SEARCH · Search NASA

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.

SourceResearch connectionFrom yearThrough year

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

At least 433 records · Page 24

All sources NASA NTRS DOE OSTI

NASA NTRS1991

Kaolinite-catalyzed air oxidation of hydrazine: Consideration of several compositional, structural and energetic factors in surface activation

Clay minerals have been shown to have numerous, curious, energetic properties by virtue of ultra-violet light release which can be triggered by gentle environmental changes such as wetting and dewetting by a variety of liquids, unique among them water and hydrazine. Since both water and hydrazine play multiple key roles in the air-oxidation of hydrazine on kaolinite surfaces, this reaction would seem to have prime potential for studying interrelationships of energy storage, release and chemical reactivity of clay surfaces, capacities basic to either the Bernal or Cairns-Smith roles of minerals in the origin of life. Establishment of the capacity for stored electronic energy to significantly alter surface chemistry is important, regardless of the reaction chosen to demonstrate it. Hydrazine air oxidation is overawingly complex, given the possibilities for step-wise control and monitoring of parameters. In the light of recently extended characterization of the kaolinite and model sheet catalysts we used to study hydrazine oxidation and gamma-irradiated silica, previous studies of hydrazine air-oxidation on aluminosilicate surfaces have been reevaluated. Our former conclusion remains intact that, whereas trace structural and surface contaminants do play some role in the catalysis of oxidation, they are not the only, nor even the dominant, catalytic centers. Initial intermediates in the oxidation can now be proposed which are consistent with production via O(-)-centers as well as ferric iron centers. The greater than square dependence of the initial reaction rate on the weight of the clay is discussed in the light of these various mechanistic possibilities.

Coyne, L. M.↗

DOE OSTI2025

Enhanced Activity in Layered Metal-Oxide-Based Oxygen Evolution Catalysts by Layer-by-Layer Modulation of Metal-Ion Identity

Few-layered potassium nickel and cobalt oxides show drastic differences in catalytic activity based on metal ion preorganization. Uniform compositions [(CoO 2 /K) 6 or (NiO 2 /K) 6 ] show limited activity, while homogeneously mixed-metal cobalt/nickel oxides [(Co n Ni (1–n) O 2 /K) 6 ] display moderate improvement. However, a layer-by-layer arrangement of alternating cobalt and nickel oxide sheets [e.g., (CoO 2 /K/NiO 2 /K)] provides superior catalytic performance, reducing the oxygen evolution overpotential by ∼200–400 mV. Density functional theory simulations provide an illustration of the electronic properties (density of states and localization of orbitals) that promote catalysis in the layer-segregated materials over those of homogeneous composition. This study reveals that atomic preorganization of metal ions within layered catalysts plays a more crucial role than the overall metal composition in enhancing catalytic efficiency for oxygen evolution.

catalysts↗

NASA NTRS1993

Balloon-borne in situ measurements of ClO and ozone - Implications for heterogeneous chemistry and mid-latitude ozone loss

In situ measurements of chlorine oxide (ClO) obtained on 31 March 1991 with a new balloon-borne instrument are compared to results from a photochemical model which incorporates hydrolysis of N2O5 on sulfate aerosols. With the addition of this process, there is better agreement between calculation and measurement over most of the profile, except below 20 km where observed ClO is greater by as much as a factor of four. In a model which is constrained to reproduce the observed ClO below 20 km, ozone loss by catalytic cycles involving halogen oxides becomes larger than that from NO(x), which would dominate under gas-phase or standard heterogeneous conditions.

Avallone, L. M.↗

DOE OSTI2020

Using anion photoelectron spectroscopy of cluster models to gain insights into mechanisms of catalyst-mediated H 2 production from water

