The reaction mechanism of the high temperature ammonia oxidation to nitric oxide over LaCoO3

Perovskites are promising catalysts for oxidation reactions. Good NO selectivity is reported for the oxidation of ammonia into nitric oxide over LaCoO3. More interestingly over this catalyst very little N2O is produced, which makes it a potential candidate for industrial ammonia oxidation. In order to further develop perovskite catalysts, an understanding of the reaction mechanism is necessary. Steady-state, TAP and oxygen exchange experiments over LaCoO3 have been carried out. A reaction mechanism that describes the product distribution (NO, N2O and N2) as a function of the oxidation degree of the catalyst has been proposed. The reaction proceeds by a Mars and Van Krevelen mechanism. NO and N2O are formed through parallel routes from ammonia via surface nitroxyl (HNO) species. Formation of nitrogen occurs through at least three routes. Decomposition of both reaction products NO and N2O leads to N2, the latter decomposition being the fastest. The third route to N2 consists of the reaction of adsorbed ammonia with short-lived oxygen surface species, such as peroxide or superoxide species.

By combining different transient (TAP, oxygen exchange) and steady-state techniques, a reaction mechanism for ammonia oxidation over LaCoO3 has been proposed.Figure optionsDownload high-quality image (87 K)Download as PowerPoint slide