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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Experimental Assessment of Mammalian Lipidome Complexity Using Multimodal 21 T FTICR Mass Spectrometry Imaging

Herein, we assess the complementarity and complexity of data that can be detected within mammalian lipidome mass spectrometry imaging (MSI) via matrix-assisted laser desorption ionization (MALDI) and nanospray desorption electrospray ionization (nano-DESI). We do so by employing 21 T Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) with absorption mode FT processing in both cases, allowing unmatched mass resolving power per unit time (≥613k at m/z 760, 1.536 s transients). While our results demonstrated that molecular coverage and dynamic range capabilities were greater in MALDI analysis, nano-DESI provided superior mass error, and all annotations for both modes had sub-ppm error. Taken together, these experiments highlight the coverage of 1676 lipids and serve as a functional guide for expected lipidome complexity within nano-DESI-MSI and MALDI-MSI. To further assess the lipidome complexity, mass splits (i.e., the difference in mass between neighboring peaks) within single pixels were collated across all pixels from each respective MSI experiment. The spatial localization of these mass splits was powerful in informing whether the observed mass splits were biological or artificial (e.g., matrix related). Mass splits down to 2.4 mDa were observed (i.e., sodium adduct ambiguity) in each experiment, and both modalities highlighted comparable degrees of lipidome complexity. Further, we highlight the persistence of certain mass splits (e.g., 8.9 mDa; double bond ambiguity) independent of ionization biases. Here, we also evaluate the need for ultrahigh mass resolving power for mass splits ≤4.6 mDa (potassium adduct ambiguity) at m/z > 1000, which may only be resolved by advanced FTICR-MS instrumentation.

21T-FTICR-MS↗
DOE OSTI2016

Gas adsorption capacity of wood pellets

In this paper, temperature-programmed desorption (TPD) analysis was used to measure and analyze the adsorption of off-gases and oxygen by wood pellets during storage. Such information on how these gases interact with the material helps in the understanding of the purging/stripping behavior of off-gases to develop effective ventilation strategies for wood pellets. Steam-exploded pellets showed the lowest carbon dioxide (CO 2 ) uptake compared to the regular and torrefied pellets. The high CO 2 adsorption capacity of the torrefied pellets could be attributed to their porous structure and therefore greater available surface area. Quantifying the uptake of carbon monoxide by pellets was challenging due to chemical adsorption, which formed a strong bond between the material and carbon monoxide. The estimated energy of desorption for CO (97.8 kJ/mol) was very high relative to that for CO 2 (7.24 kJ/mol), demonstrating the mechanism of chemical adsorption and physical adsorption for CO and CO 2 , respectively. As for oxygen, the strong bonds that formed between the material and oxygen verified the existence of chemical adsorption and formation of an intermediate material.

09 BIOMASS FUELS↗
DOE OSTI2020

An Electrochemically Mediated Amine Regeneration Process with a Mixed Absorbent for Postcombustion CO 2 Capture

Electrochemically mediated amine regeneration (EMAR) was recently developed to avoid the use of thermal means to release CO2 captured from postcombustion flue gas in the benchmark amine process. To address concerns related to the high vapor pressure of ethylenediamine (EDA) as the primary amine used in EMAR, a mixture of EDA and aminoethylethanolamine (AEEA) was investigated. The properties of the mixed amine systems, including the absorption rates, electrolyte pH and conductivity, and CO2 capacity, were evaluated in comparison with those of solely EDA. The mixed amine system had similar properties to that of EDA, indicating no significant changes would be necessary for the future implementation of the EMAR process with mixed amines as opposed to that with just EDA. The electrochemical performance of the mixed amines in terms of the cell voltage, gas desorption rate, electron utilization, and energetics was also investigated. A 50/50 mixture of EDA and AEEA displayed the lowest energetics: ~10% lower than that of 100% EDA. With this mixture, a continuous EMAR process, in which the absorption column was connected to the electrochemical cell as the desorption stage, was tested over 100 h. The cell voltage was very stable and there was a steady gas output close to theoretical values. The desorbed gas was further analyzed and found to be 100% CO2, confirming no evaporation of the amine. The mixed absorbent composition was also characterized using titration and nuclear magnetic resonance (NMR) spectroscopy, and the results showed no amine degradation. Furthermore, these findings that demonstrate a stable, low vapor pressure absorbent with improved energetics are promising and could be a guideline for the future development of EMAR for CO2 capture from flue gas and other sources.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Comparison of Designs of Hydrogen Isotope Separation Columns by Numerical Modeling

Mixtures of gas-phase hydrogen isotopologues (diatomic combinations of protium, deuterium, and tritium) can be separated using columns containing a solid such as palladium that reversibly absorbs hydrogen. A temperature-swing process can transport hydrogen into or out of a column by inducing temperature-dependent absorption or desorption reactions. Here, we consider two designs: a thermal cycling absorption process, which moves hydrogen back and forth between two columns, and a simulated moving bed (SMB), where columns are in a circular arrangement. We present a numerical mass and heat transport model of absorption columns for hydrogen isotope separation. It includes a detailed treatment of the absorption–desorption reaction for palladium. By comparing the isotope concentrations within the columns as a function of position and time, we observe that SMB can lead to sharper separations for a given number of thermal cycles by avoiding the remixing of isotopes.

