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DOE OSTI2023

Active site identification and CO oxidation in UiO-66-XX thin films

Metal-organic frameworks (MOFs) offer an intrinsically porous and chemically tunable platform for gas adsorption, separation, and catalysis. Herein we investigate thin film derivatives of the well-studied Zr–O based MOF powders to understand their adsorption properties and reactivity with their adaption to thin films, involving diverse functionality with the incorporation of different linker groups and the inclusion of embedded metal nanoparticles: UiO-66, UiO-66-NH 2 , and Pt@UiO-66-NH 2 . Using transflectance IR spectroscopy, we determine the active sites in each film upon consideration of the acid-base properties of the adsorption sites and guest species, and perform metal-based catalysis with CO oxidation of a Pt@UiO-66-NH 2 film. Our study shows how surface science characterization techniques can be used to characterize the reactivity and the chemical and electronic structure of MOFs.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Reactions of Studtite UO 4 ·4H 2 O in Alkali Hydroxides: Isolation of Single-Crystal Uranate Phases under Mild Hydrothermal Conditions

Uranyl peroxide complexes, particularly studtite (UO 4 ·4H 2 O), are important phases within the nuclear fuel cycle, forming through radiolysis-induced reactions on the surfaces of spent fuel and in waste environments. Studtite has been identified in Hanford’s irradiated fuel storage basins, Chornobyl’s corium lavas, and is anticipated on Fukushima’s fuel debris. While its formation and stability have been extensively studied, the reactivity of UO 4 ·4H 2 O in highly alkaline environments such as those encountered in high-level nuclear waste remains underexplored. These environments contain molar concentrations of [OH - ] and present a chemically dynamic and reactive environment where actinide behavior is not well understood. Reported here are investigations of uranium reactions in concentrated alkali hydroxides under mild hydrothermal conditions (<200 °C) that have resulted in the isolation of the alkali metal uranates Li 2 UO 4 , α-Na 2 UO 4 , γ-Na 2 U 2 O 7 , and K 2 U 2 O 7 . In contrast to conventional solid-state methods (>800 °C) that typically yield polycrystalline powders, our approach enables the isolation of these uranates as single crystals, allowing us to provide single-crystal structure solutions of certain uranates for the first time. Our findings match the results of high-level waste tank sampling, confirming that sodium diuranate (Na 2 U 2 O 7 ) is the most persistent uranium phase, potentially forming through reactions of uranyl peroxide intermediates with NaOH under radiolytic and highly alkaline conditions.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗

DOE OSTI2023

Direct Evidence for Excited Ligand Field State-based Oxidative Photoredox Chemistry of a Cobalt(III) Polypyridyl Photosensitizer

Increasing interest in sustainable chemistry coupled with the quest to explore new reactivity has spurred research on first-row transition metal complexes for potential applications in a variety of settings. One of the more active areas of research is photoredox catalysis, where the synthetically tunable nature of their electronic structures provides a rich palette of options for tailoring their reactivity to a desired chemical transformation. Understanding the mechanism of excited-state reactivity is critical for the informed development of next-generation catalysts, which in turn requires information concerning the propensity of their electronic excited states to engage in the desired electron or energy transfer processes. Herein we provide direct evidence of the highly oxidizing nature of the lowest-energy ligand-field (LF) excited state of a first-row d 6 -low-spin Co(III) photosensitizer [Co(4,4'-Br 2 bpy) 3 ] 3+ (where 4,4'-Br 2 bpy is 4,4'-dibromo-2,2'-bipyridine). The redox potential associated with the LF excited state of the Co(III) complex was bracketed by performing bimolecular quenching studies by using a series of simple organic electron donors. Time-resolved absorption spectroscopy confirmed a dynamic quenching process attributed to reductive quenching of the lowest-energy ligand-field excited state of the Co(III) chromophore. Analysis of the Stern–Volmer plots for each chromophore-quencher pair revealed a limiting value of E red * ~ 1.25 V vs Fc/Fc + for the metal-centered excited state, which is significantly stronger than that of more commonly employed transition metal-based photoredox agents such as [Ru(bpy) 3 ] 2+ (E red * = 0.32 V vs Fc/Fc + ) and [Ir(ppy) 2 (bpy)] + (E red * = 0.27 V vs Fc/Fc + ). Finally, these results suggest that this class of chromophores could find utility in applications requiring the activation of oxidatively resistant organic substrates for photoredox catalysis.

