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At least 1,711 records · Page 95
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Insights on the extraordinary tolerance to alcohols of Fe-N-C cathode catalysts in highly performing direct alcohol fuel cells

Direct alcohol fuel cells (DAFCs) represent the best alternative to batteries for portable and auxiliary power units application due to the high energy density of short chain alcohols. Currently, the utilization of the best platinum group metal (PGM) cathode catalysts is limited, not only by a high cost and scarce resources, but also by the inefficient oxygen reduction reaction (ORR) when permeated alcohols adsorb on the catalytic active sites. In this work, a highly active Fe-N-C catalyst derived from the pyrolysis of nicarbazin (a nitrogen charge transfer organic salt) and an iron precursor has been investigated to get insights on the extraordinary tolerance to the presence of alcohols (methanol and ethanol) of such a PGM-free catalyst. Density functional theory (DFT) calculations demonstrate for the first time that Fe-N 4 and Fe-N 2 C 2 active sites preferentially adsorb oxygen with much higher energy than methanol, ethanol and products of partial ethanol oxidation (0.73–1.16 eV stronger adsorption), while nitrogen-carbon related sites (pyridinic and graphitic nitrogen) are much less selective towards ORR. Half-cell electrochemical characterization showed that the Fe-N-C catalyst overcomes Pt ORR activity in acidic medium with methanol or ethanol concentrations as low as 0.01 M. The feasibility of DAFCs operation based on high methanol (up to 17 M) and ethanol (up to 5 M) concentration thanks to the utilization of Fe-N-C cathode catalyst is demonstrated. Lastly, a new strategy is proposed for DAFCs where using Pt only at the anode and Fe-N-C at the cathode allows extending the device energy density compared to PGM-based catalysts at both electrodes.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2013

Neutron tomography of particulate filters: A non-destructive investigation tool for applied and industrial research

This research describes the development and implementation of high-fidelity neutron imaging and the associated analysis of the images. This advanced capability allows the non-destructive, non-invasive imaging of particulate filters (PFs) and how the deposition of particulate and catalytic washcoat occurs within the filter. The majority of the efforts described here were performed at the High Flux Isotope Reactor (HFIR) CG-1D neutron imaging beamline at Oak Ridge National Laboratory; the current spatial resolution is approximately 50 μm. The sample holder is equipped with a high-precision rotation stage that allows 3D imaging (i.e., computed tomography) of the sample when combined with computerized reconstruction tools. What enables the neutron-based image is the ability of some elements to absorb or scatter neutrons where other elements allow the neutron to pass through them with negligible interaction. Of particular interest in this study is the scattering of neutrons by hydrogen-containing molecules, such as hydrocarbons (HCs) and/or water, which are adsorbed to the surface of soot, ash and catalytic washcoat. Even so, the interactions with this adsorbed water/HC is low and computational techniques were required to enhance the contrast, primarily a modified simultaneous iterative reconstruction technique (SIRT). Lastly, this effort describes the following systems: particulate randomly distributed in a PF, ash deposition in PFs, a catalyzed washcoat layer in a PF, and three particulate loadings in a SiC PF.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Predicting the performance uncertainty of a 1-MW pilot-scale carbon capture system after hierarchical laboratory-scale calibration and validation

A challenging problem in designing pilot-scale carbon capture systems is to predict, with uncertainty, the adsorber performance and capture efficiency under various operating conditions where no direct experimental data exist. Motivated by this challenge, we previously proposed a hierarchical framework in which relevant parameters of physical models were sequentially calibrated from different laboratory-scale carbon capture unit (C2U) experiments. Specifically, three models of increasing complexity were identified based on the fundamental physical and chemical processes of the sorbent-based carbon capture technology. Results from the corresponding laboratory experiments were used to statistically calibrate the physical model parameters while quantifying some of their inherent uncertainty. The parameter distributions obtained from laboratory-scale C2U calibration runs are used in this study to facilitate prediction at a larger scale where no corresponding experimental results are available. In this paper, we first describe the multiphase reactive flow model for a sorbent-based 1-MW carbon capture system then analyze results from an ensemble of simulations with the upscaled model. The simulation results are used to quantify uncertainty regarding the design’s predicted efficiency in carbon capture. In particular, we determine the minimum gas flow rate necessary to achieve 90% capture efficiency with 95% confidence.

