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.
Highlights
Water is considered to be an ideal reaction medium to proceed chemical reactions of organic molecules efficiently when organic molecules are dissolved in water
We revealed the catalytic role of H2 O molecules in chemical reactions in water by performing a number of quantum chemical simulations [7,8,9,10]
We deal with a supermolecule consisting of a CH3 OH and H2 O molecules when we examine the catalytic role of H2 O molecules in the oxidation of CH3 OH
Summary
Water is considered to be an ideal reaction medium to proceed chemical reactions of organic molecules efficiently when organic molecules are dissolved in water. It is possible to proceed chemical reactions to produce molecules as planed in water because the temperature and the pressure of water are controlled. Understanding chemical reactions of organic molecules in water provides us with valuable information to extract the energy of biomass without drying because biomass contains large amount of water [1]. CH3 OH is one of the simplest products by reformation of biomass and is the source of energy for a direct methanol fuel cell. It would be beneficial to study chemical reactions containing CH3 OH in water. We examine the oxidation of CH3 OH in water in this study
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