14 SOLAR ENERGY↗

DOE OSTI2025

Improving Bond Dissociations of Reactive Machine Learning Potentials through Physics-Constrained Data Augmentation

In the field of computational chemistry, predicting bond dissociation energies (BDEs) presents well-known challenges, particularly due to the multireference character of reactive systems. Many chemical reactions involve configurations where single-reference methods fall short, as the electronic structure can significantly change during bond breaking. As generating training data for partially broken bonds is a challenging task, even state-of-the-art reactive machine learning interatomic potentials (MLIPs) often fail to predict reliable BDEs and smooth dissociation curves. By contrast, simple and inexpensive physics-based models, such as the well-established Morse potential, do not suffer from any such limitations. This work leverages the Morse potential to improve reactive MLIPs by augmenting the training data set with inexpensive Morse data along the dissociation pathways. Further, this physics-constrained data augmentation (PCDA) approach results in MLIPs with smooth bond dissociation curves as well as near coupled-cluster level BDEs, all without requiring any expensive multireference quantum mechanical calculations. A case study for methane combustion demonstrates how the PCDA approach can improve an existing reactive MLIP, namely, ANI-1xnr. In conclusion, not only are the BDEs and bond dissociation curves for all radicals and molecules significantly improved compared to ANI-1xnr but the PCDA-trained MLIP retains the reliability of ANI-1xnr when performing reactive molecular dynamics simulations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Development Of Thermodynamic and Kinetic Simulation Tools and Testing Procedures for Enhanced Durability of Concrete Containing Industrial By-Products

This project developed screening tools that enable evaluation of alternative cementitious binders that create concretes to significantly reduce energy and emissions while remaining cost competitive on both initial and long-term costs. The team began with the viewpoint that acceptance of new cementitious binder products has a substantially greater chance of successful implementation when capital investment is not excessive and the end product has customers that have experience and resources to use this. As such, a binder system that is based on portland cement with blended using industrial by-products (alternative cementitious materials) has the potential for dramatic and meaningful impact. The team has focused on developing implementable solutions in specifications and current practice. This however requires three main factors: 1) ability to screen byproducts and alternative materials for success, 2) ability to ‘treat’ materials chemically to enhance kinetics, and 3) ability to provide predictions of performance of both binders and concrete from first principles. The project developed/refined a state of the art and scientifically based screening test for SCM called the pozzolanic reactivity test. The team developed kinetic models to simulate these materials as well as experimental approaches to alter selected reactions. Simulation tools were developed that enable the performance of concrete to be predicted based on the chemistry and reactivity of the cement and alternative SCM. Specifically, this project: • enhanced the kinetic reactivity models for use in multi-scale computational programs that use thermodynamics to predict reaction products. 2 • developed scaling models to extend thermodynamic modeling to link these models with pore structure. This enables strength, transport property, and coupled transport prediction. • developed tools to predict performance of cementitious materials using the pozzolanic reactivity test and chemical composition. The predicted properties are consistent with AASHTO R101 and the CEB-FIP model code and can be measured using associated test procedures. • demonstrated mechanical and fracture based modeling tools that thermodynamic predictions and inputs to predict concrete service life. These results have been used to demonstrate the value of enabling specifications to include ASTM C 595 cement as well ASTM C150 cement. In addition, these products are being used to expedite the evaluation of alternative SCM to aide in determining which materials have potential value and what ‘compositions’ of blended cements merit further investment.

