Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Synthesis”

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 1,387 records · Page 77
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Influence of catalyst synthesis method on selective catalytic reduction (SCR) of NO by NH 3 with V 2 O 5 -WO 3 /TiO 2 catalysts

We compared the molecular structures, surface acidity and catalytic activity for NO/NH 3 /O 2 SCR of V 2 O 5 -WO 3 /TiO 2 catalysts for two different synthesis methods: co-precipitation of aqueous vanadium and tungsten oxide precursors with TiO(OH) 2 and by incipient wetness impregnation of the aqueous precursors on a reference crystalline TiO 2 support (P25; primarily anatase phase). Bulk analysis by XRD showed that co-precipitation results in small and/or poorly ordered TiO 2 (anatase) particles and that VO x and WO x do not form solid solutions with the bulk titania lattice. Surface analysis of the co-precipitated catalyst by High Sensitivity-Low Energy Ion Scattering (HS-LEIS) confirms that the VO x and WO x are surface segregated for the co-precipitated catalysts. In situ Raman and IR spectroscopy revealed that the vanadium and tungsten oxide components are present as surface mono-oxo O = VO 3 and O = WO 4 sites on the TiO 2 supports. Co-precipitation was shown for the first time to also form new mono-oxo surface VO 4 and WO 4 sites that appear to be anchored at surface defects of the TiO 2 support. IR analysis of chemisorbed ammonia showed the presence of both surface NH 3 * on Lewis acid sites and surface NH 4 +* on Brønsted acid sites. TPSR spectroscopy demonstrated that the specific SCR kinetics was controlled by the redox surface VO 4 species and that the surface kinetics was independent of TiO 2 synthesis method or presence of surface WO 5 sites. SCR reaction studies revealed that the surface WO5 sites possess minimal activity below ~325 °C and their primary function is to increase the adsorption capacity of ammonia. A relationship between the SCR activity and surface acidity was not found. The SCR reaction is controlled by the surface VO 4 sites that initiate the reaction at ~200 °C. The co-precipitated catalysts were always more active than the corresponding impregnated catalysts. Finally, we ascribe the higher activity of the co-precipitated catalysts to the presence of the new surface WO x sites associated surface defects on the TiO 2 support that increase the ammonia adsorption capacity.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Environmentally benign synthesis of a PGM-free catalyst for low temperature CO oxidation

Dopants enhance the catalytic properties of ceria. However, conventional techniques for synthesizing doped ceria have limitations in terms of structural homogeneity, surface area, and catalytic activity of the resulting oxide. Use of toxic and corrosive chemicals presents further challenges. The sol-gel method described in this work provides a facile approach for incorporating high concentrations of dopants in a uniform, high surface area structure, yielding excellent catalytic activity. Addition of polyvinylpyrrolidone (PVP) complexing agent prevents the segregation of cerium and dopant atoms during synthesis. Surface areas up to 179 m 2 /g are achieved, which represents a substantial improvement over doped ceria produced through coprecipitation, solution combustion, or melt-synthesis methods. The resulting powders exhibit dramatically improved CO oxidation activity (T 90 = 132 °C for 3.2 wt% Cu-CeO 2 compared to 274 °C for a 2 wt% Pt-Al 2 O 3 reference catalyst). First principles calculations suggest a Mars Van Krevelen mechanism, which is facilitated by dopants causing oxygen vacancies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Acyl-chain remodeling of dioctanoyl-phosphatidylcholine in Saccharomyces cerevisiae mutant defective in de novo and salvage phosphatidylcholine synthesis

Highlights: • Dioctanoyl-PC (diC8PC) supported growth of a yeast mutant defective in PC synthesis. • diC8PC was converted to PC species containing longer acyl residues in the mutant. • Both acyl residues of diC8PC were replaced by longer fatty acids in vitro. • This system will contribute to the elucidation of the acyl chain remodeling of PC. - Abstract: A yeast strain, in which endogenous phosphatidylcholine (PC) synthesis is controllable, was constructed by the replacement of the promoter of PCT1, encoding CTP:phosphocholine cytidylyltransferase, with GAL1 promoter in a double deletion mutant of PEM1 and PEM2, encoding phosphatidylethanolamine methyltransferase and phospholipid methyltransferase, respectively. This mutant did not grow in the glucose-containing medium, but the addition of dioctanoyl-phosphatidylcholine (diC8PC) supported its growth. Analyses of the metabolism of {sup 13}C-labeled diC8PC ((methyl-{sup 13}C){sub 3}-diC8PC) in this strain using electrospray ionization tandem mass spectrometry revealed that it was converted to PC species containing acyl residues of 16 or 18 carbons at both sn-1 and sn-2 positions. In addition, both acyl residues of (methyl-{sup 13}C){sub 3}-diC8PC were replaced with 16:1 acyl chains in the in vitro reaction using the yeast cell extract in the presence of palmitoleoyl-CoA. These results indicate that PC containing short acyl residues was remodeled to those with acyl chains of physiological length in yeast.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Identification of the C-terminal domain of Daxx acts as a potential regulator of intracellular cholesterol synthesis in HepG2 cells

