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All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Local Aqueous Solvation Structure Around Ca2+ During Ca2+---Cl– Pair Formation

The molecular details of single ion solvation around Ca2+ and ion-pairing of Ca2--Cl- are investigated using ab initio molecular dynamics. The use of empirical dispersion corrections to the BLYP functional are investigated by comparison to experimentally available extended X-ray absorption fine structure (EXAFS) measurements, which probes the first solvation shell in great detail. Besides finding differences in the free-energy for both ion-pairing and the coordination number of ion solvation between the quantum and classical descriptions of interaction, there were important differences found between dispersion corrected and uncorrected density functional theory (DFT). Specifically, we show significantly different free-energy landscapes for both coordination number of Ca2+ and its ion-pairing with Cl- depending on the DFT simulation protocol. Our findings produce a self-consistent treatment of short-range solvent response to the ion and the intermediate to long-range collective response of the electrostatics of the ion-ion interaction to produce a detailed picture of ion-pairing that is consistent with experiment. MDB is supported by MS3 (Materials Synthesis and Simulation Across Scales) Initiative at Pacific Northwest National Laboratory. It was conducted under the Laboratory Directed Research and Development Program at PNNL, a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy. CJM acknowledges support from US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Additional computing resources were generously allocated by PNNL's Institutional Computing program. The authors thank Prof. Tom Beck for discussions regarding QCT, and Drs. Greg Schenter and Shawn Kathmann for insightful comments.

Baer, Marcel D.↗
DOE OSTI2016

Divalent Ion Parameterization Strongly Affects Conformation and Interactions of an Anionic Biomimetic Polymer

The description of peptides and the use of molecular dynamics simulations to refine structures and investigate the dynamics on an atomistic scale are well developed. Through a consensus in this community over multiple decades, parameters were developed for molecular interactions that only require the sequence of amino-acids and an initial guess for the three-dimensional structure. The recent discovery of peptoids will require a retooling of the currently available interaction potentials in order to have the same level of confidence in the predicted structures and pathways as there is presently in the peptide counterparts. Here we present modeling of peptoids using a combination of ab initio molecular dynamics (AIMD) and atomistic resolution classical forcefield (FF) to span the relevant time and length scales. To properly account for the dominant forces that stabilize ordered structures of peptoids, namely steric-, electrostatic, and hydrophobic interactions mediated through sidechain-sidechain interactions in the FF model, those have to be first mapped out using high fidelity atomistic representations. A key feature here is not only to use gas phase quantum chemistry tools, but also account for solvation effects in the condensed phase through AIMD. One major challenge is to elucidate ion binding to charged or polar regions of the peptoid and its concomitant role in the creation of local order. Here, similar to proteins, a specific ion effect is observed suggesting that both the net charge and the precise chemical nature of the ion will need to be described. MDD was supported by MS3 (Materials Synthesis and Simulation Across Scales) Initiative at Pacific Northwest National Laboratory. Research was funded by the Laboratory Directed Research and Development program at Pacific Northwest National Laboratory. MDB acknowledges support from US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Material & Engineering. CJM acknowledges support from US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. PNNL is a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy.

Daily, Michael D.↗
DOE OSTI2019

The Diverse Nature of Ion Speciation at the Nanoscale Hydrophobic/Water Interface

