Study on Bifunctionality of Mo／HZSM—5 Catalysts for Methane Dehydro—Aromatization under Non—oxidative Condition

The optimum Mo/[H^ ] ratio per unit cell of the active precursors in Mo/HZSM-5 catalysts for methane dehydro-aromatization,measured by ^1H MAS NMR,was found to be about 1 when adjusting the acid sites by altering either the SiO2/Al2O3 ration or the Mo loading,This implies that a concerted interaction between the Mo species and the Broensted acid sites probably features the bifunctionality of the Mo/HZSM-5 catalyst,On the other hand,it was found that the driving force for Mo species to move into the HSZM-5 zeolite channels and the interaction between the Mo species and the Broensted acid sites are closely and proportionably realtaed with the amount of Broensted acid sites per unit cell.     

Propane Aromatization over Mo／HZSM—5 Catalysts

Impregnation,mechanical mixing and hydrothermal treatment methods were used to introduce molybdenum species into the HZSM-5 zeolite ,the structure and surface acidity of the catalysts were studied by means of XRD,FT-IR ,NH3-TPD,TPR and XPS,The effects of Mo content and reaction time on stream on the aromatization of propane were investigated,It was found that the performance of the Mo/HZSM-5 catalst prepared by the hydrothermal treatment method was much better than that of the other two catalysts,For example ,under the reaction conditions of 823 K and 600h^-1, propance conversion and aromatics selectivity over the catalyst prepared by hydrothermal pretreatment could reach 89.17% and 78.56%,respectively,XRD and XPS results showed that the Mo species in the catalysts prepared by hydrothermal treatment were highly dispersed on the surface of the HZSM-5,and lartger amounts of them could penetrate into the HZSM-5 channel ,as compared with the other two kinds of catalysts,These factors may be responsibled for their high activities for propane aromatization,IR and NH3-TPD studies indicated that the number of Broensted acid centers decreased and the Lewis acid centers increased after Mo was introduced into the HZSM-5 zeolite.     

Properties and Characterization of Modified HZSM—5 Zeolites

Physicochemical and catalytic properties of phosphorus and boron modified HZSM-5 zeolites treated with 100% steam at 673K were investigated.The acidity and distribution of acidic sites were studied by infrared spectroscopy using pyridine as probe molecule and temperature programmed desortion (TPD) of ammonia.The structure of the samples was characterized by XRD,and the textural properties of the catalysts were determined by nitrogen isothermal adsorption-desorption measurements and scanning electron microscopy(SEM).The XRD results show that the modified samples have no novel crystalline phase,indicating a high dispersion of phosphorus and boron species.After treatment,the microporous volume and surface area of the samples markedly decrease,implying the bolockage of the channel.The nitrogen adsorption-desorption measurements suggest that the isothermal type of all samples is a combination of isothermal type Ⅰ and Ⅳ，and all hysteresis loops resemble the H4-type in the IUPAC classification.The total acidity of the modified samples,determined by pyrldine adsorption IR and TPD of ammonia,decreases in contrast to that of the parent HZSM-5.The conversion of n-heptane over P and B steammodified HZSM-5 is higher than that of P and B-modified HZSM-5 zeolites but lower than that of the parent HZSM-5.     

预处理条件对Mo/HZSM-5和Mo-Zn/HZSM-5甲烷芳构化性能的影响

甲烷无氧芳构化 ,具有选择性高、技术简单及产物易分离等特点 ,已引起人们的广泛关注 [1,2 ] .Mo/HZSM- 5是芳构化的良好催化剂 ,为了探讨预处理条件对反应的影响 ,我们对不同预处理条件下的 Mo/HZSM- 5及 Zn改性的 Mo/HZSM- 5催化剂上的甲烷无氧芳构化反应进行了研究 ,并以热重法对催化剂的稳定性进行了表征 .1实验部分1 .1原料和试剂钼酸铵 ( A.R.级 ) ,乙酸锌 ( A.R.级 ) ,铵型ZSM- 5分子筛 (硅铝比为 5 0～ 70 ) .1 .2催化剂制备铵型 ZSM- 5分子筛于 81 3K、空气气氛下焙烧3h,即成 HZSM- 5分子筛 .以一定浓度的钼酸铵溶液…     

Studies on Mo／HZSM-5 Complex Catalyst for Methane Aromatization

The influence of adding Fe,Cr,Co,and Ga into 3%Mo/HZSM-5 catalyst on methane aromatization,and the influence of additives ratio on methane conversion,selectivity to hydrocarbons and coke,as well as distribution of aromatics were investigated.The experimental results showed that the addition of Fe,Cr,Co and Ga promoted the dehydrogenation and dissociation of methane.The results of NH3-TPD indicated that the acidity of HZSM-5 was changed by adding Fe and Co components,consequently the catalytic properties of Mo/HZSM-5 were changed.It was also revealed that strong acid sites were the center of methane aromatization.The results of XRD characterization showed that the crystallinity of Mo on ZSM-5 zeolite was increased after adding Fe,Co additives.     

