水对Ni/MgAlO催化丙酮加氢的影响

研究了H2O对Ni/MgAlO催化剂上丙酮加氢为异丙醇的催化反应的影响。结果发现,在丙酮中添加少量H2O可提高丙酮转化率,但超过5%的H2O量则会显著降低催化剂活性。吸附量热结果表明,催化剂表面吸附少量H2O会明显降低异丙醇的吸附热,但对丙酮吸附热的影响较小,这也许是反应体系中少量的H2O能促进丙酮加氢活性的原因之一。当催化剂表面吸附较多H2O后,丙酮、异丙醇和H2的吸附热都降低了,因此反而抑制了丙酮的加氢反应。此外,红外光谱结果表明,预吸附水抑制了催化剂表面异丙醇脱氢生成丙酮,并抑制吸附的丙酮在表面生成烯醇盐或异丙叉丙酮等物种,这也许是少量水能促进丙酮加氢生成异丙醇的另一个重要原因。     

Adsorption of Acetone onto MgO: Experimental and Theoretical Evidence for the Presence of a Surface Enolate

A new band at 1640 cm ⁻¹ is revealed by diffuse reflectance FT‐IR spectroscopy of acetone adsorbed on a MgO surface (shown schematically). On the grounds of ab initio quantum‐mechanical calculations, this band is assigned to an adsorbed enolate species. This evidence proves the catalytic role of the metal oxide surface in the condensation reaction mechanism.     

Time-resolved sum-frequency generation spectroscopy of methoxy and deuterated methoxy on Ni(111) using near-infrared laser pulses

Methoxy (CH3O-) and deuterated (d-) methoxy (CD3O-) species on Ni(111) are investigated by sum-frequency generation (SFG) spectroscopy. Methoxy adsorbed on the Ni(111) surface is confirmed by SFG spectroscopy to be oriented normal to the surface. Two resonant peaks produced by methoxy, at 2921 and 2821 cm(-1), are assigned to Fermi resonance between the CH symmetric stretching and overtone modes. Deuterated methoxy exhibits a single strong peak at 2051 cm(-1) assigned to the CD symmetric stretching mode. Investigation of the sub-nanosecond transient behavior of methoxy and d-methoxy species on Ni(111) under short-pulse laser pumping at 1064 nm reveals a clear weakening and recovery of the SFG peaks upon heating. The observed temporal profile is reproduced by simulation assuming that the original methoxy in the ground state is in chemical equilibrium with a new state produced by instantaneous heating. The dependence of the SFG spectra on the initial substrate temperature is also reproduced by the simulation. The simulation suggests a temperature jump of 250 K upon laser pumping, inducing a change in the molecular orientation or adsorption site of methoxy on the Ni(111) surface without decomposition of methoxy to adsorbed CO and hydrogen, which occurs under normal heating at 200 K.     

Al2O3-supported Fe?Ni catalysts for CO hydrogenation, II. Characterization by IR spectra of CO adspecies

The surface of alumina supported catalysts containing 10 wt.% metal (Fe and/or Ni) has been spectroscopically investigated by CO adsorption. The stretching vibration range characteristic for CO bonded to metallic species shows very large absorptions, indicating a high surface heterogeneity. A certain FeNi stoichiometry seems to impose the reduction extent and the catalytic properties.     

First principles density functional study of the adsorption and dissociation of carbonyl compounds on magnesium oxide nanosurfaces

The adsorption and dissociation of three carbonyl compounds, formaldehyde, acetaldehyde, and acetone, on the magnesium oxide nanosurface, consisting of four stacked (MgO)3 hexagons, is investigated by first principles density functional theory (DFT). In the case of formaldehyde, strongly chemisorbed species, with carboxylate-like structures, are initially formed. These may subsequently undergo heterolytic cleavage of an aldehyde C-H bond to form formate ions involving a surface oxide ion and a hydride ion adsorbed over the magnesium dication [(MgH+)(HCOO-)]. For acetaldehyde, besides this reaction leading to the formation of acetate, the methyl hydrogen of the adsorbed species also tends to attach itself to a surface oxide ion, yielding surface hydroxyl ions and adsorbed [CH2=C(H)OMg]+. These results are in accord with our previous experimental and theoretical results. In particular, the shift of the aldehyde C-H vibration band to higher frequency and the appearance of OH bands in the infrared spectrum are clearly accounted for. For acetone, the mechanism is found to be similar, i.e., a methyl hydrogen shift to yield surface enolate. Again, this is in agreement with experimental studies.     

