Catalytic Wet Air Oxidation of Aqueous Ammonia Over γ-Al2O3 Based Cu-Ru Bimetallic Catalysts

Abstract

Due to the excessive use of ammonia in the industry it is one of the most important environmental issues. The presence of ammonia in the environment is harmful towards living organism. Therefore, removal of ammonia from waste water is very important in maintaining the aquatic environment. Catalytic wet air oxidation is one way of removing ammonia from the environment. Different catalysts have been used for ammonia removal. Ruthenium supported catalyst is very active towards ammonia decomposition. But due to the high cost and limited availability its industrial application is limited. Copper is also found to show some activity towards ammonia decomposition. In order to make the catalyst cost effective, the γ-Al2O3 supported Cu-Ru bimetallic catalysts with different metal loading have been successfully synthesized using impregnation method. The γ-Al2O3 was synthesized by sol-gel method. The catalysts were characterized by using different techniques including Atomic Absorption Spectrophotometry (AAS) , Surface Area Analysis, Powder X-ray diffraction (XRD), Fourier- Transformed Infra-Red Spectroscopy (FTIR), Thermal gravimetric analysis (TGA), and Field Emission Scanning Electron Microscopy (FE-SEM). The catalysts were successfully applied for catalytic wet air oxidation of aqueous ammonia. The ammonia decomposition activity was studied at three different temperatures i.e. 150 oC 200 oC 230 oC and it was found that catalytic activity increases with increase of temperature. Up to 99 % ammonia decomposition was achieved at 230 oC with catalyst containing 3% Ru loading over 10% copper. The promoting effect of Ru over catalytic activity of Cu was also studied and it was observed that activity of copper is enhanced by the addition of ruthenium. The selectivity of the catalyst towards different products was also calculated and it was found that selectivity towards nitrogen production was maximum with minimum production of nitrates. This was also confirmed by analysis of gaseous products which also indicated that no NOx were present in the products. The ammonia to catalyst ratio was also optimized. The catalyst was recovered from the reaction mixture by filtration and it was found active for five cycles. The stability of catalyst in the reaction medium was confirmed by determination of dissolution degrees of the catalyst which was quite low.