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Methane Activation and Oxidation in Sulfuric Acid
Author(s) -
Goeppert Alain,
Dinér Peter,
Ahlberg Per,
Sommer Jean
Publication year - 2002
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20020715)8:14<3277::aid-chem3277>3.0.co;2-5
Subject(s) - sulfuric acid , chemistry , inorganic chemistry , dimer , bifunctional , methane , protonation , hydrogen , activation energy , photochemistry , organic chemistry , catalysis , ion
The H/D exchange observed when methane is contacted with D 2 SO 4 at 270−330 °C shows that the alkane behaves as a σ base and undergoes rapid and reversible protonation at this temperature. DFT studies of the hydrogen exchange between a monomer and a dimer of sulfuric acid and methane show that the transition states involved in the exchange are bifunctional, that is one hydrogen atom is transferred from a hydroxy group in sulfuric acid to methane, while one hydrogen atom is abstracted from methane by a non‐hydroxy oxygen atom in sulfuric acid. All the transition states include a CH 5 moiety, which shows similarities to the methanium ion CH 5 + . The calculated potential activation energy of the hydrogen exchange for the monomer is 174 kJ mol −1 , which is close to the experimental value (176 kJ mol −1 ). Solvation of the monomer and the transition state of the monomer with an extra sulfuric acid molecule, decrease the potential activation energy by 6 kJ mol −1 . The acid–base process is in competition, however, with an oxidative process involving methane and sulfuric acid which leads to CO 2 , SO 2 , and water, and thus to a decrease of acidity and loss of reactivity of the medium.