Pd‐catalyzed bicyclization of 2‐alkynylhalobenzenes and propargylic alcohols for the formation of indeno[1,2]furans: a DFT study

The mechanism of palladium‐catalyzed bicyclization of 2‐alkynylhalobenzenes and propargylic alcohols for the formation of indeno[1,2]furans has been studied computationally with the aid of density functional theory (DFT). Full free energy profiles are computed for different reaction equations between different reaction substrates. The calculation results showed that the catalytic cycle is found to contain six steps, oxidative addition, ligand substitution, first C ≡ C triple bond insertion, rearrangement, second C ≡ C triple bond insertion and reductive elimination, with the reductive elimination being the rate‐determining step for the different reaction equations (1), (2) and (3). Our calculations are consistent with experimental observations. Copyright © 2014 John Wiley & Sons, Ltd.     

钒钨铈催化剂的低温SCR反应机理研究

本文使用等体积浸渍法制备了钒钨铈(V2O5-WO3/CeO2)选择性催化还原(SCR)脱硝催化剂,并使用一系列的原位傅里叶变换红外(In-situ FTIR)光谱详细研究了该催化剂的低温SCR反应过程(本文选用200℃)。通过将原位红外光谱与化学诱捕法耦合使用,成功捕捉并识别了低温SCR的不稳定反应中间产物亚硝酸盐(nitrites),并以该亚硝酸盐物种为主要的反应活化产物,建立了基于NO氧化活化的低温SCR还原半圈反应动力学模型.该动力学模型可准确描述V2O5-WO3/CeO2催化剂低温SCR中NO与表面吸附NH3的瞬态反应过程。     

Theoretical investigation on the mechanism of FeCl3-catalysed cross-coupling reaction of alcohols with alkenes

The mechanism of the FeCl₃-catalysed cross-coupling reaction of alcohols with alkenes has been investigated using the density functional theory. All calculations were performed in liquid phase. The structures of intermediates and transition states are computed and analysed in detail. The calculations show that the entire catalytic cycle consists in three steps: (1) H-abstraction, (2) free-radical addition, and (3) hydrogen transfer. The rate-limiting step in the whole catalytic cycle is the hydrogen-abstraction step. Only the quartet potential surface is likely to play an essential role in this cross-coupling reaction. The alpha-C(sp³)–H bond of the phenylpropanol is cleaved in a homolytic fashion. Moreover, we justify the change of the oxidation state of iron along the overall reaction pathway on the basis of the computed natural population atomic charges and spin densities. Our calculated results are consistent with and provide a reliable interpretation for the experimental observations that suggest the cross-coupling reaction occurs through a radical mechanism.     

In situ DRIFTS研究NO在Cu-ZSM-5上的表面吸附及选择性催化还原

Cu-ZSM-5分子筛催化剂选择性催化还原NO具有较好的低温活性,在613 K时NO还原成N2的转化率达70.6%。原位漫反射红外光谱(In situ DRIFTS)是研究催化剂表面吸附物种及催化机理的重要方法,应用该方法在298～773 K范围原位考察了以C₃H₆为还原剂及富O₂ 条件下,NO在Cu-ZSM-5催化剂上的表面吸附及选择性催化还原。认为NO在Cu-ZSM-5催化剂上还原为N₂的过程中,NO以一系列NO_x吸附态形式与丙稀的活化物种(C_xH_y或C_xH_iyO_z)反应,生成有机中间体,再进一步反应,最终生成N₂。有机中间体存在一个明显的从有机胺物种到腈(或—CN)再到有机氮氧物种(R—NO₂或R—ONO)的过程,催化剂表面形成有机中间物种是关键步骤,Cu的作用是促进NO_x形成,O₂ 的作用是促进C₃H₆活化,并且是有效产生有机-氮氧化物不可缺少的条件。     

The hydrolysis mechanism and kinetic analysis for COS hydrolysis: A DFT study

Density Functional Theory (DFT) was utilized to study the hydrolysis mechanism and kinetic analysis of carbonyl sulfide (COS). The structures of reactants (R), transition states (TS), intermediates (IM) and products (P) were analyzed and a conclusion reached that hydrolysis mechanism of COS occurs in two paths with One path as a C=S path and the other as a C=O path and all featuring potential for forming H₂S and CO₂. Function change analysis of COS hydrolysis indicated the rate-determining step of COS hydrolysis was the first elementary reaction as OH and H in H₂O attacked C=O and S=O in COS, respectively, with the two paths parallel and competitive and the C=S path more reactionary than the C=O path. Influence on each elementary reaction was also not consistent with reaction temperature increase. The study also included further investigation of the COS catalytic hydrolysis.     

Valence state alternation of copper species doped in HY zeolite as revealed by paramagnetic relaxation enhancement NMR spectroscopy

Paramagnetic relaxation enhancement (PRE) solid-state NMR (ssNMR) was used to monitor the valence state alternation of copper species doped in HY zeolite during catalytic reaction processes. The combination of PRE ssNMR and in-situ NMR spectroscopy facilitates the detection of copper species as well as the monitoring of evolution from reactants, intermediates to products in heterogeneously catalyzed processes, which is of great importance for elucidating the detailed catalytic reaction mechanism.     

