Studies on the decomposition of N₂O over Nd₂CuO₄, Nd_1.6Ba_0.4CuO₄ and Nd_1.8Ce_0.2CuO₄

Nd₂CuO₄, Nd_1.6Ba_0.4CuO₄ and Nd_1.8Ce_0.2CuO₄ were prepared by means of the citric acid complexing method. The catalytic performances of N₂O decomposition to N₂ over this series of K₂NF₄-type cuprates have been evaluated. Techniques such as XRD, XPS, EPR, TPD, pulsing, in situ DRIFT, and FT-Raman as well as chemical analysis were employed to investigate the nature of the active sites and to identify the possible reaction intermediates. A catalytic reaction mechanism has been proposed. The N₂O decomposition activities declined in the order of Nd_1.8Ce_0.2CuO₄ > Nd_1.6Ba_0.4CuO₄ > Nd₂CuO₄ when the reaction temperatures were below 400°C. Above 400°C. Nd_1.8Ce_0.2CuO₄ was inferior to Nd_1.6Ba_0.4CuO₄. The results of chemical analysis and XPS studies revealed that there are (i) Cu²⁺, Cu³⁺, and extra oxygen in Nd₂CuO₄; (ii) Cu²⁺, Cu⁺, and extra oxygen in Nd_1.8Ce_0.2CuO₄; and (iii) Cu³⁺, Cu²⁺, and oxygen vacancies in Nd_1.6Ba_0.4CuO₄. There are Cu⁺, Cu²⁺, Cu³⁺ and active oxygen species such as O^- (O₂^2-) or O₂^- in the used catalysts. The results of EPR, in situ DRIFT and Raman studies suggested that during N₂O decomposition NO₃^-, NO₂^-, N₂O₂^2-, NO^-, and oxygen species (O^-, O₂^2-, and O₂^-) were generated. The productions of NO and N₂ are competitive. The reaction mechanism includes the redox actions amidst Cu⁺ ⇔ Cu²⁺ ⇔ Cu³⁺ and O^2- ⇔ O^-(O₂^2-) ⇔ O₂ ^- ⇔ O₂. Oxygen vacancies are important sites for N₂O adsorption and oxygen species O^- are required for the formation of the crucial intermediate N₂O₂^2-.