Herein we investigate ion pairing at weakly charged hydrophobic/water interfaces. In particular, the speciation of the thiocyanate (SCN-) ion in the vicinity of the nano aqueous (NaSCN solution) - hydrophobic (dodecane) interface in the presence of tetraalkylammonium groups attached to dodecyl chains (DTA+). This combined simulation and experimental approach finds that the SCN- interfacial ion pairs already form at concentrations as low as 5 mM and exist in three distinct, detectable structural motifs controlled by the SCN- concentration in the aqueous phase. The first is the association with the DTA+, followed by hydrophobic adsorption to the interface with the sulfur end of the SCN-, followed by an oppositely aligned SCN- absorption with a solvated nitrogen end of the SCN-. These different structures are formed due to subtle shifts in interactions and their elucidation requires multiple surface sensitive measurements in conjunction with the description of the interface using a representation of the interactions with quantum density functional theory (DFT). Together, this study reveals that we can both simultaneously control and detect subtle changes in the speciation of ions in the vicinity of soft interfaces. This work is supported by the Julia Jacobi Foundation and the European Research Council (grant number 616305). Christopher J. Mundy is supported by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES) Division of Chemical Sciences, Geosciences, and Biosciences. Marcel D. Baer is supported within the Materials Synthesis and Simulation Across Scales (MS3) Initiative through the Laboratory Research and Development Program at Pacific Northwest National Laboratory (PNNL). The calculations utilized resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the US DOE under Contract No. DE-AC02-05CH11231. PNNL is a multiprogram national laboratory operated by Battelle for the US DOE.

Zdrali, Evangelia↗
DOE OSTI2016

Reaction Rate Theory in Coordination Number Space: An Application to Ion Solvation

Understanding reaction mechanisms in many chemical and biological processes require application of rare event theories. In these theories, an effective choice of a reaction coordinate to describe a reaction pathway is essential. To this end, we study ion solvation in water using molecular dynamics simulations and explore the utility of coordination number (n = number of water molecules in the first solvation shell) as the reaction coordinate. Here we compute the potential of mean force (W(n)) using umbrella sampling, predicting multiple metastable n-states for both cations and anions. We find with increasing ionic size, these states become more stable and structured for cations when compared to anions. We have extended transition state theory (TST) to calculate transition rates between n-states. TST overestimates the rate constant due to solvent-induced barrier recrossings that are not accounted for. We correct the TST rates by calculating transmission coefficients using the reactive flux method. This approach enables a new way of understanding rare events involving coordination complexes. We gratefully acknowledge Liem Dang and Panos Stinis for useful discussion. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. SR, CJM, and GKS were supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. MDB was supported by MS3 (Materials Synthesis and Simulation Across Scales) Initiative, a Laboratory Directed Research and Development Program at Pacific Northwest National Laboratory (PNNL). PNNL is a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy.

Roy, Santanu↗
DOE OSTI2018

Electrocatalytic Hydrogenation of Oxygenated Compounds in Aqueous Phase

Electrocatalytic hydrogenation is a fascinating strategy to hydrogenate biogenic compounds at ambient conditions by replacing the thermal and H2 inputs by cathodic potential. This work compares the performance of this approach (in aqueous phase at room temperature) for a variety of model oxygenated compounds reacted over a series of metals. The target functionalities were carbonyl groups, aromatic rings, and ether bonds. All metals explored (Pt, Rh, Pd, Cu) are active for the reduction of carbonyl compounds to alcohols. For instance, conversion rates of benzaldehyde increased as a function of metal as: Pt < Rh < Pd (Cu was tested at different conditions). In contrast, only Rh and Pt were found active for hydrogenation of aromatic rings (Rh was more active than Pt). Comparing among the target functionalities, carbonyl groups are more reactive than aromatic rings and ether bonds in phenolic compounds and di-aryl ethers on all explore metals. This carbonyl reactivity, however, is enabled by the aromaticity of the molecule. Hence, the reactivity trend of the examined molecules is: butyraldehyde < furfural < acetophenone < benzaldehyde. For phenolic compounds, phenol is more reactive than cresol and methoxy phenol. Thus, the presence of substituting groups at the functionality being converted (either carbonyl or aromatic ring) decreases conversion rates. Ether bonds are cleaved under electrocatalytic conditions, which opens two main pathways for the conversion of aryl ethers: hydrogenation of the aromatic ring and hydrogenolysis of the ether bonds, whereas hydrolysis occurs as a minor pathway. Electrocatalytic hydrogenation competes with the H2 evolution reaction at the conditions of the tests, therefore Faradaic efficiency (fraction of current utilized in hydrogenation) and hydrogenation rates are correlated. That is, within the potential range explored, increasing hydrogenation rates lead to higher Faradaic efficiencies. The slope of this correlation, however, depends on the potential and on the functionality being hydrogenated. Keywords: Hydrogenation, electrocatalysis, metal catalysis, aqueous phase hydrogenation, biomass conversion. Acknowledgements The authors would like to thank Yang Song, Prof. Johannes Lercher, and the group of Prof. Hubert A. Gasteiger at the Technische Universität München for advice and support. The authors are grateful to Donald M. Camaioni, Nirala Singh, and Juan Herranz for fruitful discussions. The research described in this paper is part of the Chemical Transformation Initiative at Pacific Northwest National Laboratory (PNNL), conducted under the Laboratory Directed Research and Development Program at PNNL, a multi-program national laboratory operated by Battelle for the U.S. Department of Energy.

