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DOE OSTI2024

A Titanium-Based Metal–Organic Framework For Tandem Metallaphotocatalysis

Metal–organic frameworks (MOFs) have garnered substantial attention for their unique properties, such as high porosity and tunable structures, making them versatile for various applications. This paper constructs photoactive titanium–organic frameworks by combining Ti(IV) clusters and a bipyridine linker. The MOF is synthesized in situ through imine condensation, resulting in NU-2300. Subsequent ex situ nickel salt complexation results in NU-2300-Ni, which is then used for light-mediated carbon–heteroatom cross-couplings. The photophysical properties of the metallaphotocatalyst were investigated by UV-vis and EPR analysis, and both the Ti cluster and the bipyridine linker were found to contribute to successful catalysis, making it a tandem catalyst. The heterogeneous material retained its performance through five cycles of thioetherification. As a result, this work contributes not only to MOF synthetic strategies, but also to expanding MOF applications as recyclable, tandem metallaphotocatalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Strong Coupling of Hydrodynamics and Reactions in Nuclear Statistical Equilibrium for Modeling Convection in Massive Stars

We build on the simplified spectral deferred corrections (SDC) coupling of hydrodynamics and reactions to handle the case of nuclear statistical equilibrium (NSE) and electron/positron captures/decays in the cores of massive stars. Our approach blends a traditional reaction network on the grid with a tabulated NSE state from a very large, ${\mathcal O }(100)$ nuclei network. We demonstrate how to achieve second-order accuracy in the simplified-SDC framework when coupling NSE to hydrodynamics, with the ability to evolve the star on the hydrodynamics time step. We discuss the application of this method to convection in massive stars leading up to core collapse. We also show how to initialize the initial convective state from a 1D model in a self-consistent fashion. All of these developments are done in the publicly available Castro simulation code and the entire simulation methodology is fully GPU-accelerated.

Explosive nucleosynthesis↗

DOE OSTI2025

Current understanding of Oxidative Coupling of Methane (OCM) reaction over supported Mn-Na 2 WO 4 catalysts

This perspective reviews the current understanding of the Oxidative Coupling of Methane (OCM) reaction over the supported Mn-Na 2 WO 4 /SiO 2 catalyst, with a focus on recent insights gained from state-of-the-art in-situ and operando spectroscopic characterization and chemical probe experiments under controlled environments. The supported Mn-Na 2 WO 4 /SiO 2 catalyst exhibits dynamic structural changes during the OCM reaction, involving multiple reactive lattice and adsorbed oxygen species, each associated with different oxide phases. These oxygen species play distinct roles in various steps of the OCM mechanism. The catalytic active sites for activation of CH 4 are associated with isolated surface Na-WO x sites on the SiO 2 support and the role of surface MnO x sites on SiO 2 is to oxidatively dehydrogenate C 2 H 6 to C 2 H 4 . Furthermore, this paper provides a detailed discussion of these roles and also introduces new experimental data from Temporal Analysis of Products (TAP) studies to clarify the ongoing debate in the literature regarding the contributions of lattice versus adsorbed oxygen species in OCM reaction product formation. Additionally, recommendations are offered for optimizing the performance of supported Mn-Na 2 WO 4 /SiO 2 catalysts to enhance CH 4 activation and C 2 product selectivity.

03 - NATURAL GAS↗

DOE OSTI2022

Molecular structure and catalytic promotional effect of Mn on supported Na 2 WO 4 /SiO 2 catalysts for oxidative coupling of methane (OCM) reaction

