Study on the Structure of Cu/ZrO2 Catalyst and the Formation Mechanism of Disodium Iminodiacetate and Sodium Glycine

Abstract

A new method to prepare Cu/ZrO2 catalysts by reducing CuO/ZrO2 with hydrazine hydrate is reported, and the prepared catalysts were used to synthesize disodium iminodiacetate by diethanolamine dehydrogenation. Hydrazine hydrate can rapidly reduce the CuO/ZrO2 precursor powder in an alkaline environment at a moderate temperature. The ratio of Cu0/Cu+ at the Cu/ZrO2 surface was controlled by the amount of hydrazine hydrate and the reduction reaction time. The formation mechanism of disodium glycine as the main byproduct and iminodiacetate were deduced by investigating the product yield, the reaction time, and the presence of acetaldehyde in the evolved gas. It has been shown that the ratio of Cu0/Cu+ in Cu/ZrO2 significantly affects the dehydrogenation of diethanolamine into disodium iminodiacetate. Cu0 and Cu+ are the catalytic activity centers in the dehydrogenation of diethanolamine which respectively produce intermediate aldehydes and an ester via nucleophilic addition reactions. The formation mechanism of sodium glycinate is related to the tautomerism of intermediate products and Schiff base hydrolysis. The formation mechanism of disodium iminodiacetate and sodium glycine producing by the dehydrogenation of diethanolamine over the Cu/ZrO2 catalysts which were prepared by a new reduction method.