Каталитическая коррозия платины, палладия и родия в процессе окисления аммиака

Abstract

To reveal the mechanism of the catalytic etching of platinum catalyst gauzes during the NH[3] oxidation, we carried out detailed investigation of the surface microstructure of platinum catalysts treated in the reaction medium (NH[3]+O[2]). The SEM study of a polycrystalline surface microstructure on platinum, palladium, and rhodium after treatment in the NH[3] + reaction air for 1 and 5 hours shows a different microstructural rearrangement of the surface. After the catalytic reaction of ammonia oxidation for 1 hour, platinum forms a granular structure with shallow furrows 1 to 4 [mu]m wide and indistinct grain boundaries. After a 5-hour reaction of catalytic ammonia oxidation, the grain boundaries are more clearly identified, the grooves on the grains are arranged in parallel and their size is 1-2 [mu]m. The photomicrographs obtained on palladium show that the entire surface of palladium is covered with agglomerates with a fibrous structure after the first hour. The size of the fibrous agglomerates varies from 2 to 10 [mu]m. After catalytic oxidation of ammonia for 5 hours on palladium is formed а deep structural reconstruction of the foil (catalytic corrosion). On rhodium for 1 hour, it is seen that light stretched regions with a width of about 2 [mu]m are located on the surface. Light, elongated areas are represented by the accumulation of rhodium nano- and microcrystals. After oxidation of ammonia on the rhodium for 5 hours, rhodium oxidation leads to the formation of a continuous surface layer of crystals of rhodium oxide.