高比表面积介孔TiO_2的制备及负载钴基催化剂费-托合成反应性能研究

以钛酸四丁酯和异丙醇钛为钛源,CTAB和Brij56为表面活性剂,采用水热合成法制备出2种高比表面积介孔二氧化钛载体TiO_2-B和TiO_2-C.以商业P25(TiO_2-P)为参比载体,采用满孔浸渍法制备了钴基费-托合成催化剂,利用氮气物理吸附-脱附、透射电子显微镜(TEM)、扫描电子显微镜(SEM)、原位X射线粉末衍射(in-situ XRD)和H_2-程序升温还原(H_2-TPR)等表征手段研究了TiO_2载体结构对钴基催化剂结构和费-托合成反应性能的影响.结果表明:合成的TiO_2-B和TiO_2-C载体具有高的比表面积和丰富的介孔结构,负载的钴基催化剂上钴物种均以Co_3O_4形式存在并高度分散在载体上;与TiO_2-P相比,TiO_2-B负载的催化剂具有更高的催化反应活性和C_(5+)选择性,以及低的CH_4选择性.     

焙烧温度对甲硫醇催化剂K_2WO_4/Al_2O_3结构和性能的影响

研究了焙烧温度对溶胶-凝胶法制备的甲硫醇催化剂K2WO4/Al2O3的表面结构和催化性能的影响.表征结果显示,K2WO4在Al2O3上分散得较好,在450和550oC焙烧的催化剂颗粒大小均匀,无明显团聚现象.随着焙烧温度的升高,催化剂的比表面积减小,表面钨物种与Al2O3的相互作用减弱,与碱物种的相互作用增强,酸碱强度降低.K2WO4/Al2O3表面不含质子酸.催化剂活性与其比表面积及表面的共轭酸碱对密切相关.评价结果表明,在550oC焙烧而制得的催化剂活性最高.     

载体焙烧温度对RuO_2/TiO_2催化HCl氧化性能的影响

以不同温度焙烧TiO(OH)_2得到的TiO_2为载体,采用湿法浸渍法制备RuO_2/TiO_2-C(C=450、550、650及750℃)催化剂,利用XRD、N_2吸附-脱附、TEM和H_2-TPR等表征手段研究催化剂的物理化学性质,并对其在HCl氧化反应中的催化性能进行考察.结果表明:载体焙烧温度对催化剂的结构与活性有显著影响.随着载体焙烧温度(≤650℃)的升高,RuO_2与TiO_2之间的晶面匹配度逐渐变高,促进了RuO_2在TiO_2表面的分散,其中RuO_2/TiO_2-650催化剂表现出最优的催化性能.而当载体焙烧温度过高时,RuO_2/TiO_2-750催化剂的反应活性大大下降,可能是由于过高的焙烧温度导致载体出现严重的烧结团聚现象,以及RuO_2与TiO_2之间过强的相互作用,阻碍了HCl氧化反应的进行.此外,减小RuO_2的粒径可以促进HCl氧化活性的提升.动力学结果显示,催化剂表面的HCl氧化反应主要受O_2分压的影响,表明O_2从催化剂表面的解离吸附为决速步骤.     

多孔Pd/TiO_2-Al_2O_3催化剂上乙醇完全氧化的研究（英文）

利用模板剂-浸渍法制备出了不同焙烧温度下的多孔复合材料TiO_2-Al_2O_3和Pd/Al_2O_3-TiO_2催化剂来催化氧化乙醇.样品经过XRD,FT-IR,孔结构分析、TEM、XPS、脉冲吸附、NH_3-TPD等进行表征分析.250℃焙烧的Pd/TiO_2-Al_2O_3催化剂具有最高的乙醇转化率和CO_2生成率.高比表面积、均匀分散的金属Pd颗粒和丰富的表面吸附氧是其具有高的催化活性的主要原因.     

