Insight into Wet Oxidation of Aqueous Aniline over a Ru/SiO2 Catalyst

Wet oxidation of aniline over a 5% Ru/SiO2 catalyst in the temperature range of 175−220 °C, oxygen partial pressure range of 0.34−1.38 MPa, and catalyst loading of 0.066−1.33 kg m-3 was studied. This heterogeneous catalyst was found to be very effective in the complete degradation of aniline and also to be active in the conversion of the −NH2 group in aniline into N2 gas. The optimum temperature for the formation of more N2 gas was between 200 and 210 °C; below this temperature range, more NH4 + ions were formed, and above this range, more NO3 - ions were found. The highest conversion of −NH2 to N2 was ∼78%. The kinetic data were modeled using the power law rate expression in terms of chemical oxygen demand (COD) and also in terms of total organic carbon (TOC). The experimental data could be best correlated by the Langmuir−Hinshelwood type reaction model involving a single-site dissociative adsorption of O2. The addition of the free radical promoter, hydroquinone, during wet oxidation of aniline resulted in increased conversion of −NH2 to N2. On the other hand, the free radical scavenger, gallic acid, resulted in decreased conversion of −NH2 to N2.