DIRECT SYNTHESIS OF METHANOL OVER METALLIC CATALYSTS

The energetics of the elementary reactions involved in the direct synthesis of methanol from methane over noble metal catalysts have been investigated using the bond order conservation Morse potential approach (BOC-MP). Enthalpy changes as well as activation energies for forward and reverse reactions were calculated for the different elementary steps which may occur by reaction of CH4 and O-2 on the noble metal series Ni, Pd, Pt and Au. The calculations indicate that fuel rich conditions are required in order to avoid the complete oxidation of methane to produce CO and CO2. Under these conditions both methanol and formaldehyde may be synthesized primarily by hydrogenation or hydrogen abstraction of the common methoxy radical intermediate, respectively. In order to increase the selectivity to methanol, efficient hydrogen donors are required to hydrogenate formaldehyde which may be converted to methanol through the methyl hydroxyl radical. The direct synthesis of methanol over noble metals may proceed mainly on the less active metals such as Pt and Au, while on Ni the model predicts that methane will be oxidized to CO and CO2.