Spectroscopic and computational studies of a Ni(+)-CO model complex: implications for the acetyl-CoA synthase catalytic mechanism

The four-coordinate Ni(+) complex [PhTt(t)(Bu)]Ni(I)CO, where PhTt(t)()(Bu) = phenyltris((tert-buthylthio)methyl)borate (a tridentate thioether donor ligand), serves as a possible model for key Ni-CO reaction intermediates in the acetyl-CoA synthase (ACS) catalytic cycle. Resonance Raman, electronic absorption, magnetic circular dichroism (MCD), variable-temperature variable-field MCD, and electron paramagnetic resonance spectroscopies were utilized in conjunction with density functional theory and semiemperical INDO/S-CI calculations to investigate the ground and excited states of [PhTt(t)()(Bu)]Ni(I)CO. These studies reveal extensive Ni(+) --> CO pi-back-bonding interactions, as evidenced by a low C-O stretching frequency (1995 cm(-)(1)), a calculated C-O stretching force constant of 15.5 mdyn/A (as compared to k(CO)(free CO) = 18.7 mdyn/A), and strong Ni(+) --> CO charge-transfer absorption intensities. Calculations reveal that this high degree of pi-back-bonding is due to the fact that the Ni(+) 3d orbitals are in close energetic proximity to the CO pi acceptor orbitals. In the ACS "paramagnetic catalytic cycle", the high degree of pi-back-bonding in the putative Ni(+)-CO intermediate (the NiFeC species) is not expected to preclude methyl transfer from CH(3)-CoFeSP.     

Mid-infrared vibrational spectra of discrete acetone-ligated cerium hydroxide cations

Cerium(iii) hydroxy reactive sites are responsible for several important heterogeneous catalysis processes, and understanding the reaction chemistry of substrate molecules like CO, H(2)O, and CH(3)OH as they occur in heterogeneous media is a challenging task. We report here the first infrared spectra of model gas-phase cerium complexes and use the results as a benchmark to assist evaluation of the accuracy of ab initio calculations. Complexes containing [CeOH](2+) ligated by three- and four-acetone molecules were generated by electrospray ionization and characterized using wavelength-selective infrared multiple photon dissociation (IRMPD). The C[double bond, length as m-dash]O stretching frequency for the [CeOH(acetone)(4)](2+) species appeared at 1650 cm(-1) and was red-shifted by 90 cm(-1) compared to unligated acetone. The magnitude of this shift for the carbonyl frequency was even greater for the [CeOH(acetone)(3)](2+) complex: the IRMPD peak consisted of two dissociation channels, an initial elimination of acetone at 1635 cm(-1), and elimination of acetone concurrent with a charge separation producing [CeO(acetone)](+) at 1599 cm(-1), with the overall frequency centered at 1616 cm(-1). The increasing red shift observed as the number of acetone ligands decreases from four to three is consistent with transfer of more electron density per ligand in the less coordinated complexes. The lower frequency measured for the elimination/charge separation process is likely due to a combination of: (a) anharmonicity resulting from population of higher vibrational states, and (b) absorption by the initially formed photofragment [CeOH(acetone)(2)](2+). The C-C stretching frequency in the complexes is also influenced by coordination to the metal: it is blue-shifted compared to bare acetone, indicating a slight strengthening of the C-C bond in the complex, with the intensity of the absorption decreasing with decreasing ligation. Density functional theory (DFT) calculations using three different functionals (VWN, B3LYP, and PBE0) were used to predict the infrared spectra of the complexes. Calculated frequencies for the carbonyl stretch are within 40 cm(-1) of the IRMPD of the three-acetone complex measured using the single acetone loss, and within 60 cm(-1) of the measurement for the four-acetone complexes. The B3LYP functionals provided the best agreement with the measured spectra, with the VWN modestly lower and PBE0 modestly higher. The C-C stretching frequencies calculated using B3LYP are higher in energy than the measured values by approximately 30 cm(-1), and reproduce the observed trend which shows that the C-C stretching frequency decreases with increasing ligation. Agreement between C-C frequency and calculation was not as good using the VWN functional, but still within 70 cm(-1). The results provide an evaluation of changes in the acceptor properties of the metal center as ligands are added, and of the utility of DFT for modeling f-block coordination complexes.     