Hydrogenation, electrocatalysis, metal catalysis, ↗
DOE OSTI2018

Kinetic Coupling of Water Splitting and Photoreforming on SrTiO 3 -Based Photocatalysts

Coupling the anodic half-reactions of overall water splitting and oxygenate photoreforming (i.e., proton reduction and oxygenate oxidations) on Al-doped SrTiO3 decorated with a co-catalyst enables efficient photocatalytic H2 generation along with oxygenate conversion without accumulating undesired intermediates such as formaldehyde. The net H2-evolution rates result from the interplay between water oxidation, oxygenate oxidation, and the back-reaction of H2 and O2 to water. When the latter pathway is quantitatively suppressed (e.g., on RhCrOx co-catalyst or in excess of oxygenated hydrocarbons), the initial H2-evolution rates are independent of the oxygenate nature and concentration. This is a consequence of the reduction equivalents for H2-evolution provided by water oxidation compensating changes in the rates of oxygenate conversion. Thus, under conditions of suppressed back-reaction, water and oxygenate oxidations have equal quantum efficiencies. The selectivities to water and oxygenate oxidation depend on oxygenate nature and concentration. Transformations mediated by indirect hole transfer dominate as a result of the water oxidation at the anode and the associated intermediates generated in O2-evolution catalysis (e.g. ·OH, ·O and ·OOH). On the undecorated semiconductor, the O2 produced during overall water splitting is reductively activated to participate in glycerol oxidation without consuming evolved H2. Acknowledgements The authors would like to thank ESRF in Grenoble, France, for providing beam time at the ID26 station for XAFS experiments. K.E.S. gratefully acknowledges financial support by the Fond der Chemischen Industrie (FCI). J.A.L. and O.Y.G. acknowledge support for his contribution by the Laboratory Directed Research and Development Program at Pacific Northwest National Laboratory, a multi-program national laboratory operated by Battelle for the U.S. Department of Energy. The authors thank Xaver Hecht for BET measurements, Martin Neukamm for SEM and AAS measurements and Dr. Udishnu Sanyal for TEM imaging. Christine Schwarz is acknowledged for technical assistance in NMR experiments.

Sanwald, Kai E.↗
DOE OSTI2018

Protein Scaffold Activates Catalytic CO 2 Hydrogenation by a Rhodium Bis(diphosphine) Complex

