Theoretical Study of the Thermodynamics and Kinetics of Hydrogen Abstractions from Hydrocarbons

Vandeputte, Aäron G.; Sabbe, Maarten; Reyniers, Marie‐Françoise; Speybroeck, Véronique Van; Waroquier, Michel; Marin, Guy

doi:10.1021/jp075132u

Cited by 139 publications

(139 citation statements)

References 55 publications

(98 reference statements)

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“…They successfully applied purely computational methods, for the first time, to correlate the computed and experimental GWPs of methyl fluoride species. The thermodynamics and kinetics of five hydrogen abstraction reactions from hydrocarbons were studied, and in this benchmark research, two composite methods (CBS-QB3 and G3B3) and two DFT methods, MPW1PW91/6-311G(2d,d,p) and BMK/6-311G(2d,d,p), were explored [204]. All four methods were successful in describing the thermochemical properties such as enthalpy change, entropy change, and barrier of the reactions.…”

Section: Global Warming Potentialmentioning

confidence: 99%

Assessment of theoretical methods for the study of hydrogen abstraction kinetics of global warming gas species during their degradation and byproduct formation (IUPAC Technical Report)

Ramasami

Abdallah

Archibong

et al. 2013

Pure and Applied Chemistry

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Global climate change is a major concern as it leads to an increase in the average temperature of the earth's atmosphere. The existence and persistence of some gaseous species in the atmosphere contribute to global warming. Experimental techniques are used to study the kinetics and degradation of global warming gases. However, quantum mechanical methods are also useful for the kinetic and radiative forcing study of global warming species and can precede experimental investigations. Research has also been targeted to develop more adapted procedures using ab initio and density functional theory (DFT) methods. This report provides a global perspective, in simplified manner, of the theoretical studies of the degradation of gas species in the atmosphere with an emphasis on the hydrogen abstraction kinetics of global warming gas species during their degradation and byproduct formation. En route, the results obtained from these studies are analysed and compared with experimental data where available. Our analyses indicate that the theoretical predictions are in agreement with experimental findings but the predicted parameters are dependent on the method being used. Theoretical methods are used to predict the thermodynamic parameters of reactions, and, with relevance to this report, the global warming potential (GWP) index can also be calculated. This report can be useful for future investigations involving global warming gaseous species while providing suggestions on how computations can fill in data gaps when experimental data are unavailable.

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Section: Global Warming Potentialmentioning

confidence: 99%

Assessment of theoretical methods for the study of hydrogen abstraction kinetics of global warming gas species during their degradation and byproduct formation (IUPAC Technical Report)

Ramasami

Abdallah

Archibong

et al. 2013

Pure and Applied Chemistry

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“…[55] Quantum tunneling coefficients, κ(T), are calculated using the Eckart tunneling scheme, [58] as this tunneling method has already proven its reliability for radical reactions. [59][60][61] Partition functions q are calculated using statistical thermodynamics based on the CBS-QB3 built-in B3LYP/6-311G(d,p) frequency calculation using a default scaling factor of 0.99. The partition functions are evaluated using the rigid rotor and harmonic oscillator (HO) approximation assuming separability of translational, external rotational, rovibrational and electronic contributions.…”

Section: Rate Coefficientsmentioning

confidence: 99%

“…As a measure for the deviation the factor of deviation, ρ, as applied in previous studies, [29,61,62] is defined as follows:…”

Section: Rate Coefficientsmentioning

confidence: 99%

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Hydrogen Radical Additions to Unsaturated Hydrocarbons and the Reverse β‐Scission Reactions: Modeling of Activation Energies and Pre‐Exponential Factors

et al. 2010

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The group additivity method for Arrhenius parameters is applied to hydrogen addition to alkenes and alkynes and the reverse β-scission reactions, an important reaction family in thermal processes based on radical chemistry. A consistent set of group additive values for 33 groups is derived to calculate the activation energy and preexponential factor for a broad range of H-addition reactions. The group additive values are determined from CBS-QB3 ab initio calculated rate coefficients. A mean factor of deviation between the CBS-QB3 and the experimental rate coefficients for 7 reactions of only 2 in the range 300-1000 K is found. Tunneling coefficients for these reactions were found to be significant below 400 K and a correlation accounting for tunneling is presented. Application of the obtained group additive values to predict the kinetics for a set of 11 additions and β scissions yields rate coefficients within a factor 3.5 from the CBS-QB3 results except for 2 β scissions with severe steric effects. The mean factor of deviation with experimental rate coefficients is 2.0, showing that the group additive method with tunneling corrections can accurately predict the kinetics, at least as accurate as the most commonly used density functional methods. The constructed group additive model can hence be applied to predict the kinetics of hydrogen radical additions to a broad range of unsaturated compounds. IntroductionThe addition of hydrogen radicals to alkenes and its reverse β scission, are important elementary steps in radical processes such as polymerization, pyrolysis, steam cracking, partial oxidation and combustion.[1] Therefore, the reaction family of hydrogen addition/β scission forms an indispensable part of any radical reaction network.A reliable reactor optimization requires an accurate kinetic model based on elementary reactions. For radical chemistry, on which many of the world largest scale chemical processes are based, the reactive nature of the radical intermediates results in huge reaction networks typically involving hundreds of species and thousands of elementary reactions. [2][3][4] Currently, most elementary reaction networks are automatically generated using advanced algorithms for the selection of the relevant reactions. [5][6][7][8][9][10][11] Sensitivity studies on these reaction networks point out that the main part of the uncertainty on the product yields stems from inaccurate knowledge of kinetic data. [12,13] Therefore, accurate kinetic data are essential to obtain reliable process simulations. Moreover, if rate-based network construction algorithms are applied, [14] accurate rate data are even more important as inaccuracies can result in the construction of an incomplete network that is not capable of grasping the underlying chemistry of the process.A quantitative description of radical processes thus requires that rate parameters be known for all of the different reactions comprising the reaction network. However, it is very difficult to measure kinetic parameters for individual radical r...