Photoelectron spectroscopic studies of the adsorption of organic molecules with lone pair orbitals on transition metal surfaces

Ultraviolet and x-ray photoelectron spectroscopy have been employed to investigate the adsorption of methanol, ethanol, diethylether, acetaldehyde, acetone, methyl acetate and methylamine on surfaces of Fe, Ni and Cu. All these molecules adsorb molecularly at low temperatures (≤100 K). Lone pair orbitals of these molecules are stabilized on these metal surfaces (by 0·4–1·0eV) due to molecular chemisorption. The molecules generally undergo transformations as the temperature is raised to 120 K or above. The new species produced seems to depend on the metal surface. Some of the product species identified are methoxy species, formaldehyde and carbon monoxide in the case of methanol and methyl acetate, ethoxy species in the case of ethanol and 2-propanol in the case of acetone. Contribution No. 166 from the Solid State and Structural Chemistry Unit.     

Computational study of the adsorption energetics and vibrational wavenumbers of NH3 Adsorbed on the Ni(111) Surface

The structure and stabilities of NH(3) adsorbed on different sites of a Ni(111) surface are compared based on density functional, plane-waves calculations within a periodic framework. The surface has been modeled by 4- and 5-layer slabs with 2 x 2 and 3 x 3 unit cells. Calculated results are in good agreement with available experimental data, confirming the atop adsorption site to be the most favorable, with no preferred azimuthal orientation for the H atoms. For NH(3) adsorbed at the atop site, the one-dimensional potential energy profiles along the N-H and N-Ni bonds and the coupling between adjacent N-H bond oscillators have been calculated and fitted to an analytical expression using an accurate anharmonic potential model. Variational calculations have been performed to obtain frequencies for the N-H and N-Ni stretching vibrations and N-H stretching line widths. The model for calculating line widths has also been tested with CO adsorbed at the hcp hollow of the Ni(111) surface.     

清洁及部分氧化的Ni_3Ti(0001)表面CO吸附的HREELS研究

用离子散射谱（ＩＳＳ）、俄歇电子能谱（ＡＥＳ）及低能电子衍射（ＬＥＥＤ）技术对Ｎｉ３Ｔｉ（０００１）表面结构与组成进行考察后，主要采用高分辨电子能量损失谱（ＨＲＥＥＬＳ），以ＣＯ为探针分子，研究了清洁及部分氧化的Ｎｉ３Ｔｉ（０００１）表面上Ｎｉ，Ｔｉ间的相互作用及对ＣＯ吸附态的影响．结果表明：（１）在最表层几乎完全为Ｎｉ的Ｎｉ３Ｔｉ（０００１）清洁规整表面上，ＣＯ没有发生解离；（２）次表层Ｔｉ原子与最表层Ｎｉ原子间的电子相互作用，使初始吸附的ＣＯ伸缩振动与Ｎｉ（１１１）相比向低频位移约６０ｃｍ－１；（３）适量ＣＯ暴露后，ＣＯ氧端与近邻Ｔｉ原子的成键作用产生了一种新的Ｎｉｘ－Ｃ－Ｏ－Ｔｉｙ物种．Ｎｉ３Ｔｉ（０００１）表面部分氧化后，上述（２）和（３）作用消失     

IR spectroscopy investigation of molecular association in the acetone-trichlormethane mixture

A significant increase in the stretching band intensity of trichloromethane in IR spectra of its solutions in acetone with increasing acetone mole fraction indicates the formation of hydrogen bonds between their molecules. The integral absorption coefficient (α) of this vibration is calculated. Experimental values of α are approximated by a theoretical dependence using the nonlinear least-squares method; association parameters are obtained. The relative volume fractions of H-bonded and free trichloromethane molecules are calculated depending on the total trichloromethane volume fraction in solution. The structure of the H-bonded associate is determined by quantum chemical calculations.     