The utilization of CO 2 to generate chemical fuels, such as formic acid, is a potentially beneficial route to balance carbon emissions and reduce dependence on fossil fuels. The development of efficient catalysts for CO 2 hydrogenation is needed to implement this fuel generation. In the molecular catalyst design presented here, we utilize covalent attachment of a rhodium complex, ([Rh(PN gly P) 2 ] + where PN Gly P is defined as P Et 2 -CH 2 -N( CH 2 CO 2 - )-CH 2 -P Et 2 ) to a protein scaffold, lactococcal multidrug resistant regulator from Lactococcus lactis, to create an environment around the metal center that can be used to control substrate delivery and therefore enable and improve catalytic activity. The reactivity of the rhodium complex and the synthetic metalloenzyme were characterized by high pressure operando NMR techniques. The rhodium complex in solution is not a catalyst for CO 2 hydrogenation. The incorporation of the molecular complex into the protein scaffold results in a gain of function, turning on CO 2 hydrogenation activity. The metalloenzyme displays a turnover frequency of 0.38 h -1 at 58 atm and 298 K; and achieved an average turnover number of 14 3. Proposed catalytic intermediates generated and characterized indicate the protein scaffold enables catalysis by facilitating the interaction between CO 2 and the hydride donor intermediate. Research was funded by the Laboratory Directed Research and Development program at Pacific Northwest National Laboratory. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy. This structural work is supported as part of the Biological and Electron Transfer and Catalysis (BETCy) EFRC, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science (DE-SC0012518) to J.W.P. and O.A.Z. No competing financial interests have been declared.This work was performed in part using the William R. Wiley Environmental Molecular Sciences Laboratory, a U.S. Department of Energy (DOE) national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located and the Pacific Northwest National Laboratory (PNNL). Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. The SSRL Structural Molecular Biology Program is supported by the DOE Office of Biological and Environmental Research, and by the National Institutes of Health, National Institute of General Medical Sciences (including P41GM103393).

structural biology, protein crystallography, bioin↗
DOE OSTI2018

Impact of pH on Aqueous-Phase Phenol Hydrogenation Catalyzed by Carbon-Supported Pt and Rh

In aqueous phase, the rates of hydrogenation of aromatic substrates such as phenol on Pt/C and Rh/C are influenced by varying activity of hydronium ions. Decreasing the pH from 8 to 1 increases the rate of hydrogenation of phenol on Pt at 20 bar H 2 and 80 °C by 15-fold. This increase is attributed to weakening of the hydrogen binding energy (HBE) on the metal surface with decreasing pH. A weaker HBE at lower pH is also predicted by ab initio molecular dynamics simulations, providing atomistic insight into the impact of electrolyte ion distribution and interfacial solvent reorganization on HBE. The lower HBE results in a decrease in the activation energy for addition of adsorbed H from the metal to the adsorbed organic (with a Brønsted–Evans–Polanyi slope of ~1). In conclusion, the kinetic model derived accounts also for the lack of pH dependence at low hydrogen coverages (at 1 bar H 2 on Pt or up to 70 bar H 2 on Rh), when the weakening of the HBE decreases the hydrogen coverage.

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

Using Transient FTIR Spectroscopy to Probe Active Sites and Reaction Intermediates for Selective Catalytic Reduction of NO on Cu/SSZ-13 Catalysts

A Cu/SSZ-13 catalyst containing predominately Z2Cu sites is prepared. Using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), two non-steady state measurements, (1) continuous NO titration of an NH3 saturated catalyst and (2) intermittent NO on/off during quasi-steady state (i.e., NO perturbation), are conducted to shed light on active sites, reaction intermediates, and possible reaction mechanisms. During continuous NO titration, a strong NH3 inhibition effect is found, where Cu active sites containing NH3 ligands are less active than Cu sites depleted of NH3 ligands. In the NO perturbation experiments, it is demonstrated that NO+NH3 interactions lead to formation of Brønsted acid sites, which further interact with NH3 to form NH4+. Such a finding is fully consistent with a redox SCR mechanism proposed recently (Angew. Chem. Int. Ed. 2014, 53, 11828–11833). Perturbation measurements, using ND3 to replace NH3 in order to distinguish ammonia and nitrate vibrations, further show that NH4NO3 and other surface nitrates are not involved in the SCR process under typical low temperature quasi-steady state conditions. This work was financially supported by the national key research and development program of China (2017YFC0211302 and 2017YFC0211003), the Sino Japanese cooperation project (2016YFE0126600) and the China Postdoctoral Science Foundation (2017M620800). FG and CHFP gratefully acknowledge financial support for their participation from the US Department of Energy (DOE), Energy Efficiency and Renewable Energy, Vehicle Technologies Office. A portion of this work was performed in the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle.

