Cobalt based catalysts for reductive amination of polypropylene glycol

Abstract

Polyetheramine (PEA) was synthesized from polypropylene glycol (PPG) through one-pot reductive amination. One of the most critical factors influencing activity toward PEA is the catalyst deactivation (the formation of cobalt nitride) via strong interaction of cobalt with ammonia. On this present work, two kinds of methods to inhibit the formation of cobalt nitride are introduced. First, $Y_2O_3$ inserted cobalt based catalysts showed high activity toward PEA even under low hydrogen partial pressures due to its basicity from $Y_2O_3$. Addition of $Y_2O_3$3 not only prevented from the formation of cobalt nitride but also promoted hydrogenation of imine to amine. Second, bimetallic Co-Pd catalysts showed enhanced $H_2$ dissociation and improved $H_2$ desorption capability by inserting a small amount of palladium. These catalysts were used for the reductive amination of PPG to yield PEA. It is noticed that the catalytic activity toward PEA was significantly increased by incorporating an extremely low content of palladium (around 0.01 wt%) into cobalt. The Pd inserted cobalt catalysts inhibited the formation of cobalt nitride that is an inactive species in the reductive amination and helped reduce cobalt oxide to cobalt metal as an active species. The bimetallic Co-Pd catalysts not only enhanced hydrogen dissociation but also accelerated hydrogen desorption by increasing the electron density of cobalt through the interaction between cobalt and palladium, which played a crucial role in providing improved catalytic performance toward PEA. In addition, it was found that the PO end-capping to both end-sides in starting material increased not only primary amine selectivity but also activity toward PEA. Also, $NH_3$ ratio, $H_2O$ amount, reaction temperature and pressure affected PEA reaction. The investigation on factors affecting activity and selectivity could give an aid to prepare high purity of PEA and to develop a competitive synthesis method for PEA.