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Results for “CATALYTIC EFFECTS”

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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Evaluation of Copper Catalytic Effects in Cable Insulation Polymers

This paper summarizes work performed to evaluate a phenomenon that occurs in electrical cable insulation polymers subjected to accelerated aging while in contact with copper metal. This effect, commonly known as the copper catalytic effect, is a result of chemical reactions that occur when copper ions diffuse into insulation polymers. This diffusion process is observed in various types of polymeric materials exposed to elevated temperatures and happens at the interface between the insulation and metallic components (e.g., conductor, shielding, etc.) in a cable. This polymer-metal interaction has only been observed in cables constructed with copper components (i.e., no interactions observed in cables with aluminum or other metal conductor/shielding) and results in a significant catalytic effect that increases the oxidation rate (e.g., aging) of the material. Under this research, the copper catalytic effects observed in cross-linked polyethylene, cross-linked polyolefin and ethylene propylene rubber insulated cables subjected to thermal accelerated aging were evaluated. These evaluations involved applying infrared spectroscopy, microscopy, and energy dispersive X-ray spectroscopy cross-sectional depth profiling to obtain an in-depth understanding of the aging characteristics of the materials under accelerated conditions. Based on the results of these assessments, the copper catalytic effect can have a significant impact on the mechanical, thermal, chemical, and electrical properties of cable insulation polymers. Here, the results acquired from this research provided the information needed to characterize the copper catalytic effects observed in these polymers, analyze how this phenomenon affected the polymer degradation process, and compare and understand the differences in the properties of the materials.

42 ENGINEERING↗
NASA NTRS2010

Possible Catalytic Effects of Ice Particles on the Production of NOx by Lightning Discharges

One mechanism by which NO(x) is produced in the atmosphere is heating in lightning discharge channels. Since most viable proposed electrification mechanisms involve ice crystals, it is reasonable to assume that lightning discharge channels frequently pass through fields of ice particles of various kinds. We address the question of whether ice crystals may serve as catalysts for the production of NO(x) by lightning discharges. If so, and if the effect is large, it would need to be taken into account in estimates of global NO(x) production by lightning. In this study, we make a series of plausible assumptions about the temperature and concentration of reactant species in the environment of discharges and we postulate a mechanism by which ice crystals are able to adsorb nitrogen atoms. We then compare production rates between uncatalyzed and catalytic reactions at 2000 K, 3000 K, and 4000 K. Catalyzed NO production rates are greater at 2000 K, whereas uncatalyzed production occurs most rapidly at 4000 K. 2010

Source record↗
DOE OSTI2022

Catalytic Effects of Silver in Iodine Reactors for Dissolved Used Nuclear Fuel

The dissolution of used nuclear fuel generates a variety of off-gasses including flammable hydrogen and other species that are a concern for environmental release. The H-Canyon facility at the Savannah River Site is currently dissolving aluminum-clad research reactor fuel from material test reactors and the High Flux Isotope Reactor (HFIR) using a mercury-catalyzed nitric acid flowsheet. Savannah River National Laboratory recently developed and deployed a Raman spectrometer to monitor the off-gas stream from the dissolution process. Results from these measurements indicated a lack of the expected hydrogen, nitrous oxide, and nitric oxide in the off-gas stream. It was proposed that the silver on the silver nitrate–coated berl saddles present in the reactors for iodine capture were acting as a catalytic hydrogen recombiner. Nitric oxide is readily oxidized to nitrogen dioxide under normal conditions, but it was unclear what happened to the nitrous oxide. A laboratory-scale iodine reactor was assembled and filled with silver nitrate–coated berl saddles to help ascertain the fate of nitrous oxide and hydrogen. Testing with this laboratory-scale reactor observed the recombination of hydrogen when a simulated dissolver off-gas was passed through the reactor containing silver nitrate–coated berl saddles at the approximate temperatures seen in H-Canyon. However, the nitrous oxide concentration was unchanged, suggesting a more complex process occurring within the off-gas stream before it reaches the iodine reactors at H-Canyon.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS2011

Possible Increase in Nitric Oxide Production by Lightning Discharges Due to Catalytic Effects of Ice Particles

We address the question of whether ice crystals with habits typically encountered by lightning discharges may serve as catalysts for the production of NOx by lightning. If so, and if the effect is sufficiently large, it would need to be taken into account in estimates of global NOx production by lightning. In this study, we make a series of plausible assumptions about the temperatures and concentrations of reactant species in the environment of discharges and we postulate a mechanism by which ice crystals could adsorb nitrogen atoms. We then compare production rates between uncatalyzed and catalyzed reactions at 2000 K, 3000 K, and 4000 K, temperatures observed in lightning channels during the cool-down period after a return stroke. Catalyzed NO production rates are greater at 2000 K, whereas uncatalyzed production occurs most rapidly at 4000 K. The channel temperature stays around 2000 K for a longer period of time than at 4000 K. The longer residence time at 2000 K is sufficient to allow fresh reactants to participate in the mix in. Therefore, our results suggest that nearly three times as much NO per flash is produced by ice-catalyzed reactions as compared with uncatalyzed reactions.