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

Coupled NO and C 3 H 6 Trapping, Release and Conversion on Pd/BEA: Evaluation of the Lean Hydrocarbon NO x Trap

Automotive emission control catalysts are not effective in eliminating CO, hydrocarbons (HCs), and NO x during engine cold start (below 200 °C). In this study, the effectiveness of coupled low-temperature NO x and C 3 H 6 trapping and conversion on the model lean HC NO x trap (LHCNT) consisting of a washcoated Pd/BEA monolith was examined. Transient uptake and release experiments were conducted to obtain insight regarding competitive adsorption, release temperature, conversion activity, and water impact. NO and C 3 H 6 uptake were found to be mutually inhibitive because of competition for adsorption on Brønsted acid sites. During desorption, the existence of multiple NO sorption sites was established. Although C 3 H 6 inhibited NO adsorption on some of these sites, it delayed NO x desorption to higher temperatures. Furthermore, above 200 °C, Pd/BEA was able to catalyze the oxidation of stored HCs and exhibited NO x reduction activity. Addition of water inhibited both NO x and C 3 H 6 uptake, but the inhibition was lessened through a high-temperature thermal pretreatment. Overall, Pd/BEA demonstrates a combination of inhibiting and promoting coupling effects during uptake and release and exhibits activity for both NO x reduction and C 3 H 6 oxidation. Lastly, the findings provide guidance for developing improved LHCNT materials.

42 ENGINEERING↗
DOE OSTI2016

Surface Magnetism of Cobalt Nanoislands Controlled by Atomic Hydrogen

Controlling the spin states of the surface and interface is key to spintronic applications of magnetic materials. We report the evolution of surface magnetism of Co nanoislands on Cu(111) upon hydrogen adsorption and desorption with the hope of realizing reversible control of spin-dependent tunneling. Spin-polarized scanning tunneling microscopy reveals three types of hydrogen-induced surface superstructures, 1H-(2 × 2), 2H-(2 × 2), and 6H-(3 × 3), with increasing H coverage. The prominent magnetic surface states of Co, while being preserved at low H coverage, become suppressed as the H coverage level increases, which can then be recovered by H desorption. First-principles calculations reveal the origin of the observed magnetic surface states by capturing the asymmetry between the spin-polarized surface states and identify the role of hydrogen in controlling the magnetic states. This study offers new insights into the chemical control of magnetism in low-dimensional systems.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Identifying the Role of Dynamic Surface Hydroxides in the Dehydrogenation of Ti-Doped NaAlH 4

Solid-state metal hydrides are prime candidates to replace compressed hydrogen for fuel cell vehicles due to their high volumetric capacities. Sodium aluminum hydride has long been studied as an archetype for higher-capacity metal hydrides, with improved reversibility demonstrated through the addition of titanium catalysts; however, atomistic mechanisms for surface processes, including hydrogen desorption, are still uncertain. Here in this paper, operando and ex situ measurements from a suite of diagnostic tools probing multiple length scales are combined with ab initio simulations to provide a detailed and unbiased view of the evolution of the surface chemistry during hydrogen release. In contrast to some previously proposed mechanisms, the titanium dopant does not directly facilitate desorption at the surface. Instead, oxidized surface species, even on well-protected NaAlH 4 samples, evolve during dehydrogenation to form surface hydroxides with differing levels of hydrogen saturation. Additionally, the presence of these oxidized species leads to considerably lower computed barriers for H 2 formation compared to pristine hydride surfaces, suggesting that oxygen may actively participate in hydrogen release, rather than merely inhibiting diffusion as is commonly presumed. These results demonstrate how close experiment–theory feedback can elucidate mechanistic understanding of complex metal hydride chemistry and potentially impactful roles of unavoidable surface impurities.

