Zn/HZSM-5分子筛催化剂对丙烷芳构化反应中芳烃分布的影响

采用浸渍法,制备了Ｚｎ／ＨＺＳＭ－５分子筛催化剂,考察了锌含量、反应温度对丙烷芳构化反应的影响,根据产物分布情况,讨论了锌物种在丙烷芳构化反应中的作用,并以氮气作载气,带入烷基芳烃乙苯、二甲苯、甲苯,考察了温度对催化剂脱烷基反应的影响。结果表明,锌物种不公能够催化丙烷的脱氢活化,提高其转化率,而且能促进随后进行的齐聚、脱氢芳构化第一系列反应,提高芳烃的选择性,并进一步催化烷基芳烃的脱烷基反应,导致     

ZSM-5分子筛催化剂上液化石油气低温芳构化制取高辛烷值汽油

 考察了反应温度、空速、压力、临氢条件以及催化剂的水热处理条件对液化石油气在ZSM-5分子筛催化剂上低温芳构化制取高辛烷值汽油反应性能的影响. 结果表明,反应温度和空速对催化剂的催化性能有明显影响,提高反应温度有利于提高芳烃的选择性,同时芳烃中的苯、甲苯和C10+芳烃含量增加; 增大进料空速,催化剂的芳构化性能下降,芳烃中的重组分增加,二甲苯中对二甲苯含量增大. 催化剂的水热处理温度升高,其初始芳构化活性下降,而催化剂经过适当的水热处理和系统中氢气的存在均可提高催化剂催化芳构化反应的稳定性.     

甲烷在6%Zn/HZSM-5催化剂上的低温转化 Catalytic Conversion of Methane at Low Temperature over 6%Zn/HZSM-5 Zeolite

 采用丙烷和甲烷混合物作为共反应物进行无氧芳构化反应. 在600 ℃,3000 h-1和甲烷/丙烷摩尔比为0.6的条件下,甲烷可以在6%Zn/HZSM-5分子筛催化剂上被有效地活化,甲烷的转化率可达32.4%,丙烷的转化率为89.5%,反应的主要产物为芳烃,其选择性达到89.7%. 甲烷与丙烷的摩尔比对芳烃产物的选择性有影响. 在没有丙烷参与时该催化剂在600 ℃下对甲烷转化没有活性. 推测是丙烷脱氢或裂解过程的中间产物活化了甲烷. 低碳烷烃对甲烷的活化可能是实现甲烷低温转化的一条有效途径.     

Cu-Zn/HZSM-5催化剂上甲烷与丙烷的共活化

 研究了xCu-6%Zn/HZSM-5(x=0～0.9%)系列催化剂对甲烷和丙烷混合气体无氧芳构化反应的催化性能. 结果表明,在此系列催化剂上,丙烷促进了甲烷的活化,使之参与到芳烃的形成过程中. 在600 ℃和甲烷/丙烷摩尔比为1.0的条件下,0.7%Cu-6%Zn/HZSM-5催化剂表现出最佳活性,甲烷转化率达到36%,芳烃选择性达到85.7%. 这说明在Zn/HZSM-5中添加第二组分Cu有助于提高催化剂的活性和稳定性. 考察了反应时间和甲烷/丙烷摩尔比对甲烷和丙烷转化率及产物分布的影响. 13CH4同位素示踪实验发现13C进入到了C6H+6, C7H+8和C8H+10碎片中,这进一步证实甲烷参与了芳烃的形成.     

Zn/HZSM-5催化剂上正/异丁烷芳构化反应性能研究

采用脉冲微反装置评价了纯正丁烷(原料I)、含有少量异丁烷的混合丁烷(原料Ⅱ)和富含异丁烷的混合丁烷(原料Ⅲ)在锌改性的纳米HZSM-5催化剂上的反应性能.通过红外吸附正丁烷羟基谱图,研究了Zn/HZSM-5催化剂的活性中心.结果表明,反应温度为550℃时,两种混合丁烷在催化剂上的转化率和芳构化选择性都远高于纯正丁烷.即异丁烷比例越高,反应效果越好,说明二者共存时,异丁烷在竞争反应中抑制了正丁烷的转化.另外,芳烃选择性均随Zn负载量的增加而增加.这是因为异丁烷在酸中心作用下脱氢生成叔碳正离子的能力高.而正丁烷的活化方式可能同时存在脱氢活化和脱甲基活化.因此,以工业碳四饱和烃为芳构化原料时,正丁烷和异丁烷可不必分离,直接以混合原料进行芳构化反应.     

Mo-V-Te-Nb-O催化剂上丙烷选择氧化制丙烯酸 I．催化剂的制备条件及稳定性

研究了催化剂的制备条件(焙烧方式、焙烧气氛和焙烧温度)对Mo-V-Te-Nb-O上丙烷选择氧化制丙烯酸反应的影响．结果表明，制备条件对催化剂的催化性能具有很大的影响．与敞开式焙烧制得的催化剂相比，封闭式焙烧制得的催化剂具有较高的丙烯酸选择性，但丙烷转化率较低．在空气中焙烧制得的催化剂对丙烯酸无选择性，但在氮气和氩气中焙烧制得的催化剂具有很高的丙烷转化率和丙烯酸选择性．随着焙烧温度的升高，丙烷转化率降低，丙烯酸选择性升高，适宜的焙烧温度为600℃．催化剂制备条件对催化剂的晶相结构也具有重要的影响．在惰性气氛中采用600℃下封闭式焙烧制得的Mo-V-Te-Nb-O催化剂经210h反应后，丙烷转化率保持为19％，而丙烯酸选择性持续升高，由32％升至50％．     