Peterson, Harold↗
NASA NTRS1983

Catalytic surface effects on space thermal protection system during Earth entry of flights STS-2 through STS-5

An on going orbiter experiment catalytic surface effects experiment being conducted on the Space Shuttle is discussed. The catalytic surface effects experiment was peformed on four of the five flights of Columbia. Temperature time histories and distributions along the midfuselage and wing of the orbiter were used to determine the surface catalytic efficiency of the baseline high temperature reusable surface insulation. Correlation parameters are shown that allow the comparison of all flight data with predictions from the design and surface emittance decreased as a result of contaminants during the five flights of the Space Shuttle.

Stewart, D. A.↗
DOE OSTI2026

From Pyrolysis Oil to Advanced Biographite Anode: Unravelling Biocoke Structural Evolution and Delayed Coking Effects

Catalytic graphitization of biomass-derived carbon offers a promising route to produce biographite as a sustainable alternative to petroleum-based synthetic graphite for lithium-ion battery (LIB) anodes. This study investigates the physicochemical properties of biocokes produced from pyrolysis oil at carbonization temperatures ranging from 150 degrees C to 500 degrees C. Using an iron (Fe) catalyst, graphitization was performed at 1500 degrees C, significantly lower than the ~3000 degrees C required for conventional synthetic graphite. The effects of introducing an intermediate-temperature hold (400 degrees C-600 degrees C) prior to graphitization were evaluated, simulating a "delayed coking" process to enable the coproduction of sustainable aviation fuels (SAFs). Chemical structure evolution during biocoke formation was analyzed, and proposed mechanisms are presented. Biographites produced via the delayed coking pathway exhibited high crystallinity and excellent electrochemical performance in both half-cell and full-cell LIB configurations. The full cells exhibited an initial discharge capacity close to the theoretical capacity of the NMC622 cathode (175 mAh/g at 4.2 V), and high capacity retention (~88%) after 150 cycles. Notably, the graphitic and electrochemical properties remained stable across the range of intermediate hold temperatures. These findings provide a foundation for optimizing temperature parameters in delayed coking systems to enable scalable, integrated production of biographite and SAFs from pyrolysis oil.

09 BIOMASS FUELS↗
NASA NTRS1991

A numerical study of shock wave/boundary layer interaction in nonequilibrium chemically reacting air - The effects of catalytic walls

This paper presents a numerical study that investigate the effects of nonequilibrium chemistry, and in particular, wall catalycity on the separated flow region generated by an oblique shock wave impinging upon a flat plate boundary layer. To obtain a solution to this problem, the full two dimensional Navier-Stokes equations were solved using MacCormack's predictor-corrector time dependent technique on a rectangular grid. Nonequilibrium chemistry was included by utilizing the 5 species, 17 reaction modified Dunn-Kang chemical kinetics model. Separate results were obtained for: calorically perfect, chemically reacting - noncatalytic wall, and chemically reacting - fully catalytic wall cases, for a given set of flow conditions. A direct comparison of all three cases revealed a slight decrease in the peak heat transfer for the noncatalytic wall case, as compared to the calorically perfect case. On the other hand, the fully catalytic wall case had a tremendous increase in the peak surface heat transfer. It is concluded that, for the particular conditons treated here (nearly frozen flow in the free stream), the effects of the nonequilibrium chemically reacting flow on the shock-wave/boundary-layer interaction depend critically on the catalycity of the wall, having virtually no effect for the case of a noncatalytic wall, and exerting a tremendous effect for a fully catalytic wall.

Grumet, Adam A.↗
NASA NTRS1984

Catalytic surface effect on ceramic coatings for an aeroassisted orbital transfer vehicle

Surface catalytic efficiencies of glassy coatings were determined from a reaction boundary layer computation and arc-jet data. The catalytic efficiencies of the various coatings examined are discussed in terms of their reaction-rate constants. These constants are a function of the wall temperature (1290 K to 2000 K). In addition, the advantage of a thermal protection system for a bent biconic, aeroassisted orbital transfer vehicle with a low surface catalytic efficiency is discussed.

Steward, D. A.↗
NASA NTRS1981

Catalytic surface effects experiment on the Space Shuttle

A Space Shuttle experiment planned to measure the surface catalytic efficiency of the baseline high-temperature reusable surface insulation (HRSI) during earth entry is described. A spray-on overcoat, with high catalytic efficiency, will be used as a comparative basis for determining the HRSI surface catalytic efficiency through surface temperature measurement. Catalytic efficiency, as well as aerothermal response of the overcoat, was evaluated, using various models made of HRSI material in arc-plasma flow environments. Agreement is obtained between the measured and computed heating rise of the coated surfaces. Computed predictions for the flight case are presented.

