Physics, Chemistry and Materials Science at the Nanoscale
Ammonia oxidation to NO in nitric acid production
Ammonia oxidation to NOx in nitric acid production
Cite as: Ammonia oxidation to NOx in nitric acid production, nano Online. (2016). DOI: https://doi.org/10.1515/nano.0131.00009
Cite as: Ammonia oxidation to NOx in nitric acid production. In: Heterogeneous Catalytic Redox Reactions. De Gruyter (2019). 191–222. DOI: https://doi.org/10.1515/9783110587777-009
Nonconcentrated nitric acid is produced via the catalytic oxidation of ammonia with air oxygen followed by adsorption of the formed nitrogen oxide by water [1, 2, 3, 4, 5, 6, 7, 8]. Therefore, the yield of the target product is determined to a great extent by activity and selectivity of the employed catalyst and conditions of its operation. At present, the prevalent catalyst for ammonia oxidation in the nitric acid production consists of gauzes that are made of platinum alloys with rhodium or with rhodium and palladium. During operation, the surface of platinum gauzes corrodes; as a result, the catalyst platinoid filament increases in diameter, the filaments become spongy and opaque, the surface area increases up to 20-fold, and platinum is lost as volatile oxides (chemical losses) due to carryover of the catalyst particles (mechanical losses). In a run over the gauzes, platinoid losses can reach two-thirds of the initial loading. In [9, 10, 11, 12], corrosion of a platinum catalyst is attributed to the increased surface diffusion in the catalytic process and formation of volatile platinum oxides, which are condensed on more cold regions of the wire or reactor. According to Salanov et al. [13, 14], the observed changes are related to an increase in the local temperature due to the catalytic reaction proceeding on oxygen coordination defects, which increases surface diffusion and platinum transfer from the regions of defects (dislocations and intergrain boundaries). As a result, defect-free crystallites and pores are formed on the initially smooth but defect wire surface.