Daxx is a highly conserved nuclear transcriptional factor, which has been implicated in many nuclear processes including transcription and cell cycle regulation. Our previous study demonstrated Daxx also plays a role in regulation of intracellular cholesterol content. Daxx contains several domains that are essential for interaction with a growing number of proteins. To delineate the underlying mechanism of hypocholesterolemic activity of Daxx, we constructed a set of plasmids which can be used to overexpress different fragments of Daxx and transfected to HepG2 cells. We found that the C- terminal region Daxx626–740 clearly reduced intracellular cholesterol levels and inhibited the expression of SREBPs and SCAP. In GST pull-down experiments and Double immunofluorescence assays, Daxx626–740 was demonstrated to bind directly to androgen receptor (AR). Our findings suggest that the interaction of Daxx626-740 and AR abolishes the AR-mediated activation of SCAP/SREBPs pathway, which suppresses the de novo cholesterol synthesis. Thus, C-terminal domain of Daxx acts as a potential regulator of intracellular cholesterol content in HepG2 cells. - Highlights: • Daxx C-terminal domain reduces cholesterol levels. • Daxx C-terminal domain binds directly to AR. • The interaction of Daxx C-terminal domain and AR suppresses cholesterol synthesis.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Visualization of local phosphatidylcholine synthesis within hippocampal neurons using a compartmentalized culture system and imaging mass spectrometry

Highlights: • A compartmentalized neuron culture system was combined with imaging mass spectrometry. • Phosphatidylcholine (PC) species within rat hippocampal neurons were visualized. • Differential synthetic activity of a PC species within neurons was observed. • Neurites synthesized a PC species using local extracellular free fatty acids in situ. Neurons extend neurites with an increased synthesis of phosphatidylcholine (PC) that is not only a membrane component but also a functional regulator with specific fatty acid composition. To analyze the local synthesis of the PC molecular species within neurons, we combined a compartmentalized culture system with matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS). We observed that a newly synthesized PC, which contains exogenously administered palmitic acid-d{sub 3}, is accumulated at the cell bodies and the tips of the distal neurites. The local accumulation within distal neurites is formed by distinct metabolic activity from cell bodies, suggesting that the local extracellular composition of free fatty acid can be a key to regulate specific functions of each PC molecular species. We expect our simple method to be a starting point for more sophisticated in vitro analytical methods for unveiling detailed lipid metabolisms within neurons.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Synthesis of wafer-scale SWCNT forests with remarkably invariant structural properties in a bulk-diffusion-controlled kinetic regime

Robust synthesis of vertically aligned carbon nanotubes (VACNT) at large scale is required to accelerate deployment of numerous cutting-edge devices to emerging commercial applications. To address this need, this work demonstrates that the structural characteristics of single-walled CNTs (SWCNTs) produced in a growth regime dominated by bulk diffusion of the gaseous carbon precursor are remarkably invariant over a broad range of process conditions (precursor concentration increased up to 30-fold, catalyst substrate area from 1 cm 2 to 180 cm 2 , growth pressure from 20 to 790 mbar, and gas flowrates up to 8-fold). A simple growth kinetics model is derived that accounts for both reactant bulk diffusion and competing byproduct formation in the presence of excess hydrogen, which quantitatively reproduces the experimental data in the entire isothermal parameter space. The model enables critical predictions for process scale-up optimization including a potential 6-fold increase in CNT production rate, a ~90% carbon conversion efficiency in select conditions, and elimination of reaction rate decay observed at high pressures by using a hydrogen-free growth environment. This model-guided opportunity to substantially improve synthesis throughput and efficiency, in conjunction with the remarkably invariant CNT properties, is appealing for reliable VACNT device fabrication at both small and industrial scales.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Ambient pressure synthesis of ammonia using a microwave reactor

Ammonia synthesis processes that can operate at low temperatures and pressure and have ability for small-scale distributed production are of interest. Microwave assisted synthesis has shown improvements in kinetics and does not have economy of scale limitations of the Haber-Bosch process. A microwave reactor was used to produce ammonia at temperatures from 300 to 500 °C. Three catalyst systems were compared: commercial Fe catalyst, and supported Ru/Al 2 O 3 , and Fe/Al 2 O 3 catalysts. Furthermore, the ammonia production of the dispersed catalysts was significantly higher than the commercial catalyst with maximum production of 128 μmol/g/h at 300 °C. This increase in production is attributed to an optimal electron movement under the microwave field.