bubbling bed↗
DOE OSTI2019

Benchmarking the accuracy of coverage-dependent models: adsorption and desorption of benzene on Pt (111) and Pt 3 Sn (111) from first principles

Bimetallic catalysts have demonstrated properties favorable for upgrading biofuel through catalytic hydrodeoxygenation. However, the design and optimization of such bimetallic catalysts requires the ability to construct accurate, predictive models of these systems. To generate a model that predicts the kinetic behavior of benzene adsorbed on Pt (111) and a Pt 3 Sn (111) surface alloy (Pt 3 Sn (111)), the adsorption of benzene was studied for a wide range of benzene coverages on both surfaces using density functional theory (DFT) calculations. The adsorption energy of benzene was found to correlate linearly with benzene coverage on Pt (111) and Pt 3 Sn (111); both surfaces exhibited net repulsive lateral interactions. Through an analysis of the d-band properties of the metal surface, it was determined that the coverage dependence is a consequence of the electronic interactions between benzene and the surface. The linear coverage dependence of the adsorption energy allowed us to quantify the influence of the lateral interactions on the heat of adsorption and temperature programmed desorption (TPD) spectra using a mean-field model. A comparison of our simulated TPD to experiment showed that this mean-field model adequately reproduces the desorption behavior of benzene on Pt (111) and Pt 3 Sn (111). In particular, the TPD correctly exhibits a broadening desorption peak as the initial coverage of benzene increases on Pt (111) as well as and a low temperature desorption peak on Pt 3 Sn (111). Furthermore, due to the sensitivity of the TPD peak temperature to the desorption energy, precise alignment of experimental and theoretical TPD spectra demands an accurate calculation of the adsorption energy. Therefore, an analysis of the effect of the exchange-correlation functional on TPD modeling is presented. Through this work, we show the necessity of incorporating lateral interactions into theoretical models in order to correctly predict experimental behavior.

09 BIOMASS FUELS↗
DOE OSTI2022

Effects of oxygen on the adsorption/oxidation of aqueous Sb(III) by Fe-loaded biochar: An X-ray absorption spectroscopy study

Fe-loaded biochar (FeBC) has been considered for Sb(III) adsorption, but the effects of oxygen (O 2 ) on the adsorption need further investigation. Liquid-/solid-phase analyses were conducted to investigate the role of O 2 in the Sb(III) adsorption by FeBC. The adsorption was best described by the pseudo-second-order (PSO) model for kinetic results and by the Langmuir model for thermodynamic results. More than 96.8 % of Sb(III) was adsorbed by FeBC, and available O 2 increased the liquid-phase Sb(III) oxidation efficiency by 2.1–7.5 times. The peak changes at ~1640 and 3450 cm -1 in FTIR spectra indicated the occurrence of inner-sphere complexation between Sb(III)/Sb(V) and hydroxyl (–OH)/carboxyl (–COOH) groups in FeBC under aerobic and anaerobic conditions. Fe/Sb X-ray absorption spectroscopy (XAS) analysis results showed aqueous Sb(III) complexed to the edge-sharing Fe(III)-O-Fe(III) in FeBC. Regardless of whether O 2 was available or not, solid-phase edge-sharing Fe(III)-O-Sb(V) complexes (~3.05 Å), which had lower toxicity and migration ability than aqueous Sb(III), formed through a ligand-to-metal charge-transfer (LMCT) process. More than 91 % of adsorbed Sb(III) was oxidized to edge-sharing Fe(III)-O-Sb(V) complexes in 3 h. Additionally, the Sb(V) from liquid-phase oxidation could also directly complex to the Fe(III)-O-Fe(III) and form edge-sharing Fe(III)-O-Sb(V) complexes. Here these results provide evidence to inform further FeBC application for the Sb-contaminated water treatment.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Selective recovery of rare earth elements with ligand-functionalized polymers in fixed-bed adsorption columns

