Microscopy Study of the Front and Back Sides of Platinum Catalyst Gauzes Used in Ammonia Oxidation
Ammonia oxidation with air on platinum catalyst gauzes is widely used in chemical industry for synthesis of nitric acid. It is well known that during this process the gauzes undergo deep structural rearrangement of surface layers (catalytic etching) leading to the platinum loss and catalytic activity decrease. To reveal the mechanism of the catalytic etching of platinum catalyst gauzes during the NH3 oxidation, we studied in detail the surface microstructure of the front and back sides of platinum catalyst gauzes used in ammonia oxidation. The platinum catalyst gauzes used in the study were made from a polycrystalline wire with d ≈ 82 μm with the chemical composition (in wt.%) 81% Pt, 15% Pd, 3.5% Rh and 0.5% Ru. A laboratory flow reactor made of quartz tube with the inner diameter of 11.2 mm was used at the feed (ca. 10% NH3 in air) flow rate 880-890 l/h, the gauze temperature 860±5 °C and total pressure ca. 3.6 bar. A pack of four gauzes was loaded into the reactor to maintain standard conditions of the catalytic process. The surface microstructure was studied using a scanning electron microscope (SEM) JSM-6460 LV (Jeol).