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

Microwave-enhanced catalytic ammonia synthesis under moderate pressure and temperature

In this study, an alternative approach based on microwave-enhanced ammonia synthesis for Haber-Bosch process was carried out under moderate pressure of 0.1–0.65 MPa and temperature range of 280–400 °C over a stable CsRu/CeO 2 catalyst. The ammonia production rate is significantly improved under microwave conditions. At 0.65 MPa and 320 °C, maximum ammonia production rate was achieved at H 2 /N 2 ratio of 1/1. Stable performance was obtained in a 6-cycles of startup-shutdown operation for cumulative on-line time of 80 h. The work demonstrates the potential of microwave catalytic technology for the distributed ammonia synthesis using renewable power having intermittent nature of energy supply.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Intuitive study on the effect of support morphology over Cs-Ru/CeO 2 catalyst for microwave-initiated ammonia synthesis

Microwave-initiated ammonia synthesis is a potential candidate to the current Haber-Bosch process that can operate from stranded renewable energy source. Our previous studies indicated Cs-Ru/CeO 2 is a promising catalyst for microwave-assisted ammonia synthesis and the morphology of CeO 2 significantly affects the catalytic performance. In this paper, CeO 2 support with distinct morphologies nanorod, nanoparticle, and microstructure, is studied comprehensively at ambient pressure and low temperature under microwave irradiation. Moreover, CeO 2 nanorods of various sizes were synthesized at different timing (24, 36, and 48 h). Nanorods synthesized at 36 h exhibited superior activity associated to high dispersion and small Ru particle size.

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

Nanoparticle dynamics in the spatial afterglows of nonthermal plasma synthesis reactors

Nonthermal plasma flow tube reactors are industrially scalable systems for the production of nanocrystal (NC) based materials and coatings. One key advantage of nonthermal plasma synthesis is the ability to both synthesize NCs and deposit films in a single reactor, as at the reactor outlet, NCs can be inertially deposited onto a target substrate. The size and morphology of deposited particles can substantially influence the film structure and function. Though NCs are typically near-spherical and monodispersed as-produced in plasma synthesis reactors, NC charge and growth dynamics can be altered substantially when NCs are sampled out of the plasma and through the spatial afterglow region, affecting deposition. Experiments have demonstrated changes of NC size and charge in the spatial afterglow; however, these dynamics remain unexplored and unexplained via theory and simulation. To address this, we developed a constant number Monte Carlo (CNMC) simulation model to examine the mechanisms of NC decharging and growth in the spatial afterglow of plasma flow tube reactors. Collisions between NC and plasma species, diffusive deposition, and electron desorption from NCs are incorporated in the CNMC simulation. The simulation results are specifically compared with previous experiments on Si NCs synthesized from a low pressure Ar-SiH 4 nonthermal plasma reactor. Furthermore, the experiment-model comparison shows that CNMC models can be implemented which accurately model NC size distribution evolution in a spatial afterglow. Simultaneously, results show that improved collision models, energetic species diffusion models, and electron desorption models will be necessary to accurately depict NC dynamics in spatial afterglows.

42 ENGINEERING↗
DOE OSTI2024

Microwave-assisted synthesis of mixed-linker covalent organic frameworks enabling tunable and ultrahigh iodine capture