The structure and promotional effect of Mn in supported Mn-Na 2 WO 4 /SiO 2 catalysts for the oxidative coupling of methane (OCM) reaction has been debated for a longtime in the literature. In the current investigation, with the aid of multiple in-situ characterization studies, we show that the freshly calcined supported 1.2Mn-5Na 2 WO 4 /SiO 2 catalyst possesses crystalline Na 2 WO 4 , Mn 2 O 3 and SiO 2 (cristobalite phase) along with surface MnO x and Na-WO x sites at low temperature and oxidizing environments. Under the OCM reaction environment (T>800°C), the crystalline Na 2 WO 4 phase melts and Mn 2 O 3 phase reduces. In contrast, the surface MnO x and Na-WO x sites exhibit excellent thermal and chemical stability. Exposure of the 1.2Mn-5Na 2 WO 4 /SiO 2 catalyst to the OCM reaction environment redisperses the molten Na 2 WO 4 phase on the SiO 2 support to form new surface WO x sites. Interestingly, the stable MnO x species interacts with both molten Na 2 WO 4 phase and surface Na-WO x sites during OCM reaction. Controlled transient kinetic experiments in TAP and detailed steady state OCM fixed-bed reaction studies reveal the role and promotional effect of Mn in the 1.2Mn-5Na 2 WO 4 /SiO 2 catalyst. The W-oxides (both molten Na 2 WO 4 and surface Na-WO x sites) are the active sites for the catalytic OCM reaction and the MnO x species only function as promoters. The promotion of MnO x strongly depends on the gas phase O 2 partial pressure and the MnO x species act as mediators for oxygen exchange between the gas phase molecular O 2 and catalyst lattice oxygen. In conclusion, the temperature dependent MnO x promotion reveals that the MnO x species selectively promote the molten Na 2 WO 4 phase at lower reaction temperature and the surface Na-WO x sites at higher temperature.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Fermi’s Golden Rule Rate Expression for Transitions Due to Nonadiabatic Derivative Couplings in the Adiabatic Basis

Starting from a general molecular Hamiltonian expressed in the basis of adiabatic electronic and nuclear position states, where a compact and complete expression for the nonadiabatic derivative coupling (NDC) Hamiltonian term is obtained, we provide a general analysis of the Fermi’s golden rule (FGR) rate expression for nonadiabatic transitions between adiabatic states. We then consider a quasi-adiabatic approximation that uses crude adiabatic states and NDC couplings, both evaluated at the minimum potential energy configuration of the initial adiabatic state, for the definition of the zeroth and first-order terms of the Hamiltonian. Although the application of this approximation is rather limited, it allows deriving a general FGR rate expression without further approximation while accounting for non-Condon contribution to the FGR rate arising from momentum operators of NDC terms and its coupling with vibronic displacements. For a generic and widely used model where all nuclear degrees of freedom and environmental effects are represented as linearly coupled harmonic oscillators, we derive a closed-form FGR rate expression that requires only Fourier transform. The resulting rate expression includes quadratic contributions of NDC terms and their couplings to Franck–Condon modes, which require evaluation of two additional bath spectral densities in addition to the conventional one that appears in a typical FGR rate theory based on the Condon approximation. Model calculations for the case where nuclear vibrations consist of both a sharp high-frequency mode and an Ohmic bath spectral density illustrate new features and implications of the rate expression. We then apply our theoretical expression to the nonradiative decay from the first excited singlet state of azulene, which illustrates the utility and implications of our theoretical results.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Thermodynamic insight into AnO 2 + bonding from ThH + /UH + reactions studied by inductively coupled plasma tandem mass spectrometry

The bonding mechanisms of actinides have been a focus of fundamental research over the past few decades. In the present study, reactions of the simplest actinide-containing species, ThH + and UH + , with O 2 and CO 2 are investigated by inductively coupled plasma tandem mass spectrometry. The reactions of ThH + and UH + with O 2 are efficient, and the reactions of ThH + and UH + with CO 2 display reduced reaction efficiencies. For both reactions involving CO 2 , ThO 2 + and UO 2 + are observed; however, there is a clear barrier to ThO 2 + formation whereas UO 2 + forms through an exothermic, barrierless process. The experimental observations and available thermodynamic information are used to predict the outcomes of reactions involving the later AnH + . The anticipated reaction enthalpies for Pa–Am display a clear correlation with the promotion energy of An + to a 6d 2 electronic configuration, E p (6d 2 ), although a shift in the slope of the correlation of reaction enthalpies and E p (6d 2 ) suggests that there is likely a change in bonding mechanism that starts with Np + . Similar shifts have also been noted in previous studies. Beginning with Np + , the 6d orbitals become less accessible than they are for the earlier An + as measured by E p (6d 2 ), and this accessibility of the 6d orbitals may drive actinide bonding.

