The dehydrogenation of methanol to methyl formate Part I: Kinetic studies using copper-based catalysts

Kinetics of the dehydrogenation of methanol to methyl formate (MF) have been determined for a commercial copper-chromite catalyst and for a skeletal copper catalyst that has undergone deactivation to a steady-state activity. The activation energy over the copper-chromite catalyst was found to be around 78 kJ/mol, considerably lower than the approximately 120 kJ/mol observed for the skeletal copper catalyst. The reaction order with respect to methanol was found to be approximately 0.5 for both catalysts whilst hydrogen and methyl formate both inhibited the reaction significantly. This inhibition is consistent with a Langmuir - Hinshelwood model in which methanol is adsorbed dissociatively and the rate-determining step is the loss of hydrogen from the resultant methoxy species. The model parameter values imply that a significant fraction of the copper sites on the skeletal catalyst are occupied by formaldehyde while the coverage is low on copper-chromite. These differences can be used to explain the presence of deactivation and the considerably higher activation energy for dehydrogenation observed for the skeletal copper catalyst.