模板-聚合法Pd/Al2O3催化剂制备及其蒽醌加氢性能研究

以丙烯酸铵为模板剂,由油柱成型法制备了系列球形Al2O3载体,采用XRD、BET等分析测试手段对其晶体结构、比表面积、孔容和孔径分布进行了表征,结果表明,600℃焙烧的球形γ-Al2O3载体具有介孔结构,并且比表面较不使用模板剂的样品有大幅度增加。焙烧温度升至960℃得到δ-Al2O3,介孔结构消失,但由于结构记忆效应,载体的大表面特性得以保持。以δ-Al2O3为载体制备Pd/Al2O3催化剂,采用氢-氧滴定(HOT)方法测定发现,比表面的增加显著提高了Pd金属的分散度,从而大幅度提高了催化剂的蒽醌加氢活性,氢化效率最高可达10.5 g.L-1。     

Cu-Zn-Zr/SBA-15介孔催化剂的制备及CO2加氢合成甲醇的催化性能

以具有骨架结构的SBA-15介孔分子筛为载体,采用浸渍法合成了具有高比表面积、不同金属氧化物含量的Cu-Zn-Zr介孔催化剂CZZx/SBA-15(x=0.3,0.4,0.5,0.6).采用N2吸附-脱附(BET)、X射线衍射(XRD)、H2程序升温还原(H2-TPR)、CO2吸附(CO2-TPD)和透射电子显微镜(TEM)等手段对样品进行了表征.在固定床反应器上评价了其CO2加氢合成甲醇的催化性能.实验结果表明,CZZx/SBA-15催化剂具有介孔结构,负载的Cu O,Zn O和Zr O2能够很好地分散在表面,并且负载氧化物晶粒尺寸不同.催化剂的铜比表面积SCu与甲醇催化活性呈近似线性关系,其中CZZ0.4/SBA-15催化剂表现出最大甲醇选择性(54.32%),与CZZ相比,甲醇选择性增加24.85%.随着金属氧化物负载量的增大,催化剂比表面积和SCu明显减小,甲醇选择性与收率也相应减小,负载型CZZx/SBA-15催化剂表面结构对CO2加氢合成甲醇反应活性起关键作用.     

TiO2-Al2O3复合氧化物载体焙烧温度对Au-Pd催化剂加氢脱硫性能的影响

 采用溶胶-凝胶法制备了介孔TiO2-Al2O3复合氧化物载体,考察了载体的焙烧温度对负载型Au-Pd双金属催化剂加氢脱硫性能的影响,并采用X射线衍射、吸附吡啶的程序升温脱附、程序升温还原、红外光谱和N2物理吸附等技术对载体及催化剂进行了表征. 结果表明,不同温度焙烧的TiO2-Al2O3复合载体都具有介孔结构,其中773 K焙烧制得的TiO2-Al2O3复合载体的比表面积和孔容较大, B酸中心较多,以其为载体的Au-Pd 催化剂具有较好的加氢脱硫活性. 表征结果表明, 773 K焙烧制得的Au-Pd/TiO2-Al2O3催化剂中Au-Pd活性组分与载体的相互作用较强,催化剂上形成的AuxPdy合金的晶粒较小且数量较多,催化剂的酸量和活性组分的分散度较大,并且其上进行的加氢脱硫反应的活化能较低,这些因素均有利于催化剂活性的提高.     

高比表面积蠕虫状介孔SnO2的合成与表征

 以聚乙二醇 (PEG) 为模板剂, 氯化锡为锡源, 尿素为沉淀剂, 采用水热法合成出高比表面积的蠕虫状介孔四方相金红石型 SnO2. 考察了 PEG 分子量及其浓度、水热温度和焙烧温度对 SnO2 孔结构和形貌的影响. 采用 X 射线衍射、N2 吸附-脱附、透射电镜、红外光谱和紫外-可见光谱等技术对样品进行了表征. 结果表明, 模板剂可被水洗除去, PEG 分子量对介孔 SnO2 的比表面积影响不大, 而 PEG 浓度、水热温度和焙烧温度的影响较大. 在以分子量为 6000 的 PEG 与 Sn 的摩尔比为 0.01 的条件下, 于 120 oC 水热处理 29 h 后可合成出比表面积高达 161 m2/g 和平均孔径为 2.6 nm 的蠕虫状介孔 SnO2. 所制得样品具有较好的紫外光吸收性能, 适宜用作催化剂、载体和气体传感器等.     