5f orbitals↗

DOE OSTI2023

MFiX: Fractional-Step Method Implementation

A comprehensive, multiphase computational fluid dynamics (CFD) simulation solves several coupled transport equations including continuity, momentum, species, and energy. Chemical reactions further couple these equations through heats of reaction and rates of formation of products and rates of destruction of reactants. A fractional-step method separates changes attributed to chemical reactions from transport phenomena like convection and diffusion. When the governing equations are split into the transport and reacting components, efficient and independent methodologies can be exploited to solve the different systems. Specifically, discretization of field variable transport equations results in large, sparse matrices which are loosely coupled. These systems are solved in succession using iterative techniques that take advantage of the matrix structure. In contrast, chemical reactions tightly couple field variables locally within the domain (e.g., within a single computational cell) resulting in low dimensional but dense, nonlinear systems that are better solved using direct integration techniques.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Vibration isolation for centrifuge testbeds

A method for isolating vibrations for centrifuge testing devices is provided. The method comprises coupling a test payload platform to a number of piezoelectric actuators and coupling the piezoelectric actuators to a reaction mass coupled to a centrifuge arm. A layer of vibration-absorbing material is sandwiched between the reaction mass and the centrifuge arm. The centrifuge arm is rotated around an axis, and the test payload platform is vibrated with the piezoelectric actuators as the centrifuge rotates, wherein the layer of vibration-absorbing material prevents vibrations from traveling down the centrifuge arm.

Siler, David Michael↗

DOE OSTI2024

Kinetic Analysis of Proton-Coupled Electron Transfer at an Electrode-Immobilized Complex

An alkyne-terminated cobalt complex, [Co(Cp)(dppe ≡H )(Cl)] + (Cp = cyclopentadienyl; dppe ≡H = 1,2-bis-(di-(4-ethynyl-phenyl)phosphino)ethane), (Co ≡H ) was immobilized onto a glassy carbon electrode using two attachment strategies: Cu(I) catalyzed azide–alkyne click chemistry and reductive electropolymerization. The modified electrodes prepared through reductive electropolymerization exhibit current densities and peak resolutions for the electrochemical reduction of the cobalt species, which are amenable to electroanalytical quantification of coupled chemical reactions. Through peak shift analysis of cyclic voltammograms recorded in the presence of 4-chloroanilinium tetrafluoroborate, we quantified the proton transfer rate constant for the stepwise proton-coupled electron transfer reaction that reduces the electrode-immobilized [Co(Cp)(dppe ≡H )(Cl)] + to [H–Co(Cp)(dppe ≡H )] + (k PT app = (9.3 ± 1.8) × 10 5 M –1 s –1 ). In conclusion, the extraction of kinetic parameters for an elementary proton-coupled electron transfer reaction of an electrode-immobilized complex represents the first experimental measurement of its type and lays crucial groundwork for kinetic analyses of hybrid catalyst–electrode architectures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Study of Self-Interaction Errors in Density Functional Calculations of Magnetic Exchange Coupling Constants Using Three Self-Interaction Correction Methods

We examine the role of self-interaction errors (SIE) removal on the evaluation of magnetic exchange coupling constants. In particular we analyze the effect of scaling down the self-interaction-correction (SIC) for three non-empirical density functional approximations (DFAs) namely, the local spin density approximation, the Perdew-Burke-Ernzerhof generalized gradient approximation, and recent SCAN family of meta-GGA functionals. To this end, we employ three one-electron SIC methods: Perdew-Zunger [Perdew, J. P.; Zunger, A. Phys. Rev. B, 1981, 23, 5048] SIC, the orbitalwise scaled SIC method [Vydrov, O. A. et al., J. Chem. Phys. 2006, 124, 094108], and the recent local scaling method [Zope, R. R. et al., J. Chem. Phys. 2019, 151, 214108]. We compute the magnetic exchange coupling constants using the spin projection and non projection approaches for sets of molecules composed of dinuclear and polynuclear H-He models, organic radical molecules, and chlorocuprate, and compare these results against accurate theories and experiment. Our results show that for the systems that mainly consist of single electron regions, PZSIC performs well but for more complex organic systems and the chlorcuprates, an overcorrecting tendency of PZSIC combined with the DFAs utilized in this work is more pronounced, and in such cases LSIC with kinetic energy density ratio performs better than PZSIC. Furthermore, analysis of the results in terms of SIC corrections to the density and to the total energy shows that both density and energy correction are required to obtain an improved prediction of magnetic exchange couplings.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Illuminating the Role of Alcohol Substrate in Nickel Photoredox Catalysis via Ground State and Transient Absorption Spectroscopy