Concepts,instruments, and model systems that enabled the rapid evolution of surface science

Over the past forty years, surface science has evolved to become both an atomic scale and a molecular scale science. Gerhard Ertl’s group has made major contributions in the field of molecular scale surface science, focusing on vacuum studies of adsorption chemistry on single crystal surfaces. In this review, we outline three important aspects which have led to recent advances in surface chemistry: the development of new concepts, in situ instruments for molecular scale surface studies at buried interfaces (solid–gas and solid–liquid), and new model nanoparticle surface systems, in addition to single crystals. Combined molecular beam surface scattering and low energy electron diffraction (LEED)- surface structure studies on metal single crystal surfaces revealed concepts, including adsorbate-induced surface restructuring and the unique activity of defects, atomic steps, and kinks on metal surfaces. We have combined high pressure catalytic reaction studies with ultra high vacuum (UHV) surface characterization techniques using a UHV chamber equipped with a high pressure reaction cell. New instruments, such as high pressure sum frequency generation (SFG) vibrational spectroscopy and scanning tunneling microscopy (STM) which permit molecular-level surface studies have been developed. Tools that access broad ranges of pressures can be used for both the in situ characterization of solid–gas and solid–liquid buried interfaces and the study of catalytic reaction intermediates. The model systems for the study of molecular surface chemistry have evolved from single crystals to nanoparticles in the 1–10 nm size range, which are currently the preferred media in catalytic reaction studies.     

Surface reaction mechanism of Y2O3 atomic layer deposition on the hydroxylated Si(1 0 0)-2 × 1: A density functional theory study

The surface reaction mechanism of Y₂O₃ atomic layer deposition (ALD) on the hydroxylated silicon surface is investigated by using density functional theory. The ALD process is designed into two half-reactions, i.e., Cp₃Y (Cp = cyclopentadienyl) and H₂O half-reactions. For the Cp₃Y half-reaction, the chemisorbed complex is formed along with the change of metal-Cp bonding from Y-C(π) to Y-C₁(σ). For the H₂O half-reactions, the chemisorbed energies are increased with the relief of steric congestion around yttrium metal center. In addition, Gibbs free energy calculations show that it is thermodynamically favorable for the Cp₃Y half-reactions. By comparing with the reaction of H₂O with {Si}-(O₂)YCp, it is thermodynamically more favorable and kinetically less favorable for the reactions of H₂O with {Si}-OYCp₂ as well as with {Si}-OYCp(OH).     

Mechanistic insights into C‐C cross coupling activities of Pd/Ni‐doped heterofullerenes

Mechanistic insights into Heck and Suzuki‐Miyaura cross coupling reactions with C₅₉M (M = Pd/Ni) catalysts were developed. Density functional theory was used for the analysis of all the intermediates and transition states possible during C‐C cross coupling reactions over the catalysts under study. Oxidative addition, a step common to both Heck and Suzuki‐Miyaura cross coupling reactions, was observed to proceed with smaller activation barriers over C₅₉Pd. Heck coupling of iodobenzene with styrene was observed to proceed via oxidative addition, migratory insertion, and reductive elimination steps. The free energy barriers for oxidative addition, migratory insertion, and reductive elimination steps were 14.8, 11.6, and 4.8 kcal/mol, respectively, over C₅₉Pd, and 17.4, 79.3, and 17.4 kcal/mol, respectively, over C₅₉Ni, indicating oxidative addition and migratory insertion to be the rate‐determining steps over C₅₉Pd and C₅₉Ni, respectively. Similarly for Suzuki‐Miyaura coupling reaction, activation barriers for oxidative addition, transmetalation, and reductive elimination steps were 14.8, 52.4, and 7.9 kcal/mol, respectively, over C₅₉Pd, and 17.4, 64.7, and 60.2 kcal/mol, respectively, over C₅₉Ni, indicating transmetalation step to be the rate‐determining step over both the heterofullerenes.     

原位漫反射红外光谱研究NO在Ag/SAPO-34催化剂上的选择性催化还原

原位漫反射红外光谱研究NO在Ag/SAPO 34催化剂上的选择性催化还原过程。考察了以丙烯为还原剂 ,在富氧及 573～ 773K温度条件下的反应。通过比较初始混合气中加氧或不加氧时反应的原位光谱 ,探讨了氧在NO还原过程中的作用。结果表明 ,氧能充分促进丙稀活化以及增加NOx 吸附态含量 ,并且氧的存在是有效产生有机 氮氧化物 (R NO2 ,R ONO)不可缺少的条件。基于光谱实验 ,认为反应机理为 :NO ,丙烯和氧反应 ,在Ag/SAPO 34催化剂上生成吸附的有机 氮氧化物 ,再由这些吸附物种分解成N2 ,催化还原的关键是形成有机 氮氧化物中间体。     