25 ENERGY STORAGE↗
DOE OSTI2019

Oxidative Cross-Esterification and Related Pathways of Co-Adsorbed Oxygen and Ethanol on Pd–Au

Ethanol is one of the most important industrial chemicals considering its wide range of uses. From ultrahigh vacuum (UHV) experiments, we were able to effectively produce acetaldehyde and ethyl acetate on a Pd–Au model catalyst. The presence of oxygen at the Pd–Au interface sites was found to be highly reactive for ethanol dehydrogenation, significantly increasing acetaldehyde production and promoting cross-esterification to produce ethyl acetate. Density functional theory calculations show that compared to the bare PdAu(111) surface, the presence of preadsorbed oxygen and the subsequently formed hydroxyl group leads to highly active and selective initial ethanol dehydrogenation at the O–H and α–C-H position, which was corroborated by isotope-labeling experiments. Specifically, using temperature-programmed desorption with the isotope CD 3 CH2OH, we identified C–C bond breakage through methane production. Furthermore, the simultaneous desorption of D2 with ethyl acetate from the oxidation of CD 3 CD 2 OD suggests that the abstraction of hydrogen from acetaldehyde and/or ethanol is a relevant step in ethyl acetate production, which is supported by our theoretical predictions. These results shed light on the mechanistic pathways of having oxygen and ethanol coadsorbed on Pd–Au surfaces, which has significant implications for industrial applications such as fuel cells where catalytic design plays a major role in the efficiency of power production.

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

Thermal Activation of a Copper-Loaded Covalent Organic Framework for Near-Ambient Temperature Hydrogen Storage and Delivery

Copper(II) formate is efficiently incorporated into the pores of a 2D imine-based covalent organic framework (COF) via coordination with the phenol and imine groups. The coordinated metal ion is then reduced to Cu(I) with a thermal treatment that evolves CO 2 . After loading with hydrogen gas, the majority of H 2 desorbs from the coordinatively saturated Cu(II) COF at temperatures < -100 degrees C. However, the activated Cu(I) COF retains adsorbed H 2 above room temperature. Adsorption/desorption of H 2 was highly reversible. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) strongly supports a molecular hydrogen interaction with Cu(I). A Kissinger analysis of variable ramp rate desorption experiments estimates the enthalpy of H 2 desorption from Cu(I) at 15 kJ mol -1 . The results represent an advance toward practical H 2 storage and delivery in a lightweight, stable, and highly versatile material.

08 HYDROGEN↗
DOE OSTI2011

Chemisorption of CO and Mechanism of CO Oxidation on Supported Platinum Nanoclusters

Kinetic, isotopic, and infrared studies on well-defined dispersed Pt clusters are combined here with first-principle theoretical methods on model cluster surfaces to probe the mechanism and structural requirements for CO oxidation catalysis at conditions typical of its industrial practice. CO oxidation turnover rates and the dynamics and thermodynamics of adsorption-desorption processes on cluster surfaces saturated with chemisorbed CO were measured on 1-20 nm Pt clusters under conditions of strict kinetic control. Turnover rates are proportional to O2 pressure and inversely proportional to CO pressure, consistent with kinetically relevant irreversible O2 activation steps on vacant sites present within saturated CO monolayers. These conclusions are consistent with the lack of isotopic scrambling in C16O-18O2-16O2 reactions, and with infrared bands for chemisorbed CO that did not change within a CO pressure range that strongly influenced CO oxidation turnover rates. Density functional theory estimates of rate and equilibrium constants show that the kinetically relevantO2 activation steps involve directO2* (or O2) reactions with CO* to form reactive O*-O-C*dO intermediates that decompose to form CO2 and chemisorbed O*, instead of unassisted activation steps involving molecular adsorption and subsequent dissociation of O2. These CO-assisted O2 dissociation pathways avoid the higher barriers imposed by the spin-forbidden transitions required for unassistedO2 dissociation on surfaces saturated with chemisorbed CO. Measured rate parameters for CO oxidation were independent of Pt cluster size; these parameters depend on the ratio of rate constants for O2 reactions with CO* and CO adsorption equilibrium constants, which reflect the respective activation barriers and reaction enthalpies for these two steps. Infrared spectra during isotopic displacement and thermal desorption with 12CO-13CO mixtures showed that the binding, dynamics, and thermodynamics of CO chemisorbed at saturation coverages do not depend on Pt cluster size in a range that strongly affects the coordination of Pt atoms exposed at cluster surfaces. These data and their theoretical and mechanistic interpretations indicate that the remarkable structure insensitivity observed for CO oxidation reactions reflects average CO binding properties that are essentially independent of cluster size. Theoretical estimates of rate and equilibriumconstants for surface reactions and CO adsorption show that both parameters increase as the coordination of exposed Pt atoms decreases in Pt201 cluster surfaces; such compensation dampens but does not eliminate coordination and cluster size effects on measured rate constants. The structural features and intrinsic non-uniformity of cluster surfaces weaken when CO forms saturated monolayers on such surfaces, apparently because surfaces and adsorbates restructure to balance CO surface binding and CO-CO interaction energies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Reversible and Selective O 2 Chemisorption in a Porous Metal-Organic Host Material

