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.

Promotional effect of colloidal alumina on the activity of the In/HZSM-5 catalyst for the selective reduction of NO with methane

Colloidal alumina was used to improve the activity of an In/HZSM-5 catalyst for the selective reduction of NO with CH4 in the excess of oxygen. Compared with In/HZSM-5, the In/HZSM-5/Al2O3 catalyst showed higher activity in a wide range of reaction temperatures. It is visualized that a synergetic effect between In/HZSM-5 and Al2O3 enhances the conversion of NOx. The addition of Al2O3 improved the conversion of NO to NO2 and facilitated the activation of methane. An In/HZSM-5/Al2O3 pre-treated with steam for 15 h at 700 degreesC still showed a high activity for the removal of NOx with methane, while an In/HZSM-5 similarly pre-treated with steam showed a lower activity than the fresh sample. The activity of the In/HZSM-5/Al2O3 catalyst could be restored completely after water vapor was removed from the feed gas. Furthermore, it was found that the In/HZSM-5/Al2O3 remained fairly active under high GHSV and O-2 concentration conditions. It was also interesting to find that an increase in NO content could enhance the conversion of methane, and this illustrates that the existence of NO is beneficial for the activation of methane. (C) 2002 Elsevier Science B.V. All rights reserved.

A facile and effective method for the distribution of Mo/HZSM-5 catalyst active centers

Post-steaming treatment of Mo/HZSM-5 catalysts results in more molybdenum species migrating into and residing in the HZSM-5 zeolite channels. This is confirmed by XRF and XPS measurements. H-1 MAS NMR and Si-29 MAS NMR also demonstrate that the number of free Bronsted acid sites decreases in the Mo/HZSM-5 catalysts that underwent post-steaming treatment, compared to untreated Mo/HZSM-5 catalysts. As a result, the deactivation rate constant (kd) on the Mo/HZSM-5 catalyst after post-steaming treatment for 0.5 h is much smaller, and the catalyst therefore shows remarkable stability in the probe reaction of methane dehydro-aromatization. The results suggest that a more beneficial bi-functional balance between active Mo species for methane activation and acid sites for the following aromatization is developed over those Mo/HZSM-5 catalysts that have experienced post-steaming treatment for 0.5 h, in comparison with the untreated Mo/HZSM-5 catalysts.

Effect of addition of Zn on the catalytic activity of a Co/HZSM-5 catalyst for the SCR of NOx with CH4

The selective catalytic reduction (SCR) of NOx by methane in the presence of excess oxygen was studied on a Zn-Co/HZSM-5 catalyst. It was found that the addition of Zn could improve effectively the selectivity of methane towards NOx reduction. When prepared by a coimpregnation method, the Zn-Co/HZSM-5 catalyst showed much higher catalytic activity than the two catalysts of a Zn/Co/HZSM-5 and Co/Zn/HZSM-5 prepared by the successive impregnation method. It is considered that there exists a cooperative effect among the Zn, Co and zeolite, which enhances the reduction of NO to NO2 reaction and the activation of methane. (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。

一种快速合成强酸型ZSM-5分子筛的方法

一种快速合成强酸型ＺＳＭ－５分子筛的方法是按一定比例将硅源与模板剂、去离子水总量的一半配置成Ａ溶液，铝源、无机酸与另一半去离子水配置成均匀的Ｂ溶液，将Ｂ溶液滴加至Ａ溶液中，制成导向剂；再按一定比例将硅源与模板剂、去离子水总量的一半配置成Ｃ溶液，铝源、无机酸与另一半去离子水配置成Ｄ溶液，Ｄ溶液滴加入Ｃ溶液，最后再加入占总体积５－１０％的导向剂，得到强酸型ＺＳＭ－５分子筛；本发明具有合成时间短，酸性强的优点。