浸渍方式对挤条成型Mo/ZSM-5催化剂甲烷无氧芳构化反应性能的影响

以SiO_2为粘结剂,通过不同浸渍方式制备了挤条成型的Mo/ZSM-5催化剂,考察其催化甲烷无氧芳构化的反应性能。采用扫描电镜(SEM)、紫外拉曼光谱(UV-Raman)及程序升温还原法(H_2-TPR)等对催化剂进行了表征。结果表明,碱性浸渍液有利于成型催化剂中Mo物种的分散,促进了Mo物种的还原,芳烃增加约13%,积碳量下降约8%。     

钇对甲烷芳构化催化剂Mo／HZSM—5性能影响的研究

研究了稀土钇的含量对Ｍｏ／ＨＺＳＭ－５催化剂的活性和选择性的影响，发现稀土钇的加入，不同程度上提高了Ｍｏ／ＨＺＳＭ－５的活性和选择性。特别是，当Ｙ／Ｍｏ＝０．０４时，活性最佳。甲烷在１０２３Ｋ芳构化反应，转化率达１９．６％，苯的选择性达９６．５％，且活性较稳定。     

Co掺杂对Mo/HZSM-5催化甲烷芳构化性能的影响

采用共浸渍法制备了不同Co含量的Mo-Co/HZSM-5系列双金属分子筛催化剂,利用N_2吸附脱附和NH3-TPD对其进行了表征,考察了其在甲烷无氧芳构化反应中的催化活性,并探讨了Co添加对催化活性的影响。结果表明,Co添加使得Mo与Co形成协同作用,提高了Mo物种的分散性和B酸位的酸强度,从而大大提高了催化剂的催化活性和苯的选择性。其中,Mo6%-Co0. 8%/HZSM-5催化剂的甲烷转化率和苯选择性为最佳。     

制备工艺条件对甲烷无氧芳构化反应催化剂Y-Mo/HZSM-5活性的影响

研究了催化剂制备工艺条件对甲烷无氧芳构化反应催化剂Y -Mo/HZSM - 5反应活性的影响 ,并得出了催化剂的最佳制备工艺条件     

改性Mo/HZSM-5催化剂甲烷无氧芳构化反应条件研究

采用Mo担载的质量分数为6%、经过先碱后酸预处理的Mo/HZSM-5作为催化剂,在不同反应温度和反应空速下,比较了甲烷的转化率、苯的生成速率和积炭的收率.结果表明,当反应温度为700℃,反应空速为1 400 mL/(g·h)时,甲烷无氧芳构化性能最佳.     

酸处理ZSM-5分子筛对甲醇芳构化反应的影响

利用酒石酸、草酸和EDTA-2Na对ZSM-5分子筛进行酸处理,并采用NH3-TPD、N2吸附-脱附、XRD、SEM、IR等表征方法对催化剂结构和酸性进行表征。在酸处理前后的ZSM-5分子筛上进行甲醇芳构化反应,考察酸处理对ZSM-5分子筛催化性能的影响。结果表明,ZSM-5分子筛经酸处理后,催化剂孔体积和表面积增加,强酸量减少,芳烃的选择性增加。相比未处理的ZSM-5分子筛,E-ZSM-5分子筛的总芳烃收率由24. 64%提升至49. 23%,BTX收率由19. 6%提升至34. 09%,表现出良好的催化性能。     

Mo/HZSM-5上甲烷无氧芳构化催化剂制备因素的考察

采用Mo/HZSM-5作为甲烷无氧芳构化催化剂,考察了催化剂制备部分影响因素.结果表明,采用较低的nSi:nAl时(25)载体制备的催化剂活性和稳定性较好;浸渍法优于固相反应法;Mo担载的质量分数为4%时,催化剂表现出最高活性;分子筛预先经碱处理,能够明显改善催化剂稳定性.     

不同载体成型的ZSM-5催化剂上甲醇芳构化反应性能

以ZSM-5分子筛为活性组分,采用不同的氧化物载体挤条制备催化剂,并对催化剂的甲醇芳构化反应性能进行评价。采用X射线衍射、氨程序升温脱附和N₂低温吸附-脱附等方法对催化剂进行表征。结果表明,添加氧化物载体后,催化剂的芳构化反应性能明显提高,催化剂芳构化反应性能与其酸性质有着密切联系,Zn/La-ZSM-5(Al₂O₃)催化剂的芳构化反应性能较好,主要归因于催化剂具有适宜的酸分布和孔结构。在反应压力0.1 MPa、空速0.8 h^-1、反应温度437 ℃和反应时间240 min条件下,轻质芳烃收率为42.36%.     

