Окисление и коррозия поликристаллической платины в O2 и в процессе окисления аммиака

Abstract

To reveal the mechanism of the catalytic etching of platinum catalyst gauzes during the NH3 oxidation, we carried out detailed investigation of the surface microstructure of platinum catalysts treated in oxygen, and in the reaction medium (NH3+O2). SEM study of the polycrystalline platinum surface microstructure after treatment in O2 and in the reaction mixture NH3 + air shows different microstructural rearrangement of the surface. In the O2 atmosphere the surface graphite-like film is destroyed during the oxygen reaction with carbon resulting in the growth of grains to 10-200 μm. During these processes the grain surface morphology does not significantly change and remains practically smooth. In the reaction mixture NH3 + air the surface graphite-like film is quickly destroyed, and oxygen is penetrated at the grain boundaries, dislocations and other defects. The NH3 reaction with the penetrated oxygen results in local overheating in the defect area leading to intense release of Pt atoms to the surface. Pt atoms migrate on the surface and gradually form new crystalline faces and facets. As a result, a continuous corrosion layer covering the entire surface of polycrystalline platinum is formed.