Catalytic reduction of NO_x by CO on hydro-talcites-derived mixed oxides Co AIM and MgAlM (M = Cr, Mn, Fe, Co, Ni, Cu)

Two series of mixed oxides, CoAlM and MgAlM (M= Cr, Mn, Fe, Co, Ni, Cu) , were prepared by calcining their corresponding hydrotalcite-like compounds (HTLc) . The ratio of Mg: Al: M (or Co: Al: M) was 3:1:1. The catalytic activity of all samples for the reaction of NO CO was investigated. The results showed that the activity of CoAlM was much higher than that of MgAlM. The structure and the property of redox were characterized by XRD and H2-TPR. The results indicated that only MgO phase was observed after calcining MgAlM hydrotalcites, and the transition metals became more stable. The spinel-like phase appeared in all of CoAlM samples after the calcination, and the transition metals were changed to be more active, and easily reduced . The activities of three series of mixed oxides CoAlCu obtained from different preparation methods, different ratio of Co:Al:Cu and at different calcination temperatures, were studied in detail for proposing the mechanism of reaction. The ability of adsorption of NO and CO     

Probing the electronic and structural properties of doped aluminum clusters: MAl12- (M=Li, Cu, and Au)

Photoelectron spectroscopy (PES) is combined with theoretical calculations to investigate the electronic and atomic structures of three doped aluminum clusters, MAl12- (M=Li, Cu, and Au). Well-resolved PES spectra have been obtained at two detachment photon energies, 266 nm (4.661 eV) and 193 nm (6.424 eV). Basin-hopping global optimization method in combination with density-functional theory calculations has been used for the structural searches. Good agreement between the measured PES spectra and theoretical simulations helps to identify the global minimum structures. It is found that LiAl12- (C(5nu)) can be viewed as replacing a surface Al atom by Li on an icosahedral Al13-, whereas Cu prefers the central site to form the encapsulated D3d-Cu@Al12-. For AuAl12- (C1), Au also prefers the central site, but severely distorts the Al12 cage due to its large size.     

Catalytic reduction of NOx by CO on hydrotalcites-derived mixed oxides CoAlM and MgAlM (M=Cr,Mn, Fe,Co, Ni,Cu)

Two series of mixed oxides, GIAlM and MgAlM (M= G, Mn, Fe, Co, Ni, Cu), were prepared by calcining their corresponding hydrotalcite-like compounds (HTLc). The ratio of Mg: Al: M (or Co: Al: M) was 3:1:1. The catalytic activity of all samples for the reaction of NO + CO was investigated. The results showed that the activity of CoAlM was much higher than that of MgAlM. The structure and the property of redox were characterized by XRD and H₂-TPR. The results indicated that only MgO phase was observed after calcining MgAlM hydrotalcites, and the transition metals became more stable. The spinel-like phase appeared in all of CoAlM samples after the calcination, and the transition metals were changed to be more active, and easily reduced. The activities of three series of mixed oxides CoAlCu obtained from different preparation methods, Different ratio of Co: Al: Cu and at different calcination temperatures. were studied in detail for proposing the mechanism of reaction. The ability of adsorption of NO and CO were investigated respectively for supporting the mechanism.     

New examples of metalloaromatic Al-clusters: (Al4M4)Fe(CO)3 (M = Li, Na and K) and (Al4M4)2Ni: rationalization for possible synthesis

Ab initio calculations reveal that all-metal antiaromatic molecules like Al4M4 (M = Li, Na and K) can be stabilized in half sandwich (Al4M4)Fe(CO)3 and full sandwich (Al4M4)2Ni complexes. The formation of the full sandwich complex [(Al4M4)2Ni] from its organometallic precursor depends on the stability of the organic-inorganic hybrid (C4H4)Ni(Al4Li4).     

