Catalytic activity of platinum catalysts such as Pt/graphite, Pt/TiO 2 , Pt/Al 2 O 3 , and Pt/active carbon was studied using a slurry phase CSTR. Three model reactions, namely, phenol, maleic acid, and malonic acid oxidation were investigated in the temperature range from 120 to 170°C and at a total reactor pressure of 1.7 MPa. Platinum on graphite was found to be most suitable for aqueous phase oxidation of phenol, maleic acid, and malonic acid. Complete conversion for both phenol oxidation as well as maleic acid oxidation to CO 2 was observed with Pt/graphite at stoichiometric oxygen excess close to 0% and at 150°C. Deactivation due to over-oxidation is gradual for Pt/graphite with a metal dispersion of 5.3% as compared to Pt/TiO 2 , Pt/Al 2 O 3 and Pt/AC, which have metal dispersions of 15.3%, 19.5% and 19.0%, respectively. It was further found that in the presence of Pt/graphite catalyst and oxygen, malonic acid reaction proceeds via non-catalysed decarboxylation, and catalytic decarboxylation to CO 2 and acetic acid, and catalytic oxidation to CO 2 and H 2 O. Acetic acid was found to be difficult to oxidise at temperatures below 200°C. KEY WORDS: platinum catalysts; catalytic supports; wastewater treatment; stoichiometric oxygen excess; platinum metal dispersion Nomenclature AC active carbon concentration of the compound i [mol/m 3 ] CWO catalytic wet oxidation molar flow rate of compound i [mol/s] volumetric flow rate [m 3 /s] F L V volumetric flow rate of liquid [m 3 /s] n c number of carbon atoms in a compound [-] P pressure [Pa] Pt platinum R w;i specific disappearance rate of compound i [mol/s.kg] SCWO supercritical water oxidation S !i selectivity to compound i [%] S.E. stoichiometric oxygen excess to model compound [%] T temperature [K] V L volume of the liquid in the reactor [m 3 ] W total mass of dry catalyst in the reactor [kg] WAO wet air oxidation conversion of compound i [%]
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