Application of Magnetic Catalyst for Catalytic Wet Air Oxidation of Organics in Aqueous Solution

This study investigated the treatment of methyl methacrylate (MMA) via wet air oxidation (WAO) and catalytic wet air oxidation (CWAO) processes. A superparamagnetic platinum catalyst (Pt/ZrO2/SiO2/Fe3O4, Pt/ZSM) was used to promote the decomposition of MMA and compared with commercial platinum catalyst Pt/γ-Al2O3. Effects of major operating parameters on the system performances in terms of normalized concentrations of MMA and chemical oxygen demand (COD) were investigated. The operating parameters examined included the setting temperature (TST), partial pressure of O2 (pO2), initial concentration of MMA (CMMA0), amount of catalyst used (mS) and reaction time (t). The decomposition efficiencies of MMA and COD (ηMMA and ηCOD) can respectively reach 87 and 30％ after 3 hr reaction time via WAO with reaction conditions at TST = 493 K, pO2 = 2.18 MPa (expressed as value at reference temperature Trf of 493 K) and CMMA0 = 500 mg L-1.he Pt/ZSM exhibits particle size of around 100-200 nm, magnetization of 6.54 emu g-1, specific external surface area of 67.46 m2 g-1, and with high platinum content of 13.37 wt.%. The pHZPC of Pt/ZSM is 4.7 which is favorable for the effective adsorption of acid intermediates on the catalyst surface. The hydrothermal method can reduce the chloride content of the Pt/ZSM which is prepared by the impregnation of Pt precursor H2PtCl6．6H2O on the support of ZSM.t TST = 453 K, pO2 = 1 MPa (Trf = 453 K), and mS = 1 g, the reactivities of HG-Pt/ZSM (Pt/ZSM with Pt reduced via H2 gas) (ηMMA = 29％ and ηCOD = 54％) and HT-Pt/ZSM (Pt/ZSM with Pt reduced via hydrothermal method) (ηMMA = 46％ and ηCOD = 36％) to decompose MMA and COD are as good as those of Pt/γ-Al2O3 (ηMMA = 39％ and ηCOD = 39％). The Pt/ZSM catalyst still holds superparamagnetic property with saturation magnetization of 6.5-7.3 emu g-1 after being used in CWAO process. Thus the used Pt/ZSM can be separated via high-gradient magnetic separation (HGMS) fot the reuse.