Каталитическая коррозия платиновых катализаторов в процессе окисления аммиака

Abstract

SEM study of the platinum catalyst gauzes treated in the NH3-air mixture at 1133 K for 50 h demonstrates deep structural rearrangement of the surface layers (catalytic etching). The surface of the gauzes is covered by a continuous corrosion layer consisting of crystalline agglomerates with the sizes 5-15 μm separated by deep voids with the width 1-10 μm. The agglomerates have different shapes, crystalline faceting and contain through pores with the diameter 1-5 μm. Catalytic etching is initiated by the reaction of ammonia molecules with oxygen atoms absorbed at the grain boundaries, dislocations and other surface defects. This reaction results in local overheating of the surface initiating the release of metal atoms to the surface. Intense release of metal atoms from grain boundaries forms extended voids between the grains. So, the grains are gradually reconstructed into faceted crystalline agglomerates forming a corrosion layer.