scholarly journals Kinetic modelling of hydrogen transfer deoxygenation of a prototypical fatty acid over a bimetallic Pd60Cu40 catalyst: an investigation of the surface reaction mechanism and rate limiting step

2020 ◽  
Vol 5 (9) ◽  
pp. 1682-1693
Author(s):  
Kin Wai Cheah ◽  
Suzana Yusup ◽  
Martin J. Taylor ◽  
Bing Shen How ◽  
Amin Osatiashtiani ◽  
...  
Keyword(s):  
Oleic Acid ◽  
Reaction Mechanism ◽  
Hydrogen Transfer ◽  
Surface Reaction ◽  
Kinetic Modelling ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Cu Catalyst ◽  
P Application ◽  
Rate Limiting

Application of tetralin as a source of hydrogen for catalytic conversion of oleic acid to diesel-like hydrocarbons using a bimetallic Pd–Cu catalyst.

scholarly journals Understanding the reaction mechanism of Kolbe electrolysis on Pt anodes

2021 ◽  
Author(s):  
Sihang Liu ◽  
Nitish Govindarajan ◽  
Hector Prats ◽  
Karen Chan
Keyword(s):  
Reaction Mechanism ◽  
Potential Range ◽  
Microkinetic Model ◽  
Rate Determining Step ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Tafel Slopes ◽  
Kolbe Electrolysis ◽  
Kolbe Reaction ◽  
Rate Limiting

Kolbe electrolysis has been proposed an efficient electrooxidation process to synthesize (un)symmetrical dimers from biomass-based carboxylic acids. However, the reaction mechanism of Kolbe electrolysis remains controversial. In this work, we develop a DFT- based microkinetic model to study the reaction mechanism of Kolbe electrolysis of acetic acid (CH3COOH) on both pristine and partially oxidized Pt anodes. We show that the shift in the rate-determining step of oxygen evolution reaction (OER) on Pt(111)@α-PtO2 surface from OH* formation to H2O adsorption gives rise to the large Tafel slopes, i.e., the inflection zones, observed at high anodic potentials in experiments on Pt anodes. The activity passivation as a result of the inflection zone is further exacerbated in the presence of Kolbe species (i.e., CH3COO* and CH3*). Our simulations find the CH3COO* decarboxylation and CH3* dimerization steps determine the activity of Kolbe reaction during inflection zone. In contrast to the Pt(111)@α-PtO2 surface, Pt(111) shows no activity towards Kolbe products as the CH3COO* decarboxylation step is limiting throughout the considered potential range. This work resolves major controversies in the mechanistic analyses of Kolbe electrolysis on Pt anodes: the origin of the inflection zone, and the identity of the rate limiting step.

scholarly journals Unveiling the Rate-Limiting Step of the Bc1 Complex Reaction Mechanism

2019 ◽  
Vol 116 (3) ◽  
pp. 419a
Author(s):  
Angela M. Barragan ◽  
Alexander V. Soudackov ◽  
Zaida Luthey-Schulten ◽  
Klaus Schulten ◽  
Sharon Hammes-Schiffer ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Complex Reaction ◽  
Bc1 Complex ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Mechanism of the Ullmann condensation

1981 ◽  
Vol 46 (1) ◽  
pp. 92-100 ◽  
Author(s):  
Zdeněk Vrba
Keyword(s):  
Reaction Mechanism ◽  
Bifunctional Catalyst ◽  
Sulphonic Acid ◽  
Condensation Rate ◽  
Kinetic Relation ◽  
Bromide Anion ◽  
Reaction Intermediate ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

It has been found that the condensation rate of 1-amino-4-bromoanthraquinone-2-sulphonic acid (I) with 1,3-diaminobenzene-4-sulphonic acid (II) giving 1-amino-4-(3'-amino-4'-sulphoanilino)anthraquinone-2-sulphonic acid (III) in media of NaHCO3-CO2 and NaHCO3-Na2CO3 with catalysis by CuI obeys the kinetic relation *u = k[I][II][Cu+][CO2-3], being controlled by the kinetic relation *u = k[I][II][Cu+]2[PO3-4] in media of NaH2PO4-Na2HPO4 buffers. The suggested reaction mechanism presumes formation of a bifunctional catalyst CuCO-3 or Cu2PO-4 which splits off the proton and bromide anion from the reaction intermediate in the rate-limiting step.

