Reaction Energy Diagram Research Articles

A Periodic Density Functional Theory Study of Intermolecular Isomerization of Toluene and Benzene Catalyzed by Acidic Mordenite Zeolite: Effect of the Zeolite Steric Constraints

A periodic density functional theory study of the isomerization reactions of toluene and benzene catalyzed by acidic mordenite is reported. Reaction energy diagrams including transition-state energies of disproportionation and direct transalkylation reactions are presented and analyzed. Alternative reaction pathways have been considered. The use of periodic structure calculations allows analysis of steric constraints that occur within zeolite micropores. General rules concerning the influence of steric constraints in relation with reaction mechanism are described.

A theoretical study of the alkylation reaction of toluene with methanol catalyzed by acidic mordenite.

A theoretical study of the alkylation reaction of toluene with methanol catalyzed by the acidic Mordenite (Si/Al = 23) is reported. Cluster DFT as well as periodical structure DFT calculations have been performed. Full reaction energy diagrams of the elementary reaction steps that lead to the formation of the three xylene isomers are given. The use of periodical structure calculations allows one to account for zeolite framework electrostatic contributions and steric constraints that take place in zeolitic catalysts. Especially the steric constraint energy contribution has a significant effect on the energies and bond formation paths. The activation energy barrier of p-xylene formation is found to be approximately 20 kJ/mol lower than the corresponding values for the formation of its isomers. Computed host-guest binding energies according to the DFT method need a correction due to the absence of the dispersive interaction with the zeolite wall. Apparent activation energies obtained with this correction are in good agreement with experimental data.

Theoretical study of nitrile hydrolysis reaction on Zn(II) ion exchanged zeolites

The hydrolysis of acetonitrile catalyzed by Zn 2+ ion exchanged zeolites has been studied theoretically by DFT (Density Functional Theory). A 4T cluster (Si/Al=1) with zinc in the cation position has been chosen to model the zeolite site. The action of the metal ion is found to be analogous to that of the hydrolyzing enzymes, especially carbonic anhydrase. The primary reaction of Zn 2+ with H 2O is a dissociate reaction, in which ZnOH + species is formed together with a zeolitic proton. Many alternate reaction paths have been analyzed and their reaction energy diagrams, including transition states, are presented. The hydrolysis reaction can be divided in three parts: hydration, isomerization and product desorption. The rate-limiting step is the nucleophilic attack of water molecule during the hydration reaction. Water molecules play an important role in many elementary reaction steps. It may act as proton donor in the hydration and tautomerization steps and facilitates the desorption of reaction products that inhibit the reaction. A detailed comparison is made with related enzymatic reactions.

Remarkable kinetic solvent isotope effect on the cycloaromatization of C-1027 chromophore, a 9-membered enediyne, and the thermochemistry

Remarkable kinetic solvent isotope effect, experimental activation energy (15.1 kcal/mol) as well as MO calculations present a reaction energy diagram for cycloaromatization reaction of C-1027 chromophore, a highly strained 1,5-diyn-3-ene molecule.