Evolution of structure, transport properties and magnetism in ternary lithium nitridometalates Li(3-x-y)M(x)N, M = Co, Ni, Cu

The structures, magnetism and ion transport properties of the ternary nitrides Li(3-x-y)M(x)N (M = Co, Ni, Cu; y= lithium vacancy) were examined by powder X-ray diffraction, solid-state NMR and SQUID magnetometry. Doping levels are achieved up to x approximately = 0.4 for M = Cu and Co, but much higher substitution levels (x approximately =1) are obtained in the Li-Ni-N system. Transition metals substitute for Li at the Li(1) interplanar site and the ensuing lithium vacancies are disordered within the [Li(2)N] planes. High substitution levels in the Li-Ni-N system lead to the formation of ordered phases. Diffusion parameters, including activation energies, correlation times and diffusion coefficients, were obtained from variable-temperature solid-state NMR measurements in several ternary compounds. SQUID magnetometry shows significant variations of the electronic properties with dopant and x. The properties of the ternary nitrides can be rationalised in terms of the identity of the dopant and the structural modifications arising from the substitution process.     

Stable transition metal complexes of an all-metal antiaromatic molecule (Al4Li4): role of complexations

We propose for the first time a few examples of stable transition metal complexes of an all-metal antiaromatic molecule Al4Li4. We demonstrate that these all-metal species can be stabilized by complexation with 3d transition metals very similar to their organic counterpart, C4H4. Complexation to transition metal ions reduces the frontier orbital energies and introduces aromatic charactersitics. We consider a series of such complexes: [eta4-(Al4Li4)-Fe(CO)3, eta2,sigma2-(Al4Li4)-Ni, and (Al4Li4)2Ni] and compare and contrast their energetics with their organometallic counterparts. Fragmentation energy, orbital correlation energy analysis, and the nucleus-independent chemical shift (NICS) values support the complexation-induced stabilities in these systems.     

Formation of CO(x)-free H2 and cup-stacked carbon nanotubes over nano-Ni dispersed single wall carbon nanohorns

Transitional metals (M) were dispersed on single-wall carbon nanohorns (M/SWCNHs, M = Fe, Co, Ni, Cu) by simple thermal treatment of the deposited metal nitrate without H(2) reduction. Nanometallic Ni particles on SWCNH were evidenced by high-resolution transmission electron microscopic observation and X-ray photoelectron spectroscopy. The nano-Ni dispersed on SWCNH showed the highest CH(4) decomposition activity; the activity of used transitional metals decreases in the order Ni ? Co > Fe ? Cu. On the other hand, the reaction rate over Ni/SWCNH was much larger than that over Ni/Al(2)O(3), and the former provided CO(x)-free H(2) and cup-stacked carbon nanotubes, while Ni/Al(2)O(3) produced CO(x) in addition to H(2). SWCNH was superior to Al(2)O(3) as the catalyst support of Ni for the CH(4) decomposition reaction.     

Sandwich-like compounds based on the all-metal aromatic unit Al(4)2- and the main-group metals M (M=Li, Na, K, Be, Mg, Ca)

Inspired by the pioneering experimental characterisation of the all-metal aromatic unit Al(4)2- in the bimetallic molecules MAl4- (M=Li, Na, Cu) and by the very recent theoretical design of sandwich-type transition-metal complexes [Al4MAl4]q- (q=0-2; M=Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W), we used density functional theory (DFT) calculations (B3LYP/6-311+G(d) to design a series of novel non-transition-metal sandwich complexes based on the all-metal aromatic unit Al4(2-) and the main-group metals M (M=Li, Na, K, Be, Mg, Ca). The traditional homo-decked sandwich compounds [Al4MAl4]q- (without counterions) and (nM)q+[Al4MAl4]q- (with counterions M) (q=2-3, M=Li, Na, K, Be, Mg, Ca), although some of them are truly energy minima, have a much higher energy than many fused isomers. We thus concluded that it seems unlikely for Al4(2-) to sandwich the main-group metal atoms in the homo-decked sandwich form. Alternatively, we proposed a new type of sandwich complex, namely hetero-decked sandwich compounds [CpMAl4]q-, that are the ground-state structures for each M both with and without counterions. It was shown that with the rigid Cp- partner, the all-metal aromatic unit Al(4)2- might indeed act as a "superatom". These new types of all-metal aromatic unit-based sandwich complexes await future experimental verification.     

