Catalytic behavior of alkali-treated Pt/HMOR in n-hexane hydroisomerization
Catalytic behavior of alkali-treated Pt/HMOR in n-hexane hydroisomerization
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DOI：
10.1016/j.apcata.2014.02.026
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发表时间：
2014-04-22
影响因子：
5.5
通讯作者：
Martins, A.
中科院分区：
文献类型：
--
作者：
Monteiro, R.;Ania, C. O.;Martins, A.
采用初湿浸渍法制备了双功能 Pt-HMOR 催化剂，采用浓度为 0.1 至 0.5 M 的 NaOH 碱处理得到的各种脱硅 MOR。通过粉末 X 射线衍射、Al-27 和 Si-29 MAS-NMR 光谱、N-2 吸附、吡啶吸附、红外光谱以及间二甲苯转化催化模型反应等技术研究了改性后沸石结构的变化。对于低碱浓度，沸石的酸性得以保留，同时由于去除了母体沸石中已经存在的骨架外碎片，对应于较大微孔的体积略有增加。在较高的 NaOH 浓度下，结晶度和酸度显着损失，并形成中孔。金属功能的表征显示 Pt-HMOR 和 Pt-M/0.1 样品的相似模式，其中 Pt 颗粒主要位于内部孔隙内部。相比之下，在强碱性条件下的脱硅处理过程中，MOR 晶体的晶间介孔中可以看到大的 Pt 颗粒。正己烷加氢异构化获得的催化结果表明，Pt-M/0.1 样品对二支化异构体的选择性优于单支化异构体，这可能是由于载体酸度的保留和微孔的轻微扩大。这项工作是一个新的例子，其中介孔的发展并没有提高沸石的催化效率，而温和的碱性脱硅可能被认为是生产针对给定应用具有增强性能的定制催化剂的有效解决方案。 (C) 2014 Elsevier B.V. 保留所有权利。
Bifunctional Pt-HMOR catalysts were prepared by incipient wetness impregnation of various desilicated MOR obtained by alkaline treatment using NaOH concentrations ranging from 0.1 to 0.5 M. The zeolite structural changes upon modification were investigated by several techniques including powder X-ray diffraction,Al-27 and Si-29 MAS-NMR spectroscopy, N-2 adsorption, pyridine adsorption followed by infrared spectroscopy and the catalytic model reaction of m-xylene transformation. For low alkaline concentration the zeolite acidity is preserved, along with a slight increase of the volume correspondent to the larger micropores due to the removal of extra-framework debris already existent at the parent zeolite. At higher NaOH concentrations there is a significant loss of crystalinity and acidity as well as the formation of mesoporosity. The characterization of the metal function shows similar patterns for Pt-HMOR and Pt-M/0.1 samples, with Pt particles located mainly inside the inner porosity. In contrast, large Pt particles become visible at the intercrystalline mesoporosity of MOR crystals developed during the desilication treatments at severe alkaline conditions. The catalytic results obtained for n-hexane hydroisomerization showed an improved selectivity for dibranched over monobranched isomers for Pt-M/0.1 sample, likely due to the preservation of the support acidity and the slight enlargement of the micropores. This work is a new example in which the mesoporous development does not improve the catalytic efficiency of the zeolites, whereas mild alkaline desilication might be considered as an effective solution to produce customized catalysts with enhanced performance for a given application. (C) 2014 Elsevier B.V. All rights reserved.