首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 203 毫秒
1.
采用微波水热合成纳米β沸石,并利用微波辅助的类芬顿法可控去除纳米β沸石孔道中的模板剂,使其具备一定的孔道深度、比表面积以及可接近酸性位.以果糖酸催化转化为5-羟甲基糠醛(5-HMF)为探针反应,探索了果糖分子在不同孔道深度和活性位的纳米β沸石中的扩散行为对催化效果的影响.研究发现,酸性位相同的条件下,纳米沸石孔道深度越深扩散限制越显著,反应选择性越差.即使在催化剂加入量相同即可接近酸性位不同时,果糖分子在孔道中的扩散限制对催化反应的影响也显著于酸量的影响,充分说明了微孔催化剂中反应物/产物分子扩散限制对于催化反应影响的重要性,使得所制备催化剂的表面酸性位和适宜的孔道深度共同对反应产生有利的影响.  相似文献   

2.
用HZSM-5沸石催化剂合成丙酸酯的研究   总被引:2,自引:0,他引:2  
赵振华  张绵吉 《催化学报》1991,12(4):328-332
迄今为止,工业上生产羧酸酯主要采用以浓硫酸作催化剂的均相酯化反应法,然而此法存在腐蚀设备、后处理工序复杂等缺点.ZSM-5沸石具有独特的晶体结构和优良的物化性能,是许多有机催化反应的理想催化剂.文献[1]报道了用HZSM-5沸石作催化剂合成乙酸乙酯,我们在常压液-固相酯化反应中用自制的ZSM-5沸石催化合成了一系列丙酸酯,该催化剂具有良好的催化活性、选择性和稳定性.  相似文献   

3.
当今世界环境与能源问题日益加剧,乙醇作为一种重要的清洁燃料和化学品受到广泛关注,迫切需要探索高效的乙醇合成方法,以满足日益增长的市场需求.其中,将煤炭、生物质、页岩气等为原料合成的二甲醚通过羰基化反应制乙酸甲酯、乙酸甲酯加氢制乙醇的串联式绿色乙醇合成路线具有重要的工业应用前景.然而,在二甲醚羰基化过程中,丝光沸石分子筛易积碳失活,阻碍了其工业应用.吡啶改性可以毒化丝光沸石12元环孔道中的酸性位,抑制积碳的形成,进而大幅度提高该催化剂的稳定性,但同时会使其催化活性降低约40%–50%.为了解决这一难题,本文从分子水平上研究了吡啶吸附行为以及分子筛骨架空间位阻对丝光沸石催化剂上二甲醚羰基化反应的影响.通过解析丝光沸石的骨架结构,我们发现位于8元环侧袋和12元环孔道共用孔壁处O_2位置上的酸性位是二甲醚羰基化反应的活性位,但它们在吡啶修饰过程中易被毒化而使催化剂活性下降.密度泛函理论计算结果表明,吡啶分子因受分子筛骨架空间位阻的影响,在O_2处酸性位上的吸附较弱.而实验结果也表明,通过673 K热处理可以再生被吡啶毒化的O_2活性位,而并不影响12元环孔道中其它吡啶分子的吸附.因此,该热处理方法可以使丝光沸石催化剂保持高稳定性的同时,将二甲醚羰基化反应催化活性提高约60%.本文从分子水平证明了丝光沸石中O_2活性位对二甲醚羰基化反应的重要作用,为绿色乙醇合成技术研究提供了新的思路,也为其它高效分子筛催化体系设计提供了有益的参考.  相似文献   

4.
本文研究了HZSM-35沸石催化剂的酸性对二甲苯异构化反应的影响。实验结果表明,在HZSM-35沸石表面存在着B酸和L酸中心,二甲苯异构化反应主要在较弱的B酸上进行。证实了不同晶化时间合成的HZSM-35沸石具有不同的酸性。以X射线衍射光谱、差热分析谱图,红外光谱关联不同晶化时间沸石的酸性与二甲苯异构化反应的活性和选择性的关系。找到了用HZMS-35沸石作催化剂进行二甲苯异构化较适宜的硅铝比、晶化时间、残钠量、脱氨温度和时间。  相似文献   

