Silicate coatings on titanium modified by cobalt and/or copper oxides and their activity in CO oxidation

Abstract

SiO2 + TiO2/Ti composites have been formed by plasma electrolytic oxidation (PEO) of titanium in alkaline aqueous solution of sodium silicate. By modifying them using impregnation in nitrate solutions followed by annealing, the oxide composites Co3O4/SiO2 + TiO2/Ti, CuO/SiO2 + TiO2/Ti, and Co3O4 + CuO/SiO2 + TiO2/Ti have been obtained. The latter composites were tested in the model reaction of CO oxidation into CO2. The activation energy has been calculated: for the initial composites, it is equal to 42.6 kJ/mol, whereas, for the composites modified by cobalt oxide, copper oxide, and cobalt/copper oxides, it is equal to 141.8, 86.9, and 97.8 kJ/mol, respectively. The surface morphology and the composition of coatings have been investigated by the methods of scanning electron microscopy, X-ray spectral microprobe analysis, and X-ray photoelectron spectroscopy. Surface morphological structures with the highest concentrations of transition metals, which could serve as catalytically active sites, have been determined: “flakes” (Co3O4), “grains’” (CuO), and “hedgehogs” (Co3O4 +CuO).