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Results for “Catalytic Oxidizer”

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.

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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

Two stage catalytic combustor

A catalytic combustor (14) includes a first catalytic stage (30), a second catalytic stage (40), and an oxidation completion stage (49). The first catalytic stage receives an oxidizer (e.g., 20) and a fuel (26) and discharges a partially oxidized fuel/oxidizer mixture (36). The second catalytic stage receives the partially oxidized fuel/oxidizer mixture and further oxidizes the mixture. The second catalytic stage may include a passageway (47) for conducting a bypass portion (46) of the mixture past a catalyst (e.g., 41) disposed therein. The second catalytic stage may have an outlet temperature elevated sufficiently to complete oxidation of the mixture without using a separate ignition source. The oxidation completion stage is disposed downstream of the second catalytic stage and may recombine the bypass portion with a catalyst exposed portion (48) of the mixture and complete oxidation of the mixture. The second catalytic stage may also include a reticulated foam support (50), a honeycomb support, a tube support or a plate support.

Alvin, Mary Anne↗
DOE OSTI2021

Base-Assisted Nitrate Mediation as the Mechanism of Electrochemical Benzyl Alcohol Oxidation

Using 2,6-lutidene as a Bronsted base renders nitrate anion oxidation to nitrate radical a catalytic system for oxidizing benzyl alcohol substrate to benzaldehyde with 80% current efficiency. The remaining current oxidizes acetonitrile solvent through the same mechanism as the substrate. But, directly observing that base is required to engender the catalysis is an advance in our mechanistic understanding of primary photo- and electrochemical alcohol oxidation reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1985

Vapor deposited emittance/catalysis coatings for superalloys in heatshield applications

Statically oxidized Inconel 617 and MA 956 superalloys were prepared with vapor deposited aluminosilicate layers and exposed to temperatures which simulated reentry conditions. The aluminosilicate layers were 1-2 microns thick. The trials consisted of exposures to 1500-2300 F heat while surface temperatures were monitored with pyrometers. Analyses were then performed of the catalytic activity, oxidation phenomena, and radiative properties after thermal cycling the specimens for 8 hr. Both alloys were found to be catalytic to the recombination processes of dissociated species in the reentry environment. The coatings reduced the catalytic activity by 40 percent for both alloys but did not change the emittance. An enhanced Cr depletion zone was detected in the Inconel samples, implying that the coating did not prevent diffusion loss of Cr. The coated MA 956, on the other hand, gained weight over the course of the trials.

Clark, R. K.↗
DOE OSTI2023

Earth Abundant Oxidation Catalysts for Removal of Contaminants of Emerging Concern from Wastewater: Homogeneous Catalytic Screening of Monomeric Complexes

Twenty novel Mn, Fe, and Cu complexes of ethylene cross-bridged tetraazamacrocycles with potentially copolymerizable allyl and benzyl pendant arms were synthesized and characterized. Multiple X-ray crystal structures demonstrate the cis-folded pseudo-octahedral geometry forced by the rigidifying ethylene cross-bridge and show that two cis coordination cites are available for interaction with substrate and oxidant. The Cu complexes were used to determine kinetic stability under harsh acidic and high-temperature conditions, which revealed that the cyclam-based ligands provide superior stabilization with half-lives of many minutes or even hours in 5 M HCl at 50–90 °C. Cyclic voltammetry studies of the Fe and Mn complexes reveal reversible redox processes indicating stabilization of Fe 2+ /Fe 3+ and Mn 2+ /Mn 3+ /Mn 4+ oxidation states, indicating the likelihood of catalytic oxidation for these complexes. Finally, dye-bleaching experiments with methylene blue, methyl orange, and rhodamine B demonstrate efficient catalytic decolorization and allow selection of the most successful monomeric catalysts for copolymerization to produce future heterogeneous water purification materials.