5.
骨架和非骨架含硼的ZSM-5沸石催化剂的催化性能   总被引:1,自引:0,他引:1  
沸石的改性是提高沸石择形催化性能的重要手段.因此,沸石的改性及改质剂作用机理的研究,受到人们的关注.本文采用浸渍法制得了非骨架含硼的催化剂,在沸石合成中引入硼得到了骨架含硼的催化剂,用高温硼酸水溶液处理制得了脱铝沸石中含硼的催化剂.用XRD,IR,TPD等对它们进行了表征.研究了硼在沸石中所处的状况及其对择形催化反应性能的影响.采用的探针反应为甲苯/乙醇烷基化反应.对于骨架含硼  相似文献   

6.
一、前言近年来在国内外文献中有许多关于在沸石分子筛上甲苯歧化反应的研究报导。苏联等人研究了在含Ⅵ族和Ⅷ族元素的沸石分子筛上甲苯歧化反应的动力学,证明在该催化剂上,反应符合朗格缪尔-欣谢伍德机理。我们用由正丁胺合成的氢型ZSM-5沸石分子筛(代号H-IDG 型)为催化剂,对甲苯歧化反应进行了动力学研究。  相似文献   

7.
采用柠檬酸等有机酸对Hβ沸石样品进行改性,研究了改性后Hβ沸石样品在2-(4′-乙基苯甲酰基)苯甲酸(BEA)脱水闭环合成 2-乙基蒽醌(2-EAQ)反应中的催化性能. 采用X射线衍射、 X射线荧光光谱、红外光谱、核磁共振和程序升温脱附方法对催化剂进行了表征. 结果表明,有机酸改性没有破坏Hβ沸石样品的骨架结构,但其有序度和结晶度均有不同程度的降低,而且酸量明显减少;其中草酸改性后的催化剂脱铝严重. 柠檬酸、酒石酸、苹果酸和丙二酸改性后的Hβ沸石样品在合成2-EAQ的反应中有较好的反应性能,以其为催化剂, BEA的转化率和2-EAQ的选择性均在95.0%以上.  相似文献   

8.
赵振华 《分子催化》2004,18(6):420-424
室温下用HY沸石取代传统催化剂通过1-甲基环己烯与乙酐的酰基化反应合成了6-乙酰基-1-甲基环己烯,考察了HY沸石的SiO2/Al2O2摩尔比、用量和活化时间以及反应时间对该酰化反应的影响.当1-甲基环己烯/乙酐/HY沸石(SiO2/Al2O3摩尔比=29)=1mmol/10mmol/0.200g、反应温度25℃、反应时间3h时,所得酰化产品的产率为60%,HY沸石能够回收和重新使用,显示出与新鲜催化剂几乎相同的催化活性.  相似文献   

9.
HZSM-5沸石上的甲苯乙基化反应   总被引:3,自引:1,他引:2  
对一甲乙苯是新型塑料聚甲基苯乙烯的重要原料.过去用AlCl_3催化剂只能得到热力学平衡组成的产物,其中含对-甲乙苯约30%.近年来,美国Mobil公司采用改性ZSM-5沸石催化剂,使产物对-甲乙苯含量高达97%.为了开发利用国产ZSM-5沸石,我们对南开大学用“直接法”、中国科学院大连化学物理研究所用四丙基溴化铵合成的样品以及美国Mobil公司的样品(分别称为NK-,DL-,MB-ZSM-5沸石)进行了甲苯乙基化反应的性能比较,并对HZSM-5沸石的催化性能和物化性质的关联进行了探讨.  相似文献   

10.
沸石分子筛催化剂因其独特的酸性、规则的孔道结构和良好的水热及化学稳定性被广泛应用于石油化工、煤化工和精细化工等重要领域.沸石分子筛活性位点的数目和分布,以及孔结构效应是沸石分子筛催化科学研究中最根本的问题,直接影响催化反应历程和反应结果.几十年来,沸石分子筛催化研究多集中在对活性位点的基本认识和合成设计,而忽视了活性位点、反应分子和沸石分子筛孔道微环境之间的相互作用.受益于先进的化学分析表征技术和化学理论计算科学的发展,沸石分子筛催化剂孔道内的微环境研究引起了越来越多研究人员的重视.通过对相关文献的分析整理,本文从沸石分子筛结构"限域"理论的发展历程,对分子扩散、吸附和催化过程的影响及其应用拓展等几个方面讨论了沸石分子筛催化剂中的"限域"效应.  相似文献   