42 ENGINEERING↗

DOE OSTI2024

SPARC-X: Quantum simulations at extreme scale - reactive dynamics from first principles

We have developed the massively parallel electronic structure code SPARC-X: a computational framework for performing Kohn-Sham Density Functional Theory (DFT) calculations that can scale linearly with the number of atoms in the system, while being able to leverage petascale and emerging exascale parallel computers to study chemical phenomena at unprecedented length and time scales. SPARC-X exploits a recent breakthrough in electronic structure methodologies: systematically improvable, strictly local, orthonormal, discontinuous real-space bases that efficiently and systematically capture the local chemistry of the system. With further adaptation using new machine-learning techniques and the use of the massively parallel Spectral Quadrature (SQ) electronic structure method, the algorithmic complexity and prefactor associated with DFT calculations involving semilocal as well as hybrid functionals are dramatically reduced. Using petascale computational resources, SPARC-X enables quantum mechanical simulations at length and time scales previously accessible only by empirical approaches, e.g., 1,000,000 atoms for a few picoseconds using semilocal functionals or 1,000 atoms for a few picoseconds using hybrid functionals. Using exascale resources, the sizes and times targeted are two orders of magnitude larger. Such a capability has applications in a wide variety of chemical sciences, including reactive interfaces where large length- and/or long time-scales are needed and traditional force fields fail. This is particularly important in dynamic catalysis, where bond breaking and formation must be understood in detail. We developed, tested, and employed the SPARC-X framework to understand the photocatalytic properties of TiO 2 nanoparticles, revealing finite size effects that cannot be captured with standard model systems or functionals. This integrated development and application strategy ensures that SPARC-X remains a robust, efficient, and scalable software package for quantum simulations on current petascale and emerging exascale computing resources.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2021

The chemical and physical origin of incineration ash reactivity in cementitious systems

Incorporating industrial byproducts and waste in concrete is the key to reducing landfill usage as well as lowering the environmental footprint of cement industry. An emerging industrial byproduct which can partly replace cement is the Municipal Solid Waste Incinerator Ash (MSWI ash: residue that is left after incineration of municipal solid waste in a Waste-to-Energy facility). These ashes are predominantly calcium-rich; however, they also contain additional elements whose speciation is not known. These elements can significantly alter the hydration characteristics of a cementitious system. Here, our results suggest these ashes can accelerate as well as retard cement hydration. Specifically, Pb, Br, S, Ca, and Cl appear to accelerate cement hydration, whereas Cu, Fe, Al, Ti, Si, K, Zn, and Sr appear to retard cement hydration. Changes in hydration characteristics can have a strong bearing on the physical characteristics of cementitious systems incorporating incineration ashes. Thus, to selectively screen ashes that synergistically enhance the physical characteristics, we introduce a novel “Incineration Ash Coefficient (IAC),” which shows a strong correlation with the compressive strength (R 2 =0.79) of cement-ash binary mixtures.

42 ENGINEERING↗

DOE OSTI2025

Detecting Reactive Products in Carbon Capture Polymers with Chemical Shift Anisotropy and Machine Learning

Aminopolymers are attractive sorbents for CO 2 direct air capture applications due to their high density of amine groups, which can readily react with atmospheric levels of CO 2 to form chemisorbed species. The identity of these chemisorbed species and the functional groups that form upon oxidative degradation depends on both material properties and processing conditions, forming a variety of carbonyl-type sites such as ammonium carbamates, bicarbonates, carbonates, carbamic acids, ureas, and amides. 13 C solid-state nuclear magnetic resonance (NMR) is often used to help elucidate the identity of these reacted species, but it is challenging due to the narrow chemical shift range of carbonyl sites. Herein, we demonstrate the application of a two-dimensional (2D) chemical shift anisotropy (CSA) recoupling pulse sequence (ROCSA) to obtain CSA tensor values at each isotropic chemical shift, overcoming limitations of isotropic peak resolution. CSA tensor values describe the local chemical environment and can readily differentiate between the chemisorbed and degradation products. To aid identification, we also developed a k-nearest neighbor (kNN) classification model to distinguish the functional groups via their CSA tensor parameters. This methodology was demonstrated on poly(ethylenimine) in γ-Al 2 O 3 exposed to CO 2 and showed that the chemisorbed products are ammonium carbamate and a mixed carbamate–carbamic acid species. The sample was analyzed again after desorption at 100 °C inducing mild degradation, and the remaining products were strongly bound carbamate and urea species. In conclusion, the combination of 2D CSA measurements coupled with a kNN classification model enhances the ability to accurately identify chemisorbed or degradation products in complex carbon capture materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Characterizing Reactive Transport Behavior in a Three-Dimensional Discrete Fracture Network

