One Step Synthesis Of Fe-SSZ-13 Zeolite By Hydrothermal Method And Catalytic Performance In NH₃-SCR Reaction

The combustion of fossil fuels will produce a large amount of nitrogen oxides?NO_x?,which will cause optical pollution and chemical pollution in the atmosphere.It is one of the main pollutants in the air,and its large amount of emissions will cause very serious environmental problems.Ammonia selective catalytic reduction?NH₃-SCR?technology for reducing nitrogen oxides is currently the most commonly used and effective method for controlling nitrogen oxide emissions.The metal-exchanged SSZ-13 zeolite has high catalytic activity in the NH₃-SCR reaction.Cu-SSZ-13 has better low-temperature catalytic activity than Fe-SSZ-13,but Fe-SSZ-13 can exhibit higher hydrothermal stability and sulfur resistance than Cu-SSZ-13,it can also still maintain high catalytic activity in the presence of H₂O,SO₂ and O₂,and is considered to be an SCR catalyst with practical application prospects.The traditional method for preparing Fe-SSZ-13 zeolite is ion exchange or impregnation method.These methods have complicated steps,and it is difficult to control the loading or existence form of iron metal on zeolite.Hydrothermal method is currently the simplest and most direct method for synthesizing zeolite materials.Therefore,this thesis studies the direct synthesis of Fe-SSZ-13 zeolite by hydrothermal synthesis method,allowing iron components to directly participate in the synthesis processHerein Fe-SSZ-13 zeolite was synthesized directly by hydrothermal method,and its crystallization process and synthesis conditions were studied.Through XRD,FT-IR,SEM,UV-Vis,H₂-TPR and other characterization,the following results were obtained:?1?Fe-SSZ-13 zeolite can be directly synthesized by hydrothermal method.The introduction of iron does not change the crystallization process of the SSZ-13 zeolite,and the obtained Fe-SSZ-13 zeolite has iron species with higher activity,such as monomer[Fe-?OH?₂]⁺and dimer[HO-Fe-O-Fe-OH]²⁺.The obtained zeolite material was directly used to catalyze the NH₃-SCR reaction after calcination.The conversion of NO was close to 100%in the range of 300⁴50°C,which indicated that Fe-SSZ-13 synthesized directly by hydrothermal method has good catalytic activity.?2?Different raw materials influence the synthesis of Fe-SSZ-13 zeolite.NaOH and KOH are used as alkali sources.It was found that K⁺helps the combination of silicon and aluminum and can increase the yield of zeolite.Na⁺can promote the combination of ferrosilicon and improve the distribution of iron species on the product zeolite.?3?The type of iron on Fe-SSZ-13 zeolite synthesized directly by hydrothermal method is affected by many factors.In the preparation of the gel precursor,the addition of iron before the aluminum can ensure that silicon and iron are fully complexed,so that the iron is finally loaded on the zeolite framework in a highly active state.During the calcination of zeolite,the temperature,time and method of calcination will affect the distribution of iron species on the zeolite product.Using a multi-stage program to quickly heat up can remove the template agent while protecting the iron species,thus ensuring the catalytic activity of Fe-SSZ-13zeolite in the SCR reaction.