大气环境中铈氧物组成研究

采用X射线衍射仪(XRD)、扫描电镜(SEM)和X射线光电子能谱(EDS)研究了大气环境中铈氧化物的组成变化. 实验结果表明, 大气环境中铈的氧化物主要由Ce2O3, Ce7O12和CeO2构成, 氧化初期主要是Ce2O3, 随着氧化时间增加, 大部分Ce2O3逐渐转变为Ce7O12, 而在局部微裂纹集中处直接生成CeO2, 随着氧化过程的进行, Ce7O12逐渐转变为CeO2, 240 h后 Ce7O12几乎完全转变为CeO2;扫描电镜结合能谱分析表明Ce7O12主要以连续致密氧化膜存在, 而CeO2则出现大量微裂纹, 这种变化与两者密度上的差异有关.     

固溶体Ce0.8Pr0.2O2-δ的合成及性质研究

利用溶胶-凝胶方法合成了Ce0.8Pr0.2O2-δ固溶体, XRD结果表明,经200 ℃焙烧就已经形成立方萤石结构固溶体,晶粒尺寸为8.1 nm, 随焙烧温度的升高,晶粒尺寸增大. X射线光电子能谱(XPS)结果表明,样品中存在氧离子缺位,铈离子主要为Ce4 离子,镨离子以混合价态Pr3 和Pr4 存在. 固溶体Ce0.8Pr0.2O2-δ的拉曼谱(Raman)观察到4个峰,458和1140 cm-1峰为特征F2g振动谱带,较宽的570和187 cm-1峰对应氧离子缺位及引起的不对称振动. 交流阻抗谱表明固溶体Ce0.8Pr0.2O2-δ在600 ℃时的电导率为1.44×10-3 S·cm-1, 活化能为Ea=0.67 eV (650～800 ℃), Ea=0.91 eV (400～600 ℃).     

纳米CeO_2的催化基础及应用研究进展

纳米CeO2作为一种重要的催化材料,在CO催化氧化、有机合成催化、光催化,以及生物抗氧化等方面都有着重要的应用。纳米CeO2中Ce3+和Ce4+间的可逆转变过程伴随着氧空穴的生成与消除,从而赋予了纳米CeO2优异的氧存储与氧释放能力,也成为CeO2催化应用的基础。本文在简要总结近年来CeO2催化研究及应用进展的基础上,以CO催化氧化反应为例,分别从尺寸、形貌、氧缺陷活性位点三个方面介绍了影响CeO2催化活性的因素,对纳米CeO2的催化基础研究及应用发展提出了展望。     

α-取代苯并噻吩钌乙炔及钌乙烯配合物的合成、表征、电化学及光谱电化学性质

以α-取代苯并噻吩乙炔及乙烯基为配体,与不同辅助配体键合的金属钌为氧化还原活性端基,分别合成并表征了α-取代苯并噻吩钌乙炔及钌乙烯配合物1和2,两个配合物均经X射线单晶衍射的确证。电化学性质表明配合物1具有较好的氧化还原可逆性,金属氧化态相对于2比较稳定。红外光谱电化学研究表明配合物1和2分别形成1~+和2~+后,与金属相连的ν(C≡C)和ν(C≡O)伸缩振动吸收均发生变化,其中ν(C≡C)变化较大,可能由于形成了Ru=C=C结构;紫外可见近红外光谱电化学研究发现电解后,中性分子1和2在紫外区域的强吸收峰均逐渐降低,1~+分别在可见及近红外580 nm,698 nm及874 nm处出现较弱的3个吸收峰,3个吸收峰可能归属于LMCT吸收。2~+在296 nm处出现1个很弱的吸收峰,这不同于配合物1~+,可能源于2~+的稳定性。     

焙烧温度对复合储氧材料性能的影响

自上世纪80年代初期以来,稀土铈氧化物(CeO2)作为一种储氧材料已在汽车三效催化剂(TWC)中得到了广泛应用。众所周知,CeO2在富氧和富燃条件下有储氧和释放氧的功能,CeO2在缺氧条件下可通过Ce4 转化成Ce3 而释放出氧气,在富氧条件下Ce3 又可氧化成Ce4 而吸收氧,即2CeO2(Ce2O3 1/2     

Pd/Ce0.8Zr0.15La0.05Oδ整体催化剂甲苯催化燃烧性能的研究

采用一次浸渍法分别制备了 Pd/Ce0.8Zr0.15La0.05Oδ及Pd/Ce0.8Zr0.2O2整体式蜂窝陶瓷催化剂,考察了不同温度焙烧的两类整体催化剂甲苯催化燃烧性能.通过X射线粉末衍射(XRD)、比表面积、拉曼光谱(Raman)、程序升温还原(H2-TPR)、PdO分散度等表征结果与催化活性进行关联.结果表明,随着焙烧温度升高,催化剂比表面积下降,Raman图谱CeO2及PdO峰强度增加,H2-TPR中Ce4+还原峰向高温方向移动,同时PdO分散度下降,相应甲苯催化氧化活性下降.与CeO0.8Zr0.2O2涂层催化剂相比,La3+掺杂催化剂在高温焙烧时,其比表面积下降较小,Raman光谱表明其氧缺位比铈锆涂层催化剂多,H2TPR谱图中Ce4+还原峰低约60～80℃,PdO分散度亦比末掺杂催化剂高.1000℃焙烧下的甲苯氧化反应活性远高于未掺杂催化剂,说明镧的掺杂提高了铈锆涂层催化剂的高温反应活性及热稳定性.     