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

Probing the initial stages of iron surface corrosion: Effect of O 2 and H 2 O on surface carbonation

Iron plays a vital role in natural processes such as water, mineral, iron, and nutrient cycles. Iron undergoes reduction-oxidation and catalytic reactions to produce various corrosion films depending on its chemical environment. Near ambient pressure X-ray photoelectron spectroscopy, polarized modulated infrared reflection absorption spectroscopy, and Auger electron spectroscopy were used to study the key reactants, from O 2 (g), H 2 O vapor, Na + and Cl – on the initial stages of iron surface corrosion. Here, with increasing the ratio of O 2 and H 2 O, surface hydrocarbons were shown to oxidize into carbonates, while the Cl – was found to migrate into the interface. The effect of each individual reactant was measured separately and water was shown to have a first order rate dependence on the carbonate growth at low pressures, with little dependence for O 2 . Near ambient pressures, both H 2 O and O 2 were found to increase the carbonate growth, which was estimated using the Langmuir isotherm model, yielding Gibbs energies between –9.8 to –8.5 kJ/mol. A mechanism is suggested to explain the oxidation is catalyzed by NaCl on iron surfaces and the adventitious hydrocarbons served as the source for surface carbonation. These findings have implications for understanding other surface catalytic and redox interface chemistry in complex environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Synthesis of α,β‐ and β‐Unsaturated Acids and Hydroxy Acids by Tandem Oxidation, Epoxidation, and Hydrolysis/Hydrogenation of Bioethanol Derivatives

Abstract We report a reaction platform for the synthesis of three different high‐value specialty chemical building blocks starting from bio‐ethanol, which might have an important impact in the implementation of biorefineries. First, oxidative dehydrogenation of ethanol to acetaldehyde generates an aldehyde‐containing stream active for the production of C 4 aldehydes via base‐catalyzed aldol‐condensation. Then, the resulting C 4 adduct is selectively converted into crotonic acid via catalytic aerobic oxidation (62 % yield). Using a sequential epoxidation and hydrogenation of crotonic acid leads to 29 % yield of β‐hydroxy acid (3‐hydroxybutanoic acid). By controlling the pH of the reaction media, it is possible to hydrolyze the oxirane moiety leading to 21 % yield of α,β‐dihydroxy acid (2,3‐dihydroxybutanoic acid). Crotonic acid, 3‐hydroxybutanoic acid, and 2,3‐dihydroxybutanoic acid are archetypal specialty chemicals used in the synthesis of polyvinyl‐co‐unsaturated acids resins, pharmaceutics, and bio‐degradable/ ‐compatible polymers, respectively.

Santhanaraj, Daniel↗
DOE OSTI2020

Synthesis of α,β‐ and β‐Unsaturated Acids and Hydroxy Acids by Tandem Oxidation, Epoxidation, and Hydrolysis/Hydrogenation of Bioethanol Derivatives

Abstract We report a reaction platform for the synthesis of three different high‐value specialty chemical building blocks starting from bio‐ethanol, which might have an important impact in the implementation of biorefineries. First, oxidative dehydrogenation of ethanol to acetaldehyde generates an aldehyde‐containing stream active for the production of C 4 aldehydes via base‐catalyzed aldol‐condensation. Then, the resulting C 4 adduct is selectively converted into crotonic acid via catalytic aerobic oxidation (62 % yield). Using a sequential epoxidation and hydrogenation of crotonic acid leads to 29 % yield of β‐hydroxy acid (3‐hydroxybutanoic acid). By controlling the pH of the reaction media, it is possible to hydrolyze the oxirane moiety leading to 21 % yield of α,β‐dihydroxy acid (2,3‐dihydroxybutanoic acid). Crotonic acid, 3‐hydroxybutanoic acid, and 2,3‐dihydroxybutanoic acid are archetypal specialty chemicals used in the synthesis of polyvinyl‐co‐unsaturated acids resins, pharmaceutics, and bio‐degradable/ ‐compatible polymers, respectively.

Santhanaraj, Daniel↗
DOE OSTI2025

A Perspective into Operando Methods for Probing Catalytic Interfaces

Rational design of electrocatalysts for (photo)electrochemical (PEC) processes like hydrogen and oxygen evolution and CO2 reduction reactions is aided by the recent improvements in capabilities of operando measurements, where morphology, composition, and/or function are probed during active catalysis. Through operando microscopy and spectroscopy, structure, catalytic microenvironment, oxidation state, adsorbates, and products can be measured to gain a better understanding of catalyst behavior and suggest possible improvements. Visualizing evolving catalyst morphologies, surface compositions, and electrochemical behavior also helps address many fundamental research questions for a better understanding of catalytic mechanisms. Correlating morphology with chemical identity or functional behavior using a variety of innovative microscopy methods is particularly promising for guiding development of next generation catalysts, and there are also many recent examples of using AI and robotics tools to innovate and speed development. In this Perspective, advances made over the past few years in operando imaging of catalysts relevant to solar fuels will be explored, followed by an outlook on technological developments in instrumentation, sample design, and computational power that may be applied to this field.

