Micropore accessibility of large mordenite crystals
Micropore accessibility of large mordenite crystals
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DOI：
10.1016/j.micromeso.2006.01.008
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发表时间：
2006-06
影响因子：
5.2
通讯作者：
D. Lozano‐Castelló;Weidong Zhu;Á. Linares-Solano;F. Kapteijn;J. Moulijn
中科院分区：
文献类型：
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作者：
D. Lozano‐Castelló;Weidong Zhu;Á. Linares-Solano;F. Kapteijn;J. Moulijn
以草酸为硅源合成了大尺寸丝光沸石晶体。酸的热处理对于生长大的莫尔晶体是有效的，并且热处理温度越高，晶体越大。以丁烷异构体吸附为探针，考察了合成的莫尔分子筛经后处理和未经后处理后的吸附性能。合成的丝光沸石的通道中的Na+阳离子的一部分的沉积限制了探针分子的可及性。草酸处理和从起始Na-莫尔样品转化为H-形式莫尔既不产生中孔也不改变Si与Al的比率以及晶体尺寸和形态，但有效地去除了这种沉积并因此改善了可接近性。Langmuir模型可以很好地描述丁烷异构体在所研究的莫尔吸附剂上的吸附等温线。在相同的莫尔样品上，正丁烷的萃取饱和容量大于异丁烷，这归因于莫尔通道内线性正丁烷分子的较高填充效率，而异丁烷的估计吸附热略高，因为支化异丁烷与莫尔通道壁之间的相互作用更密切，这是由于其分子尺寸大于正丁烷。与分子模拟研究的比较表明，仍然有约30%的孔隙体积是不可接近的。
Large mordenite crystals are synthesized using silicic acid as a silica source. Heat treatment of the silicic acid is effective to grow large MOR crystals and the higher the heat-treatment temperature the larger the crystals. The micropore accessibility of the synthesized MOR zeolites with and without post-treatments has been examined by physicochemical characterization and the adsorption of butane isomers as probes. The lodgement of a fraction of the Na+cations in the channels of the synthesized mordenites restricts the accessibility to the probe molecules. An oxalic acid treatment and the transformation from the starting Na-MOR samples into the H-form MOR do neither create mesopores nor change the ratio of Si to Al and the crystal size and morphology, but effectively remove this lodgement and consequently improve the accessibility. The Langmuir model appropriately describes the adsorption isotherms of butane isomers on the MOR adsorbents investigated. On the same MOR sample, the extracted saturation capacity for n-butane is larger than for isobutane, ascribed to the higher packing efficiency of the linear n-butane molecules inside the MOR channels, while the estimated heat of adsorption is slightly higher for isobutane because of the more intimate interactions between the branched isobutane and the MOR channel wall due to its larger molecular size compared to n-butane. Comparison with molecular modelling studies indicates that still ∼30% of the pore volume is inaccessible.