Mechanism of catalytic subcritical water oxidation of m-nitroaniline and nitrogen conversion by CuCo2O4 catalyst.

• CSWO of M−NA and nitrogen conversion by CuCo 2 O 4 catalyst was investigated. • Degradation pathways and nitrogen migration mechanism of M−NA were proposed. • Elevate temperature can promote NO 3 – to NO 2 –, resulting in NH 4 + with NO 2 – to form N 2. • CuCo 2 O 4 catalyzing the reaction of ·NO 2 with ·NH 4 , hastening N 2 generation. • CuCo 2 O 4 may induce a reaction between the nitro and amino groups on M−NA to form N 2. Catalytic subcritical water oxidation (CSWO) of M−nitroaniline (M−NA) was investigated in a fused quartz tube reactor (FQTR) to determine the effects of reaction parameters on M−NA mineralization rate, total nitrogen (TN) removal rate and nitrogen-containing products distribution. The results indicated that the TN removal rate was only 26.36 % at 200 °C, 200 % excess oxidant and 15 min residence time, while the TN removal rate reached 67.83 % at 360 °C in SWO of M−NA. Compared with SWO of M−NA, the mineralization rate and TN removal rate of CSWO of M−NA increased by about 10 % and 17.83 %, respectively. The main reason is mainly attributed to CuCo 2 O 4 catalyzing the preferential reaction of ·NO 2 with ·NH 4 , hastening N 2 generation. Alternatively, the CuCo 2 O 4 catalyst may induce a direct reaction between the nitro and amino groups on M−NA within the benzene ring to form N 2. Moreover, degradation pathways and nitrogen migration mechanism of M−NA under SWO/CSWO conditions were proposed. These crucial findings are expected to guide the development of environmentally sustainable catalytic technologies towards addressing significant water pollution challenges. [ABSTRACT FROM AUTHOR]