A mechanistic assessment of the wet air oxidation activity of MnCeOx catalyst toward toxic and refractory organic pollutants

• The activity of MnCeOx catalyst in the wet air oxidation of toxic and refractory pollutants is assessed.
• The CWAO of phenol and C1-C2 acids proceeds via a Langmuir–Hinshelwood reaction path.
• The removal efficiency of phenol and C1-C2 acids depends on different adsorption mechanisms.
• Surface oxidation is the rate determining step of the CWAO of phenol.
• The CWAO of C1-C2 acids implies comparable rates of surface adsorption and oxidation steps.

The reactivity pattern of a model MnCeOx catalyst (Mnat:Ceat, 1) in the wet air oxidation (CWAO) of toxic (phenol) and refractory (acetic, oxalic and formic acids) organic pollutants has been probed, using a stirred batch reactor with continuous oxygen feeding (PO2PO2, 0.9 MPa). In the range of 110–150 °C the MnCeOx catalyst (wcat/wsub, 5) shows high abatement and mineralization efficiency toward all the substrates. Parallel trends of substrate and total organic carbon (TOC) conversion prove that adsorption is the primary reaction step, while slower mineralization rates signal that surface oxidation is rate determining step (r.d.s.). Activity data in the pH range of 3–10 and straight relationships between conversion and dissociation constant (Ka) signal that acids adsorption is driven by electrostatic interactions with acid sites (EAds ≈ 80 kJ/mol), while a low energetic barrier (EAds ≈ 16 kJ/mol) discloses the physical nature of phenol adsorption. A kinetic analysis of conversion-selectivity data, based on a dual-site Langmuir–Hinshelwood (L–H) mechanism, sheds light into the CWAO pattern of MnCeOx catalyst toward different classes of organic pollutants.

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