Interaction of acetone with ammonia and alcohols over a HZSM-5 zeolite: Part 1. Methanol

Temperature-programmed desorption accompanied by conversion (TPDC) of preadsorbed acetone was studied on a HZSM-5 zeolite with Si/Al=13.5. The reactivity of surface species created from acetone with methanol, ammonia and mixtures of these was investigated by analysing the composition of the products released (using a mass spectrometer) and the composition of the surface species (using a ¹³C MAS NMR spectrometer). It was found that ammonia reacts with the carbonyl group of acetone surface species to imino carbocations in both the absence and presence of methanol, and methanol alkylates the acetone surface species whether ammonia is present or absent. The decomposition of the species created from acetone, methanol and ammonia leads to different products than the decomposition of the species formed on the zeolite either from acetone (or methanol) alone or from acetone (or methanol) and ammonia. The strong dehydrogenation function of HZSM-5 resulted in the release of acetonitrile and HCN from acetone and methanol, respectively (in the presence of ammonia), while pyridinium bases (in the presence of all 3 reactants) appeared only in trace amounts.     

Ni2(OCH3)2/SiO2催化剂上CO2和CH3 OH的吸附和反应性能

采用表面改性和离子交换相结合的方法制备了Ni2(OCH3)2/SiO2负载型双核金属甲氧基配合物催化剂,利用红外光谱(IR)、程序升温脱附(TPD)、程序升温表面反应(TPSR)和微反技术考察了催化剂的表面结构以及CO2和CH3OH的化学吸附和反应性能.结果表明:Ni2(OCH3)2/SiO2中Ni2+与载体SiO2表面O2-以双齿配位形式键合,甲氧基以桥基形式联结双金属离子形成双核物种Ni2(OCH3)2;CO2在催化剂表面存在甲氧碳酸酯基物种和桥式两种吸附态,CH3OH则只有一种分子吸附态;在100～200℃条件下,CO2和CH3OH在催化剂上的反应产物主要是DMC和H2O;根据反应结果,讨论了催化反应机理.     

Influence de la solvatation par le tert-butanol sur la structure et la reactivite de l'enolate de potassium de l'acetylacetate d'ethyle en presence de couronne ou de cryptand. etude par spectrometrie infra-rouge et cinetique

The structure and the nucleophilic reactivity of crowned (18-crown-6) or cryptated {cryptand (2.2.2)} potassium ethyl acetoacetate enolate have been compared in tert-butanol and in DME (or THF). In the protic solvent tert-butanol, the crowned and the cryptated potassium enolate species both exist as loose ion pairs in which the enolate anion, strongly hydrogen-bonded to the solvent, is in a “transoid” (non chelating) conformation. Both species show similar reactivities towards alkylating agents but completely different reactivities are observed in aprotic weakly dissociating media (THF, DME). In contrast to what is observed in tert-butanol, the cryptated species and the crowned species have very different nucleophilic reactivities in THF or DME; in those solvents only the cryptated species retains a loose ion pair structure; the crowned species is a contact ion pair in which the enolate anion chelates the potassium cation. The solvation of this crowned chelate species by tert-butanol has been demonstrated in binary mixtures of solvents (C₆D₆-t-BuOH, THF-t-BuOH). The oxygen basicity of the enolate anion is very different in the crowned chelated ion pair compared with the cryptand separated ion pair.     

A highly active catalyst system for the heteroarylation of acetone

A highly active catalyst system for the heteroarylation of acetone has been identified. The coupling between the in situ generated tributyltin enolate of acetone and a variety of heteroaromatic bromides, chlorides, and triflates in the presence of this catalyst system provided arylacetones in good yields.     

