Thermal behavior and catalytic activity in naphthalene destruction of Ce-, Zr- and Mn-containing oxide layers on titanium

► Mn-, Ce- and Zr-containing coatings on titanium as catalyst obtained by plasma electrolytic oxidation. ► Catalysts show activity in naphthalene degradation. ► Ce- and Zr-containing coatings have sufficiently high thermal stability until 850°C. The present paper is devoted to studies of the composition and surface structure, including those after annealing at high temperatures, and catalytic activity in the reaction of naphthalene destruction of Ce-, Zr- and Mn-containing oxide layers on titanium obtained by means of the plasma electrolytic oxidation (PEO) method. The composition and structure of the obtained systems were investigated using the methods of X-ray phase and energy dispersive analysis and scanning electron microscopy (SEM). It was demonstrated that Ce- and Zr- containing structures had relatively high thermal stability: their element and phase compositions and surface structure underwent virtually no changes after annealing in the temperature range 600–800°C. Annealing of Ce- and Zr-containing coatings in the temperature range 850–900°C resulted in substantial changes of their surface composition and structure: a relatively homogeneous and porous surface becomes coated by large pole-like crystals. The catalytic studies showed rather high activity of Ce- and Zr-containing coatings in the reaction of naphthalene destruction at temperatures up to 850°C. Mn-containing structures of the type MnOx+SiO2+TiO2/Ti have a well-developed surface coated by “nano-whiskers”. The phase composition and surface structure of manganese-containing layers changes dramatically in the course of thermal treatment. After annealing above 600°C nano-whiskers vanish with formation of molten structures on the surface. The Mn-containing oxide systems demonstrated lower conversion degrees than the Ce- and Zr-containing coatings, which can be attributed to substantial surface modification and formation of molten manganese silicates at high temperatures.