用于质子交换膜燃料电池的碳载铂电催化剂

 以甲醛为还原剂，氯铂酸为原料，XC－72碳黑为载体，制备了不同铂含量的碳载铂电催化剂，并用BET，XRD，TEM和循环伏安法对催化剂进行了表征，用质子交换膜燃料电池单电池对催化剂性能进行了评价．结果表明，铂晶粒主要吸附在碳黑的表面和大孔中．当催化剂的铂载量由20％提高到40％时，由于铂颗粒占据部分碳黑表面，使催化剂的孔体积和比表面积都有所减小；当铂载量进一步提高到60％时，由于铂晶体颗粒形成的微孔开始占一定分率，使催化剂的总体积和比表面积的减小幅度下降．铂晶体颗粒大小在2～4nm范围内；随着铂载量的提高，表面铂有部分聚结，铂晶体的粒径增大，催化剂的电化学比表面积减小．铂载量为40％时，燃料电池阴极的性能最好．     

棒状多孔氧化铝负载氧化铬催化丙烷脱氢反应性能

丙烯是一种重要的化工原料,目前工业上主要来自石脑油、轻质油以及其他石油副产物的蒸汽裂解和催化裂解.这些过程能耗巨大,碳排放严重.丙烷直接脱氢制丙烯原料利用率高,副产物少,是一条更加经济环保的丙烯生产路线.Cr_2O_3-Al_2O_3催化剂因其出色的性能和低廉的价格已在工业中应用,但氧化铝表面酸位点易催化副反应及积碳的形成,从而造成催化剂失活.因此,调控载体氧化铝结构具有重要的意义.氧化铝的结构性质取决于合成条件以及焙烧过程表面羟基和水分的逐步脱除.我们课题组通过水热法合成了一系列表面粗糙的棒状氧化铝和富含五配位铝离子的片状氧化铝,以这些氧化铝为载体制备的负载型贵金属催化剂在催化反应中表现出优异的活性和稳定性.本文在前期工作基础上研究了不同焙烧温度对棒状氧化铝表面结构的影响,采用X射线衍射(XRD)、氮吸附、电镜(SEM/TEM)、氨气程序升温脱附(NH3-TPD)和紫外-可见光谱(UV-Vis)等手段表征了氧化铝结构,并探究了其对负载氧化铬催化剂上丙烷脱氢反应的影响.XRD结果表明,低温焙烧所得主要为γ相氧化铝,提高焙烧温度至900oC时出现δ相氧化铝.氧化铝氮气吸附-脱附表现出IV型等温线,随焙烧温度升高,介孔结构保持,但比表面积和孔体积呈减小趋势.电镜观察显示氧化铝为棒状结构,表面粗糙.NH_3-TPD结果表明自制氧化铝酸量低于商业氧化铝,且随焙烧温度升高酸量下降.以上结果表明焙烧温度在氧化铝性质调控过程中起重要作用.以不同焙烧温度下制得的氧化铝等体积浸渍氧化铬制得氧化铬催化剂.丙烷脱氢反应结果表明,催化剂表现出优异的稳定性和再生性能.氮吸附等温线表明新鲜催化剂为介孔结构,这有利于反应物接触活性位点,并提供抗积碳阻塞能力.对比氧化铝负载氧化铬前后的电镜照片可知,催化剂表面粗糙度降低,说明活性组分均匀分散于氧化铝粗糙表面;反应前后催化剂形貌保持不变,催化剂在反应中表现出优异的结构稳定性.UV-Vis和H_2-TPR结果表明,自制氧化铝和参比氧化铝表面的铬物种以相似配位状态存在,但铬物种在自制氧化铝表面更难还原,表现出更强的金属与载体相互作用.NH_3-TPD结果表明,自制催化剂表面酸量(64μmol NH_3 g~(–1))远低于参比催化剂(140μmol NH_3 g~(–1)).热重分析证实反应后自制催化剂积碳量明显低于参比催化剂.自制棒状氧化铝作为载体制备的氧化铬低酸催化剂可抑制积碳形成,提高丙烯选择性,在丙烷脱氢反应中表现出优异的活性和抗积碳能力.     

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.