BaF2/La2O3催化剂上甲烷氧化偶联反应活性氧物种的原位红外光谱

用原位红外光谱研究了BaF2/La2O3催化剂上甲烷氧化偶联反应的活性氧物种.结果表明,催化剂经O2预吸附后,在1 108~1 118 cm-1处出现超氧物种O2-的O-O键伸缩振动峰.经18O2同位素交换实验后,原1 108~1 118 cm-1处谱峰的强度减弱,同时在1 086和1 051 cm-1处出现(O18O)-物种和18O2-物种的吸收峰.同位素交换实验进一步确证了1 108~1 118cm-1处谱峰确为O2-物种的吸收峰.在700℃下,O2-物种能够活化CH4生成C2H4,而且O2-物种的消耗量和C2H4的生成量呈很好的消长对应关系.超氧物种O2-是BaF2/La2O3催化剂上甲烷氧化偶联反应的活性氧物种.     

CeO_2/Pt(111)反向催化剂结构和活性的密度泛函理论研究（英文）

铈基材料因其独特的Ce~(4+)/Ce~(3+)转化性质而广泛运用于非均相催化反应中.尽管在实验和理论上对纯净二氧化铈表面的物理和/或化学性质进行了深入研究,但是与二氧化铈有关的界面结构和反应性能引起了人们的极大兴趣.其中,已有报道表明,氧化铈/金属反向催化剂相较于氧化铈、金属或者金属/氧化铈负载材料能明显提高CO催化氧化和水汽转化等反应活性.然而多数前期研究并没有从理论上给出合理解释,同时也并未说明反向催化剂中氧化铈结构(层数)和性质的关系.可以预见,因受到金属基板的影响,二氧化铈表面的物化性质,如氧空位形成能、电子分布、催化活性等必然会发生变化.本文通过库伦作用校正的密度泛函理论(DFT+U)计算,系统地研究了不同厚度的Ce O_2/Pt(111)反向催化剂几何结构和电子性质,催化CO氧化的性能.本文首先在Pt(111)载体上明确了单层Ce O_2(111)的最佳结构,然后研究随着二氧化铈厚度增加,各复合结构界面热力学稳定性、几何结构和电荷性质的变化.计算结果表明:首先,单层Ce O_2/Pt(111)比双层和三层Ce O_2/Pt(111)复合结构在界面处表现出更强的相互作用,并且其强度与界面结合结构密切相关,如界面O–Pt键的数量及其长度等;其次,氧化铈板层和Pt基板之间的接触会显著影响界面处一个氧化铈层和两个金属层内的电子分布,使氧化铈外暴露表面的氧空位形成能降低～0.3 e V,而界面氧空位形成能则显著降低1.3?1.8 e V,并且当表面上沉积≥2个氧化铈层时,氧化铈/铂复合材料的物理性能会趋向收敛;最后,通过计算单层Ce O_2/Pt(111),单层Ce O_2和模拟体相结构的三层Ce O_2(111)表面上的CO氧化过程,结果表明三者均遵循Mvk机理,并且关键步骤OC…O_s偶联的反应能垒分别是0.45,0.33和0.61 e V,表明三者的活性趋势为ML Ce O_2ML Ce O_2/Pt(111)TL Ce O_2(111).综合考虑到单层Ce O_2/Pt(111)界面处适度的二氧化铈-铂相互作用,一方面可以极大提高复合材料热力学稳定性,另一方面还成功保留了单层二氧化铈的优异催化活性,因此单层Ce O_2/Pt(111)复合材料从理论上认为是一种优异的CO氧化催化剂.     

合成方法对Rh/CeO2-ZrO2-La2O3催化剂的结构、表面性能及DeNOx活性的影响

用沉积沉淀法合成两种不同系列的CeO2-ZrO2-La2O3混合氧化物(ZrO2和La2O3沉积CeO2粒子(标记为A-x)以及CeO2和La2O3沉积ZrO2粒子(标记为B-x)),并用作Rh催化剂的载体。XRD、拉曼、TPR、XPS和O2脉冲等表征结果显示出不同的沉积顺序将导致不同的结构和氧化还原性能,且B-x具有更高的氧迁移性、储氧能力和表面Ce浓度。当其负载Rh后,Rh/B-x催化剂具有更高的NO和CO转化率及N2选择性,且Ce的最佳含量为50at%。这可能归因于Rh负载于富铈表面形成更多有利于NO分解的表面Ce3+活性位。     

纯与掺杂CeO2的氧化还原性质及其催化领域的应用

概述了纯与掺杂CeO2氧化还原性质的研究状况及CeO2单独/主成分使用方式在催化领域中的应用.由于CeO2具有优异的储放氧性能,以及吸附气体和反应中间物能与几个Ce3 同时作用,其在氧化还原、合成气生产、有机合成和有机污染物降解等反应过程中呈现出良好的催化性能,而通过恰当的掺杂往往能使之得到进一步提高.最后,结合现状对其未来研究方向进行了展望.     

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.