Rare earth elements (REE) are a group of valuable metals with growing demand and broad applications. Mineral ores, the traditional sources of REE, require significant capital investment and their refinement has been a source of environmental contamination. Industrial fluids and natural REE-bearing liquids are potential alternative sources for these metals. This work investigated the performance and REE selectivity of polymer resin beads functionalized with N,N-bis(phosponomethyl)glycine (BPG) for extraction of REE from saline solutions in fixed-bed adsorption columns. Competitive batch adsorption experiments were conducted with various metals (Nd, Gd, Ho, Al, Fe, Co, Ni, Ba, Pb, Th, and U) and the BPG-functionalized resins were up to 137 times more selective for REE than aminated resins. In column experiments, the BPG-functionalized resins preferentially adsorbed heavier metals and REE were strongly retained in the functionalized column, taking 270 times longer than the amine column to reach 10% breakthrough and 128 times longer to reach 50% breakthrough. REE bound to the BPG-functionalized resins were recovered with a dilute HNO3 solution, yielding REE concentrations up to 236 times higher than the influent feedstock. This work provides new insight into the operational performance of novel functionalized adsorbents for recovery of REE from saline fluids.

42 ENGINEERING↗
DOE OSTI2013

Dynamics of the chemo-optical response of supported films of nematic liquid crystals

We report a study that elucidates key physicochemical phenomena that underlie the dynamics of adsorbate-induced ordering transitions in micrometer-thick films of nematic liquid crystals (LCs) supported on chemically functionalized surfaces. By flowing a gas containing dimethyl methylphosphonate (DMMP) over a film of nematic 4-cyano-4'-pentylbiphenyl (5CB) supported on a surface decorated with aluminum perchlorate, we quantify the dynamics of the optical response (intensity of transmitted light) of the LC film as a function of key experimental parameters, including linear flow rate of the gas over the surface of the film and the concentration of the DMMP within the gas. Building from prior infrared spectroscopic analysis revealing that the optical response of the LC is due to an ordering transition triggered by competitive ligand-exchange reactions at the chemically functionalized surface (i.e., between the phosphonate and nitrile groups of the DMMP and LC, respectively, with the aluminum perchlorate-decorated surface), we interpret the measurements reported herein within the framework of a simple model of mass transport. The model reveals that the rate-limiting process underlying the response of the LC is the mass transport of the DMMP across the concentration boundary layer formed on the vapor side of the LC–vapor interface, and not the mass transport of DMMP across the LC film nor the intrinsic ligand exchange kinetics. The analysis also reveals that the response of the LC is triggered once the concentration of DMMP within the LC film rises to approximately 0.25 mM. By flowing a stream of gas free of DMMP over a LC film pre-exposed to DMMP, we established that the relaxation of the LC film to the initial state is also largely controlled by mass transport of the DMMP across the vapor side of the LC–vapor interface. Analysis of the relaxation of the system leads to an estimate of the sensitivity of the supported LC film to the concentration of DMMP in the gas phase (approximately 150 ppb for the non-optimized system reported in this paper). These results and others reported in this paper identify key physical phenomena that dictate the dynamics of adsorbate-induced ordering transitions in LC systems, and provide important guidance to the design of LCs as chemo-responsive materials for use in sensors.

dimethyl methylphosphonate↗
DOE OSTI2022

In-situ synthesized N-doped ZnO for enhanced CO 2 sensing: Experiments and DFT calculations

