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Goldsmith, C. Franklin

Publications and source records attributed to Goldsmith, C. Franklin.

15 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Unifying thermochemistry concepts in computational heterogeneous catalysis

Thermophysical properties of adsorbates and gas-phase species define the free energy landscape of heterogeneously catalyzed processes and are pivotal for an atomistic understanding of the catalyst performance. These thermophysical properties, such as the free energy or the enthalpy, are typically derived from density functional theory (DFT) calculations. Enthalpies are species-interdependent properties that are only meaningful when referenced to other species. The widespread use of DFT has led to a proliferation of new energetic data in the literature and databases. However, there is a lack of consistency in how DFT data is referenced and how the associated enthalpies or free energies are stored and reported, leading to challenges in reproducing or utilizing the results of prior work. Additionally, DFT suffers from exchange–correlation errors that often require corrections to align the data with other global thermochemical networks, which are not always clearly documented or explained. In this review, we introduce a set of consistent terminology and definitions, review existing approaches, and unify the techniques using the framework of linear algebra. This set of terminology and tools facilitates the correction and alignment of energies between different data formats and sources, promoting the sharing and reuse of ab initio data. Standardization of thermochemistry concepts in computational heterogeneous catalysis reduces computational cost and enhances fundamental understanding of catalytic processes, which will accelerate the computational design of optimally performing catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Automatisierte Generierung von Mikrokinetiken für heterogen katalysierte Reaktionen unter Berücksichtigung korrelierter Unsicherheiten**

Abstract Die Studie stellt eine ab initio basierte Methode für die automatische Konstruktion von detaillierten Mikrokinetiken vor, welche korrelierte Unsicherheiten in allen energetischen Parametern und Schätzroutinen berücksichtigt. Hierfür wurden innerhalb des Unsicherheitsraums des BEEF‐vdW Funktionals 2000 Mikrokinetiken für die Oxidationsreaktionen repräsentativer Abgasemissionen von stöchiometrischen Verbrennungsmotoren auf Pt(111) generiert und durch Multiskalenmodellierung mit Experimenten verglichen. Das Ensemble der Simulationsergebnisse unterstreicht die Bedeutung der Berücksichtigung von Unsicherheiten. Innerhalb dieses Ensembles ist es möglich, eine Mikrokinetik zu identifizieren, welche mit den experimentellen Daten übereinstimmt. Diese Mikrokinetik lässt sich auf ein einziges Austausch‐Korrelations‐Funktional zurückführen und legt nahe, dass Pt(111) das aktive Zentrum für die Oxidation leichter Kohlenwasserstoffe sein könnte. Die Studie bietet einen universellen Rahmen für die automatisierte Konstruktion von Reaktionsmechanismen unter Berücksichtigung korrelierter Unsicherheiten und ermöglicht eine DFT‐basierte Optimierung der Mikrokinetik auch für andere heterogen katalysierte Systeme.

Kreitz, Bjarne↗
DOE OSTI2023

Automated Generation of Microkinetics for Heterogeneously Catalyzed Reactions Considering Correlated Uncertainties**

Abstract The study presents an ab‐initio based framework for the automated construction of microkinetic mechanisms considering correlated uncertainties in all energetic parameters and estimation routines. 2000 unique microkinetic models were generated within the uncertainty space of the BEEF‐vdW functional for the oxidation reactions of representative exhaust gas emissions from stoichiometric combustion engines over Pt(111) and compared to experiments through multiscale modeling. The ensemble of simulations stresses the importance of considering uncertainties. Within this set of first‐principles‐based models, it is possible to identify a microkinetic mechanism that agrees with experimental data. This mechanism can be traced back to a single exchange‐correlation functional, and it suggests that Pt(111) could be the active site for the oxidation of light hydrocarbons. The study provides a universal framework for the automated construction of reaction mechanisms with correlated uncertainty quantification, enabling a DFT‐constrained microkinetic model optimization for other heterogeneously catalyzed systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Theory-Based Mechanism for Fluoromethane Combustion I: Thermochemistry and Abstraction Reactions

A new detailed chemical kinetic mechanism is presented for small fluorinated hydrocarbons. Ab initio electronic structure theory is used to provide heats of formation with subchemical accuracy. The ANL0 method is extended to include fluorine. The resulting heats of formation at 0 K are in excellent agreement with 36 benchmark species in the Active Thermochemical Tables, with a mean error of μ = –0.02 kJ/mol and a standard deviation of σ = 0.91 kJ/mol. The thermophysical properties for 92 small-molecule H/C/O/F species are computed. The rate coefficients for 40+ H-abstraction reactions involving H, O, F, OH, OF, HO 2 , and various methyl radicals with CH 4 , CH 3 F, CH 2 F 2 , CHF 3 , CH 2 O, and CHFO are discussed. Here, the computed rate constants are in excellent agreement with the available literature. Additionally, 30+ rate constants are provided for F abstraction, which are several orders of magnitude smaller than H abstraction. The thermophysical properties and rate constants are provided in a mechanism. This mechanism is the first in a series of theory-based investigations into the thermal destruction of per- and polyfluorinated species.