The metal-organic host material [{Co III 2 (bpbp)(O 2 )} 2 bdc](PF 6 ) 4 (1 ∙ 2O 2 ; bpbp- = 2,6-bis(N,N-bis(2-pyridylmethyl)aminomethyl)-4-tert-butylphenolato; bdc 2- = 1,4-benzenedicarboxylato) displays reversible chemisorptive desorption and resorption of dioxygen through conversion to the deoxygenated Co(II) form [{Co II 2 (bpbp)} 2 bdc](PF 6 ) 4 (1). Single crystal X-ray diffraction analysis indicates that the host lattice 1 ∙ 2O 2 , achieved through desorption of included water guests from the as-synthesized phase 1 ∙ 2O 2 ∙ 3H 2 O, consists of an ionic lattice containing discrete tetranuclear complexes, between which lie void regions that allow the migration of dioxygen and other guests. Powder X-ray diffraction analyses indicate that the host material retains crystallinity through the dioxygen desorption/chemisorption processes. Dioxygen chemisorption measurements on 1 show near-stoichiometric uptake of dioxygen at 5 mbar and 25 °C, and this capacity is largely retained at temperatures above 100 °C. Gas adsorption isotherms of major atmospheric gases on both 1 and 1 ∙ 2O 2 indicate the potential suitability of this material for air separation, with a O 2 /N 2 selectivity factor of 38 at 1 atm. Comparison of oxygen binding in solution and in the solid state indicates a dramatic increase in binding affinity to the complex when it is incorporated in a porous solid.

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

Highly Active and Selective Sites for Propane Dehydrogenation in Zeolite Ga-BEA

A highly selective Ga-modified zeolite BEA for propane dehydrogenation has been synthesized by grafting Ga on Zn-BEA followed by removal of Zn in the presence of H 2 . A propene selectivity of 82% at 19% propane conversion illustrates the high selectivity at 813 K. The kinetic model of the catalyzed dehydrogenation including the elementary steps of propane adsorption, first and second C–H bond cleavage, and propene and H 2 desorption demonstrates that the propane dehydrogenation rate is determined by the first C–H bond cleavage at low pC 3 H 8 , while at high pC 3 H 8 , the rate is limited by the desorption of H 2 . The active sites have been identified as dehydrated and tetrahedrally coordinated Ga 3+ in the *BEA lattice. Furthermore, the low selectivity toward aromatics is concluded to be associated with the high Lewis acid strength of lattice Ga 3+ and the low Brønsted acid strength of the hydrated Ga sites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Catalytic decomposition of Ba(NO3)2 on Pt(111)

The decomposition of Ba(NO3)2 formed on BaO/Pt(111) (Pt(111) surface is partially covered by BaO) in the presence of CO was studied using temperature programmed desorption (TPD), infrared reflection absorption (IRA) and X-ray photoelectron (XP) spectroscopies. The exposure of BaO/Pt(111) to elevated NO2 pressure (1.0×10-4 Torr) at 450 K leads to the formation of Ba(NO3)2, chemisorbed O (OPt) and Pt-oxide-like domains. During TPD, the Ba(NO3)2 begins to thermally decompose near 490 K, releasing NO and NO2 with the maximum NOx desorption rate seen at 605 K. The OPt species formed following the exposure of BaO/Pt(111) to NO2 react with CO to release CO2 at 450 K. The consumption of OPt during CO oxidation initiates the migration of O from the Pt-oxide-like domains to the chemisorbed phase, where the CO oxidation reaction occurs. Therefore, the removal of OPt by CO leads to the reduction of oxidized Pt, and to the formation of metallic Pt(111) domains, where, subsequently, catalytic decomposition of Ba(NO3)2 can take place. The Pt-catalyzed decomposition of Ba(NO3)2 occurs readily at 450 K, a temperature much lower than the onset of the decomposition temperature of Ba(NO3)2 in the presence of oxidized Pt. This work was supported by the US Department of Energy Basic Energy Sciences' Chemical Sciences, Geosciences & Biosciences Division. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Site Competition During Coadsorption of Acetone with Methanol and Water on TiO2(110)