Chemiresistive CO 2 sensing is attractive due to low cost and ease of chip-level integration. Our previous studies (Yong Xia, 2021) showed the well-developed ZnO material fabricated by in-situ annealing exhibited good CO 2 sensing performance. Here, we have expanded on those studies, including CO 2 cyclic tests under both dry air and N 2 background whereby a much higher response to CO 2 in N 2 background was observed. In this study, detailed density functional theory calculations were conducted to understand the behavior. The results indicated nitrogen doping is mainly responsible for the observed response. In the presence of pre-adsorbed O 2 , N-doped ZnO can no longer interact with CO 2 , which agrees well with the observation of higher response in N 2 background. Furthermore, density of states analysis showed N sp 2 hybridized orbital and N 2p orbital of the N dopant mixed with sp 2 hybridized orbital of C atom and 2p orbitals of C/O atoms in CO 2 to form σ and π bonds, respectively. However, they mixed with O 2s/2p orbitals of O atom in O 2 when pre-adsorbed O 2 was present, hindering CO 2 interaction with N-doped ZnO, and resulting in limited response in air. The illustrated mechanism does not only further the understanding of metal oxide-based CO 2 sensing, but also guide the design of new functional materials for CO 2 sensing or capture.

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

Visible Light Induced Photodesorption of NO from the α-Cr2O3(0001) Surface

Nitric oxide chemistry and photochemistry on the Cr-terminated surface of α-Cr2O3(0001) was examined using temperature programmed desorption (TPD), sticking coefficient measurements and photodesorption. NO adsorbed at 100 K binds at surface Cr cation sites forming a strongly bound surface species that thermally desorbs at 320-340 K, depending on coverage. No thermal decomposition was detected in TPD in agreement with previous results in the literature. Sticking probability measurements of NO at 100 K indicated near unity sticking for NO coverages up to ~1.3 ML, with additional adsorption with higher exposures at decreased sticking probability. These results suggest that each surface Cr cation site on the α-Cr2O3(0001) surface was capable of binding more than one NO molecule, although it is unclear whether this was as separate NO molecules or as dimers. Photodesorption of adsorbed NO was examined for surface coverages below the 1 ML point. Both visible and UV light were shown to photodesorb NO without detectable NO photodecomposition. Visible light photodesorption of NO occurred with a cross section of ~2x10-19 cm2, which was estimated to greater than that obtained with UV light. The visible light photodesorption event was not associated with bandgap excitation in α-Cr2O3(0001), but instead was linked to excitation of a surface Cr3+-NO- charge transfer complex. These results illustrate that localized photoabsorption events at surface sites with unique optical properties (relative to the bulk) can result in unexpected surface photochemistry. This work was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Stability of Surface and Subsurface Hydrogen on and in Au/Ni Near-Surface Alloys

Periodic, self-consistent DFT-GGA (PW91) calculations were used to study the interaction of hydrogen atoms with the (111) surfaces of substitutional near-surface alloys (NSAs) of Au and Ni with different surface layer compositions and different arrangements of Au atoms in the surface layer. The effect of hydrogen adsorption on the surface and in the first and second subsurface layers of the NSAs was studied. Increasing the Au content in the surface layer weakens hydrogen binding on the surface, but strengthens subsurface binding, suggesting that the distribution of surface and subsurface hydrogen will be different than that on pure Ni(111). While the metal composition of the surface layer has an effect on the binding energy of hydrogen on NSA surfaces, the local composition of the binding site has a stronger effect. For example, fcc hollow sites consisting of three Ni atoms bind H nearly as strongly as on Ni(111), and fcc sites consisting of three Au atoms bind H nearly as weakly as on Au(111). Sites with one or two Au atoms show intermediate binding energies. The preference of hydrogen for three-fold Ni hollow sites alters the relative stabilities of different surface metal atom arrangements, and may provide a driving force for adsorbate-induced surface rearrangement.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2015

Soft X-ray spectroscopy studies of adsorption and reaction of CO in the presence of H 2 over 6 nm MnO nanoparticles supported on mesoporous Co 3 O 4