Catalysts↗
NASA NTRS1985

Multiplex gas chromatography for use in space craft

Gas chromatography is a powerful technique for the analysis of gaseous mixtures. Some limitations in this technique still exist which can be alleviated with multiplex gas chromatography (MGC). In MGC, rapid multiple sample injections are made into the column without having to wait for one determination to be finished before taking a new sample. The resulting data must then be reduced using computational methods such as cross correlation. In order to efficiently perform multiplexgas chromatography, experiments in the laboratory and on board future space craft, skills, equipment, and computer software were developed. Three new techniques for modulating, i.e., changing, sample concentrations were demonstrated by using desorption, decomposition, and catalytic modulators. In all of them, the need for a separate gas stream as the carrier was avoided by placing the modulator at the head of the column to directly modulate a sample stream. Finally, the analysis of an environmental sample by multiplex chromatography was accomplished by employing silver oxide to catalytically modulate methane in ambient air.

Valentin, J. R.↗
DOE OSTI2022

Structure Matters: Asymmetric CO Oxidation at Rh Steps with Different Atomic Packing

Curved crystals are a simple but powerful approach to bridge the gap between single crystal surfaces and nanoparticle catalysts, by allowing a rational assessment of the role of active step sites in gas-surface reactions. Using a curved Rh(111) crystal, here, we investigate the effect of A-type (square geometry) and B-type (triangular geometry) atomic packing of steps on the catalytic CO oxidation on Rh at millibar pressures. Imaging the crystal during reaction ignition with laser-induced CO 2 fluorescence demonstrates a two-step process, where B-steps ignite at lower temperature than A-steps. Such fundamental dissimilarity is explained in ambient pressure X-ray photoemission (AP-XPS) experiments, which reveal partial CO desorption and oxygen buildup only at B-steps. AP-XPS also proves that A-B step asymmetries extend to the active stage: at A-steps, low-active O–Rh–O trilayers buildup immediately after ignition, while highly active chemisorbed O is the dominant species on B-type steps. We conclude that B-steps are more efficient than A-steps for the CO oxidation.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Alkali-induced catalytic tuning at metal and metal oxide interfaces

Alkali metals have been recognized as effective promoters in heterogeneous catalysis, capable of enhancing catalytic activity and tuning product distributions. Over the past few decades, significant efforts have been made aiming to reveal the mechanisms underlying the promoting effect of alkalis. However, the roles that alkali metals play in the catalytic process remain elusive due to challenges in capturing their catalytic behaviours upon exposure to reactive environments. This review summarizes recent surface science and theoretical studies of alkali (potassium, cesium)-decorated metal and metal oxide model catalysts, revealing the crucial tuning by alkalis of activity and selectivity for CO 2 hydrogenation. The analysis of electronic structures identifies the selective binding mechanism of the positively charged alkali ions on the surface, being able to reduce the surface work function and lead to strong electron polarization on the surfaces. Depending on the alkali–support interaction, the deposition of alkalis can selectively modify the bindings of reaction intermediates involved in CO 2 hydrogenation via the interplay among the ionic, covalent and electrostatic tunings. As a result, CO 2 can be effectively activated and converted into diverse products at the alkali–support interface, ranging from formic acid to methanol and ethanol. The identified selective bond-tuning advances the application of alkalis in promoting catalytic activity and controlling catalytic selectivity at alkali–support interfaces.