The competitive interaction between acetone and two solvent molecules (methanol and water) for surface sites on rutile TiO2(110) was studied using temperature programmed desorption (TPD). On a vacuum reduced TiO2(110) surface, which possessed ~5% oxygen vacancy sites, excess methanol displaced preadsorbed acetone molecules to weakly bound and physisorbed desorption states below 200 K, whereas acetone was stabilized to 250 K against displacement by methanol on an oxidized surface through formation of an acetone-diolate species. These behaviors of acetone differ from the competitive interactions between acetone and water in that acetone is less susceptible to displacement by water. Examination of acetone+methanol and acetone+water multilayer combinations shows that acetone is more compatible in water-ice films than in methanol-ice films, presumably because water has greater potential as a hydrogen-bond donor than does methanol. Acetone molecules displaced from the TiO2(110) surface by water are more likely to be retained in the near-surface region, having a greater opportunity to revisit the surface, than when methanol is used as a coadsorbate. This work was supported by the US Department of Energy Basic Energy Sciences' Chemical Sciences, Geosciences & Biosciences Division. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

10 SYNTHETIC FUELS↗
DOE OSTI2025

Photo-Swing CO2 Capture Using a Branched Polyethylenimine As Sorbents and TiN Light Absorber

Using branched polyethylenimine as the sorbent material for dilute CO2 capture, a photo-swing method is demonstrated in an industrially relevant support architecture using titanium nitride (TiN) nanosized light absorbers coupled with low-power LEDs with irradiances up to 420 mW cm-2. The photo-swing desorption process is applied to dry and humid streams of 400 ppm CO2 diluted in N2. Consistent with known sorption mechanisms for aminopolymers, humid CO2 streams increased the CO2 uptake, in our case by ~30%. The photo-swing CO2 capture desorbed ~83% and ~100% CO2 compared to thermally-driven desorption over the same period for a dry and humid CO2 stream, respectively. The photo-swing CO2 capture exhibits robust performance over >90 cycles without significant signs of photo(thermal) induced sorbent degradation. This work lays the groundwork for photo-swing DAC technology as a scalable, energy-efficient solution for CO2 capture, well-suited for modular systems in remote locations utilizing intermittent renewable energy sources.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Deuterium retention in tungsten exposed to low-energy pure and helium-seeded deuterium plasmas

Influence of helium (He) on the deuterium (D) retention in tungsten (W) under simultaneous He-D plasma exposure was investigated. Bulk polycrystalline tungsten and two W coatings on carbon substrate, namely, plasma-sprayed tungsten and combined magnetron-sputtered and ion implanted tungsten (CMSII-W) were exposed to pure and He-seeded D plasmas generated by electron-cyclotron-resonance plasma source. The D retention in each sample was subsequently analyzed by various methods such as nuclear reaction analysis for the D depth profiling up to 6 {mu}m and thermal desorption spectroscopy for the determination of total amount of D retention. It is shown that seeding of helium into D plasma with helium ion flux fraction of 10% reduces the deuterium retention for all tungsten grades but more significant reduction was observed for polycrystalline W and less significant effect was found for W coatings. From the thermal desorption spectroscopy measurements, we conclude that the presence of He modifies the density of existing traps for D but does not modify the nature of traps. Maximum effect of a reduction in the deuterium retention due to helium seeding was observed at around 500 K for bulk polycrystalline W. Mechanisms of deuterium retention and He effect in different W materials are discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2010

Effect of long duration UV irradiation on diamondlike carbon surfaces in the presence of a hydrocarbon gaseous atmosphere

Measurements of the effect of long duration UV irradiation (up to 2905 min) of flight quality diamondlike carbon charge state conversion surfaces for application in space research in the presence of a hydrocarbon atmosphere were done. An isopropanol atmosphere was used for simulating the hydrocarbon gaseous environment for an instrument on a satellite in space. Charge state conversion surfaces are used in neutral particle sensing instruments where neutral atoms have to be ionized prior to the analysis. A narrow-band (126{+-}5 nm) discharge lamp and a broad-band deuterium lamp (112-370 nm) were used as sources of UV radiation. The UV irradiation of a surface results in the desorption of some volatiles present on the surface and the decomposition of others. Desorption of volatiles, mostly water, is observed for both UV sources. The decomposition of the hydrocarbons and the subsequent build-up of a hydrocarbonaceous layer is only observed for the broad-band UV lamp, which is more representative for the space environment. Unfortunately, the hydrocarbonaceous layer cannot be removed thermally, i.e., it is permanent, and causes a degradation of the performance of the charge state conversion surfaces. With the present measurements we can quantify the UV influence at which the degradation of the conversion surfaces becomes noticeable.

36 MATERIALS SCIENCE↗