Cu, SSZ-13, SCR, DRIFTS, transient kinetics, mecha↗
DOE OSTI2014

In Situ Observation of Directed Nanoparticle Aggregation During the Synthesis of Ordered Nanoporous Metal in Soft Templates

The prevalent approach to developing new nanomaterials is a trial and error process of iteratively altering synthesis procedures and then characterizing the resulting nanostructures. This is fundamentally limited in that the growth processes that occur during synthesis can only be inferred from the final synthetic structure. Directly observing real-time nanomaterial growth provides unprecedented insight into the relationship between synthesis conditions and product evolution, and facilitates a mechanistic approach to nanomaterial development. Here we use in situ liquid stage scanning transmission electron microscopy to observe the growth of mesoporous palladium in a solvated block copolymer (BCP) template under various synthesis conditions, and ultimately determine a refined synthesis procedure that yields ordered pores. We find that at low organic solvent (tetrahydrofuran, THF) content, the BCP assembles into a rigid, cylindrical micelle array with a high degree of short-range order, but poor long-range order. Upon slowing the THF evaporation rate using a solvent-vapor anneal step, the long-range order is greatly improved. The electron beam induces nucleation of small particles in the aqueous phase around the micelles. The small particles then flocculate and grow into denser structures that surround the micelles, forming an ordered mesoporous structure. The microscope observations revealed that template disorder can be addressed prior to reaction, and is not invariably induced by the growth process itself, allowing us to more quickly optimize the synthetic method. This work was conducted in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy under contract DE-AC05-76RL01830. This research was funded in part by: the Presidential Early Career Award for Scientist and Engineers for I.A., the University of California Academic Senate and the University of California Laboratory fee research grant, the Laboratory-Directed Research and Development program at Sandia National Laboratories, and the Chemical Imaging Initiative at Pacific Northwest National Laboratory. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

cylindrical micelle↗
DOE OSTI2015

Impact of zeolite aging in hot liquid water on activity for acid-catalyzed dehydration of alcohols

The catalytic performance of zeolite in aqueous medium depends on a multitude of factors, such as the concentration and distribution of active sites and framework integrity. Al K–edge extended X–ray absorption fine structure and 27Al MAS NMR spectroscopies in combination with DFT calculations are used to determine the distribution of tetrahedral Al sites both qualitatively and quantitatively for both parent and 48 h 160 ºC water treated HBEA catalysts. There is no evidence of Al coordination modification after aging in water. The distribution and concentration of Al T–sites, active centers for the dehydration of cyclohexanol, do not markedly impact the catalytic performance in water, because the Brønsted acidic protons are present in the form of hydrated hydronium ions and thus have very similar acid properties. The results suggest that all Brønsted acid sites are equally active in aqueous medium. The decrease of zeolite catalytic performance after water treatment is attributed to the reduced concentration of Brønsted acid sites. Increasing the stability of pore walls and decreasing the rate of Si–O–Si group hydrolysis may result in improved apparent zeolite catalytic performance in aqueous medium. Authors thank B. W. Arey (PNNL) for HIM measurements, T. Huthwelker for support during Al XAFS measurements at the Swiss Light Source (PSI, Switzerland), J. Z. Hu and S. D. Burton (PNNL) for support during NMR experiments. This work was supported by the U. S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. MD acknowledges support by the Materials Synthesis and Simulation Across Scales (MS3 Initiative) conducted under Laboratory Directed Research & Development Program at PNNL. HIM imaging and NMR experiments were performed at the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the DOE Office of Science, Office of Biological and Environmental Research, located at Pacific Northwest National Laboratory (PNNL). PNNL is a multiprogram national laboratory operated for the DOE by Battelle Memorial Institute under contract # DE-AC05-76RL0-1830

alcohol dehydration↗
DOE OSTI2016

Improving Stability of Zeolites in Aqueous Phase via Selective Removal of Structural Defects

