Catalytic wet air oxidation of ammonia over alumina supported metals

Wet air oxidation (WAO) of ammonia to dinitrogen has been investigated using various heterogeneous catalysts. Among them RuO2/Al2O3 exhibited remarkable activities that at least 99% of ammonia (1500 ppm) was decomposed at 503 K under 1.5 MPa in a NaOH added water (pH of 12). The product was dinitrogen exclusively, and the quantities of NO3- formed were very small. The reaction proceeded rapidly in the high pH region indicating that ammonia was more reactive than ammonium ion. The activity and selectivity were found to have a relation with the oxygen affinity of the metal element. It was discussed that elements (Ru, Pd) with medium weakness of M-O bond showed the high activity and selectivity and the reason was proposed. (C) 1998 Elsevier Science B.V.