Combination of Plasma Jet and Magnetron Sputtering─A New Method for Preparing Thin Ni–Co–Mn Oxide Coatings on Stainless Steel Meshes and Their Efficiency in the Total Oxidation of Volatile Organic Compounds

For the first time, ternary Ni–Co–Mn oxide catalysts were prepared by a combination of sputtering techniques. Thin coatings of Ni–Co–Mn oxides were deposited on stainless steel meshes by using a new method that involved a combination of plasma jet sputtering from a hollow Ni–Co cathode and simultaneous magnetron sputtering of manganese. The resulting thin-film catalysts are suitable for various oxidation reactions such as total oxidation of volatile organic compounds. The catalysts with a Ni/Co molar ratio of 1:1 and varying amounts of Mn were compared with the binary Ni–Co oxide catalyst in terms of their ability to oxidize ethanol and toluene. The powder X-ray diffraction showed spinel-type mixed oxides and NiO-like oxides in the oxide coatings. The TPR profiles revealed easier reducibility of the Ni–Co–Mn oxides compared with that of the Ni–Co oxide and the synergistic effect of Mn addition. The Ni–Co–Mn oxide catalysts exhibited higher catalytic activity than the binary catalysts due to mixed oxide phases with disordered structure and the presence of Mn4+. The catalysts showing the highest activity in the oxidation of ethanol and toluene were prepared at a low plasma jet energy input and a high magnetron sputtering energy input. The thin-film catalysts prepared by this method have a primary advantage over pelletized catalysts due to their extremely low contents of active Ni, Co, and Mn oxides in the catalyst bed and negligible internal diffusion effects. The proposed novel method of plasma sputtering of Ni and Co components from a hollow cathode, combined with simultaneous magnetron sputtering of Mn, has potential for industrial application. It allows the preparation of ternary catalysts that are more active than the previously reported binary catalysts. Moreover, the preparation procedure can be applied to other transition metal oxides, not just Ni–Co–Mn.