This work reports significant improvement in the hydrothermal stability of a well-characterized BEA zeolite via the selective removal of structural defects. Recent work suggests that the presence of silanol defects destabilizes the framework integrity of most zeolites and makes them susceptible to hydrolysis of the siloxy bonds by hot liquid water. The described approach allows for a key removal of silanols as shown with 29Si-MAS-NMR. Subsequently, the material stability in hot liquid water, measured by retention of its crystallinity with X-ray diffraction (XRD), is found to be superior to defective zeolites. In addition, N2-sorption measurements (BET) and transmission electron microscopy (TEM) show the formation of different types of mesoporosity for water-treated stabilized and unmodified materials. While the sorption capacity for untreated materials drops, related to re-precipitation of dissolved silica and pore blocking, the stabilized material retains its microporosity and improves its overall sorption capacity. The authors would like to thank B. W. Arey (PNNL) for HIM measurements and I. Arslan for TEM imaging. This work was supported by the U. S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. SP and MD acknowledge support by the Materials Synthesis and Simulation Across Scales (MS3 Initiative) conducted under Laboratory Directed Research & Development Program at PNNL.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2014

Persistent Ion Pairing in Aqueous Hydrochloric Acid

For strong acids, like hydrochloric acid, the complete dissociation into an excess proton and conjugated base as well as the formation of independent solvated charged fragments is assumed. The existence of a chloride-Hyronium (Cl-H3O+) contact ion pairs even in moderate concentration hydrochloric acid (2.5 m) demonstrates that the counter ions do not behave merely as spectators. Through the use of modern extended X-ray absorption fine structure (EXAFS) measurements in conjunction with state-of-the-art density functional theory (DFT) simulations, we are able to obtain an unprecedented view into the molecular structure of medium to high concentrated electrolytes. Here we report that the Cl-H3O+ contact ion pair structure persists throughout the entire concentration range studied and that these structures differ significantly from moieties studied in micro-solvated hydrochloric acid clusters. Characterizing distinct populations of these ion pairs gives rise to a novel molecular level description of how to think about the activity of the proton that impacts our picture of the pH scale. Funding for CJM, GKS, and JLF was provided by DOE Office of Science, Office of Basic Energy Science, Division of Chemical Sciences, Geosciences, and Biosciences. Funding for MDB was provided throught the Laboratory Directed Research and Development program at Pacific Northwest National Laboratory. MB was funded through Argonne National Laboratory.

Baer, Marcel D.↗
DOE OSTI2020

Analyzing Wildland Fire Smoke Emissions Data Using Compositional Data Techniques

By conservation of mass, the mass of wildland fuel that is pyrolyzed and combusted must equal the mass of smoke emissions, residual char and ash. For a given set of conditions, these amounts are fixed. This places a constraint on smoke emissions data which violates statistical assumptions for many of the methods currently used to analyze these data such as linear regression, analysis of variance, and t-tests. These data are inherently multivariate and non-negative parts of a whole. This paper introduces the field of compositional data analysis to the emissions community and provides examples of appropriate statistical treatment of emissions data. It is shown that modified combustion efficiency should not be used as a predictor variable for other smoke emissions because it is not an independent variable. An alternative method based on compositional linear trends to estimate trace gas composition using CO and CO2 is presented. The data used in this paper resulted from projects the DOD/DOE/EPA Strategic 586 Environmental Research and Development Program projects RC-1648 and 1649. The senior 587 author appreciates the guidance and R scripts provided by Prof. Girty at San Diego State 588 University to estimate linear trends by perturbation. J. P.-A. was supported by the Spanish 589 Ministry of Science, Innovation and Universities under the project CODAMET (RTI2018-590 095518-B-C21, 2019-2021). The data used in this study have been previously published and are 591 available in the original publications. DRW conceived the initial manuscript (70 percent) and 592 performed the bulk of the data analysis. JPA provided statistical guidance and compositional data 593 expertise and contributed 20 percent of the manuscript. TJJ and HJ were extensively involved in 594 the study that provided the data. TJJ provide smoke emissions expertise and HJ provided 595 combustion expertise. The authors declare that they have no conflict of interest. The use of trade 596 or firm names in this publication is for reader information and does not imply endorsement by 597 the U.S. Department of Agriculture of any product or service.