Direct excitation of nickel photocatalysts has gained popularity over the last several years following the successful activation of nickel by Ir and Ru photosensitizers. The ability to pair these photosensitizers with Ni catalysts facilitates the formation of crucial chemical bonds under relatively mild conditions. However, there are still gaps in our understanding of what influences the performance of these Ni photocatalysts. Previous work from our group identified a nickel photocatalyst supported by a tridentate pyridinophane ligand that undergoes wavelength-dependent cross-coupling reactivity. Herein, we report detailed studies of the wavelength dependence of the C–O cross-coupling reactivity, illustrating that the catalytic activity has an optimal wavelength, and excitation on both the blue and red sides of this optimal wavelength leads to a reduction in product yield. We also reveal a crucial catalyst-alcohol preirradiation interaction that drastically alters the catalyst’s optical properties. Furthermore, we investigate both wavelength dependency and alcohol dependency via optical transient absorption spectroscopy and reveal a substrate binding process responsible for the observed wavelength-dependent cross-coupling catalysis.

alcohol↗

DOE OSTI2021

New Mechanistic and Reaction Pathway Insights for Oxidative Coupling of Methane (OCM) over Supported Na 2 WO 4 /SiO 2 Catalysts

Abstract The complex structure of the catalytic active phase, and surface‐gas reaction networks have hindered understanding of the oxidative coupling of methane (OCM) reaction mechanism by supported Na 2 WO 4 /SiO 2 catalysts. The present study demonstrates, with the aid of in situ Raman spectroscopy and chemical probe (H 2 ‐TPR, TAP and steady‐state kinetics) experiments, that the long speculated crystalline Na 2 WO 4 active phase is unstable and melts under OCM reaction conditions, partially transforming to thermally stable surface Na‐WO x sites. Kinetic analysis via temporal analysis of products (TAP) and steady‐state OCM reaction studies demonstrate that ( i ) surface Na‐WO x sites are responsible for selectively activating CH 4 to C 2 H x and over‐oxidizing CH y to CO and ( ii ) molten Na 2 WO 4 phase is mainly responsible for over‐oxidation of CH 4 to CO 2 and also assists in oxidative dehydrogenation of C 2 H 6 to C 2 H 4 . These new insights reveal the nature of catalytic active sites and resolve the OCM reaction mechanism over supported Na 2 WO 4 /SiO 2 catalysts.

Sourav, Sagar↗

DOE OSTI2021

New Mechanistic and Reaction Pathway Insights for Oxidative Coupling of Methane (OCM) over Supported Na 2 WO 4 /SiO 2 Catalysts

Sourav, Sagar↗

DOE OSTI2025

A compartmentalized model of multiphase chemical kinetics

There are significant challenges in predicting multiphase chemical kinetics due to the complex coupling of reaction and mass transport across a phase boundary (i.e., interface). Here, we describe a framework for predicting multiphase kinetics that embeds the elementary kinetic steps of reaction, solvation, and diffusion into a coarse grain spatial description of two phases. The model is constructed to bridge the short-timescale interfacial dynamics observed in molecular simulations with the longer timescales observed in kinetic experiments. A simple set of governing differential equations is derived, which, when solved numerically or analytically, yield accurate predictions of multiphase kinetics in microdroplets. Although the equations are formulated for gas-liquid reactions, the underlying conceptual framework is general and can be applied to transformations in other two-phase systems (solid-liquid, liquid-liquid, etc.).

Chemical kinetics and dynamics↗

DOE OSTI2023

Impact of Pycnonuclear Fusion Uncertainties on the Cooling of Accreting Neutron Star Crusts

