甲烷在Mo/HZSM-5催化剂上的脱氢聚合反应

对不同Mo含量的Mo／HZSM－5催化剂的结构进行了表征，并对这些催化剂的甲烷非氧气氛下的转化反应进行了考察．催化剂的BET比表面积及酸性随Mo含量的增加而降低，当Mo含量大于5％时，Mo对ZSM－5分子筛的晶型有影响，并出现MoO3物相．甲烷在700℃时可高选择性地生成苯和乙烯，最佳Mo含量大约为2％．纯的MoO3或HZSM－5上该反应几乎不进行，因此，可能是分散的钼氧离子和分子筛的酸中心是甲烷转化的活性中心，只有二者的协同作用才能促进甲烷的转化．反应后催化剂中的钼物种被还原了．催化剂上的积炭可能是催化剂失活的主要原因之一，烧炭后催化剂活性基本恢复．     

HZSM-5分子筛焙烧脱铝的27Al MQMAS NMR研究

用29Si、27Al魔角旋转固体核磁共振(MAS NMR)结合二维多量子魔角旋转(2D MQMAS)技术对焙烧脱铝的HZSM-5分子筛中铝的配位状态进行了研究.结果表明,HZSM-5分子筛经焙烧后,在化学位移(δ)45处出现一宽峰信号,其主要来自扭曲四配位铝.通过二维三量子铝谱计算出扭曲四配位铝的四极作用常数约为5.2 MHz.对700和750 ℃焙烧样品的铝谱进行分峰拟合,发现在δ 30处又出现一个小峰,归属为非骨架五配位铝.同时,在750 ℃焙烧样品的二维多量子铝谱中直接观察到非骨架五配位铝的信号.焙烧温度低于700 ℃,脱铝不明显；高于700 ℃,引起分子筛骨架的显著脱铝.焙烧还造成部分骨架铝的信号变得“不可观测”.     

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%。     

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．     

N掺杂Mo/HZSM-5催化剂制备及对甲烷无氧芳构化催化性能影响

采用三聚氰胺作为N源,N掺杂改性HZSM-5沸石分子筛后负载Mo活性金属组分,制备了一种用于甲烷无氧芳构化反应(MDA)的催化剂.采用XPS、N2吸附-脱附、XRD、H2-TPR、TEM和NH3-TPD对催化剂性质和Mo金属组分状态进行了分析表征,并考察了催化剂的甲烷无氧芳构化反应催化性能.结果表明,HZSM-5经过N...     

Mo-Zn/HZSM-5催化剂上甲烷与丙烷混合物的无氧芳构化

研究了甲烷和丙烷的混合气体在x%Mo+6%Zn/HZSM-5催化剂上(x=0.3,0.5,0.7,0.9)的无氧芳构化反应性能.结果表明,在873K,GHSV=3L/(g·h)和n(C₁)/n(C₃)=1.0条件下,甲烷的转化率在29%～35%之间,芳烃选择性大于80%.其中0.7%Mo+6%Zn/HZSM-5对甲烷表现出最优的活性,甲烷转化率达到34.8%,丙烷转化率为69.6%.探讨了反应时间和n(C₁)/n(C₃)比对甲烷和丙烷转化率及其产物分布的影响.结果显示,丙烷的存在促使甲烷活化并参与芳构化反应.同位素13^CH₄示踪实验发现,13^C进入了C₆H₆⁺,C₇H₈⁺和C₈H₁₀⁺碎片中,进一步证实了甲烷进入芳烃形成过程.此种用丙烷活化甲烷的过程可能为天然气和炼厂气的直接利用提供了一个新的反应途径.     

甲烷无氧芳构化反应催化剂Mo/HZSM-5的H2-TPR研究

 采用H2-TPR技术研究了不同方法制备的Mo/HZSM-5催化剂,并借助 1H MAS NMR等表征手段对Mo/HZSM-5催化剂还原过程中可能出现的6个TPR谱峰进行了详细归属,首次指认了分布于分子筛孔道内并与B酸性位相互作用的Mo物种的还原峰. 此外,还考察了各种Mo基催化剂在甲烷无氧芳构化反应中的催化性能. 结果表明,与B酸中心相互作用的Mo物种比其他形式的Mo物种具有更好的活性和稳定性.     

