Catalytic role of H₂O molecules in oxidation of CH₃OH in water

We have examined the catalytic role of H₂O molecules in the oxidation of CH₃OH in water by quantum chemical simulations. A CH₃OH is decomposed into molecules, a formaldehyde and an H₂, in water, while it is converted into radicals in a gas phase reaction at a high temperature. H₂O molecules located near a CH₃OH form a first hydration shell and act as catalyst for the oxidation of CH₃OH in water. The oxidation process of a CH₃OH in water begins when a proton is delivered to a neighbor H₂O molecule from a hydroxyl of a CH₃OH. The H₂O molecule transfers an extra proton to a second H₂O molecule, a proton of which is combined with a proton detached from the methyl of the CH₃OH, forming an H₂. The energy barrier to decompose a CH₃OH is significantly reduced by the catalyst of H₂O molecules in water. A cluster of H₂O molecules arise in water as an enclosed chain of hydrogen bonds between H₂O molecules. A proton is transferred with less energy between H₂O molecules within a cluster of H₂O molecules. A cluster of five H₂O molecules further reduces the energy barrier. The calculated oxidation rate of CH₃OH with the transition state theory agrees well with that determined by experiments.