The use of covalent organic frameworks (COFs) for hazardous radioiodine capture has been highly sought after recently. However, the synthesis of high-performance COF adsorbents while circumventing the limitations of traditional solvothermal methods remains largely unexplored. Herein, we for the first time combine microwave-assisted synthesis and mixed-linker strategy to fabricate multivariate COF adsorbents (X% OMe-TFB-BD COFs, X% = 0, 33, 50, 67, and 100 mol%) with varying ratios of benzidine (BD) and 3,3'-dimethoxylbenzidine (BD-OMe) linkers in a rapid and facile manner. Adjusting the BD-OMe/BD mole ratios has led to distinct variations in density, crystallinity, porosity, morphology, and thermal/chemical stability of the resultant COFs, which empowered fine-tuning of the adsorption performance towards static iodine vapor. Remarkably, the 50% OMe-TFB-BD COF exhibited an ultrahigh iodine adsorption capability of 8.2 g g –1 , surpassing those of single-component COFs, mixed-linker COFs with other methoxy content, physically blended mixtures, and most existing COF adsorbents. Moreover, 50% OMe-TFB-BD COF was recyclable seven times without obvious loss in its adsorption capacity. Finally, this work underscores the substantial potential of microwave-assisted mixed-linker strategy as a viable approach for developing multivariate COFs with shortened reaction times, precisely tailored pore environment, and tunable sorption properties, which are of considerable promise for environmental remediation and other niche applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Dielectric and magnetic properties of microwave-absorbing FeAl x O y catalysts fabricated via solution combustion synthesis

Iron-based alumina (FeAl x O y ) nanocomposites are microwave-absorbers and catalysts, which makes them promising for emerging microwave-assisted thermocatalytic technologies. Solution combustion synthesis (SCS) has been used to synthesize FeAl x O y powders, and prior work has demonstrated that adjusting SCS parameters significantly changes phase composition and specific surface area of the products. However, it is unclear how synthesis parameters affect their microwave-absorbing properties, which are essential for optimizing microwave-assisted technologies. To address this challenge, in the present work, twelve different FeAl x O y products were synthesized at different combinations of the SCS parameters such as two fuels (citric acid and glycine), two heating modes (hotplate and muffle furnace), and three Fe:Al molar ratios (2:1, 1:1, 1:2). Dielectric and magnetic properties of the products were characterized using a network analyzer and a vibrating sample magnetometer. Based on the measured permittivity and permeability, penetration depth and reflection loss were calculated as a function of frequency and bed thickness. The products were heated by microwaves at 2.45 GHz and then examined with X-ray diffraction (XRD) analysis. For all products, the magnetic saturation was lower than for bulk iron oxides because of the small crystallite size and aluminum substitution. The use of glycine induced high dielectric losses and enabled fast microwave-heating rates compared to citric acid. Higher Fe:Al ratio also led to higher dielectric and magnetic losses. With glycine fuel, SCS in a furnace induced larger penetration depth and lower microwave absorption than SCS on a hotplate. The minimization of reflected power was more sensitive to the thickness of the product bed than to the frequency of the electromagnetic field. Post-heating XRD analysis revealed different phase transformations in the FeAl x O y powders depending on the SCS parameters. As a result, an FeAl x O y material, synthesized via incipient wetness impregnation, lacked magnetic losses and did not heat well as compared to the SCS products.

Combustion synthesis↗
DOE OSTI2021

A generalized distillation network synthesis model

In this report we propose a generalized superstructure-based distillation network synthesis model with improved modeling capabilities resulting in an extended solution space. The model can assign multiple mixtures to be separated (e.g., reactor network effluents) to different columns of the network while considering the interactions among different separation steps. In terms of outlets, products with general specifications, including pure components and multi-component mixtures, as well as streams without strict specifications (e.g., reactor recycle streams) can be readily handled. Furthermore, stream bypass is considered to avoid unnecessary separations, and thermal coupling is considered to yield novel solutions. The proposed model enables seamless integration with reactor network synthesis models thereby leading to solutions that are superior to the ones obtained by conventional sequential approaches.

42 ENGINEERING↗
DOE OSTI2018

A superstructure optimization approach for process synthesis under complex reaction networks

Here in this work, we present mixed integer linear programming methods for the synthesis of processes that involve complex reaction networks. Specifically, we consider the modeling of reactors and interconnecting streams in systems where the composition of the reactor inlet streams can vary substantially, thereby making the determination of the limiting component as well as the calculation of the stream heating/cooling and power requirements challenging. First, towards the modeling of reactors, we develop an extent-based method which detects the limiting reactant of each reaction occurring in parallel with others, based on the inlet flows of the reactants. Second, we develop a computationally tractable method for the calculation of the work and heating/cooling duty needed to condition any stream of a process based on simple calculations that can be performed offline. Finally, we present how the two aforementioned components can be integrated in an optimization model generated based on a process superstructure. We demonstrate the application of the developed methods for the synthesis of a biorefinery.