11.
A metal–organic framework (MOF)‐based catalyst, chromium hydroxide/MIL‐101(Cr), was prepared by a one‐pot synthesis method. The combination of chromium hydroxide particles on and within Lewis acidic MIL‐101 accomplishes highly selective conversion of glucose to fructose in the presence of ethanol, matching the performance of optimized Sn‐containing Lewis acidic zeolites. Differently from zeolites, NMR spectroscopy studies with isotopically labeled molecules demonstrate that isomerization of glucose to fructose on this catalyst, proceeds predominantly via a proton transfer mechanism.  相似文献   

12.
基于脱铝多级孔BEA沸石与二氯二茂钛的固相反应,开展了钛掺杂量可调的多级孔Ti-beta后处理工艺制备研究.对制备的多级孔Ti-beta样品的理化性质进行了表征,包括X射线衍射、氮气吸附脱附测试、扫描电镜、透射电镜、紫外可见吸收光谱和紫外拉曼光谱等.结果表明,多级孔BEA沸石具有较好的化学稳定性,脱铝-钛化的后处理过程未对样品多级孔结构产生明显影响. ;以环己烯和十二烯的烯烃环氧化为探针反应表征了合成多级孔Ti-beta与纯相微孔Ti-beta沸石的催化性能.结果表明,在小分子环己烯的环氧化反应中,多级孔Ti-beta沸石的催化活性(转化率59.4%)与微孔Ti-beta相当(转化率57.9%);但是在较大分子十二烯的催化反应中,多级孔结构Ti-beta材料的催化性能(转化率11.1%)明显优于纯相微孔材料(转化率6.8%),且产物中环氧化物选择性更高(分别为60.3%和37.8%).  相似文献   

13.
The facile isomerization of glucose into fructose has been developed using commercially available anion-exchange resins (AERs) in organic solvents. Following extensive screening for the amount and type of AERs, solvents and reaction time, glucose was transformed into fructose in yields of up to 50% using Amberlite A-26 with macroreticular morphology and tertiary amine functionality in a protic solvent (ethanol). AERs could be used five times without a significant loss of activity. This isomerization method could be applied to the direct conversion of glucose into furan compounds by integrating the dehydration of fructose with cation-exchange resins.  相似文献   

14.
The parent NaX and KL samples were prepared by hydrothermal crystallization and their corresponding K- and Na-exchanged forms were obtained by post-synthesis modification by conventional ion-exchange technique. NaX, NaKX, KL and NaKL samples were characterized by powder XRD, IR, low temperature nitrogen adsorption and chemical analyses. Their sorption uptake behaviour has been investigated by gravimetric method. The kinetics of sorption using different sorbate probe molecules such as water, benzene and n-hexane was measured at 298 K, at P/P 0 = 0.5 for 90 minutes. All the results obtained were discussed in terms of the compositional and structural variations of the adsorbents. Lack of high dimensionality of the pore system, less openness in structure, low average framework oxygen charge and less number of accessible nonframework cations are some of the prominent factors which has resulted in reduced hydro- and organo-philicity in LTL type zeolites as compared to X-type. The size and concentration of the accessible nonframework cations were also found to influence the sorptive properties of these aluminous large pore zeolites. Among all the probe molecules, n-hexane was found to be as a promising probe for differentiating the structural peculiarities especially dimensionality of the pore system.  相似文献   

15.
Thermal and hydrothermal stabilities of the alkali-treated HZSM-5 zeolites   总被引:1,自引:0,他引:1  
HZSM-5 zeolites with the micro-mesopore hierarchical porosity have been prepared by the post-synthesis of alkali-treatment, and their thermal and hydrothermal stabilities were studied using DTA, XRD, and NH3-TPD characterization techniques. Compared to the unmodified zeolite, the thermal and hydrothermal stabilities of the alkali-treated ZSM-5 zeolites were slightly deteriorated because of the introduction of mesopores caused by the desilication. Nevertheless, the alkali-treated zeolite framework could be maintained until the temperature increased to 1175 ℃.  相似文献   

