Comparison of 6Mo/MCM-22 and 6Mo/ZSM-5 in the MDA process

A comparison of methane dehydroaromatization (MDA) on 6Mo/MCM-22 and 6Mo/ZSM-5 was carried out using a gas mixture of 90%CH4, 2%CO2 and 8%Ar as the feed. The results indicate that the stability of 6Mo/MCM-22 is better than that of 6Mo/ZSM-5. A detailed study reveals that the ability for coke accommodation and the retention of the shape selectivity for aromatics formation is responsible for the stability of a MDA catalyst.

The effect of acidity on olefin aromatization over potassium modified ZSM-5 catalysts

The transformation of olefin to aromatics over ZSM-5 catalysts with different K-loadings has been investigated both in a continuous flow fixed-bed reactor and in a pulse microreactor. Investigation of variation of olefin aromatization activity with K-loadings shows that strong acid sites are indispensable for the converting of olefin to aromatics. As intermediates of olefin aromatization process, butadiene and cyclopentene not only show much higher aromatization activity than mono-olefins, but also can be transformed into aromatics over relatively weak acid sites of K/ZSM-5. A proposal is put forward, stating that among all the steps experienced in olefins aromatization, the formation of diene or cycloolfin from mono-olefins through hydrogen transfer is the key step and can be catalyzed by strong acid sites.

Unique properties of Ir/ZSM-5 catalyst for NO reduction with CO in the presence of excess oxygen

The reduction of NO with CO in the presence of excess oxygen was investigated over different noble metal catalysts for probing the relationship between catalytic properties and adsorption behaviors. Among the four precious metal catalysts investigated, Ir/ZSM-5 was found to be the only active one for NO reduction with CO under lean conditions. With the decreasing of the Ir content, higher NO conversion and CO selectivity was obtained. Temperature-programmed reaction (TPR) studies of NO/H-2/O-2 and NO/CO/O-2 showed that the Pt/ZSM-5 was active when H-2 was used as the reductant, whereas, the Ir/ZSM-5 was active when CO was the reducing agent. This difference is due to the different mechanisms of the two reactions. Temperature-programmed desorption (TPD) of NO, CO and O-2 showed that NO could dissociate more easily over the Ir/ZSM-5 than on the Pt/ZSM-5, while the oxidation of CO by O-2 proceeded more rapidly on the Pt/ZSM-5 than on the Ir/ZSM-5. The presence of excess O-2 inhibited drastically the dissociation of NO, which is considered as the key step for the NO-CO reaction. The high dissociation rate of NO over the Ir/ZSM-5 is visualized as the key factor for its superior high activity in NO reduction with CO under lean conditions. (C) 2002 Elsevier Science B.V. All rights reserved.

On configuration of exchanged La3+ on ZSM-5: A theoretical approach to the improvement in hydrothermal stability of La-modified ZSM-5 zeolite

Density functional calculations have been employed to investigate the locating and binding of lanthanum cation, i.e., La(OH)(2)(+), on HZSM-5 zeolite. Through geometry optimization, it was determined that lanthanum ions are favorably accommodated in the two 6-T rings of the straight channels (Clusters 1 and 2, see Sec. III A for details). Cluster 1 was found to exist in prior to Cluster 2 due to the preference of Al substitution in the T11 site (Cluster 1) rather than in the T8 site (Cluster 2). Geometry-optimization of Cluster 1 containing another two lanthanide ions Nd3+ and Yb3+ was also carried out and it was found that a monotonic decrease in Ln-O bond length will take place as the atomic number increases, conforming well to the rule of lanthanide contraction. Some of the optimized parameters are comparable to the corresponding experimental values in Y zeolite, which confirms that the optimized configurations are acceptable. The average frequencies of hydroxyls attached to La3+ or Yb3+ in Cluster 1 fall at 3609.16 and 3579.76 cm(-1), respectively, with the gap of these two frequencies close to that in the sodalite cage of Y zeolite. Compared to H-form zeolite, the charges on both Al and O atoms in Ln-ZSM-5 zeolite show an obvious increase, which will undoubtedly lead to a stronger mutual interaction and hence enhance the stability of the [AlO4](-) anion. Moreover, the Ln(OH)(2)(+) seem to have thickened the zeolite framework, which can effectively retard the process of dealumination. Through the evaluation of the possibility for dimer formation, it turned out that when the exchange degree arrived to approximately 0.28, lanthanum monomers began to aggregate into dimers, and were completely converted into dimers when the exchange degree approached 0.60. (C) 2003 American Institute of Physics.

小晶粒含锆ZSM-5分子筛催化剂及其制备方法

一种小晶粒含锆ZSM-5分子筛催化剂的百分重量组成为SiO2:Al2O3:NaO2:锆＝70-95:1-4:1-2:0.05-3，平均晶粒度为0.2-0.5μm总酸量为0.8-1.1毫摩尔/克分子筛，其平均晶粒度为0.2-0.5μm。本发明具有由合成气经甲醇/二甲醚制汽油反应中，甲醇/二甲醚转化率100％，汽油馏分(C5↑[+])选择性高，且产物油品烯烃含量<10％，更具有环保性，且催化剂抗积碳性能强，单程寿命可达1000小时以上的。

一种快速合成含锆原子ZSM-5分子筛的方法

一种快速合成含锆原子ＺＳＭ－５分子筛的方法是将硅源、钠盐和去离子水配制成Ａ溶液；将铝源、酸和去离子水按摩尔比为配制成Ｂ溶液；将锆源、去离子水配制成Ｃ溶液，在剧烈搅拌下，将Ｂ溶液滴加到Ａ溶液中，然后加入有机模板剂，再加入溶液Ｃ，搅拌使其混合均匀，老化、晶化、固液分离，对滤饼干燥、焙烧２得到分子筛原粉。本发明具有合成出含锆原子ＺＳＭ－５分子筛的结晶度（９０％＞）。合成周期短，晶化时间少的优点。