A mathematical modelling of acid catalyzed decomposition of 3-methyl-1,3-diphenyltriazene

1987 ◽  
Vol 52 (10) ◽  
pp. 2492-2499 ◽  
Author(s):  
Oldřich Pytela ◽  
Petr Svoboda ◽  
Miroslav Večeřa
Keyword(s):  
Reaction Mechanism ◽  
Linear Regression ◽  
Organic Solvent ◽  
Mathematical Modelling ◽  
Aqueous Ethanol ◽  
Activation Parameters ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Acid Catalyzed ◽  
Rate Limiting

The effect of acids on the decomposition of 3-methyl-1,3-diphenyltriazene has been studied in aqueous ethanol (40% (v/v) ethanol). The dependences found between the rate constant and acid concentration have been analyzed by means of non-linear regression using models including the specific and general catalysis and formation of associates between the substrate and the buffer components. The substrate has been found to form electrostatic associates with the conjugated base of acid. The complex formed is decomposed with the assistance of the proton or a general acid in the rate-limiting step to form the product. The Bronsted coefficient α = 0.81 has been found. Investigation of the activation parameters supports the earlier conclusions, indicating a dependence between the reaction mechanism and composition of the aqueous organic solvent.

scholarly journals The influence of active site conformations on the hydride transfer step of the thymidylate synthase reaction mechanism

2015 ◽  
Vol 17 (46) ◽  
pp. 30793-30804 ◽  
Author(s):  
Katarzyna Świderek ◽  
Amnon Kohen ◽  
Vicent Moliner
Keyword(s):  
Reaction Mechanism ◽  
Thymidylate Synthase ◽  
Active Site ◽  
Hydride Transfer ◽  
Md Simulations ◽  
Concerted Mechanism ◽  
X Ray ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

QM/MM MD simulations from different X-ray structures support the concerted mechanism character in the rate limiting step of thymidylate synthase catalysis.

scholarly journals Observation of fast release of NO from ferrous d1 haem allows formulation of a unified reaction mechanism for cytochrome cd1 nitrite reductases

2011 ◽  
Vol 435 (1) ◽  
pp. 217-225 ◽  
Author(s):  
Serena Rinaldo ◽  
Katharine A. Sam ◽  
Nicoletta Castiglione ◽  
Valentina Stelitano ◽  
Alessandro Arcovito ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Turnover Number ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Nitrite Reductases ◽  
Cytochrome Cd1 ◽  
Paracoccus Pantotrophus ◽  
Rate Limiting ◽  
Fast Release ◽  
Present Experimental Evidence

Cytochrome cd1 nitrite reductase is a haem-containing enzyme responsible for the reduction of nitrite into NO, a key step in the anaerobic respiratory process of denitrification. The active site of cytochrome cd1 contains the unique d1 haem cofactor, from which NO must be released. In general, reduced haems bind NO tightly relative to oxidized haems. In the present paper, we present experimental evidence that the reduced d1 haem of cytochrome cd1 from Paracoccus pantotrophus releases NO rapidly (k=65–200 s−1); this result suggests that NO release is the rate-limiting step of the catalytic cycle (turnover number=72 s−1). We also demonstrate, using a complex of the d1 haem and apomyoglobin, that the rapid dissociation of NO is largely controlled by the d1 haem cofactor itself. We present a reaction mechanism proposed to be applicable to all cytochromes cd1 and conclude that the d1 haem has evolved to have low affinity for NO, as compared with other ferrous haems.

