丙烷芳构化催化剂Zn/HZSM-5中助剂锌的稳定性

 分别用离子交换法和等体积浸渍法制备了2．0％Zn／HZSM－5催化剂,并对催化剂中锌组分的不稳定性进行了研究．高温还原条件下,锌由催化剂中缓慢流失,而氧化条件下锌组分是稳定的．锌在氢热处理条件下的流失速率与催化剂的制备方法有关,锌组分的稳定性与锌在沸石上的分布及锌物种的状态有关．将离子交换法制备的Zn／HZSM－5在550℃下氢处理20h,并分别用XRD,TEM,XPS以及丙烷芳构化反应评价对其理化性质进行了表征．结果表明,该催化剂保持了沸石阳离子交换位锌物种的存在,催化活性基本不变．     

稀土对HZSM—5上正己烷芳构化性能的影响

以正己烷为原料,在连续流动常压反应装置上考察了稀土改性HZSM－5沸石催化剂的芳构化和裂解性能,用红光谱,X射线衍射,X光电子能谱等研究了这些离子改性的沸石催化剂的表面性质,比较了机械混合法和浸渍法引入稀土对催化剂性能的影响,稀土可提高混合法制备的改性催化剂的芳构化性能,B酸中心是正已烷构化的活性中心,L酸中心则对正己烷的裂解起重要作用。     

锌含量对Zn/HZSM-5催化剂性能的影响

 研究了不同锌含量的Zn／HZSM－5分子筛的表面酸性及其对正己\r\n烷芳构化反应的催化活性、选择性和稳定性．结果表明,锌组元的引入\r\n减少了HZSM－5表面的B酸,增加了L酸,总酸量增大;正己烷转化率随\r\n锌含量的增加先降低后升高;芳烃产率和芳构化选择性则随锌含量的增\r\n加先增大后趋于平缓;反应过程中催化剂的积炭速度、孔体积和比表面\r\n积下降速度都随着锌含量的增加而加快;锌含量大于1％时,Zn／HZSM\r\n－5的催化稳定性不如HZSM－5,且随着锌含量的增加失活速度加快．优\r\n选的锌含量为1．0％～2．9％．此外,讨论了Zn／HZSM－5的催化性能\r\n与其表面性质的关系．     

分子筛性质对Mo／HZSM－5催化剂上甲烷无氧脱氢芳构化反应的影响

 通过改变合成条件与合成体系，考察了不同硅源合成的HZSM－5分子筛对Mo／HZSM－5催化剂上甲烷无氧脱氢芳构化反应性能的影响．结果表明，用水玻璃合成的HZSM－5分子筛负载Mo后，其催化性能优于用硅溶胶合成的分子筛．1HMASNMR测定结果表明，前者的Br¨onsted酸 浓度较后者大．通过改变合成条件，减小HZSM－5分子筛的粒度，可以提高催化剂在甲烷无氧脱氢芳构化反应中的稳定性．     

Mo/HZSM-5催化剂上丙烷的芳构化反应

 采用浸渍法、机械混合法和水热法制备了Mo／HZSM－5分子筛催化剂,考察了Mo含量和在线反应时间对丙烷芳构化反应的影响,并以IR,XRD,NH3－TPD和XPS等表征手段研究了Mo物种对HZSM－5分子筛结构和酸性的影响．结果表明,水热法制备的催化剂丙烷芳构化活性最高,且具有较高的活性稳定性,在焙烧过程中Mo物种易在HZSM－5分子筛上分散,且比浸渍法更多地进入分子筛孔道内,并与分子筛产生强相互作用,使B酸中心减少,L酸中心增多．而浸渍法制备的催化剂的芳构化性能比相应的水热法催化剂低,活性稳定性较差,经焙烧后在分子筛外部形成结晶,进入孔道内的数量较少,对分子筛酸性的影响也低于水热法催化剂．     

La／HZSM—5催化剂上丙烷的芳构化反应研究

采用浸渍法和离子交换法制备了La/HZSM-5分子筛催化剂,用于丙烷芳构化反应,利用XRD,SPS,FT－IR,NH3－TPD技术考察了La对HZSM－5分子筛结构和表面酸性的影响,引入La后能显著提高HZSM－5的丙烷芳构化活性,其中由离子交换法得到的催化剂效果最佳,在反应温度550度,空速600h^-1条件下,丙烷转化率和芳烃选择性分别达到94．58％,68．99％,在La/HZSM-5中分子筛结晶度下降,B酸中心减少,L酸中心增多,离子交换法制备的催化剂比浸渍法催化剂的这种变化更显著,同时更有利于La3 进入分子筛孔道内,并与分子筛产生强相互作用,新增加的L酸中心可能是芳构化反应的活性中心。     