MnO nanoparticles (6 nm) were supported on mesoporous spinel Co 3 O 4 and studied using ambient pressure X-ray photoelectron spectroscopy (APXPS) and in situ X-ray absorption spectroscopy (XAS) during hydrogenation of CO. The nature and evolution of surface adsorbed species as well as the oxidation states of the metal oxide surfaces were evaluated under oxidizing, reducing, and H 2 + CO (2:1) reaction atmospheres. From APXPS, MnO nanoparticle surfaces were found to be progressively reduced in H 2 atmospheres with increasing temperature. Surface adsorbed CO was found to be formed at the expense of lattice O under H 2 + CO reaction conditions. In situ XAS indicated that the dominant oxide species were Co(OH) 2 , Co (II) oxides, MnO, and Mn 3 O 4 under reaction conditions. In situ XAS also indicated the formation of gas phase CO 2 , the disappearance of lattice O, and the further reduction of Mn 3 O 4 to MnO upon prolonged reaction in H 2 + CO. Mass spectroscopy measurements showed the formation of CO 2 and hydrocarbons. Finally, the spent catalyst was investigated using scanning transmission X-ray microscopy and (scanning) transmission electron microscopy; the catalyst grains were found to be homogeneous.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Quenching of electron transfer reactions through coadsorption: A study of oxygen photodesorption from TiO2(110)

Using temperature programmed desorption (TPD) and photon stimulated desorption (PSD), we show that coadsorbates of varying binding energies on the rutile TiO2(110) surface exert a commensurate inhibiting influence on the hole-mediated photodesorption of adsorbed O2. A variety of coadsorbates (Ar, Kr, Xe, N2, CO, CO2, CH4, N2O, acetone, methanol or water) were shown to quench O2 photoactivity, with the extent correlating with the coadsorbate’s gas phase basicity, which in turn determines the strength of the coadsorbate-Ti4+ bond. Coadsorbed rare gases inhibited the photodesorption of O2 by ~10-25%, whereas strongly bound species (water, methanol and acetone) nearly completely inhibited O2 PSD. We suggest that coadsorption of these molecules inhibit the arrival probability of holes to the surface. Band bending effects, which vary with the extent of charge transfer between the coadsorbate and the TiO2(110) surface, are not expected to be significant in the cases of the rare gases and physisorbed species. These results indicate that neutral coadsorbates can exert a significant influence on charge transfer events by altering the interfacial dipole in the vicinity of the target molecule. This work was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. The work was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is a multiprogram national laboratory operated for DOE by Battelle under Contract DE-AC05-76RL01830.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2016

Reaction pathways of furfural, furfuryl alcohol and 2-methylfuran on Cu(111) and NiCu bimetallic surfaces

Hydrodeoxygenation (HDO) is an important reaction for converting biomass-derived furfural to value-added 2-methylfuran, which is a promising fuel additive. In this work, the HDO of furfural to produce 2-methylfuran occurred on the NiCu bimetallic surfaces prepared on either Ni(111) or Cu(111). The reaction pathways of furfural were investigated on Cu(111) and Ni/Cu(111) surfaces using density functional theory (DFT) calculations, temperature programmed desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS) experiments. These studies provided mechanistic insights into the effects of bimetallic formation on enhancing the HDO activity. Specifically, furfural weakly adsorbed on Cu(111), while it strongly adsorbed on Ni/Cu(111) through an η 2 (C,O) configuration which led to the HDO of furfural on Ni/Cu(111). Lastly, the ability to dissociate H 2 on Ni/Cu(111) is also an important factor for enhancing the HDO activity over Cu(111).

