Related Experiment Video
Updated: Jun 6, 2026
10:52
Multiscale Sampling of a Heterogeneous Water/Metal Catalyst Interface using Density Functional Theory and Force-Field Molecular Dynamics
Published on: April 12, 2019
How to conceptualize catalytic cycles? The energetic span model.
Sebastian Kozuch1, Sason Shaik
1Department of Organic Chemistry, The Weizmann Institute of Science, Rehovot, Israel. sebastian.kozuch@weizmann.ac.il
Accounts of Chemical Research
|November 12, 2010
Summary
The energetic span model links theoretical energy profiles to catalytic cycle efficiency, calculating turnover frequency (TOF) using key rate-determining states. This computational approach simplifies predicting catalyst performance by identifying the TOF-determining intermediate and transition state.
Area of Science:
- Computational Chemistry
- Catalysis
- Chemical Kinetics
Background:
- Catalytic cycle efficiency is experimentally measured by rate constants (k-representation) but theoretically calculated via state energies (E-representation).
- A direct link between theoretical energy profiles and catalytic turnover frequency (TOF) has been lacking.
- Transition State Theory (TST) posits equivalence between energy and rate representations but lacks a simple predictive tool for TOF.
Purpose of the Study:
- Introduce the energetic span model to bridge the gap between theoretical energy profiles and experimental TOF.
- Provide a straightforward method for calculating catalytic cycle efficiency from computational data.
- Reframe kinetic concepts in catalysis, moving from rate-determining steps to rate-determining states.
Main Methods:
- Developed the energetic span (δE) model based on Eyring's TST and steady-state approximations.
- Identified the TOF-determining transition state (TDTS) and TOF-determining intermediate (TDI) using the degree of TOF control (X(TOF)).
- Applied the model to analyze catalytic cycles, including the effect of reactant and product concentrations.
Main Results:
- The energetic span model enables direct TOF calculation from energy profiles, analogous to Ohm's law (TOF = chemical potential / chemical resistance).
- Identified TDTS and TDI as critical states governing catalytic efficiency, not necessarily the highest or lowest energy states.
- Demonstrated that only species between TDI and TDTS influence reaction rate, linking theory to experimental observations.
Conclusions:
- The energetic span model provides a robust theoretical framework for predicting and understanding catalyst efficiency.
- Catalytic cycles are better conceptualized by rate-determining states (TDI and TDTS) rather than rate-determining steps.
- The model facilitates a direct correlation between computational predictions and experimental catalytic performance in organometallic reactions.
Related Concept Videos
02:50Catalysis
The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed during the process. A basic comprehension of a catalysts’ role during chemical reactions can be understood from the concept of reaction mechanisms and energy diagrams.
01:27Catalysis
Catalysis influences the rate of chemical reactions by providing an alternative reaction pathway with lower activation energy. A catalyst speeds up a reaction, but it is not consumed during the process. The fundamental principle of catalysis is the ability of a catalyst to alter the reaction mechanism, often introducing a more efficient pathway than the uncatalyzed process.In a catalyzed reaction, the catalyst participates directly in the reaction mechanism. It interacts with reactants to form...
01:22Heterogeneous Catalysis
Heterogeneous catalysis involves a catalyst in a different phase from the reactants. It is a process where the catalyst and the reactants are in distinct phases, typically solid and gas or liquid.Most heterogeneous catalysts are metals, metal oxides, or acids. The list includes transition metals like iron (Fe), cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt), chromium (Cr), manganese (Mn), tungsten (W), silver (Ag), and copper (Cu). These metals possess partially vacant d orbitals that...
01:25Transition State Theory
Transition-state theory, also known as activated-complex theory, provides a molecular-level explanation of reaction rates in both gas-phase and solution-phase reactions. It extends earlier kinetic models by considering the formation of a short-lived, high-energy configuration during a reaction.The progress of a chemical reaction can be represented using a reaction profile, which plots potential energy against the reaction coordinate. As two reactant molecules approach one another, their...
01:13Introduction to Mechanisms of Enzyme Catalysis
For many years, scientists thought that enzyme-substrate binding took place in a simple "lock-and-key" fashion. This model stated that the enzyme and substrate fit together perfectly in one instantaneous step. However, current research supports a more refined view scientists call induced fit. The induced-fit model expands upon the lock-and-key model by describing a more dynamic interaction between enzyme and substrate. As the enzyme and substrate come together, their interaction causes a mild...
01:13Introduction to Mechanisms of Enzyme Catalysis
For many years, scientists thought that enzyme-substrate binding took place in a simple "lock-and-key" fashion. This model stated that the enzyme and substrate fit together perfectly in one instantaneous step. However, current research supports a more refined view scientists call induced fit. The induced-fit model expands upon the lock-and-key model by describing a more dynamic interaction between enzyme and substrate. As the enzyme and substrate come together, their interaction causes a mild...