Associative versus dissociative binding of CO to 4d transition metal trimers: A density functional study

Density functional calculations were performed to determine equilibrium geometrical structures, transition states and relative energies for M(3) clusters (M = Nb, Mo, Tc, Ru, Rh, Pd, Ag) reacting with CO, leading to proposed reaction pathways. For the Nb(3), Mo(3), and Tc(3) clusters, the lowest energy structure correlates to dissociated CO, with the C and O atoms bound on opposite sides of the metal triangle. For all other trimers, the lowest energy structures maintain the CO moiety. In the case of Pd(3) and Ag(3) the dissociated geometries lie higher in energy than the sum of the separated reactants. In most cases, several multiplicities were found to be similar in energy and for Mo(3)CO and Pd(3)CO singlet-triplet minimum energy crossing points were identified. In the case of Rh(3)CO, minimum energy crossing points for the doublet, quartet, and sextet reaction pathways were determined and compared. The electron densities of pertinent M(3)CO species were investigated using Natural Bond Order calculations. It was found that the effect of the metal trimer on the energy of the pure p-type pi* antibonding orbital of carbon monoxide directly correlates with the occurrence of CO dissociation.     

Reaction mechanism of the reverse water-gas shift reaction using first-row middle transition metal catalysts L'M (M = Fe, Mn, Co): a computational study

The mechanism of the reverse water-gas shift reaction (CO(2) + H(2) → CO + H(2)O) was investigated using the 3d transition metal complexes L'M (M = Fe, Mn, and Co, L' = parent β-diketiminate). The thermodynamics and reaction barriers of the elementary reaction pathways were studied with the B3LYP density functional and two different basis sets: 6-311+G(d) and aug-cc-pVTZ. Plausible reactants, intermediates, transition states, and products were modeled, with different conformers and multiplicities for each identified. Different reaction pathways and side reactions were also considered. Reaction Gibbs free energies and activation energies for all steps were determined for each transition metal. Calculations indicate that the most desirable mechanism involves mostly monometallic complexes. Among the three catalysts modeled, the Mn complex shows the most favorable catalytic properties. Considering the individual reaction barriers, the Fe complex shows the lowest barrier for activation of CO(2).     

Synthesis and structural characterization of group 6 transition metal complexes with terminal fluoromethylidyne (CF) ligands; a DFT/NBO/NRT comparison of bonding characteristics of terminal NO, CF and CH ligands

A family of group 6 transition metal complexes M(C(5)R(5))(CO)(2)(CF) [M = Cr, Mo, W; R = H, Me] with terminal fluoromethylidyne ligands have been synthesized through the reduction of the corresponding trifluoromethyl precursors with potassium graphite or magnesium graphite. They have been characterized spectroscopically and in some cases crystallographically, although the structures show disorder between the CO and CF ligands. The M[triple bond]CF subunit reacts as a triple bond to form cluster complexes containing μ(3)-CF ligands on reaction with Co(2)(CO)(8). Computational (DFT/NBO/NRT) studies on M(C(5)H(5))(CO)(2)(CF) [M = Cr, Mo, W] and the corresponding cationic fragments M(CO)(2)(XY)(+) illustrate significant differences in the metal-ligand bonding between CF and its isoelectronic analogue NO, as well as with its hydrocarbon analogue CH.     

结构助剂SiO2、Al2O3对铁基催化剂浆态床F-T合成性能的影响

采用连续共沉淀与喷雾干燥成型技术相结合的方法制备了微球状Fe/Cu/K/SiO2和Fe/Cu/K/Al2O3催化剂,研究SiO2和Al2O3作为结构助剂对铁基催化剂吸附行为、炭化行为及F-T合成反应性能的影响。表征结果表明,与Al2O3相比较,SiO2抑制了H2的吸附,但促进了CO的吸附,有利于催化剂的炭化。催化剂在260℃、1.5MPa、H2/CO=0.67和2000h-1下的浆态床F-T合成反应评价表明,Fe/Cu/K/SiO2催化剂具有较高的F-T合成活性、高的水煤气变换反应（WGS）活性,且其烃产物选择性明显向高炭数方向偏移,而Fe/Cu/K/Al2O3催化剂则表现出较低的F-T合成活性、低的水煤气变换反应（WGS）活性和高的轻质烃选择性。但Fe/Cu/K/Al2O3催化剂比Fe/Cu/K/SiO2催化剂具有更好的运行稳定性。     

在Cu-Zn-Al和Cu-Zn-Al-Li催化剂上CO/CO_2氢化制甲醇的研究(英文)