03 NATURAL GAS↗
DOE OSTI2025

A simplified CFD approach for modeling mass transport in catalytic open-cell foams

A simplified macroscopic CFD approach is presented to model mass transport including chemical reactions in washcoated open-cell foams. The foam is treated as a porous medium. Species conversion during chemical reactions is modeled using appropriate source terms based on reaction rate expressions and modified to account for the mass transport resistances occurring at the fluid-washcoat interfaces and within the washcoat layers. As example, the catalytic CO oxidation over platinum is studied. The simulation results show good agreement with experimental data from literature. A parametric study on washcoat parameters, such as thickness, tortuosity, porosity, and size, is carried out. Increasing the washcoat thickness from 5 to 100 µm or decreasing the tortuosity to porosity ratio from 5 to 20 decreases the CO conversion by 10 %. The proposed model is found to be reliable and has the advantage of lower computational cost, making it a suitable tool for foam-based catalytic reactor design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Three-dimensional strain dynamics govern the hysteresis in heterogeneous catalysis

Understanding catalysts strain dynamic behaviours is crucial for the development of cost-effective, efficient, stable and long-lasting catalysts. Here, we reveal in situ three-dimensional strain evolution of single gold nanocrystals during a catalytic CO oxidation reaction under operando conditions with coherent X-ray diffractive imaging. We report direct observation of anisotropic strain dynamics at the nanoscale, where identically crystallographically-oriented facets are qualitatively differently affected by strain leading to preferential active sites formation. Interestingly, the single nanoparticle elastic energy landscape, which we map with attojoule precision, depends on heating versus cooling cycles. The hysteresis observed at the single particle level is following the normal/inverse hysteresis loops of the catalytic performances. This approach opens a powerful avenue for studying, at the single particle level, catalytic nanomaterials and deactivation processes under operando conditions that will enable profound insights into nanoscale catalytic mechanisms.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Electrocatalytic alkene epoxidation at disrupted metal ensembles in blended electrolytes

The project aims to achieve a molecular understanding of oxygen-atom transfer from water to alkenes at electrocatalytic interfaces. Molecular oxygen is the most common oxygen-atom source for epoxidations, and our group is developing sustainable routes through which epoxidation of olefins is achieved using water as the oxygen source. This route can improve the safety of the reaction while also co-producing hydrogen, demonstrating the relevance of this reaction to the energy transition. If successful in our efforts, we may enable oxygen-atom transfer reactions at the anode of water electrolyzers in the place of conventional oxygen evolution, allowing for the synthesis of sustainable value-added co-products. In this vein, we explore several approaches to acquiring high selectivity toward epoxidation over competing reactions, such as oxygen evolution. One of our aims is to allow for rational control of epoxide selectivity by disrupting contiguous metal ensembles at the surface of catalytic metal oxide nanoparticles. Specifically, we aim to synthesize single-atom, few-atom, and many-atom clusters supported on metal oxides and study the mechanism of oxygen evolution and alkene epoxidation on these materials. Thus, this approach will determine the impact of disrupting metal ensembles on the selectivity for alkene epoxidation versus oxygen evolution in blended electrolytes. Another aim is to develop a molecular-level understanding of how a blended electrolyte (i.e., a mixture of aqueous and organic solvents) influences rates of alkene epoxidation versus oxygen evolution. In other words, we are interested in understanding the catalytic influence of the solvent, as our preliminary work shows that the selectivity and reactivity of epoxidation depend strongly on the solvent composition. This investigation includes blended electrolytes and electrolytes containing redox mediator species that improve selectivity toward the desired epoxidation reaction. Overall, our proposed work will help to provide a detailed molecular-level picture of how solvents interact with substrates at the electrode-electrolyte interface, including their involvement in proton transfer reactions and screening of electric fields.

14 SOLAR ENERGY↗
DOE OSTI2023

Counterintuitive Catalytic Reactivity of the Aluminum Oxide “Passivation” Shell of Aluminum Nanoparticles Facilitating the Thermal Decomposition of exo -Tetrahydrodicyclopentadiene (JP-10)