ZSM-5催化剂成型条件对其性能的影响

采用X射线衍射(XRD)、N_2吸附-脱附和激光粒度分析等方法对不同成型条件下的ZSM-5分子筛催化剂的晶相、孔结构和粒度进行了表征,并对比分析了优化成型条件后制备的催化剂与进口催化剂的催化性能。结果表明,使用不同厂家生产的SB粉成型后的催化剂晶相结构未出现明显变化,但强度差异较大。成型后的催化剂强度随着分子筛原粉粒度的减小和硝酸用量的增加呈显著递增趋势,孔结构和相对结晶度均无明显变化。在一定范围内,挤出速度及强度都随着水粉比的增加呈先增加后降低的趋势。催化结果显示,优化成型条件后制备的催化剂性能与进口催化剂相当。     

稀土助剂Y对甲烷芳构化反应催化剂Y-Mo/HZSM-5表面性质的影响

用吡啶 -TPD实验和异丙醇分解反应研究了稀土助剂Y对甲烷芳构化反应催化剂Mo/HZSM - 5表面性质的影响 ,说明了稀土Y对Mo/HZSM - 5催化剂的添加增强了催化剂表面的酸性 ,从而促进了甲烷的活化 ,提高了甲烷转化率。     

Methane aromatization over Mo/H-ZSM-5: on the reaction pathway

Rates of benzene formation on Mo/HZSM-5, H-ZSM-5 and Mo/SiO₂ were measured with different reactants: methane, mixture of C₂H₄/H₂/N₂ and mixture of C₂H₂/H₂/N₂. Since the rate of benzene formation starting from C₂H₄/H₂/N₂ is higher on Mo/H-ZSM-5 compared to H-ZSM-5 it is concluded that the aromatization of methane on Mo/H-ZSM-5 is not going via ethylene which is aromatized over acid sites. Another reaction pathway is proposed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis of Mo/IM-5 catalyst and its catalytic behavior in methane non-oxidative aromatization

A Mo-modified catalyst, Mo-IM-5, was prepared for the non-oxidative aromatization of methane, and for comparison, Mo-ZSM-5 was also synthesized for the same reaction. The physical properties and acidities of the samples were characterized by XRD, SEM, BET and IR spectroscopy. Compared with Mo-ZSM-5, the Mo-IM-5 catalyst showed both a higher methane conversion and higher benzene selectivity. In addition, Mo-IM-5 was slightly more stable than Mo-ZSM-5. The catalytic behavior of Mo-IM-5 may be attributed to its unusual two-dimensional 10-member-ring channel system with the character of three-dimensional cavity. Furthermore, the effects of different Si/Al ratios, Mo loadings and temperatures on the catalytic performance of Mo-IM-5 were also investigated.     

Dehydrogenation of Methane over Mo/ZSM-5. Effects of Additives in the Methane Stream

The dehydrogenation of methane was carried out over a Mo/ZSM-5 catalyst. It was revealed that the purity of the methane was very critical for the evaluation of the catalyst activity. In order to study the phenomenon, the effects of the addition of O₂, CO₂, CO or H₂ to the feed were investigated. A small amount of O₂ increased the amounts of aromatic compounds and CO produced. The addition of H₂ scarcely affected the conversion of methane, but it prevented the deactivation of the catalyst, i.e., benzene production remained constant during a 6 h test.     