制备了Ｃｕ－Ｚｎ－Ａｌ （４／５０／５）催化剂（Ｃａｔ）和Ｃｕ－Ｚｎ－Ａｌ－Ｌｉ（４０／５０／５／５）催化剂（Ｃａｔ－Ｌｉ）．并将其分别用于由ＣＯ／Ｈ_２和ＣＯ_２／Ｈ_２合成甲醇。诸如ＴＰＤ、ＴＰＲ、ＴＰＳＲ、脉冲、ＣＤ３Ｉ－捕获、同位素标记、ＥＰＲ及原位ＤＲＩＦＴ等技术和方法被用来表征这两种催化剂及研究反应机理,对处于去氢、含氢及含氧态催化剂进行了对比研究以期阐明表面氧和表面氢对ＣＯ_２和ＣＯ活化所起的作用。提出了一个由甲酸根和甲醛氢化及甲醇氧化结果为证的ＣＯ／ＣＯ_２氢化机理。由于通过Ｌｉ 取代ＣｕＯ晶格上的Ｃｕ２＋形成的氢空位,在Ｃａｔ中添加Ｌｉ＋改善了甲醇合成活性。ＣＯ_２能被一捕获的电子（Ｆ-中心）活化,生成的ＣＯ2-能容易地被氢化成甲酸根和亚甲基双草酰,后者分解生成Ｈ２ＣＯ和表面氧。ＣＯ能被表面氧活化,生成的ＣＯ２－将遵循ＣＯ_２氢化的途径。在ＣＤ３Ｉ－捕获的实验中,我们捕获了表面氧。在无表面氧时,ＣＯ可能直接氢化成甲酸基,即ＣＯ_２氢化中的一途径。由亚甲基双草酰产生的Ｈ２ＣＯ表面模型可能与由甲醛吸附或ＣＯ氢化生成的Ｈ２ＣＯ表面模型不同。     

Theoretical exploration of hydrogen loss from Al3H9

The Al(3)H(9) and Al(3)H(7) potential energy surfaces were explored using quantum chemistry calculations to investigate the H(2) loss mechanism from Al(3)H(9), which provide new insights into hydrogen production from bulk alane, [AlH(3)](x), a possible energy storage material. We present results of B3LYP/6-311++G(d,p) calculations for the various Al(3)H(9) and Al(3)H(7) optimized local minima and transition state structures along with some reaction pathways for their interconversion. We find the energy for Al(3)H(9) decomposition into Al(2)H(6) and AlH(3) is slightly lower than that for H(2) loss and Al(3)H(7) formation, but the calculations show that H(2) loss from Al(3)H(9) is a lower energy process than for losing hydrogen from either Al(2)H(6) or AlH(3). We found four transition state structures and reaction pathways for Al(3)H(9) → Al(3)H(7) + H(2), where the lowest energy activation barrier is around 25-73 kJ/mol greater than the experimental value for H(2) loss from bulk alane. Intrinsic reaction coordinate calculations show that the H(2) loss pathway involves considerable rearrangement of the H atom positions around a single Al center. Three of the pathways start with the formation of an AlH(3) moiety, which then enables a terminal H on the AlH(3) to get within 1.1 to 1.2 ? of a nearby bridging H atom. The bridging and terminal H atoms eventually combine to form H(2) and leave Al(3)H(9). One implication of these H(2) loss reaction pathways is that, since the H atoms in bulk alanes are all at bridging positions, if a similar H(2) loss mechanism were to apply to bulk alane, then H(2) loss would most likely occur on the bulk alane surface or at a defect site where there should be more terminal H atoms available for reaction with nearby bridging H atoms.     

Theoretical investigation of the reactivity of copper atoms with OCS: comparison with CS2 and CO2

The reaction mechanism of the Cu atom with OCS and CO2 has been studied by means of density functional method (B3LYP). The overall energetics has been refined at the CCSD(T) level. In the case of the Cu + OCS reaction, the CS insertion route is found much more favorable than the CO insertion one. This later reaction is direct and involves an activation energy of 83.3 kcal/mol and is endothermic by 50.0 kcal/mol at the CCSD(T) level. The insertion into the CS bond proceeds through the eta1s and eta2cs coordination species as intermediates and is found exothermic by about 20 kcal/mol. The highest transition structure along this route is only 11.5 kcal/mol higher in energy than the reactant's ground states. In the case of the Cu + CO2 reaction, the insertion route into the CO bond is also found direct but with a lower endothermicity (30.6 kcal/mol) and smaller activation energy (61.1 kcal/mol) than that into the CO bond of OCS. In all cases, the insertion mechanism proceeds simultaneously with electron transfer from the Cu atom to OCS (or CO2) molecule.     