simplex, compositional data analysis, balance, log↗
DOE OSTI2018

Controlled synthesis of highly-branched plasmonic gold nanoparticles through peptoid engineering

Inspired by peptide- and protein-controlled formation of hierarchical inorganic nanostructures in nature, herein we report the design of sequence-defined peptoids for biomimetic synthesis of flower-like gold nanosuperstruc-tures. We demonstrate that the peptoid-induced morphosyn-thesis of gold nanoflowers is sequence-dependent. By varying the hydrophobicity, number of carboxylate and amino groups, and side-chain positions of peptoids, we develop a rule of thumb for designing peptoids that yield gold nanoflowers. Through a combination of hyperspectral UV-Vis absorption micro-spectroscopy (H-UVVIS-AMS) and three-photon photoemission electron microscopy (TP-PEEM), we measured the plasmonic properties of individual nanoflowers. Whereas H-UVVIS-AMS experiments revealed well-defined plasmon resonances centered at ~528 nm, TP-PEEM measurements showed an unprecedented plasmonic enhancement as high as 105 for a single nanoflower. A com-bination of the unique plasmonic property and the high sta-bility endows the peptoid-engineered nanoflowers with po-tential applications in chemical and biological imaging. FY, YC, HJ and C-LC acknowledge support by the Materials Synthesis and Simulation Across Scales (MS3) Initiative, through the Laboratory Directed Research & Development (LDRD) fund at Pacific Northwest National Laboratory (PNNL). FY was also partially supported by fellowships from Shandong Provincial Education Association for International Exchanges. YG was supported by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. PZE acknowledges support from the Laboratory Directed Research and Development Program through a Linus Pauling Fellowship at PNNL. PNNL is multi-program national laboratory operated for the Department of Energy by Battelle under Contracts No. DE-AC05-76RL01830. The authors are most grateful to Alan Joly and Wayne Hess (PNNL) for their support with the PEEM measurements and several useful discussions.

Yan, Feng↗
DOE OSTI2013

A Thermodynamic and Kenetic Study of the Heterolytic Activation of Hydrogen by Frustrated Borane-Amine Lewis Pairs

Calorimetry is used to measure the reaction enthalpies of hydrogen activation by 2,6-lutidine (Lut), 2,2,6,6-tetramethylpiperidine (TMP), N-methyl-2,2,6,6-tetramethylpiperidine (MeTMP) and tri-tert-butylphosphine (TBP) with tris(pentafluorophenyl)borane (BCF). At 6.6 bar H2 the conversion of the Lewis acid Lewis base pair to the corresponding ionic pair in bromobenzene at 294 K was quantitative in under 60 minutes. Integration of the heat release from the reaction of the Frustrated Lewis Pair (FLP) with hydrogen as a function of time yields a relative rate of hydrogenation in addition to the enthalpy of hydrogenation. The half-lives of hydrogenation range from 230 seconds with TMP, ΔHH2 = -31.5(0.2) kcal/mol, to 1400 seconds with Lut, ΔHH2 = -23.4(0.4) kcal/mol. The 11B NMR spectrum of B(C6F5)3 in bromobenzene exhibits three distinct traits depending on the sterics of the Lewis base; (i) in the presence of pyridine, only the dative bond adduct pyridine--B(C6F5)3 is observed, (ii) in the presence of TMP and MeTMP only the free B(C6F5)3 is observed, and (iii) in the presence of Lut both the free B(C6F5)3 and the Lut--B(C6F5)3 adduct appear in equilibrium. A measure of the change in Keq of Lut + B(C6F5)3 <->Lut--B(C6F5)3 as a function of temperature provides thermodynamic properties of the Lewis acid Lewis base adduct, ΔH = -17.9(1.0) kcal/mol and a ΔS = -49.2(2.5) cal/mol K, suggesting the Lut--B(C6F5)3 adduct is more stable in bromobenzene than in toluene. This research was supported by the U.S. Department of Energy’s Basic Energy Sciences, Division of Chemical Sciences, Biosciences and Geosciences. D.M.C. and A.K. acknowledges support by the Laboratory Directed Research and Development program at the Pacific Northwest National Laboratory (PNNL) to perform kinetic analyses of the calorimetry data. The work was performed in part at EMSL, a national scientific user facility sponsored by the DOE Office of Biological and Environmental Research. EMSL is located at Pacific Northwest National Laboratory (PNNL), which is operated by Battelle for DOE.

