| Sumario: | Density functional theory has been used to investigate the thermodynamics and activation barriers associated with the direct oxidation of methane to acetic acid catalyzed by Pd cation in concentrated sulfuric acid. Pd cations in such solutions are ligated by two bisulfate anions and by one or two molecules of sulfuric acid. Methane oxidation is initiated by the addition of CH across one of the PdO bonds of a bisulfate ligand to form Pd(HSO)(CH)(HSO). The latter species will react with CO to produce Pd(HSO)(CHCO)(HSO). The most likely path to the final products is found to be via oxidation of Pd(HSO)(CH)(HSO) and Pd(HSO)(CHCO)(HSO) to form Pd(η²-HSO)(HSO)(CH)(HSO) and Pd(η²-HSO)(HSO)(CHCO)(HSO), respectively. CHHSO or CHCOHSO is then produced by reductive elimination from the latter two species, and CHCOOH is then formed by hydrolysis of CHCOHSO. The loss of Pd from solution to form Pd(0) or Pd-black is predicted to occur via reduction with CO. This process is offset, though, by reoxidation of palladium by either HSO or O.
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