While several studies have linked network and in-fracture scale properties to conservative transport behavior in subsurface fractured media, studies on reactive transport cases remain relatively underdeveloped. In this study, we explore the behavior of an irreversible kinetic reaction during the interaction of two solute plumes, one consisting of species A and the other species B. When the plumes converge, these species react kinetically to form a new species C via A+B→kC. This reactive system is studied using a three-dimensional discrete fracture network (DFN) model coupled with reactive Lagrangian particle tracking. We find that the interplay of network topology and chemical properties of the reactive solutes controls reactive transport processes. The network topology drives species A and B together, and the chemical properties dictate whether and how quickly a reaction occurs. Results demonstrate that reactions are most likely to occur in high-velocity fractures that make up the network backbone. The interplay between species’ chemical properties and transport is characterized by a non-dimensional Damköhler (Da) number. We show that the spatial distribution of reactions is sensitive to Da, which subsequently influences late-time tailing behavior in outlet breakthrough time distributions. The results of this study provide initial insights into how an irreversible reaction occurs during transport in a fracture network, using a methodology that can be applied to study reactive transport in a wide range of fractured media environments and contexts.

58 GEOSCIENCES↗

DOE OSTI2021

Simultaneously Blocking Chemical Crosstalk and Internal Short Circuit via Gel-Stretching Derived Nanoporous Non-Shrinkage Separator for Safe Lithium-Ion Batteries

The separator, an ionic permeable and electronic insulating membrane between cathode and anode, plays a crucial role in the electrochemical and safety performance of batteries. However, the commercial polyolefin separators not only suffer from inevitable thermal shrinkage at elevated temperature, but also fail to inhibit the hidden chemical crosstalk of reactive gases such as O 2 , leading to often reported thermal runaway (TR) and hence preventing large-scale implementation of high-energy-density lithium-ion batteries. Herein, a nanoporous non-shrinkage separator (GS-PI) was fabricated via a novel gel-stretching orientation approach to eliminate TR. In situ synchrotron small angle X-ray scattering during heating clearly showed that the as-prepared thin GS-PI separator exhibits superior mechanical tolerance at high temperature, thus effectively preventing internal short circuit. Meanwhile, the unique nanoporous structure design further blocks chemical crosstalk and the associated exothermic reactions. Accelerating Rate Calorimetry test revealed that the practical 1 Ah LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622)/graphite pouch cell using GS-PI nanoporous separator show a maximum temperature rise (dT/dt max ) of only 3.7 °C s -1 compared to 131.6 °C s -1 in the case of Al 2 O 3 @PE macroporous separator. Furthermore, despite the reduced pore size, the GS-PI separator demonstrates better cycling stability than conventional Al 2 O 3 @PE separator at high temperature without sacrificing specific capacity and rate capability.

