A DFT study of the methanol oxidation catalyzed by a copper surface

The energy variation in the overall catalytic oxidation of methanol to carbon dioxide on a copper surface is analyzed using the density functional theory. Adsorption energies, geometries and charges for methanol and the various intermediates were computed from geometry optimized calculations on a large cluster containing 22 copper atoms used to model the Cu(1 1 1) surface. The calculated parameters are reported for the most stable adsorption modes of the various species considered: CH3OH, CH3O, H2CO, H2CO2, HCO2, H and O. The results obtained are in good agreement with available experimental data. The adsorption energies obtained were then used to plot the energy variation along the decomposition of methanol. The energy profile shows that the several reaction steps are lower in energy than the initial state: CH3OH(g)+O(ads). It is also shown that the stability of the adsorbed formaldehyde species is responsible for getting H2CO or CO2 as the final oxidation products. The decomposition of formaldehyde to formate is highly exothermic and this is the main reason for the high reactivity of the dioxymethylene intermediate. This prevents, therefore, the experimental verification of its existence. The total energy of the final products is 210 kJ/mol lower than that of the initial state.