Catalytic wet air oxidation of aqueous ammonia with activated carbon

The oxidation of aqueous ammonia to nitrogen by the catalytic wet air oxidation (CWAO) process with activated carbon as catalyst was studied. A commercial activated carbon CUDU1000 chemically modified by oxidation with HNO3 and/or reduction with H2 was used. The characterization of the activated carbons was carried out by N2 adsorption, thermal programmed decomposition (TPD), Fourier transformed infrared (FTIR) spectroscopy, Boehm titration and zero point charge (ZPC) techniques. Studies of aqueous ammonia adsorption on the activated carbons under atmospheric conditions showed that carboxylic, lactonic and anhydride surface groups increase both the rate and capacity of adsorption. The oxidized carbons had lower activity towards selective aqueous ammonia oxidation in CWAO process because of a strong ammonia adsorption. However, hydrogenated activated carbons had higher activity for selective aqueous ammonia oxidation. It is establish that a strong ammonia adsorption takes place onto carboxylic, lactonic and/or anhydride surface groups while the quinonic surface groups are responsible of the catalytic activity shown by these carbons.