We report that metal oxide cluster models of catalyst materials offer a powerful platform for probing the molecular-scale features and interactions that govern catalysis. This perspective gives an overview of studies implementing the combination of anion photoelectron (PE) spectroscopy and density functional theory calculations toward exploring cluster models of metal oxides and metal-oxide supported Pt that catalytically drive the hydrogen evolution reaction (HER) or the water–gas shift reaction. The utility in the combination of these experimental and computational techniques lies in our ability to unambiguously determine electronic and molecular structures, which can then connect to results of reactivity studies. In particular, we focus on the activity of oxygen vacancies modeled by suboxide clusters, the critical mechanistic step of forming proximal metal hydride and hydroxide groups as a prerequisite for H2 production, and the structural features that lead to trapped dihydroxide groups. The pronounced asymmetric oxidation found in heterometallic group 6 oxides and near-neighbor group 5/group 6 results in higher activity toward water, while group 7/group 6 oxides form very specific stoichiometries that suggest facile regeneration. Studies on the trans-periodic combination of cerium oxide and platinum as a model for ceria supported Pt atoms and nanoparticles reveal striking negative charge accumulation by Pt, which, combined with the ionic conductivity of ceria, suggests a mechanism for the exceptionally high activity of this system towards the water–gas shift reaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Postsynthetic Oxidation of the Coordination Site in a Heterometallic Metal-Organic Framework: Tuning Catalytic Behaviors

Postsynthetic modification (PSM) in metal-organic frameworks (MOFs) can introduce multiple functionalities and alter the structural function for the desired application. However, the PSM of the coordination site faces the challenges of structural collapse or incompatibility between the original metal site and the newly formed coordination group. Herein, we developed a novel concept of introducing “primary” and “secondary” nodes, coexisting in a water-stable, Zr-based heterometallic MOF, [Zr6(µ3-OH)8(OH)8][CuI4(L1)4]2 (1-SH-a, H2L1 = 6-mercaptopyridine-3-carboxylic acid). The post-synthetic oxidation at the coordination site was successfully achieved in the “secondary” nodes [CuI4(L1)4]4-, while the robust “primary” nodes [Zr6(µ3-OH)8(OH)8]8+ stabilized the whole framework to form [Zr6(µ3-OH)8(OH)8][(CuI0.44CuII0.56(OH)0.56)4(L2)4]2 (1-SO3H, H2L2 = 6-sulfonicotinic acid). PSM of 1-SH-a to form 1-SO3H dramatically tuned the catalytic properties toward the styrene oxide ring-opening reaction to give a regioselectivity of primary alcohol (A) of ~99% compared with 1-SH-a (~71%).

Han, Yi↗

NASA NTRS2008

Stabilized tin-oxide-based oxidation/reduction catalysts

The invention described herein involves a novel approach to the production of oxidation/reduction catalytic systems. The present invention serves to stabilize the tin oxide reducible metal-oxide coating by co-incorporating at least another metal-oxide species, such as zirconium. In one embodiment, a third metal-oxide species is incorporated, selected from the group consisting of cerium, lanthanum, hafnium, and ruthenium. The incorporation of the additional metal oxide components serves to stabilize the active tin-oxide layer in the catalytic process during high-temperature operation in a reducing environment (e.g., automobile exhaust). Moreover, the additional metal oxides are active components due to their oxygen-retention capabilities. Together, these features provide a mechanism to extend the range of operation of the tin-oxide-based catalyst system for automotive applications, while maintaining the existing advantages.

Jordan, Jeffrey D.↗

NASA NTRS2011

Methodology for the effective stabilization of tin-oxide-based oxidation/reduction catalysts

Jordan, Jeffrey D.↗

DOE OSTI2020

Oxidative dehydrogenation of propane on the oxygen adsorbed edges of boron nitride nanoribbons

Metal-free boron nitride has recently been reported to exhibit high catalytic activity and selectivity towards oxidative dehydrogenation of propane (ODHP). Despite several experimental studies, the exact nature and function of the active sites in this emerging catalyst are unknown. In the present work, density functional theory calculations are combined with microkinetic modeling to systematically explore the ODHP on oxygen passivated boron nitride nanoribbons (BNNRs). Here, the relative stabilities of different edge structures of BNNR were examined using ab initio thermodynamic analysis, and the most stable oxygen passivated edge structure was used for a mechanistic study. Microkinetic analysis revealed that a N 2 O or NO x -type active site is active and selective for the conversion of propane to propene. In addition to a heterogeneous catalytic cycle, the proposed N 2 O/NO x -type active sites are expected to be able to generate gas phase C 3 H 7 ˙, which in turn can trigger gas phase reactions of ODHP as experimentally speculated.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Metal-free carbocatalyst for room temperature acceptorless dehydrogenation of N-heterocycles