Stewart, D. A.↗
DOE OSTI2020

Water Catalysis of the Reaction of Methanol with OH Radical in the Atmosphere is Negligible

Abstract Faced with the contradictory results of two recent experimental studies [Jara‐Toro et al., Angew. Chem. Int. Ed . 2017 , 56 , 2166 and Chao et al., Angew. Chem. Int. Ed . 2019 , 58 , 5013] of the possible catalytic effect of water vapor on CH 3 OH + OH reaction, we report calculations that corroborate the conclusion made by Chao et al. and extend the rate constant evaluation down to 200 K. The rate constants of the CH 3 OH + OH reaction catalyzed by a water molecule are computed as functions of temperature and relative humidity using high‐level electronic structure and kinetics calculations. The Wuhan–Minnesota Scaling (WMS) method is used to provide accurate energetics to benchmark a density functional for direct dynamics. Both high‐frequency and low‐frequency anharmonicities are included. Variational and tunneling effects are treated by canonical variational transition state theory with multidimensional small‐curvature tunneling. And, most significantly, we include multistructural effects in the rate constant calculations. Our calculations show that the catalytic effect of water vapor is not observable at 200–400 K.

Wu, Junjun↗
DOE OSTI2021

Solvent Effects on Catalytic Reactions and Related Phenomena at Liquid-Solid Interfaces

Catalytic reactions involve the direct interaction of reactants, intermediates and products with the catalyst surface. We not only need to control the atomic structure and electronic properties of the active site, but also explore the multiple molecular interactions that occur beyond the active site; they play an essential role in altering the binding and reactivity of surface species. In liquid-phase catalysis, solvents provide additional degrees of freedom in the design of the catalytic process for desirable activity and selectivity. Here, the multi-faceted effects of solvents have a profound impact on the catalyst performance by restricting the mass transfer to the site, tuning the chemical potential of the surface species, competing for active sites, stabilizing the initial and transition states, and causing mechanistic changes by participating in the kinetically relevant elementary steps. This review addresses the different aspects of solvent effects, using a few prototype solid-liquid interfaces to illustrate these fundamental features. Recent experimental and computational studies that provide new insight at the molecular level are examined. Solvent structures in the proximity of the catalyst surface are discussed along with their influence in molecular binding and reaction at the solid-liquid interfaces. Furthermore, opportunities to alter such a solid-liquid interaction by tuning the wettability of the catalyst surfaces are explored.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Evaluation of a catalytically aided thermal regeneration method for quartz filter-based black carbon sensing

Black carbon (BC)–a strong indicator of diesel particulate matter and other sources of incomplete carbonaceous fuel combustion–is an important air pollutant that affects public health, yet low-cost sensors capable of long-term, autonomous BC monitoring remain underdeveloped. We report on the development and evaluation of a novel BC prototype sensor that integrates soot collection on a quartz filter, in-situ optical transmission measurement, and thermal filter regeneration. To enable regeneration at lower temperatures, we evaluated the catalytic effects of various alkali metal salts pre-applied to the filter. Among these, cesium carbonate (Cs 2 CO 3 ) exhibited the strongest catalytic activity, lowering the temperature required for complete BC removal by up to 190 °C and reducing energy consumption by more than 75% compared to that required for untreated filters. The catalytic effect persisted through 10 BC collection–regeneration cycles. These findings demonstrate the potential of catalytically aided thermal regeneration in BC sensors and suggest a pathway toward energy-efficient and reduced maintenance air quality monitoring suitable for distributed BC monitoring networks.

Tang, Xiaochen [Lawrence Berkeley National Laborat↗
DOE OSTI2023

Synthesis of Mg–K-biochar bimetallic catalyst and its evaluation of glucose isomerization

Highly efficient isomerization of glucose to fructose is essential for valorizing cellulose fraction of biomass to value-added chemicals. This work provided an innovative method for preparing Mg-biochar and Mg–K-biochar catalysts by impregnating either MgCl 2 alone or in combination with different K compounds (Ding et al. in Bioresour Technol 341:125835, 2021, https://doi.org/10.1016/j.biortech.2021.125835 and KHCO 3 ) on cellulose-derived biochar, followed by hydrothermal carbonization and pyrolysis. Single active substance MgO existing in the 10 Mg–C could give better catalytic effect on glucose isomerization than the synergy of MgO and KCl crystalline material present in 10 Mg–KCl–C. But the catalytic effect of 10 Mg–C was decreased when the basic site of MgO was overloaded. Compared to other carbon-based metal catalysts, 10 Mg–KHCO3–C with 10 wt% MgCl 2 loading had excellent catalytic performance, which gave a higher fructose yield (36.7%) and selectivity (74.54%), and catalyzed excellent glucose conversion (53.99%) at 100 °C in 30 min. Scanning electron microscope–energy dispersive spectrometer and X-Ray diffraction revealed that the distribution of Mg 2+ and K+ in 10 Mg–KHCO 3 –C was uniform and the catalytic active substances (MgO, KCl and K2CO 3 ) were more than 10 Mg–C (only MgO). The synergy effects of MgO and K 2 CO 3 active sites enhanced the pH of reaction system and induced H 2 O ionization to form considerable OH– ions, thus easily realizing a deprotonation of glucose and effectively catalyzing the isomerization of glucose. In this study, we developed a highly efficient Mg–K-biochar bimetallic catalyst for glucose isomerization and provided an efficient method for cellulose valorization.

59 BASIC BIOLOGICAL SCIENCES↗