scholarly journals Unveiling the Reaction Mechanism of the Das/Chechik/Marek Synthesis of Stereodefined Quaternary Carbon Centers

2021 ◽  
Vol 11 (11) ◽  
pp. 5002
Author(s):  
Pedro J. Silva ◽  
Carlos E. P. Bernardo
Keyword(s):  
Reaction Mechanism ◽  
Grignard Reagent ◽  
Density Functional ◽  
Initial Step ◽  
Nucleophilic Attack ◽  
Carbon Centers ◽  
Rate Limiting Step ◽  
Cu Catalyst ◽  
Rate Limiting ◽  
Zinc Carbenoid

The reaction mechanism of the Cu+-catalyzed introduction of two all-carbon-substituted stereocenters in an ynamide system using a Grignard reagent, a zinc carbenoid, and an aldehyde, was investigated using density-functional theory. In contrast to the formation of an organocopper(I) compound and subsequent carbocupration reaction, previously postulated as the initial step, the reaction proved to instead proceed through an initial complexation of the substrate alkyne bond by the Cu+-catalyst, which primes this bond for reaction with the Grignard reagent. Subsequent addition of the zinc carbenoid then enables the nucleophilic attack on the incoming aldehyde, which is revealed as the rate-limiting step. Our computations have also identified the factors governing the regio- and setereoselectivity of this interesting reaction, and suggest possible paths for its further development

Thermal Decomposition of Aromatic Thioureas [1]

1986 ◽  
Vol 41 (1) ◽  
pp. 101-104 ◽  
Author(s):  
Cyril Párkányi ◽  
Mohammed A. Al-Salamah
Keyword(s):  
Thermal Decomposition ◽  
Hydrogen Transfer ◽  
Chemical Reactivity ◽  
Order Reaction ◽  
First Order ◽  
Reactivity Indices ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Intramolecular Hydrogen ◽  
Rate Limiting

Thermal decomposition of aromatic and heteroaromatic thioureas in boiling chlorobenzene is a first-order reaction. The reaction involves intramolecular hydrogen transfer followed by a cleavage of the C - N bond which is the rate-limiting step. The rate constants of decom position have been determined and correlated with quantum-chemical reactivity indices.

scholarly journals Requiem for the Rate-Determining Step in Complex Heterogeneous Catalytic Reactions?

Reactions ◽  
2020 ◽  
Vol 1 (1) ◽  
pp. 37-46 ◽  
Author(s):  
Dmitry Yu. Murzin
Keyword(s):  
Rate Equation ◽  
Reaction Rate ◽  
Kinetic Modelling ◽  
Catalytic Reactions ◽  
Heterogeneous Catalytic ◽  
Rate Determining Step ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Theoretical Insight

The concept of the rate determining step, i.e., the step having the strongest influence on the reaction rate or even being the only one present in the rate equation, is often used in heterogeneous catalytic reactions. The utilization of this concept mainly stems from a need to reduce complexity in deriving explicit rate equations or searching for a better catalyst based on the theoretical insight. When the aim is to derive a rate equation with eventual kinetic modelling for single-route mechanisms with linear sequences, the analytical rate expressions can be obtained based on the theory of complex reactions. For such mechanisms, a single rate limiting step might not be present at all and the common practice of introducing such steps is due mainly to the convenience of using simpler expressions. For mechanisms with a combination of linear and nonlinear steps or those just comprising non-linear steps, the reaction rates are influenced by several steps depending on reaction conditions, thus a reduction in complexity to a single rate limiting step can lead to misinterpretations. More widespread utilization of a microkinetic approach when the reaction rate constants can be computed with reasonable accuracy based on the theoretical insight, and availability of software for kinetic modelling, when a system of differential equations for reactants and products will be solved together with differential equations for catalytic species and the algebraic conservation equation for the latter, will eventually make the concept of the rate limiting step obsolete.

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