共查询到20条相似文献,搜索用时 31 毫秒
1.
HZSM-5沸石上酯化反应的研究 总被引:5,自引:0,他引:5
以醋酸和乙醇的酯化为典型反应,讨论了一系列HNaZSM-5沸石的阳离子交换度对酯化活性和选择性的影响,并与不同交换度的HNaZSM-5沸石的TPD酸性测定结果进行了关联。考察了不同温度焙烧的HZSM-5对酯化活性和选择性的影响,并与不同温度焙烧的HZSM-5沸石吸附吡啶的红外光谱进行了关联。结果表明,酯化反应既可以在B酸中心上进行,亦可以在L酸中心上进行;而乙醇分子间脱水主要是在B酸中心上进行。有机胺中毒实验的结果证明,酯化反应主要是在HZSM-5沸石的内表面上进行的。 相似文献
2.
碳四烃在改性HZSM-5分子筛上芳构化研究 总被引:8,自引:0,他引:8
研究了炼厂混合C_4烃在Zn、Ga、Cr、La改性的HZSM-5分子筛催化剂上的芳构化反应,采用TPD和IR测定了催化剂的表面酸性质。结果表明,用Zn(3%)和Zn(2%)Ga(1%)改性的HZSM-5分子筛具有较好的芳构化性能;各改性HZSM-5分子筛催化剂芳构化性能变化与表面酸性有关,总酸量下降,芳构化活性下降,强B酸中心减少,深度裂解反应减少;Zn的单组分和双组分改性的HZSM-5分子筛催化剂芳构化活性的增高与表面强L酸浓度增加和吡啶吸附IR谱中的1615cm~(-1)吸收峰出现有关。 相似文献
3.
NorAishahSaidinaAmin Kusmiyati 《天然气化学杂志》2004,13(3):148-159
The dehydroaramatization of methane over W-supported ZSM-5 with varying degrees of Li^ ion-exchanged catalysts was studied with and without oxygen at 1073 K and atmospheric pressure.Catalyst activity and stability were found to be influenced by the catalyst acidity related to BrSnsted acid sites and by the presence of oxygen in the feed. The NH3-TPD and FTIR-pyridine results demonstrated that partially exchanged of H^ ions by Li^ into the W/HZSM-5 catalysts could be used to control the amount of strong acid sites on the catalyst surface. Without oxygen, the 3WHLi-Z (5:1) catalyst that has strong acid sites equal to nearly 74% of the original strong acid sites in the parent HZSM-5 exhibited the highest methane conversion and selectivity towards aromatics. However, the catalyst deactivated in a five hour period. In the presence of oxygen, the catalyst activity and stability could be improved further.The results of this study revealed that a suitable amount of strong Bronsted acid sites as well as oxygen addition in the feed increased the catalyst activity and stability. The 3WHLi-Z(5:1) catalyst exhibited improved performance in the dehydroaromatization of methane. 相似文献
4.
对商用HZSM-5分子筛进行高温热处理,利用X射线衍射(XRD)、核磁共振波谱法(27Al-MAS NMR)低温氮吸附、电感耦和等离子体放射光谱(ICP-AES)、氨-程序升温脱附(NH3-TPD)和吡啶吸附傅里叶变换红外(FT-IR)光谱等技术对高温热处理改性前后样品进行了表征,并考察了高温热处理对分子筛的结构、酸性及催化乙醇脱水制乙烯反应性能的影响。结果表明,热处理改性后的HZSM-5分子筛发生骨架脱铝,B酸减少,L酸增多,孔容增大,出现新的介孔;适中的酸性位和复合型的介-微双孔道结构使其减少了反应中的副反应,乙烯的选择性得到提高,催化剂寿命显著提高。 相似文献
5.
采用等量浸渍法制得一系列不同担载量的Mo/HZSM-5催化剂,运用XRD和FTIR方法考察了Mo物种在催化剂表面的分散状态,首次采用微分吸一热技术对Mo/HzSM-5催化剂的表面酸性进行表征。同时研究了催化剂对丙烷芳构化的反应活性。结果表明:对于担载Mo的HZSM-5分子筛催化剂,Mo物种在HZSM-5分子筛表面上顺序为HZSM-5〉1%Mo/HZSM-5〉2%Mo/HZSM-5分子筛本身表面的酸 相似文献
6.
本文利用红外光谱法研究了几种类型的沸石分子筛对于2,6-二甲基吡啶的吸附特性。结果发现2,6-二甲基吡啶在同一种类型的沸石分子筛表面上与B酸中心、L酸中心结合的稳定性是不同的,前者比后者稳定;它在不同类型的沸石分子筛表面上与L酸中心结合的稳定性也是不相同的:对于NaHY分子筛在300-400℃,对于HM、HZSM-5、HZSM-11在150-400℃,2,6-二甲基吡啶只能选择性地被吸附在B酸中心上。在HZSM-5上进行的置换吸附实验表明,150℃在时吡啶可以定量地置换与L酸中心结合的2,6-二甲基吡啶。 相似文献
7.
混合金属络合物羟基镍铝交联蒙托土的表面酸性及催化性能 总被引:16,自引:0,他引:16
用NH_3-TPD,IR技术研究了混合金属络合物羟基镍铝交联蒙托土的表面羟基和表面酸性。考察了制备方法、Al/Ni比对其表面酸性的影响,同时用异丙苯裂解反应表征了其催化性能。结果表明,交联蒙托土存在L酸和B酸,其中以L酸为主。表面酸性可能来源于柱子和表面羟基,柱子的热稳定性对表面羟基,表面酸性均有较大影响。Ni的引入增加了L酸和B酸,取代法制备的样品具有比共聚法的样品更强的酸性。交联蒙托土具有较好的异丙苯裂解性能,Ni的引入使其活性有较大的增加。 相似文献
8.