25 ENERGY STORAGE↗

DOE OSTI2020

Steering the Methane Dry Reforming Reactivity of Ni/La 2 O 3 Catalysts by Controlled In Situ Decomposition of Doped La 2 NiO 4 Precursor Structures

The influence of A- and/or B-site doping of Ruddlesden-Popper perovskite materials on the crystal structure, stability, and dry reforming of methane (DRM) reactivity of specific A 2 BO 4 phases (A = La, Ba; B = Cu, Ni) has been evaluated by a combination of catalytic experiments, in situ X-ray diffraction, X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and aberration-corrected electron microscopy. At room temperature, B-site doping of La 2 NiO 4 with Cu stabilizes the orthorhombic structure ( Fmmm ) of the perovskite, while A-site doping with Ba yields a tetragonal space group ( I 4/ mmm ). We observed the orthorhombic-to-tetragonal transformation above 170 °C for La 2 Ni 0.9 Cu 0.1 O 4 and La 2 Ni 0.8 Cu 0.2 O 4 , slightly higher than for undoped La 2 NiO 4 . Loss of oxygen in interstitial sites of the tetragonal structure causes further structure transformations for all samples before decomposition in the temperature range of 400 °C-600 °C. Controlled in situ decomposition of the parent or A/B-site doped perovskite structures in a DRM mixture (CH 4 :CO 2 = 1:1) in all cases yields an active phase consisting of exsolved nanocrystalline metallic Ni particles in contact with hexagonal La 2 O 3 and a mixture of (oxy)carbonate phases (hexagonal and monoclinic La 2 O 2 CO 3 , BaCO 3 ). Differences in the catalytic activity evolve because of (i) the in situ formation of Ni-Cu alloy phases (in a composition of >7:1 = Ni:Cu) for La 2 Ni 0.9 Cu 0.1 O 4 , La 2 Ni 0.8 Cu 0.2 O 4 , and La 1.8 Ba 0.2 Ni 0.9 Cu 0.1 O 4 , (ii) the resulting Ni particle size and amount of exsolved Ni, and (iii) the inherently different reactivity of the present (oxy)carbonate species. Based on the onset temperature of catalytic DRM activity, the latter decreases in the order of La 2 Ni 0.9 Cu 0.1 O 4 ~ La 2 Ni 0.8 Cu 0.2 O 4 ≥ La 1.8 Ba 0.2 Ni 0.9 Cu 0.1 O 4 > La 2 NiO 4 > La 1.8 Ba 0.2 NiO 4 . Simple A-site doped La 1.8 Ba 0.2 NiO 4 is essentially DRM inactive. The Ni particle size can be efficiently influenced by introducing Ba into the A site of the respective Ruddlesden-Popper structures, allowing us to control the Ni particle size between 10 nm and 30 nm both for simple B-site and A-site doped structures. Hence, it is possible to steer both the extent of the metal-oxide-(oxy)carbonate interface and its chemical composition and reactivity. Counteracting the limitation of the larger Ni particle size, the activity can, however, be improved by additional Cu-doping on the B-site, enhancing the carbon reactivity. Exemplified for the La 2 NiO 4 based systems, we show how the delicate antagonistic balance of doping with Cu (rendering the La 2 NiO 4 structure less stable and suppressing coking by efficiently removing surface carbon) and Ba (rendering the La 2 NiO 4 structure more stable and forming unreactive surface or interfacial carbonates) can be used to tailor prospective DRM-active catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Applying the core-satellite species concept: Characteristics of rare and common riverine dissolved organic matter

Introduction: Dissolved organic matter (DOM) composition varies over space and time, with a multitude of factors driving the presence or absence of each compound found in the complex DOM mixture. Compounds ubiquitously present across a wide range of river systems (hereafter termed core compounds) may differ in chemical composition and reactivity from compounds present in only a few settings (hereafter termed satellite compounds). Here, we investigated the spatial patterns in DOM molecular formulae presence (occupancy) in surface water and sediments across 97 river corridors at a continental scale using the “Worldwide Hydrobiogeochemical Observation Network for Dynamic River Systems—WHONDRS” research consortium. Methods: We used a novel data-driven approach to identify core and satellite compounds and compared their molecular properties identified with Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Results: In this work, we found that core compounds clustered around intermediate hydrogen/carbon and oxygen/carbon ratios across both sediment and surface water samples, whereas the satellite compounds varied widely in their elemental composition. Within surface water samples, core compounds were dominated by lignin-like formulae, whereas protein-like formulae dominated the core pool in sediment samples. In contrast, satellite molecular formulae were more evenly distributed between compound classes in both sediment and water molecules. Core compounds found in both sediment and water exhibited lower molecular mass, lower oxidation state, and a higher degree of aromaticity, and were inferred to be more persistent than global satellite compounds. Higher putative biochemical transformations were found in core than satellite compounds, suggesting that the core pool was more processed. Discussion: The observed differences in chemical properties of core and satellite compounds point to potential differences in their sources and contribution to DOM processing in river corridors. Overall, our work points to the potential of data-driven approaches separating rare and common compounds to reduce some of the complexity inherent in studying riverine DOM.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2023