Composition-dependent sintering behaviour of chemically synthesised CuNi nanoparticles and their application in aerosol printing for preparation of conductive microstructures

Copper, nickel and copper–nickel nanoparticles were prepared by solution combustion method for use in direct write printing. Structural (X-ray diffraction) and morphological (transmission electron microscope) investigations showed that pure metal (Cu and Ni) and CuNi alloy particles with face-centred cubic crystal structure were formed. Atomic absorption spectrometer studies confirmed that the nanoparticle compositions corresponded to the initial Cu/Ni molar ratios selected for synthesis. Particle size and morphology were significantly influenced by composition, with high Cu content coinciding with small, spherical particles as opposed to larger, irregular shapes observed at high Ni concentrations. X-ray photoelectron spectroscopy measurements revealed that after the reduction process the surface of the alloy nanoparticles was partially oxidised in air and the amount of metallic surface species decreased, while the concentration of oxidic surface species and hydroxides increased with increasing Cu concentration (i.e. decreasing particle size). Dispersions of CuNi nanoparticles have been deposited by use of AerosolJet? and sintered under reducing atmosphere at 300–800?°C in order to prepare conductive structures. Resistivity measurements and microscopical studies (SEM-FIB) of printed and sintered CuNi structures showed that the sintering properties of nanoparticles were dependent on their chemical composition.     

Stable Structure and Characteristic Spectroscopy of(CH3COCH3)n(n=1～7)Clusters

The stable acetone molecule clusters have been studied by using Beeke's threeparameter(B3LYP)density functional theory(DFT)with standard 6-31G(d)basis set.The calculated results show that the optimal structures of acetone clustets are cyclic and the cycles become larger and larger with the increase of cluster size.The strongest vibration peaks for neutral clusters are C=O stretching vibration.The C=O stretching peaks of cyclic acetone clusters split into double ones when n≥3,the frequencies are red-shifted and corresponding intensities increase with the increase of cluster size.     

Infrared detection of a phenylboronic acid terminated alkane thiol monolayer on gold surfaces

Polarization modulation infrared reflectance absorption spectroscopy (PM-IRRAS) and infrared reflectance absorption spectroscopy (IRRAS) have been used to characterize the formation of a self-assembled monolayer of N-(3-dihydroxyborylphenyl)-11-mercaptoundecanamide) (abbreviated PBA) on a gold surface and the subsequent binding of various sugars to the PBA adlayer through the phenylboronic acid moiety to form a phenylboronate ester. Vibrationally resonant sum frequency generation (VR-SFG) spectroscopy confirmed the ordering of the substituted phenyl groups of the PBA adlayer on the gold surface. Solution FTIR spectra and density functional theory were used to confirm the identity of the observed vibrational modes on the gold surface of PBA with and without bound sugar. The detection of the binding of glucose on the gold surface was confirmed in part by the presence of a C-O stretching mode of glucose and the observed O-H stretching mode of glucose that is shifted in position relative to the O-H stretching mode of boronic acid. An IR marker mode was also observed at 1734 cm(-1) upon the binding of glucose. Additionally, changes in the peak profile of the B-O stretching band were observed upon binding, confirming formation of a phenylboronate ester on the gold surface. The binding of mannose and lactose were also detected primarily through the IR marker mode at approximately 1736 to 1742 cm(-1) depending on the identity of the bound sugar.     

载Ni双功能碱性沸石催化剂的研究

采用分步浸渍法制备了负载Ni和KOH的NaX沸石催化剂 ,用XRD、TPR、CO2 TPD和XPS等手段对样品的结构、表面碱性、金属组分的可还原性、表面Ni物种的形态等进行了表征 ,对金属组分和碱性组分间的相互作用进行了研究 ,并揭示了这种作用的本质.同时结合丙酮一步法合成甲基异丁基酮的反应 ,探讨了反应性与样品碱性、金属性的关系 ,阐明了该反应中双功能催化剂上金属组分与碱性组分必须匹配合宜的原因     

电化学方法获得具有表面增强拉曼活性镍电极的研究

利用纯电化学手段获得了具有较强表面增强拉曼活性的镍电极, 改进了原有的镍电极表面预处理方法. 结果表明, 在0.5 mol/L的NaClO4溶液中, 结合电化学阶跃技术和循环伏安技术, 可以得到合适的粗糙镍电极; 同时, 还得到了探针分子吡啶在该粗糙镍电极表面随电极电位变化的表面增强拉曼光谱(SERS), 此时谱峰强度获得了极大的增强; 还研究了粗糙镍电极的扫描电子显微镜(SEM)图像, 并估算出其SERS增强因子约为104, 此结果比以前的镍电极表面粗糙方法所能达到的增强因子高一个数量级.