Abstract The observation of X-rays during quiescence from transiently accreting neutron stars provides unique clues about the nature of dense matter. This, however, requires extensive modeling of the crusts and matching the results to observations. The pycnonuclear fusion reaction rates implemented in these models are theoretically calculated by extending phenomenological expressions and have large uncertainties spanning many orders of magnitude. We present the first sensitivity studies of these pycnonuclear fusion reactions in realistic network calculations. We also couple the reaction network with the thermal evolution code dStar to further study their impact on the neutron star cooling curves in quiescence. Varying the pycnonuclear fusion reaction rates alters the depth at which nuclear heat is deposited although the total heating remains constant. The enhancement of the pycnonuclear fusion reaction rates leads to an overall shallower deposition of nuclear heat. The impurity factors are also altered depending on the type of ashes deposited on the crust. These total changes correspond to a variation of up to 9 eV in the modeled cooling curves. While this is not sufficient to explain the shallow heat source, it is comparable to the observational uncertainties and can still be important for modeling the neutron star crust.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Unified description of the coupled-channels and statistical Hauser-Feshbach nuclear reaction theories for low energy neutron incident reactions

We incorporate the coupled-channels optical model into the statistical Hauser-Feshbach nuclear reaction theory, where the scattering matrix is diagonalized by performing the Engelbrecht-Weidenmüller transformation. This technique has been implemented in the coupled-channels optical model code ECIS by J. Raynal, and we extend this method so that all the open channels in a nucleon-induced reaction on a deformed nucleus can be calculated consistently.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2026

Mechanism of Catechol Oxidation by the Coupled Bicupric Active Site of Tyrosinase: Completion of the Oxygenase/Oxidase Reaction Cycle

Tyrosinase contains a coupled binuclear copper (CBC) active site, which in its bicuprous form (deoxy-Ty) binds O 2 to form a side-on peroxide [Cu(II) 2 O 2 ] 2+ intermediate (oxy-Ty) that performs the regioselective monooxygenation of monophenols to catechols and their subsequent 2e − oxidation to quinones. Previously, we used spectroscopic, kinetic, and computational methods to elucidate the mechanism of the initial steps in the monooxygenation reaction. Herein, we investigated the final step in catecholate formation and provide experimental and computational results elucidating the catechol oxidation reaction, formally a proton-coupled 2e − process. We employed single-turnover stoppedflow absorption to observe the elusive catecholate-Cu(II) 2 OH intermediate via the anaerobic reaction of resting Cu(II) 2 OH Ty (met-Ty) with the catecholate substrate. This intermediate was cryo-trapped and characterized by electron paramagnetic resonance and X-ray absorption spectroscopies. These experimental results were correlated to quantum mechanics/molecular mechanics (QM/MM) and QM calculations to describe the complete catalytic cycle of tyrosinase, revealing that the 2e − oxidation of catechol to quinone involves two steps: (i) coupled 1H + /1e − transfer from the bound monoanionic catecholate to the bridged hydroxide of the met-Ty active site, followed by (ii) the second 1e − transfer. The latter is calculated to be the rate-limiting step in catechol oxidation, confirmed by experimental solvent kinetic isotope effect studies. Our computational data suggest that quinone release from the protein provides the necessary driving force for this reaction. These results establish a detailed description of this oxidase cycle of the tyrosinase mechanism and more broadly provide molecular-level insights into the diverse reactivity of CBC sites in biology.

QM/MM modeling↗

DOE OSTI2022

A Multicomponent Reactive Transport Model for Integrated Surface‐Subsurface Hydrology Problems

Abstract Despite the widespread use of integrated hydrology models in a variety of applications, consideration of multicomponent reactive transport is still not common. The implementation of these processes requires coupling transport at the surface‐subsurface interface and efficient solution of the non‐linear geochemical model that is consistent with the integrated hydrology solution. The Advanced Terrestrial Simulator provides a flexible multiphysics framework that facilitated this process. In this work, the integrated reactive transport process kernel (PK) was weakly coupled to the integrated hydrology PK. In turn, integrated transport and reactions were coupled using an operator splitting approach. This splitting enabled an explicit solution of the integrated transport problem, including a novel algorithm to calculate exchange fluxes across the surface‐subsurface interface and a point‐by‐point solution of the geochemical problem. Geochemical capabilities were added using well‐established external codes, but rather than using a custom interface to each, a generic interface was used that clearly specifies the variables and operations used by the chemistry PK. The implementation is demonstrated with two example simulations: transport of a tracer in a soil column as it saturates over time and water ponds on the surface and reactive transport in a hillslope driven by successive wet‐dry cycles that result in infiltration, runoff and exfiltration processes.

54 ENVIRONMENTAL SCIENCES↗