Electrolyte Reactivity on the MgV 2 O 4 Cathode Surface

Predictive understanding of the solvation-dependent reactivity and molecular interaction of electrolyte ions and solvent molecules on reactive electrodes has been a major challenge but is essential for addressing instabilities and surface passivation that occur at electrode-electrolyte interface (EEI) of multivalent Mg batteries. In this work, the isolated intrinsic reactivities of prominent chemical species present in magnesium bis(trifluoromethanesulfonimide) (Mg(TFSI) 2 ) in diglyme (G2) electrolytes, including ionic (TFSI - , [Mg(TFSI)] + , [Mg(TFSI):G2] + , [Mg(TFSI):2G2] + ) as well as neutral molecules (G2) on magnesium vanadate cathode (MgV 2 O 4 ) surface has been studied using a combination of first-principles calculations and multimodal analysis of well-defined cathode electrolyte interphase (CEI) layers. Here, our calculations show that non-solvated [Mg(TFSI)] + is the strongest adsorbing species on the MgV 2 O 4 surface compared to all other ions while fully solvated [Mg(TFSI):2G2] + are least favorable to decomposition. The cleavage of C-S bonds in TFSI - to form CF 3 - is predicted to be most desired pathway for all ionic species, which is followed by the cleavage of C-O bonds of G2 to yield CH 3 + or OCH 3 - species. The strong stabilization and electron transfer between ionic electrolyte species and MgV 2 O 4 is found to significantly favor these decomposition reactions on the surface compared to intrinsic gas phase dissociation. Experimentally, we used state-of-the-art ion soft landing to selectively deposit mass-selected TFSI - , [Mg(TFSI):G2] + and [Mg(TFSI):2G2] + on MgV 2 O 4 thin film to form well-defined electrolyte-MgV 2 O 4 interface. Analysis of soft-landed interphase using X-ray photoelectron, X-ray absorption near edge structure, electron energy-loss spectroscopies as well as transmission electron microscopy confirmed the presence of decomposition species (e.g., MgFx, carbonates) formed in the interfacial region and the higher amount of MgFx with [Mg(TFSI):G2] + , which corroborates the theoretical observation. Overall, we established the mechanistic pathway for the electrolyte-induced formation of passivating fluorides on MgV 2 O 4 cathode facilitated by the surface adsorption and charge transfer, which provided essential knowledge for rational design of stable electrolytes for multivalent cathodes.

Cathode-electrolyte interphase formation↗

DOE OSTI2024

Friends or Foes: Fundamental Principles of Th-Organic Scaffold Chemistry Using Zr-Analogs as a Guide

The fundamental interest in actinide chemistry, particularly for the development of thorium-based materials, is experiencing a renaissance owing to the recent and rapidly growing attention to fuel cycle reactors, radiological daughters for nuclear medicine, and efficient nuclear stockpile development. Herein, we uncover fundamental principles of thorium chemistry on the example of Th-based extended structures such as metal–organic frameworks in comparison with the discrete systems and zirconium extended analogs, demonstrating remarkable over two-and-half-year chemical stability of Th-based frameworks as a function of metal node connectivity, amount of defects, and conformational linker rigidity through comprehensive spectroscopic and crystallographic analysis as well as theoretical modeling. Despite exceptional chemical stability, we report the first example of studies focusing on the reactivity of the most chemically stable Th-based frameworks in comparison with the discrete Th-based systems such as metal–organic complexes and a cage, contrasting multicycle recyclability and selectivity (>97%) of the extended structures in comparison with the molecular compounds. Altogether, the presented work not only establishes the conceptual foundation for evaluating the capabilities of Th-based materials but also represents a milestone for their multifaceted future and foreshadows their potential to shape the next era of actinide chemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Abstraction of Hydride from Alkanes and Dihydrogen by the Perfluorotrityl Cation

