What is the rate-limiting step of a multistep reaction?

Murdoch, Joseph R.

doi:10.1021/ed058p32

Cited by 175 publications

(124 citation statements)

References 12 publications

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“…The system under study undergoes a two-consecutive-step process, which can be schematically described as Two initial assumptions concerning the overall behavior of the system can be done: 53 (a) The two steps are essentially irreversible. This assumption can be justified because the two processes are decompositions and the entropy of the system increases along the reaction pathway.…”

Section: Resultsmentioning

confidence: 99%

Theoretical Study of the Elimination Kinetics of Carboxylic Acid Derivatives in the Gas Phase. Decomposition of 2-Chloropropionic Acid

et al. 1997

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The reaction mechanism for the decomposition of 2-chloropropionic acid in the gas phase to form hydrogen chloride, carbon monoxide, and acetaldehyde has been theoretically characterized. Analytical gradients have been used by means of AM1 and PM3 semiempirical procedures and ab initio methods at HF and DFT (BLYP) levels with the 6-31G** basis set. The correlation effects were also included by using the perturbational approach at the MP2 level with the 6-31G** and 6-31++G** basis sets and the variational approach at the CISD/6-31G** level and by means of MCSCF wave functions with a (6,6) complete active space and the 6-31G** basis set. The global potential energy surface has been studied, and the stationary points were localized and characterized. The geometries, electronic structure, and transition vector associated with the transition structures have been analyzed and the dependence of these properties upon theoretical methods is discussed. The present study points out, in agreement with the experimental data, that the decomposition process occurs through a two-step mechanism involving the formation of the R-propiolactone intermediate. The transition structure associated with the first step can be described as a five-membered ring with participation of leaving chloride and hydrogen, assisted by the carbonyl oxygen of the carboxyl group. The second transition structure, controlling the R-propiolactone decomposition step, yields the formation of CO and CH 3 CHO molecules. The rate constants and the Arrhenius preexponential factors for the different interconversion steps have been calculated in terms of the transition state theory. The comparison of experimental and theoretical values for these parameters allows us to prove the validity of theoretical methods. The results suggest that the process must be considered as essentially irreversible, the first step being the rate-determining step. From a computational point of view, the inclusion of the correlation energy at the MP2/6-31G** level is necessary to obtain an accurate calculation of the kinetic parameters.

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Section: Resultsmentioning

confidence: 99%

Theoretical Study of the Elimination Kinetics of Carboxylic Acid Derivatives in the Gas Phase. Decomposition of 2-Chloropropionic Acid

et al. 1997

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“…Without a detailed microkinetic model, we utilize the procedure outlined by Murdoch to the estimate the apparent reaction barrier and rate limiting reaction process [38]. Murdoch's procedure involves breaking the reaction energy diagram into sections terminated by an intermediate more stable than that which began the section.…”

Section: Apparent Reaction Barrier and Rate Limiting Step Estimationmentioning

confidence: 99%

Catalytic propane reforming mechanism over Mn-Doped CeO2 (111)

Krcha

Janik²

2015

Surface Science

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a b s t r a c t a r t i c l e i n f o Available online xxxx Keywords: Ceria DFT + U Manganese Doped oxide ReformingMnO x /CeO x mixed oxide systems exhibit encouraging hydrocarbon oxidation activity, without the inclusion of a noble metal. Using density functional theory (DFT) methods, we examined the oxidative reforming path of propane over the Mn-doped CeO 2 (1 1 1) surface. A plausible set of elementary reaction steps are identified for conversion of propane to CO/CO 2 and H 2 /H 2 O over the oxide surface. The rate-limiting reaction process may vary with redox conditions, with C-H dissociation limiting under more oxidizing conditions and more complex reaction sequences, including surface re-oxidation, limiting under highly reducing conditions. The possibility of intermediate desorption from the surface during the reforming process is low, with desorption energies of the intermediates being much less favorable than further surface reactions until CO/CO 2 products are formed. The reforming paths over Mn-doped ceria are similar to those previously identified over Zr-doped ceria. The extent of surface reduction and the electronic structure of the surface intermediates are examined.

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“…The previous definition of RD-Step ("The step with the smallest rate constant") can work here, but the "highest transition state" definition is erroneous (especially for irreversible steps [2,32] ). In Section 4 (catalytic reactions), we show that even for steady-state reactions this definition can be misleading.…”

Section: Thementioning

confidence: 99%

The Rate‐Determining Step is Dead. Long Live the Rate‐Determining State!

2011

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The concept of a rate-determining step (RD-Step) is central to the kinetics community, and it is basic knowledge even for the undergraduate chemical student. In spite of this, too many different definitions of the RD-Step appear in the literature, all of them with drawbacks. This dilemma has been thoroughly studied by several authors in the attempt to "patch" the drawbacks and bring the RD-Step to a correct physical meaning. Herein we review with simple models the most notable definitions and some challengers of the RD-Step concept, to conclude with the deduction that there are no rate-determining steps, only rate-determining states.

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What is the rate-limiting step of a multistep reaction?

Cited by 175 publications

References 12 publications

Theoretical Study of the Elimination Kinetics of Carboxylic Acid Derivatives in the Gas Phase. Decomposition of 2-Chloropropionic Acid

Theoretical Study of the Elimination Kinetics of Carboxylic Acid Derivatives in the Gas Phase. Decomposition of 2-Chloropropionic Acid

Catalytic propane reforming mechanism over Mn-Doped CeO2 (111)

The Rate‐Determining Step is Dead. Long Live the Rate‐Determining State!

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