The Fabrication Of Cu-SAPO-34 Catalyst And Its Property In The Selective Catalytic Oxidation Of Ammonia

With the development of social industry and the improvement of people living standard, auto industry progresses quickly, and the ammonia slip problem of NH₃-SCR process using ammonia as a reactant to remove NOx from motor vehicle exhaust has attracted broad attention. NH₃ is a toxic and harmful odor pollutant and does harm to human health and natural environment. Therefore, it is imminent to solve the problem of NH₃ pollution. At present, ammonia selective catalytic oxidation technology is regarded as an ideal technology with high efficiency and cleanness to remove NH₃, and the key issue is the selection of catalysts.In recent years, copper-based catalyst has been studied widely due to its excellent NH₃ catalytic activity and N₂ selectivity; SAPO-34 molecular sieve has become a research focus because of its higher thermal stability, hydrothermal stability and low preparation cost. Therefore, we synthesised a series of Cu/SAPO-34 and Cu/Ce-SAPO-34 catalysts by impregnation method, and the ammonia catalytic activities were measured. The main substances of our work are as follows:1. A series of Cu/SAPO-34 catalysts were prepared and used for ammonia catalytic oxidation. The experimental results showed that when the loading of copper was 10 wt.%, the NH₃ conversion was nearly 100% at 300℃ and N₂ selectivity was more than 90% in the range of test temperature. The characterization results showed that the highly dispersed CuO species were more active than agglomerated CuO species, especially for the N₂ selectivity.10%Cu/SAPO-34 had the lowest reduction temperature, which would shift to high temperature with the increasing loading of copper. The aged 10%Cu/SAPO-34 catalyst performed better NH₃-SCO activity at low temperature, but the N₂ selectivity of the catalyst was plummeting at 325℃. From the intensity of diffraction peak at 9.4°, we speculated that the SAPO-34 zeolite crystallinity would deterior under hydrothermal treatment; and it could be found that amount of copper species migrated and more stable Cu2+ formed after hydrothermal treatment.2. The Cu/SAPO-34 catalysts were modified by cerium, and the results showed that the catalyst displayed excellent catalytic activity and N₂ selectivity. The results suggested that interaction between Cu and Ce could improve the dispersion of copper species. The catalyst modified by cerium obviously decreased the reduction temperature, and thereby it was beneficial to the redox reaction. The characterization results of the 25%Cu/Ce-SAPO-34 treated by hydrothermal method indicated that the hydrothermal treatment increased the catalytic activity at low temperature, and N₂ selectivity was more than 90% in the range of test temperature; The catalysts modified by cerium effectively improved the textural and structural stability of SAPO-34 molecular sieve.