硅烷化和有机弱碱改性Mo/HZSM-5对甲烷无氧芳构化催化性能的影响

催化剂的形态及晶粒的组装对其催化性能有重要影响,采用硅烷化处理对Mo基催化剂表面酸性进行毒化制备了核壳型（Mo基催化剂@Silicalite-1）复合材料;采用四丙基氢氧化铵或正丁胺有机弱碱对Mo/HZSM-5进行刻蚀,然后经过脱硅再结晶分别制备了表面富硅型中空结构Mo/HZSM-5微球和表面富硅、核内含有多级孔道的Mo/HZSM-5微球。采用XRD、TEM、N₂等温吸脱附和NH₃-TPD对催化剂结构进行表征,并考察了三种不同后处理方法对Mo基催化剂在甲烷无氧芳构化反应中催化性能的影响。硅烷化和有机碱处理均能够调变Mo/HZSM-5催化剂的表面酸性,而经有机碱处理以后,催化剂结晶度、介孔比表面积和孔容均具有不同程度的增加,三种不同后处理方法均能改善Mo/HZSM-5催化剂的反应稳定性,对产物的分布也产生了显著影响。     

Aromatization of Methane Over Mo-Fe/ZSM-5 Catalysts

Two groups of samples were studied for the aromatization of methane over Mo-Fe/ZSM-5 catalysts. The first group contains fixed loading (5 wt%) and variable Mo/Fe ratio. The second group was prepared with fixed Mo/Fe ratio and variable loading. The samples were characterized by TGA, S _BET, XRD, NH₃-TPD and TPO analysis. NH₃-TPD results indicate that the strength of strong acid sites increases when Mo/Fe ratio decreases for samples with fixed loading. The amount of strong sites decreases and new intermediate acid sites appear on samples containing both Mo and Fe. XRD results show the presence of iron molybdate for samples impregnated with both Mo and Fe. The catalytic properties of these samples were related not only to the amount and strength of acid sites but also to the iron molybdate phase.     

Marked Enhancement of the Methane Dehydrocondensation Toward Benzene Using Effective Pd Catalytic Membrane Reactor with Mo/ZSM-5

Steady state product formation rates of benzene, hydrogen, naphthalene, toluene in methane dehydrocondensation reaction on 3wt% Mo loaded ZSM-5 catalyst was enhanced 2–10 times by the removal of hydrogen using Pd membrane for 100h at 883K. The amount of permeated hydrogen through the Pd membrane was measured before and during the methane dehydrocondensation reaction. About 50–60% of hydrogen from the total hydrogen produced during the methane dehydrocondensation was selectively removed by the Pd membrane, owing to which the equilibrium of the methane dehydrocondensation was shifted toward the product side.     

The study of methanol aromatization on transition metal modified ZSM-5 catalyst

In this article, transition metals of Cu, La and Zn were used as adjuvant to prepare modified HZSM-5 by impregnation method. The catalysts were characterized by XRD, BET, NH₃-TPD and Py-IR to reveal the microstructure and acid property. The catalysis performances of methanol aromatization of catalysts were investigated in a fixed-bed reactor. The results show that the strength and distribution of acid center of these catalysts are significantly influenced by the species of transition metal. There are more mediate strong Lewis acid center in Zn modified HZSM-5 catalyst and therefore exhibits higher selectivity to aromatic, benzene, toluene and xylenes in the MTA reaction..     

Creating Mesopores in ZSM-5 Zeolite by Alkali Treatment: A New Way to Enhance the Catalytic Performance of Methane Dehydroaromatization on Mo/HZSM-5 Catalysts

Well-controlled treatment with alkali solution causes the etching of HZSM-5 framework, which results in the formation of the new porosity and channel structure with the coexistence of micropores and mesopores, as evidenced by nitrogen adsorption experiments. The dissolution of the zeolite framework, as revealed by the investigation of solid-state NMR, begins from the crystalline site with Si–O–Si linkages. The inertness of the alkali treatment toward Si–O–Al bond in the framework preserves the specific Brønsted acid site that is defined to be the bridging OH species over Si–O–Al units in zeolite. The Mo-modified catalysts derived from the alkali treatments showed a very high catalytic performance in the conversion of methane to aromatics (MDA) when compared with the conventional Mo/HZSM-5 catalyst. The unique selectivity to aromatics and stability of the catalysts derived from the alkali-treated ZSM-5 are attributed to the coexistence of mesopores and inherent micropores in the zeolites, which optimizes an environment for catalytic reaction and mass transfers. The channel with mainly 3–5?nm in diameters in the zeolites serves as the “aisle” to enhance the diffusion of molecules, especially the aromatics molecules, while the micropores have been identified to be the active cavities for the aromatics formation.