Synthesis Of ZSM-5/Cordierite Monolith Catalyst

Compared with traditional powder catalyst,monolith catalyst has the advantages of low pressure drop,low mass transfer resistance,high thermal resistance,high mechanical stability and small scale-up effect.Monolith catalyst has aroused great interesting in environment application.But how to control the synthesis conditions to get desired monolith catalyst has been a problem.Early researches show that,dip-molding process is a simple way to get monolith catalyst,but it has a big disadvantage that the coatings can't deposit on the substrate firmly and the thickness of the coating can't be controlled.Extrusion method is also a usual method to get monolith catalyst,but the coating made by extrusion always has a low mechanical strength.Considering these problems,ZSM-5/cordierite monolith catalyst were synthesized by hydrothermal method to detect the influence of n?SiO₂?/n?Al₂O₃?,n?TPAOH?/n?SiO₂?,n?H₂O?/n?SiO₂?and synthesis temperature on the growth of ZSM-5 zeolite on the cordierite substrate.The mass increase and thickness of the zeolite coating were tried to control by regulating the ratio of different raw materials.In order to obtain a homogeneous zeolite layer,a new synthesis method called varying-temperature synthesis and flowing system synthesis were used.NO catalytic oxidation activities of ZSM-5/cordierite monolith catalyst were also inspected.The main results and conclusions were listed below:In-situ hydrothermal synthesis method was used to synthesize ZSM-5/cordierite monolith catalyst with different SiO₂/Al₂O₃ ratio.The result shows that the particle size of ZSM-5 zeolite was effected by n?TPAOH?/n?SiO₂?,n?H₂O?/n?SiO₂?and synthesis temperature.With the increase of n?H₂O?/n?SiO₂?,the particle size increased.The particle size was ranged from 2?m to 12?m when the n?H₂O?/n?SiO₂?was ranged between 20 and 60.The particle size also increased with the increasing of synthesis temperature,the particle size could range from 500 nm to 17?m when synthesis temperature increases from 120?to 170?.The amount of TPAOH greatly influenced the particle size,when n?TPAOH?/n?SiO₂?were ranged from 0.25 to 0.15,particle size increased from 200 nm to 27?m.It could be seen that a small amount change of TPAOH leads to a big size change of ZSM-5 zeolite.The weight increase of ZSM-5 zeolite was increased with the increase of temperature,decrease of n?TPAOH?and n?H₂O?/n?SiO₂?.Zeolite layer can be controlled from 2?m to 60?m by changing the ratio of n?TPAOH?:n?SiO₂?,n?H₂O?/n?SiO₂?and synthesis temperature.A homogeneous zeolite layer could be obtained under low synthesis temperature.A homogeneous zeolite layer can be obtained by varying-temperature synthesis.A single zeolite layer can be formed at the first stage of low synthesis temperature,and then a dense homogeneous zeolite layer can be formed at the second stage of the increased temperature.Thus we can control the growth of zeolite layer by a varying-temperature synthesis.Zeolite particles synthesized under flowing system were smaller and the weight increase were also lower than those synthesized by varying-temperature synthesis.It means that zeolite was not easy to grow on the cordierite substrate in flowing system.Overall,the weight increase;particle size and the homogeneity of zeolite layer on the cordierite substrate can be controlled by regulating the raw material ratio and different crystallization methods.ZSM-5/cordierite monolith catalysts exhibited a good catalytic activity for NO oxidation at the ambient termperature.The results show that NO conversion increased with the loading of ZSM-5 zeolite on the cordierite substrate and the decrease of the particle size.