Hydrogenolysis of diethyl oxalate over copper-based catalysts

The gas-phase hydrogenolysis of diethyl oxalate to ethylene glycol has been studied over a series of copper-based catalysts. Catalyst deactivation was significant but could be minimized by using a high-surface-area silica supported copper catalyst. The use of either acidic or basic supports resulted in lower product selectivity due to dehydration reactions over acidic supports, and decomposition reactions over basic supports. Using ion-exchanged Cu/SiO₂, conversions of ≫ 99% were possible at moderate temperature and pressure (513 K, 600 kPa), with ≫ 85% selectivity to ethylene glycol. Studies of the kinetics of reaction over this catalyst have shown that the reaction proceeds via dissociative adsorption of diethyl oxalate on the copper surface, leading to the formation of ethanol and ethyl glycolate. The ethyl glycolate intermediate then reacts via an analogous mechanism to form a second ethanol molecule and ethylene glycol.