Efficient degradation of MDEA-containing wastewater over Pd-based catalysts via a catalytic wet air oxidation process: supports, conditions and kinetics†

The simultaneous effective removal of organic nitrogen and organic carbon in N-methyldiethanolamine (MDEA)-containing wastewater presents a significant challenge. This study investigates the influence of Pd-based catalysts supported by cerium–zirconium solid solution (CeO₂–ZrO₂), titanium dioxide (TiO₂), alumina (Al₂O₃) and activated carbon (AC) on the total organic carbon (TOC) and total nitrogen (TN) in MDEA-containing wastewater during the catalytic wet air oxidation (CWAO) process by analyzing the phase, morphology and pore structure of the catalyst. The effects of CWAO conditions on the removal ratio of TOC and TN in the wastewater were investigated. The kinetics of TOC and TN of MDEA using Pd/CeO₂–ZrO₂ were also analyzed. Results indicate that the choice of support significantly affects the surface oxygen content, oxygen activity and Pd⁰ content, which are crucial for achieving a high removal ratio of TOC and TN and maintaining the stability of Pd-based catalysts. The removal ratio of TOC and TN of the wastewater reaches 90% and 75% in the CWAO reaction with Pd/CeO₂–ZrO₂, respectively. The catalytic oxidation degradation process of TOC and TN in MDEA can be correlated well with the lumped kinetic models. The reaction rate constants for TOC and TN increased by factors of 220 and 34, respectively, in the presence of Pd/CeO₂–ZrO₂. Additionally, the removal rate of TN increased by 64% in CWAO with a lower activation energy.