Oxidised plasma-sprayed transition metal – Reusable supported catalysts for organic waste treatment

Abstract

Transition metals were plasma-sprayed onto stainless-steel substrates and further oxidised to form a surface layer of the metal oxides. Catalytic wet oxidation of glucose, a model compound for organic waste was carried out at temperature range of 150–170 °C for 60 min. Rietveld patterns showed evidence of metal oxides in the oxidised coatings of MoO3, Co3O4, CuO and CuNiIn oxide. The SEM cross-sections reveal two-layered coatings for MoO3, Co3O4 and CuO. Highest COD reduction was obtained by Co3O4 after 60 min at 160 °C for the low-oxygen screening trials. Initial screening trials detected a high concentration of metallic Mo, Co and Cu by ICP-MS. The re-oxidised MoO3 catalysts yielded the highest concentration of acetic acid (96 mg L−1) post 60 min of CWO reaction at 170 °C using 40 bar O2. The leaching of Mo metal with spallation of the top oxide layer was confirmed with the reuse trials. On contrary, CuNiIn oxide showed minimum amounts of leached Cu, Ni, and In metals into the reaction media, with the catalyst producing 67 mg L−1 of acetic acid at 170 °C using 40 bar O2. Therefore, CuNiIn oxide was selected as the best oxidised transition metal catalyst for CWO of glucose.