原位水热合成法制备ZSM-5/堇青石整体式催化剂

In-situ Hydrothermal Synthesis of ZSM-5/Cordierite Monolith Catalyst

以蜂窝状堇青石为载体,采用原位水热合成法制备了ZSM-5/堇青石整体式催化剂。考察了四丙基氢氧化铵(TPAOH)含量、水硅摩尔比和晶化温度等对ZSM-5分子筛在堇青石载体上负载量的影响。结果表明:模板剂TPAOH的含量对负载量有显著影响,当摩尔比n(TPAOH)/n(SiO2)≤0.2时,改变晶化温度和水硅摩尔比均可获得较佳的分子筛负载量;当n(TPAOH)/n(Si O2)>0.2时,较高的碱度导致前驱体溶胶的溶解,使分子筛多在溶液中晶化,显著减小分子筛在堇青石载体上的负载量。当n(TPAOH)/n(Si O2)≤0.2时,水硅比减小,ZSM-5分子筛负载量逐渐增大,最大负载量可达42.8%。晶化温度降低,分子筛的负载量和晶粒均减小。整体式催化剂用于NO的催化氧化活性研究表明,堇青石载体上分子筛的负载量越高,整体式催化剂的比表面积越大,催化活性越好。

ZSM-5/cordierite monolith catalyst was synthesized by an in-situ hydrothermal method. The effects of amount of tetrapropyl ammonium hydroxide （TPAOH）, n（H2O）/n（SiO2） ratio and crystallization temperature on the deposition of ZSM-5 on cordierite supporter were investigated. The results reveal that the deposition of ZSM-5 on the cordierite supporter is related to the amount of TPAOH. When n（TPAOH）/n（SiO2）≤0.2, a desired deposition of ZSM-5 zeolite can be obtained via the adjustment of temperature or n（H2O）/n（SiO2） ratio. When n（TPAOH）/n（SiO2）〉0.2, a high alkalinity leads to the dissolution of the precursor sol, making that zeolite tends to grow in solution rather than on the cordierite surface, and thus decrease the deposition of zeolite on the cordierite. When n（TPAOH）/n（SiO2≤0.2, the deposition of ZSM-5 increases with the decrease of n（H2O）/n（SiO2） ratio, and the maximum deposition amount is 42.8%. The crystal particle size and the loading amount decrease with the decrease of the crystallization temperature. According to the catalytic activity of monolith catalysts for NO, a high loading amount and a small crystal particle size of ZSM-5 zeolite on the surface of the monolith catalyst lead to a high specific surface area, which can favor the NO catalytic oxidation.