Preparation of nitrogen-doped Mo₂C/AC via urea pyrolysis and its performance enhancement mechanism in catalytic reduction of NO₂

To address the issues of high-temperature deactivation of molybdenum furnace conversion agents used in traditional NO₂ detection and the interference of side reactions with detection accuracy, this study prepared Mo₂C/AC using an impregnation-carbonization method, and achieved nitrogen doping modification through pyrolysis of urea in the temperature range of 400−800 ℃ to obtain the Mo₂C/ACN-X series of catalysts. The catalyst structure was characterized by N₂ physical adsorption-desorption, Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy, and the mechanism by which nitrogen doping regulates the catalyst structure and enhances its catalytic NO₂ conversion performance was investigated in depth. The research results showed that after nitrogen doping, the specific surface area of the catalyst decreases, while the average pore size of Mo₂C/ACN-800 increases; the urea pyrolysis temperature has a regulatory effect on the bulk molybdenum species of the catalyst and the distribution of their surface valence states. Under the pyrolysis conditions of 400 ℃ and 600 ℃, MoO₂ and Mo₂C coexisted, whereas Mo₂C became the dominant crystalline phase when pyrolyzed at 800 ℃. With the increase of pyrolysis temperature, the content of Mo²⁺ on the surface of the nitrogen-doped catalyst increases, among which the Mo²⁺ content of Mo₂C/ACN-800 increases significantly; the surface nitrogen content first increases and then decreases, and the proportion of pyridinic nitrogen increases. Under the condition of 60 ℃, the NO₂ conversion rate of the Mo₂C/ACN-800 catalyst reached 97.5%, which was 9.7% higher than that of the undoped sample. This study opens up new material design ideas for the development of efficient low-temperature NO₂ catalyst and has important theoretical and practical application values.