氢预处理对Zn/HZSM-5分子筛催化乙烯芳构化反应性能的影响

采用浸渍法制备了Zn/HZSM-5分子筛催化剂,进行了不同温度的氢气预处理,通过X射线衍射(XRD)、氮气吸附-脱附、傅里叶变换红外(FT-IR)光谱、NH_3程序升温脱附(NH_3-TPD)、X射线光电子能谱(XPS)等表征技术,系统考察氢气预处理对Zn/HZSM-5分子筛结构、孔道、酸性、Zn存在状态以及在乙烯芳构化反应中的催化性能等的影响。研究结果表明,氢气预处理温度显著影响Zn/HZSM-5中Zn物种的含量和存在状态:600℃以下的氢处理,几乎不影响分子筛上Zn物种的总含量,而600℃以上氢处理时会造成Zn物种的大量流失;XPS研究显示,氢预处理的温度不同,分子筛上ZnOH~+与ZnO的相对比例变化显著。结合乙烯芳构化反应性能,可以发现ZnOH~+物种的含量与芳烃选择性存在较好的线性关系,说明其是促进烯烃脱氢、芳构化的主要活性中心,Zn存在状态的变化使得氢气预处理温度显著影响乙烯芳构化反应产物的分布。     

ZnHZSM-5上丙烷芳构化的研究-丙烷的活化

研究了HZSM－5、ZnHZSM－5和ZnNaZSM－5上的羟基振动光谱和一氧化碳吸附的红外光谱，以及丙烷的芳构化反应．红外光谱中发现表征强B酸的3610cm－1羟基振动峰相对强度由于锌离子的引入和浸渍氢氧化钠而减小，说明了锌离子和钠离子均进入了分子筛的阳离子位；一氧化碳在锌离子上的吸附峰位在2232cm－1，说明进入阳离子位的锌离子是一种强L酸．反应结果表明，锌离子的引入大大地促进了丙烷的转化和芳烃选择性的提高；在一定范围内，随浸渍氢氧化钠量的增加，丙烷转化率下降，而丙烯的选择性和产率增加，说明了锌组份直接参与了丙烷的脱氢过程．Zn－L酸是丙烷活化脱氢的中心，丙烷在该中心上异裂活化直接脱氢．     

ZnHZSM-5上丙烷芳构化的研究─丙烷的活化

研究了HZSM－5、ZnHZSM－5和ZnNaZSM－5上的羟基振动光谱和一氧化碳吸附的红外光谱，以及丙烷的芳构化反应．红外光谱中发现表征强B酸的3610cm－1羟基振动峰相对强度由于锌离子的引入和浸渍氢氧化钠而减小，说明了锌离子和钠离子均进入了分子筛的阳离子位；一氧化碳在锌离子上的吸附峰位在2232cm－1，说明进入阳离子位的锌离子是一种强L酸．反应结果表明，锌离子的引入大大地促进了丙烷的转化和芳烃选择性的提高；在一定范围内，随浸渍氢氧化钠量的增加，丙烷转化率下降，而丙烯的选择性和产率增加，说明了锌组份直接参与了丙烷的脱氢过程．Zn－L酸是丙烷活化脱氢的中心，丙烷在该中心上异裂活化直接脱氢．     

Mo-V-Te-Nb-O催化剂上丙烷选择氧化制丙烯酸Ⅰ.催化剂的制备条件及稳定性

 研究了催化剂的制备条件(焙烧方式、焙烧气氛和焙烧温度)对Mo-V-Te-Nb-O上丙烷选择氧化制丙烯酸反应的影响. 结果表明,制备条件对催化剂的催化性能具有很大的影响. 与敞开式焙烧制得的催化剂相比,封闭式焙烧制得的催化剂具有较高的丙烯酸选择性,但丙烷转化率较低. 在空气中焙烧制得的催化剂对丙烯酸无选择性,但在氮气和氩气中焙烧制得的催化剂具有很高的丙烷转化率和丙烯酸选择性. 随着焙烧温度的升高,丙烷转化率降低,丙烯酸选择性升高,适宜的焙烧温度为600 ℃. 催化剂制备条件对催化剂的晶相结构也具有重要的影响. 在惰性气氛中采用600 ℃下封闭式焙烧制得的Mo-V-Te-Nb-O催化剂经210 h反应后,丙烷转化率保持为19%,而丙烯酸选择性持续升高,由32%升至50%.     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.     

Synthesis of N-substituted carbazolones from α-iodo enaminones via Pd(0)-catalyzed intramolecular coupling under microwave irradiation

A variety of N-aryl and N-alkyl carbazolones were conveniently achieved in good to high yields via Pd₂(dba)₃-mediated intramolecular coupling of N-substituted α-iodo enaminones under microwave irradiation. The Pd(0)-catalyzed cyclization was found to proceed favorably with the more electron-deficient phenyl ring during the reactions involving unsymmetrical N,N-diaryl α-iodo enaminones. This unique property enables the construction of carbazolone skeleton containing nitro substituted benzenoid ring.     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Synthesis of substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles by intramolecular nitrilimine cycloaddition

Both substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles have been synthesized by the 3+2 intramolecular dipolar cycloaddition of nitrilimines to alkynes. This cyclization has been extended to more versatile 3-bromo derivatives by the use of alkynylbromides as dipolarophiles.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.