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“…15,16 Outras propriedades muito estudadas são as afinidades por próton [17][18][19][20][21][22][23] e por elétron, [24][25][26][27] a acidez, 28 bem como a identificação da estrutura mais estável para um determinado isômero. 29,30 Compostos inorgânicos também podem ser explorados utilizando métodos compostos pelo cálculo do potencial de redução 31 em reações de óxido-redução.…”

Section: Introductionunclassified

Comparação entre métodos compostos no cálculo de afinidades por próton e elétron em sistemas moleculares

Lima

Morgon

2010

Quím. Nova

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. The CBS-4M, CBS-QB3, G2, G2(MP2), G3 and G3(MP2) model chemistry methods have been used to calculate proton and electron affinities for a set of molecular and atomic systems. Agreement with the experimental value for these electronic properties is quite good considering the uncertainty in the experimental data. A comparison among the six theories using statistical analysis (average value, standard deviation and root-mean-square) showed a better performance of CBS-QB3 to obtain these properties.Keywords: composite methods; CBS-QB3 method; proton and electron affinities. INTRODUÇÃOA partir da década de 1980 começaram a surgir métodos para obter a energia eletrônica de sistemas moleculares, utilizando cálculos teóricos em diferentes níveis de teoria e com conjuntos de funções de base específicos para cada um desses níveis. Estes métodos ficaram conhecidos como métodos compostos. A principal idéia por trás destes métodos é obter a energia eletrônica na geometria de equilíbrio de forma aditiva, ou seja, calculada pela soma das contribuições de cada etapa do cálculo.Existem diversos métodos computacionais, sendo os mais utilizados aqueles que derivam da teoria Gaussian desenvolvidos por Pople e colaboradores 1-4 e da teoria do Conjunto de Base Completo desenvolvidos por Petersson e colaboradores. 5,6Usando a energia do sistema é possível obter propriedades termodinâmicas como a entalpia e a energia livre de Gibbs. Assim, através da variação da entalpia de uma reação é possível o cálculo de propriedades como afinidade por próton e por elétron. Além disso, podem ser obtidas propriedades eletrônicas e estruturais de cálculos teóricos como densidade de carga, comprimento e ângulo de ligação.Os métodos compostos podem ser utilizados, por exemplo, na determinação de mecanismos de reações utilizando as propriedades termodinâmicas no cálculo da energia de ativação e de constantes de velocidade, 7-14 úteis em pesquisas que examinam em detalhes o mecanismo através do cálculo de constantes de velocidade para cada etapa da reação. 15,16 Outras propriedades muito estudadas são as afinidades por próton 17-23 e por elétron, 24-27 a acidez, 28 bem como a identificação da estrutura mais estável para um determinado isômero. 29,30 Compostos inorgânicos também podem ser explorados utilizando métodos compostos pelo cálculo do potencial de redução 31 em reações de óxido-redução.No trabalho de um químico, informações a respeito de entalpia de formação e energia de dissociação são muito importantes, existindo diversos estudos neste campo, onde os métodos compostos são amplamente utilizados.32-44 Outra aplicação interessante é no estudo do mecanismo em processos envolvidos em espectroscopia de massas. 45A variedade de aplicações utilizando métodos compostos vem aumentando tanto em trabalhos teóricos como em trabalhos experimentais, devido à sua praticidade, confiabilidade e precisão em prever parâmetros físico-químicos. Este trabalho avaliou alguns métodos compostos considerando-se a capacidade de reprodução de parâmetros experimentais e o ...

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Theoretical Study of the Thermodynamics and Kinetics of Hydrogen Abstractions from Hydrocarbons

Cited by 139 publications

References 55 publications

Assessment of theoretical methods for the study of hydrogen abstraction kinetics of global warming gas species during their degradation and byproduct formation (IUPAC Technical Report)

Assessment of theoretical methods for the study of hydrogen abstraction kinetics of global warming gas species during their degradation and byproduct formation (IUPAC Technical Report)

Hydrogen Radical Additions to Unsaturated Hydrocarbons and the Reverse β‐Scission Reactions: Modeling of Activation Energies and Pre‐Exponential Factors

Comparação entre métodos compostos no cálculo de afinidades por próton e elétron em sistemas moleculares

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