Study Of Fe,Al-SBA-15 Prepared By A New Method And Application In Selective Catalytic Reduction Of NO With NH₃

Nitric oxides (NOx) are hazardous pollutants and not only contribute to many environmental problems such as acid rain and smog, but also have negative impacts on human health. Selective catalytic reduction (SCR) of NOX with ammonia is considered to be an effective technology for the removal of NOx, The catalysts of Fe,Al-SBA-15 are environmental-friendly, high-efficiency, and promising.A series of bimetallic Fe,Al-SBA-15 DeNOx catalysts were synthesized by microwave (MW) and conventional heating (CH) methods with various levels of iron and aluminium contents, all of which was used to identify and study the roles of aluminium and different iron species in SCR. Synergistic effect between iron and alumina was achieved showing a satisfactory NO conversation of approximately 95% over Fe,Al-SBA-15-MW at temperature as low as 350℃. The catalysts were characterized by XRD, TEM, N2 desorption/adsorption, UV-Vis DRS,27Al MAS NMR, In situ DRIFTS and EPR. Through UV-Vis DRS and 27A1 MAS NMR, We found that MW method produced more oligomeric FexOy clusters and tetrahedral framework aluminium than CH method. NH3 were mainly adsorpted to tetrahedral framework aluminium and existed as NH4+ ions. Although the reaction between adsorbed ammonia and oxygen occurred, the reaction rate was much slower than that between ammonia and NO+O2. Moreover, in situ EPR indicated that Fe3+ species, which did not react with pure NH3, could be easily reduced to Fe2+ by NH3+NO. When O2 was introduced as well, the non-paramagnetic Fe2+ species would be reoxidezd to Fe3+. Besides, the active complex NH4+(NO2) which attributed to g’-3.3 in EPR might be the key intermediates in the SCR reaction.In the end, we also did some research about micro-mesoporous composite molecular sieves. A description is given below of the methods employed to modify mesoporous SBA-15 by secondary crystallization in a hydroxide medium containing the organic template of the microporous MFI structure. When SBA-15 was thermally treated at 170℃ in the presence of TPAOH and water for 24 h, the mesopore structure was partly maintained and large crystals of microporous zeolite with MFI structure were obtained. However, the SEM indicated that the generated ZSM-5 did not combine with SBA-15 very well. The SBA-15 structure probably acted simply as a silica source, with the MFI structure crystallizing from the silica gel formed after the dissolution of SBA-15.