FTIR研究不同硅铝比HZSM-5沸石的酸性质 总被引:9,自引:0,他引:9
用IR和NH3-TPD测定了硅铝比为31.4~137.1的HZSM-5沸石样品的酸中心数;由Lang-muir吸附模型推导出B、L酸的吸附热公式,并由此计算了B酸的吸附热。发现在Al/u.c.为3.64附近,酸中心数与Al/u.c的关系发生了转折,并发现B酸吸附符合Langmuir模型,L酸强度不均匀而不符合该模型,测定了HZSM-5分子筛的B、L酸消光系数8B=7.52×105cm·mol-1、8L=1.09×106cm·mol-1。 相似文献
9.
NorAishahSaidinaAmin DidiDwiAnggoro 《天然气化学杂志》2003,12(2):123-119
Direct conversion of methane using a metal-loaded ZSM-5 zeolite prepared via acidic ion exchange was investigated to elucidate the roles of metal and acidity in the formation of liquid hydrocarbons. ZSM-5 (SiO2/A12O3=30) was loaded with different metals (Cr, Cu and Ga) according to the acidic ion-exchange method to produce metal-loaded ZSM-5 zeolite catalysts. XRD, NMR, FT-IR and N2 adsorption analyses indicated that Cr and Ga species managed to occupy the alllmlnum positions in the ZSM-5 framework. In addition, Cr species were deposited in the pores of the structure. However, Cu oxides were deposited on the surface and in the mesopores of the ZSM-5 zeolite. An acidity study using TPD-NH3, FT-IR, and IR-pyridine analyses revealed that the total number of acid sites and the strengths of the BrSusted and Lewis acid sites were significantly different after the acidic ion exchange treatment.Cu loaded HZSM-5 is a potential catalyst for direct conversion of methane to liquid hydrocarbons. The successful production of gasoline via the direct conversion of methane depends on the amount of aluminum in the zeolite framework and the strength of the BrSnsted acid sites. 相似文献
10.
Study on Bifunctionality of Mo/HZSM—5 Catalysts for Methane Dehydro—Aromatization under Non—oxidative Condition
下载免费PDF全文
![点击此处可从《天然气化学杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
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. 相似文献
11.
The hydroxyl groups and their acidic properties of AlPO_4-5, SAPO-5 and HZSM-5 havebeen examined by means of IR spectroscopy using the adsorption of D_2O and pyridine asa probe. Four hydroxyl groups characterized by the bands near 3745, 3677, 3630 and 3520cm~(-1) are clearly observed and they are acidic on the sample of SAPO-5. Only two very weakbands at 3677 and 3630 cm~(-1) on AlPO_4-5 could be found. The experiments further indicatethat both of Bronsted and Lewis acid sites are present on the SAPO-5. From NH_3-TPD itis found that the HZSM-5 contains two types of acid sites, medium and strong, while theSAPO-5 contains only one type of medium acid sites. The order of a total amount ofacidity and acid strength is HZSM-5>SAPO-5>AlPO_4-5. 相似文献
12.
13.
Study on Bifunctionality of Mo/HZSM-5 Catalysts for Methane Dehydro-Aromatization under Non-oxidative Condition
下载免费PDF全文
![点击此处可从《天然气化学杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Lingling Su Yide Xu Xinhe BaoState Key Laboratory of Catalysis Dalian Institute of Chemical Physics Chinese Academy of Sciences Zhongshan Road P. O. Box Dalian ChinaManuscript received June revised July 《天然气化学杂志》2002,(Z1)
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. 相似文献
14.
MoCl_5在HZSM-5和APO-5上没有发生“双聚”,沸石的酸性对MoCl_5负载量的影响大于孔结构。APO-5负载MoCl_5后,仅生成数量和强度都很小的B酸中心。Mo-ZSM-5沸石在MTG反应中有Mo和Al的表面迁移,负载的MoCl_5通过氧化-还原及水解等过程产生羟基,增加了ZSM-5沸石的B酸量,通过B酸-L酸中心的电子协同效应增加载体的B酸强度,调变了催化剂的酸性分布。 相似文献
15.
CoAPSO—5分子筛的合成与性能 总被引:1,自引:0,他引:1
用水热晶化法合成了CoAPSO-5分子筛,用X射线衍射,电子探针,红外光谱以及吸附吡啶的红外光谱等方法对其结构和表面性质进行了研究,并用甲苯甲醇烷基化反应考察了其催化性能,结果表明,CoAPSO-5为中强酸性分子筛,具有较高的甲苯甲醇烷基化活性和对二甲苯选择性,对二苯收率高于20%,且烷基化活性和对二甲茉选择性出现了“同向效应”。 相似文献
16.
用氘代吡啶和三甲基膦(TMP)作为碱性探针分子,用1H和31P魔角旋转(MAS)NMR谱对脱铝和未脱铝微孔HY分子筛中的Br#nsted酸(B酸)进行了定量研究.发现在脱铝HY中,吸附探针分子后的B酸量比吸附前的要多,而在未脱铝的HY样中,吸附吡啶分子前后测得的B酸量基本一致,证实了在微孔分子筛中存在碱“诱导”B酸位,即靠近铝的端位SiOH能在碱性探针分子的诱导下形成桥式羟基(SiOHAl).对这种碱“诱导”B酸位的形成机制进行了讨论. 相似文献
17.
18.
19.
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. 相似文献
20.