Catalytic dehydrogenation enables reversible hydrogen storage in liquid organics as a critical technology to achieve carbon neutrality. However, oxidant or base-free catalytic dehydrogenation at mild temperatures remains a challenge. Here, we demonstrate a metal-free carbocatalyst, nitrogen-assembly carbons (NCs), for acceptorless dehydrogenation of N-heterocycles even at ambient temperature, showing greater activity than transition metal–based catalysts. Mechanistic studies indicate that the observed catalytic activity of NCs is because of the unique closely placed graphitic nitrogens (CGNs), formed by the assembly of precursors during the carbonization process. The CGN site catalyzes the activation of C–H bonds in N-heterocycles to form labile C–H bonds on catalyst surface. The subsequent facile recombination of this surface hydrogen to desorb H 2 allows the NCs to work without any H-acceptor. With reverse transfer hydrogenation of various N-heterocycles demonstrated in this work, these NC catalysts, without precious metals, exhibit great potential for completing the cycle of hydrogen storage.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Glycerol Binding at the Narrow Channel of Photosystem II Stabilizes the Low-Spin S 2 State of the Oxygen-Evolving Complex

The oxygen-evolving complex (OEC) of photosystem II (PSII) cycles through redox intermediate states S i (i = 0–4) during the photochemical oxidation of water. The S 2 state involves an equilibrium of two isomers including the low-spin S 2 (LS-S 2 ) state with its characteristic electron paramagnetic resonance (EPR) multiline signal centered at g = 2.0, and a high-spin S 2 (HS-S 2 ) state with its g = 4.1 EPR signal. The relative intensities of the two EPR signals change under experimental conditions that shift the HS-S 2 /LS-S 2 state equilibrium. Here, we analyze the effect of glycerol on the relative stability of the LS-S 2 and HS-S 2 states when bound at the narrow channel of PSII, as reported in an X-ray crystal structure of cyanobacterial PSII. Our quantum mechanics/molecular mechanics (QM/MM) hybrid models of cyanobacterial PSII show that the glycerol molecule perturbs the hydrogen-bond network in the narrow channel, increasing the pK a of D1-Asp61 and stabilizing the LS-S 2 state relative to the HS-S 2 state. Here, the reported results are consistent with the absence of the HS-S 2 state EPR signal in native cyanobacterial PSII EPR spectra and suggest that the narrow water channel hydrogen-bond network regulates the relative stability of OEC catalytic intermediates during water oxidation.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2025

An experimental and numerical investigation of HD diesel engine DOC efficiency in oxidizing NO to NO 2

Reducing pollutant emissions from heavy-duty (HD) diesel engines is critical due to their significant environmental impact, particularly concerning NOx emissions. Understanding and optimizing modern diesel oxidation catalyst (DOC) and selective catalytic reduction (SCR) performance is essential for improving exhaust aftertreatment (EAT) system efficiency to meet stringent emissions regulations. The oxidation of nitric oxide (NO) to nitrogen dioxide (NO 2 ) in DOC plays a key role in improving SCR efficiency in reducing NO x . This study investigates the DOC performance in oxidizing NO to NO2 and its impact on the SCR efficiency of a 2021 MY Navistar E39 HD diesel engine. The influence of engine speed, load, exhaust gas temperature, and composition on DOC efficiency is experimentally investigated. The relationships between DOC inlet temperature, oxygen availability and NO 2 /NO x ratio at the DOC inlet are examined to better understand their effects on the overall DOC efficiency. The results indicate that DOC NO oxidation efficiency is highly dependent on exhaust temperature, with optimal oxidation occurring within a specific temperature range (275-350°C). Below this threshold, the chemical reactions are kinetically limited, while at higher temperatures, thermodynamic constraints reduce the efficiency of DOC in oxidizing NO to NO 2 . The experimental data further reveal that the NO 2 /NO x ratio peaks at medium loads before declining at higher loads due to reduced residence time and mass transfer effects. Additionally, the SCR NO x conversion efficiency is significantly influenced by the NO 2 /NO x ratio, achieving peak performance when the NO 2 /NO x ratio approaches 0.5. A DOC chemistry model was developed and validated against the experimental data to predict DOC oxidation behavior under various operating conditions. The findings of this study provide insights into the interdependencies between DOC and SCR performance, contributing to the optimization of SCR systems for optimized NOx reduction.

