Oxidation of NH₃ over YBa₂Cu₃O₇(123) oxide systems

Abstract

A temperature-programmed desorption study showed that the activation energy of oxygen desorption from YBa₂Cu₃O_7-x (x = 0.05), PrBa₂Cu₃O_7-x (x =0.02), and YBa₂Cu₂CoO_7-x (x = 0.26) were 28.2, 26.4, and 22.3 kcal/mole, respectively. Anaerobic oxidation of NH₃ over these oxide systems shows the formation of H₂0, N₂ and NO transforming the oxides to tetragonal phases. Aerobic oxidation of NH₃ is NO specific over all the three oxide catalysts. The Co-substituted YBa₂Cu₂ CoO_7+x was the most reactive and stable oxide in this family; the lower oxygen desorption energy and higher reactivity are suggested to be due to the presence of holes in the form Co⁴⁺O^2- Co³⁺O^-. The conversion of NH₃ to NO was nearly 100% above 400°C when the ammonia flow rates were 10 μmole/cm²/s over 0.3 g of the YBa₂Cu₂CoO_7+x catalyst. Structural Chemistry Unit.