###### Abstract  
The production of nitric acid represents the primary source of nitrous oxide (N\({}_{2}\)O) emissions. During pilot-scale studies of N\({}_{2}\)O reduction on a low-temperature catalyst on nitric acid plants, it was observed that increasing the concentration of NH\({}_{3}\) resulted in a decrease in the degree of N\({}_{2}\)O decomposition. This suggested that N\({}_{2}\)O was formed by the oxidation of NH\({}_{3}\). Measurements at different temperatures, conducted after the N\({}_{2}\)O reduction trials, resulted in the N\({}_{2}\)O concentration at the inlet equal to the concentration at the outlet, indicating catalyst deactivation. To identify the causes of deactivation, the physicochemical properties of the catalyst were investigated. XRF analysis revealed the presence of sulfur. The results suggest the necessity of removing sulfur from the raw gas before the reduction of N\({}_{2}\)O on the low-temperature catalyst in practical applications. N\({}_{2}\)O decomposition; low-temperature catalyst; deactivation; nitric acid plant; catalysis; sulfur +
Footnote †: journal: Applied Sciences  
research focuses on assessing changes in the chemical composition, morphology, and structure of the catalyst after operation. The article provides evidence of permanent catalyst poisoning, which prevents its regeneration, and it presents experimental results confirming the presence of sulfur compounds as the main cause of catalyst deactivation. A review of the literature on catalysts for N\({}_{2}\)O decomposition reveals significant challenges faced by these materials, including insufficient stability, durability, and susceptibility to deactivation, particularly in the presence of SO\({}_{2}\). Studies on catalysts based on noble metals and transition metal oxides often overlook critical industrial requirements for long-term durability and resistance to deactivation. Many of the analyzed catalysts have not been tested under conditions involving SO\({}_{2}\). The activity of most catalysts discussed in the literature is not limited to N\({}_{2}\)O decomposition but also includes the oxidation of SO\({}_{2}\) to SO\({}_{3}\), which accelerates the deactivation process. The literature indicates that catalysts such as rhodium on zirconia are stable only in the absence of SO\({}_{2}\), whereas Fe-ZSM-5 catalysts demonstrate resistance to deactivation even during prolonged exposure to SO\({}_{2}\), making them more promising for industrial applications. The literature presents mixed findings regarding cobalt-based catalysts: CoMgAl-Ox exhibits resistance to deactivation in the presence of SO\({}_{2}\), while the K/Co-CeO\({}_{2}\) catalysts becomes completely deactivated under the same conditions, despite its excellent performance in the presence of O\({}_{2}\) and H\({}_{2}\)O [21; 22; 23; 24]. The available literature on the deactivation of deN\({}_{2}\)O catalysts by sulfur compounds is limited, indicating a significant research gap in this area. Although some studies describe general mechanisms of sulfur poisoning of catalysts, which partially helps in understanding the deN\({}_{2}\)O catalyst deactivation process, there is a need for more detailed investigations to fully explain this mechanism. According to the literature, the deactivation of the CuO/Al\({}_{2}\)O\({}_{3}\) sorbent at temperatures of 200-300 \({}^{\circ}\)C by SO\({}_{2}\) is attributed to the formation of ammonium sulfate and copper sulfate. Ammonium sulfate deactivates the SCR process by blocking or clogging the catalyst pores, while copper sulfate further contributes to this process by reducing catalyst activity and blocking pores, leading to lower activity compared to CuO. In addition, studies on the ZnCo\({}_{2}\)O\({}_{4}\) catalyst indicate that SO\({}_{2}\) significantly reduces its catalytic activity during soot oxidation. This reduction in activity may result from the formation of sulfate or sulfide on the catalyst surface, which limits the number of active sites and decreases the specific surface area of the catalyst [25; 26].