Catalytic wet air oxidation of wastewater containing ammonia and phenol over activated carbon supported Pt catalysts

Noble metal catalysts on activated carbon (AC) (Pt/AC and Ru/AC) and base metal catalysts (Cu/AC, CoMo/AC, Mo/AC, Mn/AC, Ru/Al2O3) were developed and examined for the simultaneous removal of organic pollutants and ammonia from wastewater using the wet air oxidation (WAO) process in the liquid phase. The noble metal catalysts were much more active than were the base metal catalysts. Ammonia removal was the rate-controlling step. Nitrate and nitrite accounted for a minor portion of the decomposed ammonia (<5% for Ru/AC and <3% for Pt/AC). Pt/AC was superior to Ru/AC in terms of ammonia removal, pH sensitivity and stability. Activated carbon was a better support for Pt than was TiO2, Al2O3 or MCM-41. The optimal preparation conditions of Pt/AC were: calcination at 300 °C for 6 h followed by H2 reduction at 600 °C without pretreatment of AC. The catalyst so prepared, Pt(opt)/AC, produced ammonia removals of 52 and 88% at 200 °C, initial pH of 5.6 and 12, respectively. The experimental results based on the Pt(opt)/AC showed that the Pt/AC catalyst was able to remove ammonia (>50%) and phenol (≈100%) simultaneously from highly polluted wastewater containing up to 1500 mg/l N ammonia and up to 8000 mg/l COD.