Mesoporous ZSM-5 zeolite catalysts prepared by desilication with organic hydroxides and comparison with NaOH leaching
Mesoporous ZSM-5 zeolite catalysts prepared by desilication with organic hydroxides and comparison with NaOH leaching
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DOI：
10.1016/j.apcata.2009.05.055
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发表时间：
2009-07-31
影响因子：
5.5
通讯作者：
Perez-Ramirez, Javier
中科院分区：
文献类型：
--
作者：
Abello, Sonia;Bonilla, Adriana;Perez-Ramirez, Javier
以ZSM-5 （Si/Al = 42）为原料，在四烷基氢氧化铵（TPAOH， TBAOH）水溶液中脱硅，制备了微孔和介孔相结合的分级沸石。有机氢氧化物处理与传统NaOH浸出的相似之处包括：(i)需要在最佳Si/Al窗口25-50内使用起始沸石；（ii）反阳离子（H+, NH4+, Na+）对介孔形成程度的影响较小。但两种脱硅介质均表现出不同的动力学和机理特征。利用有机氢氧化物直接煅烧生成质子形式的介孔沸石，简化了最终与NH4NO3离子交换的NaOH处理特点。硅在TPAOH（或TBAOH）中的溶解比在NaOH中的溶解要慢得多，这使得脱金属过程具有高度的可控性。有机碱处理对硅的萃取选择性较低，即与NaOH处理相比，溶液中铝的浸出量较高。孔隙发育和最终固体化学成分的差异可归因于体积较大的四烷基铵阳离子的影响。最佳分级ZSM-5沸石（在338k和8h的1 M TPAOH中处理）的介孔表面积为160 M (2) g(-1)，基本保持了沸石的固有性质。与母分子筛和naoh处理的沸石相比，该样品在液相苯与乙烯的烷基化反应中表现出更好的催化性能。(C) 2009 Elsevier B.V.版权所有
Hierarchical zeolites combining micro- and mesoporosity were prepared by desilication of ZSM-5 (Si/Al = 42) in aqueous solutions of tetraalkylammonium hydroxides (TPAOH, TBAOH). Similarities between the treatment mediated by organic hydroxides and the conventional NaOH leaching comprised (i) the requirement to work with a starting zeolite in the optimal Si/Al window of 25-50 and (ii) the minor influence of the counter-cation (H+, NH4+, Na+) on the degree of mesoporosity developed. However, both desilication media presented distinctive kinetic and mechanistic characteristics. The use of organic hydroxides directly produced the protonic form of the mesoporous zeolite upon calcination, simplifying the final ion exchange with NH4NO3 characteristic of the NaOH treatment. Silicon dissolution in TPAOH (or TBAOH) was much slower than in NaOH, making the demetallation process highly controllable. The treatment in the organic base was less selective for silicon extraction, i.e. a higher amount of aluminum was leached to the solution compared to the NaOH treatment. The differences in porosity development and chemical composition of the final solid can be assigned to the effect of the bulky tetraalkylammonium cation. The optimal hierarchical ZSM-5 zeolite (treated in I M TPAOH at 338 K and 8 h) had a mesopore surface area of 160 m(2) g(-1) and the intrinsic zeolite properties were largely preserved. This sample displayed improved catalytic performance in the liquid-phase benzene alkylation with ethylene compared to the parent and NaOH-treated zeolites. (C) 2009 Elsevier B.V. All rights reserved.