A New Type of Heterobimetallic Compound Containing Tungstenocene: Synthesis, Reactivity, NMR, and Stereochemical Studies

Reaction of [PPh(2)M(CO)(5)]Li salts (M = Cr or W) toward tungstenocene dichloride occurs via a cyclopentadienyl ring substitution and yields the corresponding binuclear compounds (eta(5)-C(5)H(5))[eta(5)-C(5)H(4)PPh(2)M(CO)(5)]W(H)Cl, 2. They react with LiAlH(4) to give the corresponding dihydride complexes (eta(5)-C(5)H(5))[eta(5)-C(5)H(4)PPh(2)M(CO)(5)]WH(2), 3. These species have been proven to be photosensitive leading to the cyclic heterobimetallic (eta(5)-C(5)H(5))[eta(5)-C(5)H(4)PPh(2)M(CO)(4)]W(&mgr;-H)H compounds, 4; analytical data and spectroscopic measurements on complexes 4 indicate that a hydride group functions as a bridging ligand. Crystals of 4a (M = Cr) were obtained as red needles, grown from toluene solution. An isotropic refinement of only 1243 data (F > 5sigma(F)) from a low resolution data set (3707 data, d(min) = 0.9 ?) indicated significant systematic error. Thus it was possible only to ascertain that the connectivity of the non-hydrogen atoms is not inconsistent with the model proposed from solution NMR and that the Cr.W separation of 3.30 ? precludes a direct Cr-W bond. 4a crystallizes in space group Pbca(No. 61), with a = 19.693(8) ?, b = 20.34(1) ?, c = 11.695(5) ?, V = 46823 ?(3), and Z = 8. Further information on this preliminary structure determination is provided in the Supporting Information. These reactions have been investigated with stereochemical factors in mind using the ring substituted tungtenocene complex (eta(5)-C(5)H(4)Me)(2)WCl(2); the 1-3 regioselectivity of the ring disubstitution reaction is proposed on the basis of (1)H NMR experiments. The temperature dependent relaxation time measured between 295 and 213 K by the inversion recovery method makes it possible to determine a proton-proton distance between the two H ligands of 2.0 ? in 4'a.     

An aluminum ate base: its design, structure, function, and reaction mechanism

An aluminum ate base, i-Bu(3)Al(TMP)Li, has been designed and developed for regio- and chemoselective direct generation of functionalized aromatic aluminum compounds. Direct alumination followed by electrophilic trapping with I(2), Cu/Pd-catalyzed C-C bond formation, or direct oxidation with molecular O(2) proved to be a powerful tool for the preparation of 1,2- or 1,2,3-multisubstituted aromatic compounds. This deprotonative alumination using i-Bu3Al(TMP)Li was found to be effective in aliphatic chemistry as well, enabling regio- and chemoselective addition of functionalized allylic ethers and carbamates to aliphatic and aromatic aldehydes. A combined multinuclear NMR spectroscopy, X-ray crystallography, and theoretical study showed that the aluminum ate base is a Li/Al bimetallic complex bridged by the nitrogen atom of TMP and the alpha-carbon of an i-Bu ligand and that the Li exclusively serves as a recognition point for electronegative functional groups or coordinative solvents. The mechanism of directed ortho alumination reaction of functionalized aromatic compounds has been studied by NMR and in situ FT-IR spectroscopy, X-ray analysis, and DFT calculation. It has been found that the reaction proceeds with facile formation of an initial adduct of the base and aromatic, followed by deprotonative formation of the functionalized aromatic aluminum compound. Deprotonation by the TMP ligand rather than the isobutyl ligand was suggested and reasoned by means of spectroscopic and theoretical study. The remarkable regioselectivity of the ortho alumination reaction was explained by a coordinative approximation effect between the functional groups and the counter Li(+) ion, enabling stable initial complex formation and creation of a less strained transition state structure.     