33 ADVANCED PROPULSION SYSTEMS↗

NASA NTRS1984

The role of surface generated radicals in catalytic combustion

The role of surface generated OH radicals in determining the catalytic ignition characteristics for propane oxidation on platinum were studied. The experiments were conducted in a stacked-plate, catalyst bed. Transient measurements, during catalytic ignition, of the catalyst's axial temperature profile were made and the effect of equivalence ratio, inlet temperature and inlet velocity was investigated. These measurements will provide insights which will be useful in planning and interpreting to OH measurements. Attempts to measure OH concentration in the catalyst bed using resonance absorption spectroscopy were unsuccessful, indicating that OH concentrations are below 10 to the 16th power/cc but still possibly above equilibrium values. Measurements are currently underway using forward scatter laser induced fluorescence which should extend the OH detection limits several orders of magnitude below the equilibrium concentrations.

Santavicca, D. A.↗

DOE OSTI2020

Oxidation kinetics of biochar from woody and herbaceous biomass

The goal of this study was to determine oxidation kinetics for biochar produced from fast pyrolysis of various biomass feedstocks. In particular, the role of inherent ash content on the oxidation rate was evaluated. Thermogravimetric analysis (TGA) and fluidized bed combustion experiments were used to explore oxidation kinetics of six fast pyrolysis produced biochars with diverse ash content. Here, the reaction rates varied by a factor of three under chemical kinetic-limited conditions, demonstrating inorganic content impacts oxidation rate. Chemical kinetic rate coefficients were proposed as a function of compositional parameters to determine overall fit and impact. Potassium content was found to have a positive correlation, best describing the differences in the oxidation kinetic rate coefficients. Additionally, feedstocks were subjected to a 1 M HCl acid wash mitigating the catalytic activity of the metals. Acid washed biochars had lower oxidation kinetic rates compared to their unwashed counterparts, indicating the removal of catalytically active metals reduced oxidation rate. Gas composition (CO/CO 2 ) was measured during fluidized bed experiments for both acid-washed and unwashed biochars, which varied between the six biochars. Formation of CO 2 was greatly affected by catalytic metals, finding potassium content to correlate well with a higher percentage of CO 2 formation as compared to CO. Comparison of oxidation rates were made between the two experimental apparatuses to measure the effect of attrition on biochar oxidation.

09 BIOMASS FUELS↗

DOE OSTI2020

Crystal-growth-dominated fabrication of metal-organic frameworks with orderly distributed hierarchical porosity

Constructing architectures with hierarchical porosity has been widely considered as the most efficient way to bypass the problems related to slow mass transfer and inaccessibility of internal space in MOFs. Now, a crystal-growth-dominated strategy is proposed to fabricate hierarchically porous MOFs (HP-MOFs). When the crystal growth is dominated by the monomer attachment, the aggregation of nonionic surfactant or polymer can be easily captured and released during the crystal growth process, resulting in the formation and ordering hierarchical pores along the radial direction. Furthermore, owing to the accelerated mass diffusion and more exposed active sites of this design, HP-MOFs exhibited an enhanced catalytic efficiency in styrene oxidation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Facile Synthesis of Rhodium‐Based Nanocrystals in a Metastable Phase and Evaluation of Their Thermal and Catalytic Properties

Abstract Controlling the polymorphism of metal nanocrystals is a promising strategy for enhancing properties and discovering new phenomena. However, previous studies on Rh nanocrystals have focused on their thermodynamically stable face‐centered‐cubic (fcc) phase. Herein, a facile synthesis of Rh‐based nanocrystals featuring the metastable hexagonal close‐packed (hcp) phase is reported by using Ru seeds in their native hcp phase to template the deposition of Rh atoms. The success of such phase‐controlled synthesis relies on the templating effect promoted by the small lattice mismatch between Ru and Rh and the slow dropwise titration of the precursor at an elevated temperature, ensuring the layer‐by‐layer growth mode and thus the formation of a conformal hcp‐Rh shell. Faster injection rate of Rh(III) precursor leads to the formation of a rough Rh shell in the conventional fcc phase due to accelerated reaction kinetics. Considering both thermodynamic and kinetic aspects of this system, the hcp‐Rh phase is favored when the low surface energy from smooth overlayers balances the high bulk energy of the metastable phase, achieved through tight control of reaction rates and deposition patterns. These Ru hcp @Rh hcp core–shell nanocrystals demonstrate thermal stability up to 400 °C, while exhibiting higher catalytic activity toward ethanol oxidation reaction compared to Ru hcp @Rh fcc counterparts.