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

Configuration Space Integration for Adsorbate Partition Functions: The Effect of Anharmonicity on the Thermophysical Properties of CO–Pt(111) and CH 3 OH–Cu(111)

A method for computing anharmonic thermophysical properties for adsorbates on metal surfaces has been extended to include libration, or frustrated rotation. Classical phase space integration is used with Monte Carlo sampling of the configuration space to obtain the partition function of CO on Pt(111) and CH 3 OH on Cu(111). A minima-preserving neural network potential energy surrogate is used within the integration routines. Direct state counting using discrete variable representation is used to benchmark the results. We find that the phase space integration approach is in excellent agreement with the direct state counting results. Comparison with standard models such as the harmonic oscillator indicates that anharmonicity contributes significantly to the thermodynamic properties of CH 3 OH on Cu(111). We find that there is also a considerable difference between the harmonic oscillator and phase space integration for CO on Pt(111), although the discrepancy can largely be attributed to the presence of multiple binding sites within the unit cell. We demonstrate that a multisite harmonic oscillator model might be sufficient for CO-Pt(111). A more thorough description of the potential energy surface, which can be achieved with phase space integration, is necessary for weakly bound adsorbates such as CH 3 OH. In conclusion, the thermophysical properties were used to calculate free energies of adsorption on the respective metals, and subsequently the equilibrium constants and Langmuir isotherms in relevant temperature ranges. The results show that the choice of model to obtain partition functions greatly affects the resulting surface coverages in kinetic models.

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

Microkinetic Modeling of the Transient CO 2 Methanation with DFT–Based Uncertainties in a Berty Reactor

The transient operation of methanation reactors can become desirable when coupled with fluctuating renewable energies in Power-to-Gas scenarios, which requires suitable kinetic approaches that can describe the transient catalytic phenomena. A combined experimental and theoretical investigation of the transient CO 2 methanation is conducted using concentration forcing to derive a suitable microkinetic model. Methanation experiments are performed with a Ni/SiO 2 catalyst in a Berty-type reactor at industrially relevant conditions. The microkinetics are based on previous work and were automatically constructed for the Ni(111) facet using the Reaction Mechanism Generator. A feasible set of energetic parameters of the microkinetic models was identified in a theory-constrained optimization procedure within the DFT uncertainty space that can accurately reproduce the experimental results on a first-principles basis. The microkinetic model unravels that the formation of H 2 O* and CH 3 * control the activity and selectivity of Ni(111) under the investigated conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2007

Pressure and Temperature Dependence of the Reaction of Vinyl Radical with Ethylene

This work reports measurements of absolute rate coefficients and Rice-Ramsperger-Kassel-Marcus (RRKM) master equation simulations of the C2H3 + C2H4 reaction. Direct kinetic studies were performed over a temperature range of 300-700 K and pressures of 20 and 133 mbar. Vinyl radicals (H2C=CH) were generated by laser photolysis of vinyl iodide (C2H31) at 266 nm, and time-resolved absorption spectroscopy was used to probe vinyl radicals through absorption at 423.2 nm. Measurements at 20 mbar are in good agreement with previous determinations at higher temperature. A weighted three-parameter Arrhenius fit to the experimental rate constant at 133 mbar, with the temperature exponent fixed, gives k = (7 +/- 1) x 10(exp -l4) cu cm/molecule/s (T/298 K)(exp 2) exp[-(1430 +/- 70) K/T]. RRKM master equation simulations, based on G3 calculations of stationary points on the C4H7 potential energy surface, were carried out to predict rate coefficients and product branching fractions. The predicted branching to 1-methylallyl product is relatively small under the conditions of the present experiments but increases as the pressure is lowered. Analysis of end products of 248 nm photolysis of vinyl iodide/ethylene mixtures at total pressures between 27 and 933 mbar provides no direct evidence for participation of I -methylallyl.

Ismail, Huzeifa↗