Acidic and catalytic properties of hierarchical zeolites and hybrid ordered mesoporous materials assembled from MFI protozeolitic units
Acidic and catalytic properties of hierarchical zeolites and hybrid ordered mesoporous materials assembled from MFI protozeolitic units
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DOI：
10.1016/j.jcat.2011.02.007
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发表时间：
2011-04
影响因子：
7.3
通讯作者：
D. Serrano;Rafael García;G. Vicente;Mauricio Linares;D. Procházková;J. Čejka
中科院分区：
文献类型：
--
作者：
D. Serrano;Rafael García;G. Vicente;Mauricio Linares;D. Procházková;J. Čejka
两种类型的MFI沸石材料具有改善的可及性，分层沸石和杂化有序介孔材料在这里比较的织构，酸性和催化性能。在这两种情况下，采用原沸石单元作为起始结构单元，其生长受到硅烷化剂（分级ZSM-5）的干扰或通过在表面活性剂胶束周围组装来控制（混合有序中孔材料，HZM）。同样地，使用两种标准样品（纳米晶体ZSM-5和Al-MCM-41）作为参考。氮吸附测量证实了存在的次生孔隙率和高份额的非微孔表面积在分级ZSM-5，而没有显着量的微孔混合HZM样品中检测到。然而，27 Al MAS NMR测量表明沸石碎片存在于后一样品的壁内。通过对不同碱基探针分子的吸附-脱附，对所研究材料的酸性进行了广泛的研究。具体而言，吡啶吸附后取得的FTIR光谱显示在分级ZSM-5和HZM样品中均存在大量强刘易斯酸位点。这一事实，沿着与高的可及性的活性位点，提出主要负责增强的催化活性所表现出的这些材料在1，2-环氧辛烷重排和苯甲醚酰化。所得结果清楚地表明，分级材料的结构和酸性特征对其催化性能产生了强烈而积极的影响。
Two types of MFI zeolitic materials with improved accessibility, hierarchical zeolites and hybrid ordered mesoporous materials are here compared in terms of textural, acidic and catalytic properties. In both cases, protozeolitic units were employed as starting building blocks, the growth of which was perturbed by a silanization agent (hierarchical ZSM-5) or controlled by assembling around surfactant micelles (hybrid ordered mesoporous material, HZM). Likewise, two standard samples (nanocrystalline ZSM-5 and Al-MCM-41) were used as reference. Nitrogen adsorption measurements confirmed the presence of a secondary porosity and a high share of non-microporous surface area in hierarchical ZSM-5, whereas no significant amount of micropores was detected in the hybrid HZM sample. However,27Al MAS NMR measurements indicated that zeolitic fragments are present within the walls of the latter sample. The acidic properties of the materials under study were extensively investigated by adsorption–desorption of different base probe molecules. Specifically, FTIR spectra taken after pyridine adsorption show the presence of a high population of strong Lewis acid sites in both hierarchical ZSM-5 and HZM samples. This fact, along with a high accessibility to the active sites, is proposed to be mainly responsible for the enhanced catalytic activity exhibited by these materials in 1,2-epoxyoctane rearrangement and anisole acylation. The results obtained clearly indicate the strong and positive influence of the textural and acidic features of the hierarchical materials on their catalytic properties.