High energy density aluminum nanoparticles (AlNP) have been at the center of attention as additives to hydrocarbon jet fuels like exo-tetrahydrodicyclopentadiene (JP-10, C 10 H 16 ) aiming at a superior performance of volume-limited air-breathing propulsion systems. However, a fundamental understanding of the ignition and combustion chemistry of JP-10 in presence of AlNPs has been elusive. Exploiting an isomer-selective comprehensive identification of the decomposition products in a newly designed high temperature chemical microreactor coupled to vacuum ultraviolet photoionization, we reveal an active low temperature heterogeneous surface chemistry commencing at 650 K involving the alumina (Al 2 O 3 ) shell. Contrary to textbook knowledge of an “inactive alumina surface”, this unconventional reactivity, where oxygen is transferred from alumina to JP-10, leads to generating cyclic, oxygenated organics like phenol (C 6 H 5 OH) and 2,4-cyclopentadiene-1-one (C 5 H 4 O) - key tracers of an alumina-mediated interfacial chemistry. Furthermore, this counterintuitive reactivity transforms our knowledge on the (catalytic) processes of alumina-coated AlNPs on the molecular level.

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

Predicting Thermal Excursions During in situ Oxidative Regeneration of Packed Bed Catalytic Fast Pyrolysis Catalyst

Ex situ catalytic fast pyrolysis (CFP) uses a secondary reactor to upgrade biomass pyrolysis vapors to stabilized CFP oils with reduced oxygen content. In one configuration, the secondary reactor is operated as a packed-bed swing reactor system which allows coke-deactivated beds to be decarbonized in situ while other beds remain online for vapor upgrading. In situ decarbonization must be done carefully to avoid irreversible deactivation and/or physical degradation of catalyst pellets. Given that packed bed reactors are well known to have poor heat transfer characteristics, this is a critical issue impacting scaleability and commercial viability of the technology. To predict thermal excursions during regeneration, finite element computational models have been built to assist in scaling up oxidative decarbonization of a Pt/TiO2 CFP catalyst (0.5 mm spheres) from a bench scale packed bed with 100 g of catalyst to a pilot scale packed bed with 2 kg of catalyst and internal cooling tubes. Based on transient measurements of outlet temperature and effluent CO2 concentration, and using an assumed coke profile and activation energy, this paper demonstrates that specific combinations of effective thermal conductivity and wall heat transfer coefficient can fit bench scale oxidative regeneration data equally well. For the upscaled 2 kg bed, four bench-scale “best fit” parameter pairs give different predictions for location and magnitude of thermal excursions, with the maximum computed bed temperature gradients ranging from 30 °C cm-1 to as high as 3000 °C cm-1. The larger the fraction of heat removal by conduction through the cooling tubes, the greater the differences between the parameter pairs. The modelling results presented in this paper cast doubt on the industrial viability of the proposed combination of catalyst, bed and regeneration process, and point to the need for alternate reactor designs. However, there is considerable uncertainly in some of the key model parameters. The reliability of model predictions can be increased by adding more temperature measurements at key bed locations, testing additional variations in process conditions, performing careful bed dissections to determine the true coke profile, and perhaps most importantly, directly measuring the effective thermal conductivity of the catalyst pellets.

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

Developing Robust Ceria-Supported Catalysts for Catalytic NO Reduction and CO/Hydrocarbon Oxidation

Synthesis of robust and hydrothermally stable PGM/ceria materials for NO, CO, and hydrocarbon abatement remains a formidable challenge, as ceria and PGMs are known to sinter severely >800 °C under hydrothermal conditions, leading to irreversible activity loss. In this work, we tackle this challenge by synthesizing well-defined catalysts with atomically dispersed rhodium supported on ceria with varying abundance of (100), (101), and (111) facets. Evaluation of these catalysts for NO reduction by CO as well as CO and propylene oxidation under model and industrially relevant conditions reveals pronounced reactivity and stability differences. Different modes of interaction of Rh ions with the ceria facets and their facile reducibility were shown to be the crucial parameters controlling reactivity, resulting in pronounced activity and stability variations. Facet-dependent poisoning of surfaces by nitrites was identified as the main reason for deactivation of the catalysts at low temperature, which is mitigated for (111) ceria facets. (111)-enriched ceria nanoparticles survive very harsh hydrothermal aging at 950 °C by maintaining and preserving (111) facets, unlike other ceria nanoparticles which sinter into poorly defined shapes. Thus, putting atomically dispersed PGM sites on (111) ceria facets lead to the catalytic material with the highest activity and stability for all studied reactions, providing the pathway to catalysts that can endure extremely harsh hydrothermal aging conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