid–base properties of CeO 2 play vital roles in the surface chemistry and structure evolution during the interactions of acid gases with CeO 2 and CeO 2 -based catalysts.
While highly reactive cerium oxide nanoparticles (CeO 2 NPs) are widely used in industry, their transport in aquatic systems is not well understood. To fill this knowledge gap, the interactions of CeO 2 NPs with arsenite (As 3+ ), a toxic metalloid and potential co-present contaminant, were investigated with respect to CeO 2 NP colloidal stability, dissolution, and surface redox reactions. Arsenite showed distinctive effects at different concentrations, with a high As 3+ concentration (10 –4 M) inducing 90% of CeO 2 NPs to settle from solution after 8 hours, while lower As 3+ concentrations (10 –5 or 10 –6 M) led to only 20% of CeO 2 NPs settling. The dissolution of NPs was most significant in the 10 –5 M As 3+ system owing to a lesser extent of aggregation, exposing more CeO 2 surface for dissolution. In the three As 3+ concentration systems, >97% of aqueous arsenic remained as As 3+ over 6 hours. On the NP surface, adsorbed As III was oxidized to As V , resulting in 58–70% of the adsorbed arsenic remaining as As III . Simultaneously Ce IV was reduced to Ce III , increasing Ce III on the CeO 2 NP surface from 17% (without arsenite) to 21–25% (with arsenite). Further mechanistic analyses revealed that the adsorption of arsenite was the main contributor to neutralizing the CeO 2 NP surface potential, enhancing particle sedimentation. These findings suggest that the fate and transport of CeO 2 NPs in our experimental systems are strongly affected by arsenite concentration and its adsorption on NPs. Here, the results also highlight the importance of the interplay between NP aggregation, oxidation, and dissolution in predicting the behaviors of CeO 2 NPs and associated toxic elements in aquatic systems.
This work presents a detailed study on the chemical composition and bond structures of CeO{sub 2}/La{sub 2}O{sub 3} stacked gate dielectrics based on x-ray photoelectron spectroscopy (XPS) measurements at different depths. The chemical bonding structures in the interfacial layers were revealed by Gaussian decompositions of Ce 3d, La 3d, Si 2s, and O 1s photoemission spectra at different depths. We found that La atoms can diffuse into the CeO{sub 2} layer and a cerium-lanthanum complex oxide was formed in between the CeO{sub 2} and La{sub 2}O{sub 3} films. Ce{sup 3+} and Ce{sup 4+} states always coexist in the as-deposited CeO{sub 2} film. Quantitative analyses were also conducted. The amount of CeO{sub 2} phase decreases by about 8% as approaching the CeO{sub 2}/La{sub 2}O{sub 3} interface. In addition, as compared with the single layer La{sub 2}O{sub 3} sample, the CeO{sub 2}/La{sub 2}O{sub 3} stack exhibits a larger extent of silicon oxidation at the La{sub 2}O{sub 3}/Si interface. For the CeO{sub 2}/La{sub 2}O{sub 3} gate stack, the out-diffused lanthanum atoms can promote the reduction of CeO{sub 2} which produce more atomic oxygen. This result confirms the significant improvement of electrical properties of CeO{sub 2}/La{sub 2}O{sub 3} gated devices as the excess oxygen would help to reduce the oxygen vacancies in the film and would suppress the formation of interfacial La-silicide also.