四丙基氢氧化铵改性Mo/HZSM-5催化甲烷甲醇共芳构化反应性能

采用四丙基氢氧化铵（TPAOH）处理HZSM-5分子筛,并负载金属Mo。利用XRD、低温氮气吸附、27Al MAS NMR、29Si MAS NMR和NH3-TPD等表征技术对TPAOH改性前后催化剂的结构和酸性进行了研究,考察了其对甲烷甲醇共芳构化反应的催化性能。结构表征结果表明,适量的TPAOH改性可提高HZSM-5分子筛的相对结晶度,样品中介孔含量明显增加并且弱酸量和强酸量也有所增加。反应性能测试表明,以6 % Mo 负载的HZSM-5（6Mo/HZSM-5）为催化剂,在700 ℃、甲烷体积空速为2000h-1的反应条件下,甲烷中添加少量甲醇（nCH4/nCH3OH=20）时,甲烷转化率稳定在10 %左右,苯选择性在70 %以上,C7-C9高碳芳烃的选择性为4 %。在0.1 M TPAOH改性6Mo/HZSM-5催化剂上,甲烷转化率为8%左右,苯选择性稳定在60%以上,C7-C9高碳芳烃的选择性提升到10-17 %。利用TG和TPO技术对反应后样品的积碳情况进行了表征,发现甲烷甲醇共进料时催化剂积碳量由甲烷单独进料时的15%降低至5%,0.1 M的TPAOH改性后积碳量则进一步降低至1.4 %。TPAOH改性的催化剂上介孔含量的增加和强酸中心上的稠环芳烃含量的减少是反应后积碳量显著下降的主要原因,这有利于提高芳构化催化剂的稳定性和碳原子的有效利用率。     

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     

Mo/HZSM-5催化剂载体对甲烷无氧芳构化反应的影响

着重研究了挤条成型的纳米Mo/HZSM-5催化剂在甲烷无氧芳构化反应中的催化性能.结果表明,Al2O3载体的加入减少了催化剂的B酸量,对甲烷无氧芳构化反应不利,导致甲烷转化率降低,并且催化剂积碳严重.通过适量添加SiO2载体,减少Al2O3载体的量,可以使催化剂的B酸量提高,从而可提高甲烷转化率,并且可降低催化剂的积碳量.     

Methane dehydrogenation and aromatization in the absence of oxygen on Mo/HZSM-5: A study on the interaction between Mo species and HZSM-5 by using Al and Si MAS NMR

By using a high-resolution solid state nuclear magnetic resonance spectrometer with ²⁷Al and ²⁹Si probes, the interaction between Mo species and HZSM-5 of frsol|Mo/HZSM-5 catalysts has been studied. The results show that there is a strong interaction between Mo species and HZSM-5 zeolite. The framework aluminum in the zeolite can be easily extracted by the introduction of Mo species. The extractability of framework aluminum by Mo species increases with increasing Mo loading and the calcination temperature. The extraction process leads to the formation of non-framework Al at first and then a new crystalline phase of Al₂(MoO₄)₃. The dealumination of the catalyst having a Mo loading of 15% and had been calcined at 973 K is so severe that all the aluminum in the framework are extracted and no framework Al could be detected by ²⁷Al MAS NMR. The catalyst, therefore, lost its catalytic activity for methane dehydrogenation and aromatization in the absence of oxygen. The Si/Al ratio measured from ²⁹Si MAS NMR further confirms the dealumination process observed by ²⁷Al MAS NMR. The MAS NMR results give us an evidence that Al₂(MoO₄)₃ crystallites are much less active for the reaction.     

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.     

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 ratios or the Mo loading. This implies that a concerted interaction between the Mo species and the Bronsted 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 Bronsted acid sites are closely and proportionably related with the amount of Bronsted acid sites per unit cell.     

甲烷在Mo/HZSM-5催化剂上的脱氢聚合反应

对不同Mo含量的Mo／HZSM－5催化剂的结构进行了表征，并对这些催化剂的甲烷非氧气氛下的转化反应进行了考察．催化剂的BET比表面积及酸性随Mo含量的增加而降低，当Mo含量大于5％时，Mo对ZSM－5分子筛的晶型有影响，并出现MoO3物相．甲烷在700℃时可高选择性地生成苯和乙烯，最佳Mo含量大约为2％．纯的MoO3或HZSM－5上该反应几乎不进行，因此，可能是分散的钼氧离子和分子筛的酸中心是甲烷转化的活性中心，只有二者的协同作用才能促进甲烷的转化．反应后催化剂中的钼物种被还原了．催化剂上的积炭可能是催化剂失活的主要原因之一，烧炭后催化剂活性基本恢复．     

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.     

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     

Influence of Pretreatment Conditions on Methane Aromatization Performance of Mo／HZSM—5 and Mo—Cu／HZSM—5 Catalysts

Mo/HZSM-5 is a good catalyst for methane aromatization, and the reaction performance of Mo/HZSM-5 and Cu modified Mo/HZSM-5 catalysts under various pretreatment conditions has been studied. The results indicate that the catalyst presented a distinguished catalytic activity, benzene selectivity and a high stability when the bed temperature was raised in N2 atmosphere.     

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…     

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.