2-Methylfuran↗
DOE OSTI2017

Atomic and molecular adsorption on Fe(110)

Iron is the principal catalyst for the ammonia synthesis process and the Fischer–Tropsch process, as well as many other heterogeneously catalyzed reactions. It is thus of fundamental importance to understand the interactions between the iron surface and various reaction intermediates. Here in this paper, we present a systematic study of atomic and molecular adsorption behavior over Fe(110) using periodic, self-consistent density functional theory (DFT-GGA) calculations. The preferred binding sites, binding energies, and the corresponding surface deformation energies of five atomic species (H, C, N, O, and S), six molecular species (NH 3 , CH 4 , N 2 , CO, HCN, and NO), and eleven molecular fragments (CH, CH 2 , CH 3 , NH, NH 2 , OH, CN, COH, HCO, NOH, and HNO) were determined on the Fe(110) surface at a coverage of 0.25 monolayer. The binding strengths calculated using the PW91 functional decreased in the following order: C> CH > N > O > S > NH > COH > CN > CH2 > NOH > OH > HNO > HCO > NH2 > H > NO > HCN > CH 3 > CO > N 2 > NH 3 . No stable binding structures were observed for CH 4 . The estimated diffusion barriers and pathways, as well as the adsorbate-surface and intramolecular vibrational modes of all the adsorbates at their preferred binding sites, were identified. Using the calculated adsorption energetics, we constructed the potential energy surfaces for a few surface reactions including the decomposition of methane, ammonia, dinitrogen, carbon monoxide, and nitric oxide. These potential energy surfaces provide valuable insight into the ability of Fe(110) to catalyze common elementary steps.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Complex reactions on a convertible catalyst surface: A study of the S-O-Cu system

The interaction of clean and partially oxidized Cu(110) with sulphur was studied by scanning tunneling microscopy and density functional theory calculations in the low-coverage range. On the clean Cu surface individual S atoms adsorb in the troughs between the Cu atom rows. Hollow sites are preferred, but long-bridge sites are occasionally occupied as well. The majority of adsorbed S, however, seems to be involved in the formation of highly mobile Cu x S y clusters of various sizes. The clusters preferentially attach to steps thus changing the step morphology completely. Some of the clusters form aggregates on the terraces. On the partially oxidized surface similar clusters form and cause long-range mass transport to steps. Additionally, nanowires form in [001] direction on and along the surface oxide stress domains. These nanowires have a complex composition, exhibit different corrugations and appear sometimes as three-dimensional needles. Occasionally they flip their direction by 90°, but doing so they partially decompose. Finally, annealing of the S-O-Cu surface leads to consumption of the surface oxide stripes indicating loss of oxygen presumably via SO 2 formation. Simultaneously, linear sulphur chains suspended between the [001] –O-Cu-O- chains form in [11¯0] direction. The surprising multitude of processes and products even at low-pressure, low-temperature conditions in the comparatively simple S-O-Cu system highlights the difficulty of controlling reactivity and selectivity on such convertible catalyst surfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Subtle and reversible interactions of ambient pressure H 2 with Pt/Cu(111) single-atom alloy surfaces

Pt-Cu single-atom alloys (SAA) have been identified as promising hydrogenation catalysts with an ability to activate H 2 better than the individual metals alone. We studied the interaction between H 2 and Pt/Cu(111) SAA model surface using ambient pressure X-ray photoelectron spectroscopy (AP-XPS). A binding energy shift in the Pt 4f spectrum indicates the presence of adsorbed H at 350 K, occurring because of HeH bond activation. No evidence was found of either surface segregation, subsurface diffusion of Pt atoms, or any effects on the thermal stability of the surface, likely due to the subtle interaction between Pt and H. This shift is reversible upon evacuation of H 2 , which is a sign of a weak interaction. In addition, we studied the effect of H 2 and CO coadsorption and found that while the surface is unaffected by poisoning by a small amount of CO at 350 K, CO can displace adsorbed H on almost half of the surface Pt sites at 300 K. The susceptibility to CO poisoning increases after the surface was heated to 450 K due to changes in the structure of the subsurface layer that enhance the binding of CO to the surface Pt sites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