Effect of Dimethyl Ether Co-feed on Catalytic Performance of Methane Dehydroaromatization over Mo／HZSM-5 Catalyst

The effect of dimethyl ether (DME) co-feed on the catalytic performance of methane dehydroaxomatization (MDA) over 6Mo/HZSM-5 catalyst was investigated as a function of DME concentration under reaction conditions of T=1023 K, p=101 kPa and SV=1500 ml/(g.h). A high benzene yield wasobtained and the stability of the catalyst was improved by adding 1.5%DME to the CH4 feed. The C6H6 yield was as high as ca. 10% even after reaction for 6 h. The stability of the catalyst was further improved when DME concentration in the co-feed gas was increased to an appropriate value. TGA and TPO results of the used 6Mo/HZSM-5 catalyst showed that the amount of coke on the used catalyst was reduced and the chemical nature of the coke was changed. When 1.5%DME was added to the CH4 feed, the coke formed on the catalyst could be burned off more easily than that when only CH4 was used as reactant. It is supposed that the oxygen in DME may play a role in preventing the coke burnt off at lower temperature from transforming into the coke burnt off at higher temperature, which results in the improvement of the stability of the catalyst.     

Methane dehydro-aromatization over Mo/HZSM-5 catalysts in the absence of oxygen: Effect of steam-treatment on catalyst stability

The effect of steam-treatment to HZSM-5 zeolite and Mo/HZSM-5 with a steaming time range of 0.5-1 h on the catalytic performance of methane dehydro-aromatization (MDA) over Mo/HZSM-5 catalyst prepared with impregnation has been studied in detail in combination with the characterization of 1H MAS NMR technique. Both the deactivation rate constant (kd) and the Brnsted acid sites per unit cell were calculated to quantitatively evaluate the stability of Mo/HZSM-5 catalysts treated with steam at 813 K before and after impregnation of molybdenum species, and the corresponding variation of their Brnsted acid sites. The results reveal that a V-shape relationship between kd and the number of B1 acid sites per unit cell is presented on Mo/HZSM-5 catalyst under the tested steam-treatment and reaction conditions.     

A Novel Cu-Mo／ZSM-5 Catalyst for NOx Catalytic Reduction with Ammonia

The Cu-Mo/ZSM-5 catalysts with different Cu/Mo ratios were prepared by wet impregnation method, and their catalytic performance for selective catalytic reduction of NOx was studied. The results showed that Cu-Mo/ZSM-5 is a very effective catalyst for NOx catalytic reduction with ammonia, especially when Cu/Mo molar ratio is about 1.5. It not only exhibited the extremely high catalytic activity, but also showed good stability for 02. The bulk phase structure of Cu-Mo/ZSM-5 catalysts was determined by XRD technique, and the results indicated that there is a maximum dispersion for Cu species when Cu/Mo molar ratio is 1.5, and an interaction between Cu and Mo along with HZSM-5 may be present in Cu-Mo/ZSM-5, which may possibly result in a special structure favorable for the catalytic reduction of NOx over Cu-Mo/ZSM-5 catalyst.     

Mo／MCM－49催化剂上甲烷的脱氢芳构化反应

In recent years, the catalytic dehydroaromatization of methane to benzene has been a challenging and intriguing research subject in heterogeneous catalysis and natural gas chemical industry. Since the first report on non-oxidative conversion of methane to benzene on Mo/HZSM-5[1], many attractive studies regarding the development of new catalyst, the catalyst characterization[2～4], the reaction mechanism and the bifunctional role of Mo carbide and HZSM-5 have been reported. However, Mo/HZSM-5 catalyst was thought to have the best catalytic performance for CH4 dehydroaromatization to benzene. Recently, another kind of zeolite, MCM-22, was found to be a promising catalyst support for formation of benzene from methane[5]. Xu et al[6] studied the catalytic performance of MoO3/MCM-49 for this reaction without accounting for coke formation. In this paper, we present MCM-49 as a support, and the catalyst Mo/MCM-49 shows high ratio of benzene to aromatics in selective dehydroaromatization of methane.     

以稀土离子交换的HZSM-5为载体的甲烷非氧化芳构化催化剂

The declining crude oil reserves has led to natural gas being considered as an alternative supply to produce important organic raw materials such as ethene and aromatics. Mo/HZSM-5 is found to be able to act effectively for the title reaction[1]. In order to clarify how the cation in the channel of HZSM-5 effects the behavior of the catalyst, different rare earth ion exchanged HZSM-5 ([ RE3+] HZSM-5 ) zeolites were investigated as supports of the Mo/[ RE3 + ] HZSM-5 catalyst.     