Abstract Lewis acids play a central role in a large variety of chemical transformations. The reactivity of the strongest Lewis acids is typically studied in the context of affinity towards hard bases, such as fluoride or oxygenous species. Carbocations can be viewed as soft Lewis acids, possessing significant affinity for softer bases, such as hydride. This work presents the ambient‐temperature isolation of salts of the perfluorotrityl cation ((C 6 F 5 ) 3 C + or F 15 Tr + ) in combination with halogenated carborane anions. The F 15 Tr + cation exhibits remarkable hydride affinity, illustrated by the observation of hydride abstraction from dihydrogen, and of the rapid abstraction of hydride from −CH 2 −groups in alkanes. Theoretical studies support the favorability of hydride abstraction from dihydrogen, and indicate that the hydride abstraction from alkanes proceeds via a concerted hydride transfer process that is sensitive to steric effects.

Leong, Derek W. [Department of Chemistry Texas A&a↗

DOE OSTI2025

Abstraction of Hydride from Alkanes and Dihydrogen by the Perfluorotrityl Cation

Leong, Derek W. [Department of Chemistry Texas A&a↗

DOE OSTI2023

Tracing the transient reaction kinetics of adsorbed species by in situ/operando infrared spectroscopy

The dynamic reaction behavior (i.e., transient responses) of IR-observable adsorbed species and gaseous products obtained from transient kinetic studies provide valuable kinetic and mechanistic information, namely: the abundance of active intermediates and their reactivity distribution, the chemical structure of IR-observable active and spectator species, the sequence of their formation, and the kinetically significant and rate-determining step under reaction conditions of practical catalysis. We discuss the use of transient response data to elucidate the reaction mechanisms of several gas-solid reactions: CO/H 2 , CO/H 2 /C 2 H 4 , photocatalytic oxidation of ethanol, and the CO 2 -amine reaction. The IR coupled with transient kinetic techniques is especially useful for investigating the mechanisms of photocatalytic reactions because both photogenerated electrons and many adsorbed species are IR-active (exhibiting measurable IR bands), and their evolution occurs on a time scale of seconds at ambient temperature. We highlight the key features and limitations of in situ IR with transient kinetics, as well as their significance in catalyst design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Surface evolution of synthetic bilgewater emulsion

Bilgewater is oil-in-water emulsion emitted from shipboard and it is a source of pollution to the ocean. Wastewater treatment needs fundamental knowledge of the bilgewater surface changes; however, limited information is available. We have reported the first surface characterization of synthetic bilgewater emulsion using time-of-flight secondary ion mass spectrometry (ToF-SIMS) coupled with optical microscopy. A NAVY synthetic bilgewater emulsion consisting of three oils and a detergent mixture is used as the synthetic bilgewater model. Both fresh and aged emulsion samples are analyzed to determine their droplet size distributions (DSDs) and surface chemical compositions. Our results show that fresh emulsions are largely mono-modal with hydrocarbon fragments as the main surface composition. Aged emulsions are also monomodal with slightly larger size. Both SIMS spectral comparison and Principal Component Analysis (PCA) show that some surfactant components appear on the fresh emulsion surface immediately while larger molecular weight components appear at the aged bilge droplet surface. Our results indicate that the oil-water interface evolves after emulsion droplet forms. More importantly, surface evolution not only changes the bilgewater DSD but also surface chemical composition and reactivity.

bilgewater, droplet size distribution, ToF-SIMS, s↗