Formation, composition, structure, and catalytic activity in CO oxidation of SiO 2 + TiO 2 /Ti composite before and after modification by MnO x or CoO x
Abstract The composition and structure of SiO 2  + TiO 2 oxide layers formed on titanium by plasma electrolytic oxidation (PEO) and MO x (M = Co or Mn) + SiO 2  + TiO 2 /Ti composites fabricated on their basis using impregnation and annealing methods have been investigated. It has been demonstrated that silicon and titanium are rather homogeneously distributed within the SiO 2  + TiO 2 coating bulk. In the galvanostatic process mode, the titanium/silicon ratio in the coating bulk can be controlled by the current density value. The coating outer part is silicon-enriched and titanium-depleted. The MnO x  + SiO 2  + TiO 2 /Ti composites catalyze the CO oxidation into CO 2 at temperatures above 100 °C, whereas the CoO x  + SiO 2  + TiO 2 /Ti composites do the same above 200 °C. Nanosized particles have been found on the surface of the composites under study: for CoO x  + SiO 2  + TiO 2 /Ti — granules of a diameter of a few dozen nm; for MnO x  + SiO 2  + TiO 2 /Ti — nanowhiskers consisting predominantly of manganese oxides. The obtained oxide catalysts are promising for testing as catalysts of redox reactions, including titanium-based microreactors.