Catalytic role of H2O molecules in oxidation of CH3OH in water

Abstract

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.