calorimetry↗
DOE OSTI2014

A Facile Approach Using MgCl2 to Formulate High Performance Mg2+ Electrolytes for Rechargeable Mg Batteries

Rechargeable Mg batteries have been regarded as a viable battery technology for grid scale energy storage and transportation applications. However, the limited performance of Mg2+ electrolytes has been a primary technical hurdle to develop high energy density rechargeable Mg batteries. In this study, MgCl2 is demonstrated as a non-nucleophilic and cheap Mg2+ source in combining with Al Lewis acids (AlCl3, AlPh3 and AlEtCl2) to formulate a series of Mg2+ electrolytes characteristic of high oxidation stability (up to 3.4 V vs Mg), sulfur compatibility and electrochemical reversibility (up to 100% coulombic efficiency). Three electrolyte systems (MgCl2-AlCl3, MgCl2-AlPh3, and MgCl2-AlEtCl2) were prepared free of purification and fully characterized by multinuclear NMR (27Al{1H} and 25Mg{1H}) spectroscopies, single crystal X-ray diffraction, and electrochemical analysis. The reaction mechanism of MgCl2 and the Al Lewis acids in THF is discussed to highlight the formation of the electrochemically active [(µ-Cl)3Mg2(THF)6]+ monocation in these electrolytes. We are grateful for the financial support from the Pacific Northwest National Laboratory (PNNL)-Laboratory Directed Research and Development (LDRD) program for developing magnesium battery technology. The XRD and SEM data were collected at the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at PNNL. PNNL is a multiprogram laboratory operated by Battelle Memorial Institute for the Department of Energy under Contract DE-AC05-76RL01830.

electrolytes↗
DOE OSTI2016

Modelling the local atomic structure of molybdenum in nuclear waste glasses with ab initio molecular dynamics simulations

The nature of chemical bonding of molybdenum in high level nuclear waste glasses has been elucidated by ab initio molecular dynamics simulations. Two compositions, (SiO2)57.5 – (B2O3)10 – (Na2O)15 – (CaO)15 – (MoO3)2.5 and (SiO2)57.3 – (B2O3)20 – (Na2O)6.8 – (Li2O)13.4 – (MoO3)2.5 , were considered in order to investigate the effect of ionic and covalent components on the glass structure and the formation of the crystallisation precursors (Na2MoO4 and CaMoO4). The coordination environments of Mo cations and the corresponding bond lengths calculated from our model are in excellent agreement with experimental observations. The analysis of the first coordination shell reveals two different types of molybdenum host matrix bonds in the lithium sodium borosilicate glass. Based on the structural data and the bond valence model, we demonstrate that the Mo cation can be found in a redox state and the molybdate tetrahedron can be connected with the borosilicate network in a way that inhibits the formation of crystalline molybdates. These results significantly extend our understanding of bonding in Mo-containing nuclear waste glasses and demonstrate that tailoring the glass composition to specific heavy metal constituents can facilitate incorporation of heavy metals at high concentrations. K.K. was supported through the Impact Studentship scheme at UCL co-funded by the IHI Corporation and UCL. P.V.S. thanks the Royal Society, which supported preliminary work on this project, and the Laboratory Directed Research and Development program at PNNL, a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy. Via our membership of the UK's HEC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202), this work used the ARCHER UK National Supercomputing Service (http://www.archer.ac.uk).

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