Quantum chemical modelling of ethene epoxidation with hydrogen peroxide—role of catalytic sites
Journal article, 2007

Ethene epoxidation with hydrogen peroxide was studied on hydroxylated binuclear metal sites, using DFT calculations at the B3LYP/6-311+G(d,p) level of theory. A decrease of the activation enthalpy of 100 kJ mol–1 was observed compared to the gas phase reaction between hydrogen peroxide and ethene. It was previously shown that micro-solvation with water reduces the activation enthalpy by 77 kJ mol–1 and only the additional 24 kJ mol–1 can be attributed to the binuclear site. Three different metal centres were tested, Ti(IV), Si(IV) and Ge(IV), in order to investigate any specific role of the metal centre on the activation enthalpy. The results clearly show that the activation enthalpy is independent on the nature of the metal centre. This emphasises the role of the hydrogen bonded network provided by the hydroxylated metal sites, on the stabilisation of the transitions state. In ref. 1 (A. Lundin, I. Panas and E. Ahlberg, J. Phys. Chem. A, 2007, 111, 9080) it was demonstrated that, at the transition state and upon micro-solvation, the hydrogen peroxide entity becomes polarized within the hydrogen bonding network, forming a negatively-charged fragment distant from the ethene molecule and a positively-charged fragment directly involved in the oxygen insertion step. The same mechanism was found to hold also for the reaction at the binuclear catalytic site, since the required hydrogen bonding is effectively provided by the hydroxylated metal centres. This mechanism is compared to the two-step pathway which employs a metal peroxide intermediate. Both reaction channels were found to be plausible in confined environments.

Author

Angelica Lundin

University of Gothenburg

Itai Panas

Chalmers, Chemical and Biological Engineering, Environmental Inorganic Chemistry

Elisabet Ahlberg

University of Gothenburg

Physical Chemistry Chemical Physics

1463-9076 (ISSN) 1463-9084 (eISSN)

Vol. 9 45 5997-6003

Subject Categories

Chemical Sciences

DOI

10.1039/b710784f

More information

Created

10/7/2017