STRUCTURE AND PROPERTIES OF HETEROGENEOUS CATALYST ON AN OXIDE CARRIER BASED ON ALUMINIUM

Abstract

In this study, the MAO technology was optimized in order to obtain a high development of coatings and their good adhesion to the substrate for the creation of a highly efficient heterogeneous catalyst on the oxide carrier of the Pt/Al2O3 system. Oxide coatings of different phase composition, surface structure and roughness, with a thickness of 20 –100 μm were obtained by MAO methods on D16 alloy and A97 commercial aluminum. It is shown that the structure and morphology of the surface of the coatings is determined by the conditions of electrolysis, which allows their optimization to improve efficiency. It is determined that the surface coating layer consists of the following phases: γ-Al2O3, α-Al2O3 and 3 Al2O3 • 2SiO2 (mullite). On the D16 alloy there was a predominant formation of γ-Al2O3 and α-Al2O3 phases. Increasing the duration of microarc oxidation increases the content in the coating of the α-Al2O3 phase. It is established that the use of MAO technology allows to change the morphology of the surface and its roughness in a wide range. The formation of two types of surface inhomogeneity in the planar growth region of coatings is revealed: with a relatively small size of such formations (up to 50 μm) and with the formations of the second type, the sizes of which in the planar growth region of MAO coatings reach 300 μm.It is determined that the purification coefficient of nitrogen oxide in Pt/Al2O3 catalysts is temperature dependent. At relatively low (150°C) and high (300°C) temperatures the highest value of α is achieved in systems based on MAO coatings with binary (γ-Al2O3 and α-Al2O3) phase composition. In the temperature range of the most effective cleaning (200–250°C) the greatest influence on their efficiency, apparently, has a surface morphology, namely, the formation of large (up to 300 μm) formations of surface inhomogeneity in the growth plane. In this case, the purification coefficient (for the reduction of nitrogen oxides) α reaches 92 %.The results of the study can be used in the development and creation of a new type of catalysts for the Pt/Al2O3 system.