16.
Phosphorus-modified all-silica zeolites exhibit activity and selectivity in certain Brønsted acid catalyzed reactions for biomass conversion. In an effort to achieve similar performance with catalysts having well-defined sites, we report the incorporation of Brønsted acidity to metal–organic frameworks with the UiO-66 topology, achieved by attaching phosphonic acid to the 1,4-benzenedicarboxylate ligand and using it to form UiO-66-PO3H2 by post-synthesis modification. Characterization reveals that UiO-66-PO3H2 retains stability similar to UiO-66, and exhibits weak Brønsted acidity, as demonstrated by titrations, alcohol dehydration, and dehydra-decyclization of 2-methyltetrahydrofuran (2-MTHF). For the later reaction, the reported catalyst exhibits site-time yields and selectivity approaching that of phosphoric acid on all-silica zeolites. Using solid-state NMR and deprotonation energy calculations, the chemical environments of P and the corresponding acidities are determined.  相似文献   

17.
改性Y沸石上的氢转移反应   总被引:1,自引:0,他引:1  
高滋  张羚 《化学学报》1993,51(2):125-130
本文试图用环已烯和邻二甲苯两典型反应考察改性Y沸石的氢转移反应性能。发现在改性Y沸石上环已烯的氢转移, 异构化和聚合反应时发生。在反应开始时SY沸石的氢转移反应和异构化反应活性与铝含量之间的关系与沸石强酸量和铝含量的关系一致, 呈火山形曲线, 极大值在Al/(Al+Si)为0.15左右, 结焦以后反应总转化迅速下降, 且氢转移活性和异构化活性随铝含量减少而单调下降。USY沸石的氢转移活性大幅度降低。在改性Y沸石上邻二甲苯异构化和歧化反应同时进行, SY沸石的歧化反应变化规律与环乙烯氢转移反应相似。当沸石样品中有大量非质子酸位存在时, 两个反应的数据会出现予盾。  相似文献   

18.
The MgO/NaY catalysts prepared by impregnation method were used for the conversion of glucose to fructose in water medium.The effects of MgO loading, reaction temperature, glucose concentration and reaction time on the catalytic performance for the reaction were studied.The activity testing results indicated that fructose could be generated effectively by controlling the components of the catalyst and reaction conditions.The maximal fructose yield of 33.8% with the selectivity of 67.3% was achieved over the 10% MgO/NaY catalyst at 100 ℃ for 2 h.Moreover, the catalysts were characterized by XRD, BET, and CO2-TPD techniques.The structural property of NaY with higher surface area facilitated glucose conversion, and the modulated basicity of the catalyst with MgO addition contributed to the formation of fructose in the tautomerization of aldose to ketose.  相似文献   

19.
Nanodispersed aggregates of MnO2 were prepared in the aqueous core of the H2O/Aerosol OT (AOT)/heptane reverse micelle using the comproportionation reaction between and Mn2+ ions. The formed nanoparticles were characterized by transmission electron microscopy (TEM), UV–visible spectroscopy and cyclic voltammetry. The electro-oxidation of dextrose and fructose on platinum modified by reverse micellar MnO2 deposits was studied. The oxidation of fructose was found to be much more facile than dextrose oxidation. There was a linear correlation between the steady state oxidation currents and the carbohydrate concentrations, which was shown to be useful for analytical application. The sensitivity for fructose detection was found to be about seven times higher than that of dextrose. The scope of developing an electroanalytical method for estimation of dextrose and fructose individually in their mixture was explored.  相似文献   

20.
K, Zn, Cs and La ion-exchanged Y zeolites were prepared and used as photocatalysts for the isomerization of norbornadiene. The prepared catalysts were characterized by EDS, XRD, 27Al- and 29Si-NMR, UV-vis and IR. The La-exchanged sample showed the highest degree of exchange, but accompanied with some dealumination. La-exchange generated both B-acid and L-acid sites, whereas other metals produced only L-acid sites. For the photocatalytic isomerization reaction, the activity order was LaY > CsY > ZnY > KY. The heavy atom effect and B-acidity are expected to play important roles in the reaction.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号