CH_4在Mo/HZSM-5及其改性催化剂上的无氧芳构化(英文)

运用微型固定床反应器装置,研究了Mo/HZSM-5催化剂的Mo载量、金属助剂改性、载体模数对甲烷无氧芳构化反应性能的影响。结果表明,Ni/Mo摩尔比为0.1的Mo-Ni/HZSM-5(SiO2/Al2O3=25)催化性能最好,其稳定性较好,芳烃收率最高可达15.74%;此时甲烷转化率60.24%,芳烃选择性26.13%。     

硅烷化处理对Mo/HZSM-5催化剂上甲烷脱氢芳构化活性的影响

 结合催化剂的活性评价及固体高分辨核磁共振谱、X射线光电子能谱和X射线荧光光谱和热重等技术,考察了硅烷化处理对Mo/HZSM-5催化剂上甲烷脱氢芳构化活性的影响. 结果表明,采用大分子有机硅烷对HZSM-5分子筛进行硅烷化处理,除去了分子筛外表面的酸性位,并使分子筛本身发生了脱铝. 硅烷化处理使Mo/HZSM-5催化剂在进行甲烷脱氢芳构化反应时催化剂上总的积碳量明显减少,从而提高了催化剂的活性.     

Propane Aromatization over Mo/HZSM-5 Catalysts

Impregnation, mechanical mixing and hydrothermal treatment methods were used to introduce molybdenum species into the HZSM-5 zeolite. The structure and surface acidity of the catalysts were studied by means of XRD, FT-IR, NH3-TPD, TPR and XPS. The effects of Mo content and reaction time on stream on the aromatization of propane were investigated. It was found that the performance of the Mo/HZSM-5 catalyst prepared by the hydrothermal treatment method was much better than that of the other two catalysts. For example, under the reaction conditions of 823 K and 600 h-1, propane conversion and aromatics selectivity over the catalyst prepared by hydrothermal pretreatment could reach 89.17% and 78.56%, respectively. XRD and XPS results showed that the Mo species in the catalysts prepared by hydrothermal treatment were highly dispersed on the surface of the HZSM-5, and larger amounts of them could penetrate into the HZSM-5 channel, as compared with the other two kinds of catalysts. These factors may be responsi     

Methane Aromatization Under O2-Free Conditions on Zinc Modified Mo/HZSM-5 Catalyst

The influence of Zn content, reaction temperature and pretreatment conditions on a Zn-modified Mo/HZSM-5 catalyst for methane aromatization were studied. It was found that the addition of Zn promoted the reaction. Methane conversion of 10.9% and aromatics selectivity of 96.7% were obtained with a Zn/Mo molar ratio of 0.03 and N₂ pretreatment at 973 K. The results of isopropanol decomposition, NH₃-TPD and TG-DTA suggest that the addition of Zn decrease the acidity of the catalyst, which may be the reason for the high activity on the Mo-Zn/HZSM-5 catalyst. This revised version was published online in June 2006 with corrections to the Cover Date.     

甲烷脱氢芳构化Mo/HZSM-5基催化剂表征

利用H2-TPR、XPS、EPR等谱学方法，对Mo／HZSM－5基催化剂的可还原性以及工作态催化剂上钼物种的价态进行了表征研究．结果表明，随着焙烧温度的升高，前驱态催化剂中可还原钢物种在总钼量中所占比率明显下降；工作态催化剂表面存在混合价态的Mo物种：以Mo4 为主，Mo5 为次；673K焙烧制备并经DHAM反应操作的催化剂上检测到Mo5 的EPR讯号相当弱，而973K焙烧制备并经同样反应操作的催化剂，其Mo5 EPR讯号却强得多；酸促进的Mo／HZSM－5基催化剂上高的甲烷转化活性与工作态催化剂表面Mo5 物种的浓度并不存在顺变关系，而与表面酸位（尤其是B酸位）及Mo4 物种的浓度密切相关．     

预处理条件对Mo／HZSM—5催化剂上丙烷芳构化的影响

采用浸渍法制备了Ｍｏ／ＨＺＳＭ－５ 分子筛催化剂,考察了Ｈ２ 、Ｎ２ 、空气预处理对催化剂丙烷芳构化活性的影响。在相同处理条件下,空气气氛更有利于提高催化剂的丙烷芳构化活性。在空气焙烧过程中,氧化钼物种向分子筛内表面分散。在Ｈ２ 还原处理过程中,表面钼物种部分被还原为Ｍｏ４ ＋ 。随还原时间延长,催化剂芳构化活性升高,同时发生少量Ｍｏ 物种向分子筛孔道内迁移     

添加Mo对Cu/HZSM-5催化剂性能影响

负载催化剂;二氧化碳加氢;二氧化碳;添加Mo对Cu/HZSM-5催化剂性能影响