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

Synthesis of operable process intensification systems: advances and challenges

Process intensification (PI) has been gaining increasing momentum in the chemical engineering research community and the chemical/energy industry. While many PI alternative technologies and their conventional counterparts exist, systematic approaches and tools to decide on the most promising intensified process solutions are currently rather lacking. Process Systems Engineering (PSE) can contribute uniquely to this challenge by leveraging process synthesis, design, analysis, and optimization tools. However, key open questions in this area still remain, including: (i) how to efficiently address the combinatorial design space and systematically deliver intensified designs, and (ii) how to ensure the operablility performances of the derived intensified structures at an early design stage. Here, this paper provides a brief review of recent progress towards the synthesis of operable process intensification systems, highlights major challenges, and discusses future research opportunities.

42 ENGINEERING↗
DOE OSTI2020

Thermodynamics and kinetics of solution combustion synthesis: Ni(NO 3 ) 2 + fuels systems

Solution combustion synthesis (SCS) utilizes exothermic self-propagating reactions to prepare nanoscale materials that can be used widely in energy, electronics, and biomedical technologies and other applications. SCS is a specific variety of a more general combustion synthesis (CS) method. Investigations of the thermodynamics, kinetics, and the mechanisms of SCS reactions, are not as well studied as the other CS processes. This work reports on a systematic study of the thermodynamics and kinetics of SCS reactions involving Ni(NO 3 ) 2 , an oxidizer, and either glycine (C 2 H 5 NO 2 ) or hexamethylenetetramine (HMT, C 6 H 12 N 4 ) as fuels. A thermodynamic modeling approach, based on the Gibbs free energy minimization principle, is applied to the simultaneous calculations of the adiabatic temperatures and compositions of the equilibrium products. Our calculations reveal the influence of fuel-to-oxidizer ratio, amount of water, and the oxygen in air on the combustion temperature under adiabatic conditions and the composition of the resulting products. We have, in turn, measured the combustion temperature and phase composition of products and compared them with the calculations. Variations of drying times for the solutions yield precursor gels with varying water contents. This approach enables the manipulation of combustion parameters and confirms the use of calculated activation energies for reactions using the Merzhanov-Khaikin method. Here, the results show that SCS reactions in fuel-lean solutions producing NiO have higher activation energy in contrast to reactions with fuel-rich solutions that form Ni. Reduction of activation energies due to the increase in the fuel-to-oxidizer ratio could be related to the observed change of the rate-limiting stages of the endothermic decomposition of the individual reactants to the exothermic decomposition of coordinate compounds formed between the reactants.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

North American Carbon Project (NACP) Regional Interim Synthesis: Terrestrial Biospheric Model Intercomparison

Understanding of carbon exchange between terrestrial ecosystems and the atmosphere can be improved through direct observations and experiments, as well as through modeling activities. Terrestrial biosphere models (TBMs) have become an integral tool for extrapolating local observations and understanding to much larger terrestrial regions. Although models vary in their specific goals and approaches, their central role within carbon cycle science is to provide a better understanding of the mechanisms currently controlling carbon exchange. Recently, the North American Carbon Program (NACP) organized several interim-synthesis activities to evaluate and inter-compare models and observations at local to continental scales for the years 2000 to 2005. Here, we compare the results from the TBMs collected as part of the regional and continental interim-synthesis (RCIS) activities. The primary objective of this work is to synthesize and compare the 19 participating TBMs to assess current understanding of the terrestrial carbon cycle in North America.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2013

Mechanistic Studies of Methanol Synthesis over Cu from CO/CO2/H2/H2O Mixtures: the Source of C in Methanol and the Role of Water

The low temperature (403 – 453K) conversions of CO:hydrogen and CO2:hydrogen mixtures (6 bar total pressure) to methanol over copper catalysts are both assisted by the presence of small amounts of water (mole fraction ~0.04%-0.5%). For CO2:hydrogen reaction mixtures, the water product from both methanol synthesis and reverse water gas shift serves to initiate both reactions in an autocatalytic manner. In the case of CO:D2 mixtures, very little methanol is produced until small amounts of water are added. The effect of water on methanol production is more immediate than in CO2:D2, yet the steady state rates are similar. Tracer experiments in 13CO:12CO2:hydrogen (with or without added water), show that the dominant source of C in the methanol product gradually shifts from CO2 to CO as the temperature is lowered. Cu-bound formate, the major IR visible surface species under CO2:hydrogen, is not visible in CO:moist hydrogen. Though formate is visible in the tracer experiments, the symmetric stretch is absent. These results, in conjunction with recent DFT calculations on Cu(111), point to carboxyl as a common intermediate for both methanol synthesis and reverse water gas shift, with formate playing a spectator co-adsorbate role.

copper catalysts↗