甲烷无氧芳构化反应中Co助剂对Mo／HZSM-5

 甲烷在Co－Mo／HZSM－5催化剂上进行无氧芳构化反应的评价结果表明，Co的添加大大提高了Mo／HZSM－5催化剂在反应过程中的稳定性．BET实验证明，反应后的积炭对Co－Mo／HZSM－5催化剂孔道堵塞的程度较小．对积炭催化剂进行的一系列程序升温表面反应（如TPH，TPCO2和TPO）结果表明，TPO谱上有两个峰温明显不同的烧炭峰，Co的添加明显抑制了高温积炭的生成．H2主要与高温积炭发生反应，这部分积炭是催化剂失活的主要原因；CO2对低温积炭的影响则尤为明显．TEM结果表明，积炭催化剂上存在丝状积炭物种．碳丝不能与H2反应，但能被CO2除去．Co的添加促进了丝状积炭物种的生成，碳丝并不是导致催化剂失活的因素．     

不同方法制备的Mo/HZSM-5催化剂上甲烷的芳构化反应

 采用机械混合、机械混合后焙烧和机械混合后微波处理等方法制备Mo／HZSM－5催化剂,并对催化剂上甲烷芳构化反应性能进行了考察．结果表明,与浸渍法相比,用机械混合法、固相反应法和微波法制备的催化剂,在保持甲烷转化率不变的前提下,能明显提高芳烃选择性并减少积炭的生成;不同方法制备的Mo／HZSM－5催化剂上Mo物种的落位不同,机械混合法、固相反应法和微波法使Mo物种较多地落位于分子筛外表面．结合反应结果可以得出,落位于分子筛外表面的Mo物种对甲烷芳构化反应更为有利,而且明显减少积炭的生成．     

微量氧对MoHZSM-5上甲烷芳构化反应的影响

 研究了微量氧对Mo／HZSM－5沸石上甲烷芳构化反应的影响．结\r\n果表明，氧的浓度存在阈值，当甲烷中氧的浓度低于阈值时，氧的加入\r\n可提高Mo／HZSM－5沸石对甲烷芳构化反应的稳定性；高于此值则发生\r\n甲烷的完全氧化反应．用紫外拉曼光谱和紫外激光诱导荧光光谱对在不\r\n同氧浓度的甲烷中反应后的Mo／HZSM－5样品进行了表征．催化剂上的\r\n积碳量，钼物种的碳化程度以及反应后样品在520～580nm间出现的荧光\r\n谱带峰位都随反应气氛中氧浓度的增加而降低．完全氧化时，钼物种被\r\n氧化为氧化钼，而此时荧光谱带下降到520nm．可以认为，荧光光谱的\r\n变化反映了钼物种的碳化程度，从而可将发生完全氧化反应后Mo／HZS\r\nM－5样品的520nm荧光谱带归属为氧化钼，而580nm附近的谱带可归属为\r\nMoOxCy；加氧时，MoOxCy／HZSM－5是甲烷芳构化反应的活性相．     

Mo/HZSM-5催化剂上甲烷无氧芳构化反应中积炭的研究

 对经过程序升温表面甲烷无氧芳构化反应后的Mo／HZSM－5催化剂上的积炭进行程序升温加氢反应和程序升温二氧化碳反应,并对相应的催化剂上的积炭进行程序升温氧化反应和热重实验,以研究催化剂上的不同积炭物种．结果表明,甲烷无氧芳构化反应后有两类烧炭峰,一类是低温烧炭峰,另一类是高温烧炭峰;H2主要对高温烧炭峰发生作用,对低温烧炭峰几乎没有影响;CO2可同时对两种烧炭峰产生影响．由此推论,甲烷在无氧条件下直接转化生成芳烃的反应过程中,沉积在Mo／HZSM－5催化剂上的积炭有三种形式,即：能够与H2反应的积炭,能够与CO2反应的积炭和可能以Mo2C形式存在的物种．     

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.     

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.     

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.