Nguyen, Quynh N.↗

DOE OSTI2021

Structure sensitivity of ammonia electro-oxidation on transition metal surfaces: A first-principles study

Ammonia electro-oxidation is a promising catalytic reaction for application in alkaline fuel cells. In this paper we study the trends in this reaction on the (1 0 0) facet of eight fcc transition metals: Au, Ag, Cu, Pt, Pd, Ni, Ir, and Rh. We calculate from first-principles (DFT-GGA-PW91) the energetics for two mechanisms: (i) the N + N mechanism and (ii) the Gerischer-Mauerer mechanism. The onset potentials for both mechanisms are provided for both (1 0 0) and (1 1 1) facets. We also calculate the activation energies for the N-N bond-making non-Faradaic events on Cu, Pt, Pd, Ni, Ir, and Rh. We discover that N* – which is considered a poison for Pt(1 1 1) – is a reactive intermediate on Pt(1 0 0), allowing for a facile dimerization to N2 on Pt(1 0 0) at high potentials. We draw similar analyses for the structure sensitivity on the other metals, and we conclude with some general principles to guide catalyst design for this reaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Identifying the Molecular Edge Termination of Exfoliated Hexagonal Boron Nitride Nanosheets with Solid-State NMR Spectroscopy and Plane-Wave DFT Calculations

Hexagonal boron nitride nanosheets (h-BNNS), the isoelectronic analog to graphene, have received interest over the past decade due to their high thermal oxidative resistance, high bandgap, catalytic activity, and low cost. The functional groups that terminate boron and nitrogen zigzag and/or armchair edges directly affect their chemical, physical, and electronic properties. However, an understanding of the molecular edge termination present in h-BNNS is lacking. Here, high-resolution magic-angle spinning (MAS) solid-state NMR (SSNMR) spectroscopy, and plane-wave density-functional theory (DFT) calculations are used to determine the molecular edge termination in exfoliated h-BNNS. 1 H → 11 B cross-polarization MAS (CPMAS) SSNMR spectra of h-BNNS revealed multiple hydroxyl/oxygen coordinated boron edge sites that were not detectable in direct excitation experiments. A dynamic nuclear polarization (DNP)-enhanced 1 H → 15 N CPMAS spectrum of h-BNNS displayed four distinct 15 N resonances while a 2D 1 H{ 14 N} dipolar-HMQC spectrum acquired with fast MAS revealed three distinct 14 N environments. Plane-wave DFT calculations were used to construct model edge structures and predict the corresponding 11 B, 14 N and 15 N SSNMR spectra. Comparison of the experimental and predicted SSNMR spectra confirms that zigzag and armchair edges with both amine and boron hydroxide/oxide termination are present. The detailed characterization of h-BNNS molecular edge termination will prove useful for many material science applications. The techniques outlined here should also be applicable to understand the molecular edge terminations in other 2D materials

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Chemically Controllable Porous Polymer–Nanocrystal Composites with Hierarchical Arrangement Show Substrate Transport Selectivity

Functional organic–inorganic hybrid materials with tunable properties are useful across many application areas, ranging from gas storage to electronics, flame retardants, separations, and catalysis. Combining polymers, with a suite of functional groups and conformational flexibility, and inorganic nanoparticles, with tunable surface chemistry and composition, yields hybrids with novel functional properties. Specifically, in catalysis, control of the electronic environment at a metal interface is paramount in determining the catalytic properties. In this contribution, we describe a modular process to prepare porous polymer–nanocrystal (NC) composites in a hierarchical, multilayered synthesis, in which multiple parameters can be accurately tuned: polymer functional groups and the corresponding pore structure, the polymer layer thickness, and the NC size, shape, and composition. This process provides for a variety of controlled materials with high surface area, tunable chemistry, and thermal and chemical stabilities. Furthermore, we demonstrate their utility for shape- and size-selective catalytic conversions both in oxidation and hydrogenation reactions, where they show increased selectivity by orders of magnitude compared to conventional polymer-supported metal catalysts. In light of the high degree of control in the composite structure, this method allows for the design and realization of catalysts for several reactions and reaction environments and for nanomaterials with other applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