(p-CH3OC6H4)2TeO存在下M2(CO)10(M=Mn,Re)的CO取代反应动力学研究

测定了(p-CH₃OC₆H₄)₂TeO存在下M₂(CO)₁₀(M=Mn,Re)的CO取代反应速率及活化参数。其表观速率常数分别与M₂(CO)₁₀和(p-CH₃OC₆H₄)₂TeO的浓度的一次方成正比。本文所建议的缔合机理与前人用(CH₃)₃NO作氧原子转移试剂的相应反应所提出的机理相似。讨论了在(CH₃)₃NO和(p-CH₃OC₆H₄)₂TeO存在下影响M₂(CO)₁₀的CO取代反应速率的因素。     

Electrospray ionization/tandem quadrupole mass spectrometric studies on phosphatidylcholines: the fragmentation processes

We applied low-energy collisionally activated dissociation (CAD) tandem quadrupole mass spectrometry to study the fragmentation pathways of the [M + H](+) and [M + Li](+) ions of phosphatidylcholine (PC), generated by electrospray ionization (ESI). It is revealed that the fragmentation pathways leading to loss of the polar head group and of the fatty acid substituents do not involve the hydrogens attached to the glycerol backbone as previously reported. The pathway for formation of the major ion of m/z 184 by loss of the polar head group from the [M + H](+) precursor of a diacyl PC involves the participation of the alpha-hydrogen of the fatty acyl substituents, whereas the H(+) participates in the loss of fatty acid moieties. The alpha-hydrogens of the fatty acid substituents also participate in the major fragmentation processes, including formation of [M + Li-R(x)CO(2)H](+) and [M + Li-59-R(x)CO(2)H](+) ions for the [M + Li](+) ions of diacyl PCs, when subjected to low-energy CAD. These fragmentation processes are deterred by substitution of the fatty acyl moieties with alkyl, alkenyl, or hydroxyl groups and consequentially, result in a distinct product-ion spectrum for various PC, including diacyl-, plasmanyl- plasmenyl-, and lyso-PC isomers. The alpha-hydrogens of the fatty acyl substituents at sn-2 are more labile than those at sn-1. This is reflected by the preferential loss of the R(1)CO(2)H over the R(2)CO(2)H observed for the [M + Li](+) ions of diacyl PCs. The spectrum features resulting from the preferential losses permit identification and assignment of the fatty acid moieties in the glycerol backbone. The new fragmentation pathways established by tandem and source CAD tandem mass spectra of various PC molecules, including deuterium-labeling analogs, were proposed. These pathways would clarify the mechanisms underlying the ion formations that lead to the structural characterization of PC molecules.     

杂多阴离子的相转移化学 Ⅰ.取代的Keggin及Dawson结构杂多阴离子在非极性溶剂中的溶剂化行为研究

利用四庚基溴化铵将Keggin结构的杂多阴离子ZW~1~1O~3~9M(H~2O)^n^-(Z=Si,Ge,P,M=Ni^2^+,Cu^2^+,Cr^3^+,Co^2^+,n=4～6)和Dawson结构的杂多阴离子P~2W~1~7O~6~1M(H~2O)^n^-(M=Ni^2^+,Cu^2^+,Cr^3^+,Co^2^+,n=7,8) 从水溶液中转移至非极性溶剂(苯或甲苯)中,并观察到在水溶液中难以进行的配位水的脱去反应,形成配位不饱和的杂多阴离子.当加入Lewis碱如丙酮,吡啶等,可迅速恢复饱和配位,其电子吸收光谱也相应变化,基本恢复到配位饱和时的数值,有ESR信号.实验表明,在非极性溶剂中,配体之间相互进行的取代反应,吡啶的配位能力最强, 发生了取代反应ZW~1~1O~3~9M(L)^n^-+Py→ZW~1~1O~3~9M(Py)^n^-+L(L=丙酮,乙腈等).同时我们也研究了温度,杂多阴离子浓度,惰性气体流量对杂多阴离子在非极性溶剂中的溶剂化行为的影响,得到了相转移的一般规律,为杂多阴离子在非极性溶剂中的催化研究提供了理论依据