Mechanism of Electrocatalytic Wet Air Oxidation of PPCPs over Solid Catalysts: Kinetic Insight with a Universal Model

Electrocatalytic wet air oxidation (ECWAO) is a novel wet air oxidation technology using an anodic electric field to stimulate oxygen for catalytic oxidation of water pollutants at ambient condition. Herein, a mechanistic kinetic model is established based on the degradation of bisphenol A in an ECWAO process with manganese oxide (MnO_x) catalysts, and the general applicability of the model is verified by triclosan degradation over a Ni@NiO catalyst and sulfamethoxazole degradation over a MnMoO_x catalyst. Elementary steps involved in solid-catalyzed reaction and the assistant role of anodic electric field in the catalysis are taken into consideration. A group of kinetic equations based on the Langmuir–Hinshelwood–Hougen–Watson (LHHW) or Eley–Rideal (ER) rate laws are evaluated using the criteria of the minimization of the residual sum of squares and average error. The results show that the ECWAO reaction is best described by the LHHW model in which the surface reaction between adsorbed oxygen and adsorbed organic molecules is the rate-determining step. The key parameters controlling ECWAO reaction kinetics are the adsorption equilibrium constant of oxygen and rate constant of the surface reaction. According to the kinetic model, the reaction rates of organic pollutants are nearly linear dependent upon their concentrations within a certain range. With the increment of the circuit current, the reaction rates of organic pollutants first rise, then reach a plateau, and finally decline. The mechanistic kinetic model proves to be applicable for interpreting and predicting the ECWAO rates of organics over the transition metal oxide catalysts.