Enhancement of carbon nanotube growth yield on Inconel 600 substrates through the surface pretreatments combining thermal annealing and plasma ion bombardment

We report the drastic growth yield enhancement of carbon nanotubes (CNT) on Inconel 600 metal substrate which contains catalytic components through the surface pretreatments combining thermal annealing and plasma ion bombardment. We comparatively investigated the effect of different substrate pretreatments of air annealing, plasma treatment, and their combination affecting CNT growth yield. The roughness of the substrates was significantly enhanced by the air annealing at 725 °C but reduced after the following plasma treatment, which produce nano-sized particle structures. Finally, a significant enhancement in the CNT growth yield was observed when the Inconel 600 substrate was undergone the pretreatment, which consists of oxidative annealing and subsequent plasma treatment.     

Copper(I)‐catalyzed reaction of unsymmetrical alkyne with HB(pin): a density functional theory study

With the aid of density functional theory calculations, we have investigated the mechanism of copper(I)‐catalyzed reaction between unsymmetrical alkyne 1‐phenyl‐1‐butyne and HB(pin). The results of the density functional theory calculations show that the reaction mechanism involves syn‐addition of catalyst ([NHC]CuH) (NHC = N‐heterocyclic carbene) to 1‐phenyl‐1‐butyne to form the alkenyl copper intermediates 2a and 5a , and then intermediates 2a and 5a react with HB(pin) to give intermediates 3 ( 3a , 3b ) and 6 ( 6a , 6b ), and finally elimination of catalyst completes the catalytic cycle and yields the α‐product P₁ and β‐product P₂ . We found that α‐product should be more favored than β‐product. The calculated results are consistent with the experimental findings. The present paper may provide a useful guide for understanding other analogous copper‐catalyzed hydroboration of unsymmetrical alkynes.     

Effect of the preparation conditions of Ni-supported shock-wave synthesized nanodiamond catalysts: FT-IR and catalytic considerations

On the basis of the results from the FT-IR, XRD and catalytic studies, a suggestion about the mechanism of surface transformations of Ni-supported detonation-synthesized ultradispersed diamond and the influence of these transformations on the state of the loaded metal have been made. It was proposed that in dependence on the inert or oxidative atmosphere applied for the elimination of the Ni salt precursor, different interactions of the support with the NiO species have taken place that determined the way of their coordination and stability as well as the dispersion of the metal nickel phase formed upon their reduction. The catalytic activity of the latter has been tested in the reaction of toluene hydrogenation.     

A low-dimensional crystal growth model on an isotropic and quasi-free sustained substrate

A new crystal growth theoretical model is established for the low-dimensional nanocrystals on an isotropic and quasifree sustained substrate. The driven mechanism of the model is based on the competitive growth among the preferential growth directions of the crystals possessing anisotropic crystal structures, such as the hexagonal close-packed and wurtzite structures. The calculation results are in good agreement with the experimental findings in the growth process of the lowdimensional Zn nanocrystals on silicone oil surfaces. Our model shows a growth mechanism of various low-dimensional crystals on/in the isotropic substrates.     

Rhodium‐catalysed hydrogenation of enamides with monodentate phosphorous ligands. A density functional theory study

The hydrogenation of enamides catalysed by rhodium complexes of monodentate phosphorous ligands has been studied by density functional theory. The role of trans intermediates, made accessible by the non‐chelating nature of the ligand, has been taken into account. The findings here reported show that cis intermediates play the major role in the mechanism of the reaction, suggesting that data obtained with chiral monodentate phosphorous ligands or with a mixture of them should be interpreted excluding the intervention of structures with trans phosphine arrangement. Thus, results observed with monodentate phosphorous ligands must be interpreted in the light of the exclusive intervention of cis intermediates, without involvement of structures with trans phosphine arrangements. Copyright © 2010 John Wiley & Sons, Ltd.     

Tracking X‐ray‐derived redox changes in crystals of a methylamine dehydrogenase/amicyanin complex using single‐crystal UV/Vis microspectrophotometry

X‐ray exposure during crystallographic data collection can result in unintended redox changes in proteins containing functionally important redox centers. In order to directly monitor X‐ray‐derived redox changes in trapped oxidative half‐reaction intermediates of Paracoccus denitrificans methylamine dehydrogenase, a commercially available single‐crystal UV/Vis microspectrophotometer was installed on‐line at the BioCARS beamline 14‐BM‐C at the Advanced Photon Source, Argonne, USA. Monitoring the redox state of the intermediates during X‐ray exposure permitted the creation of a general multi‐crystal data collection strategy to generate true structures of each redox intermediate.     

利用快速扫描伏安法测定醋酸根和甲酸根在铂(111)电极上吸附等温线 (cited: 3)

快速扫描伏安法是一种可以用来区分氧化/还原,吸附/脱附反应的有效工具. 这里,我们将提供一种新的方法,在一种相对浓度较低的反应物溶液中,利用不同的电位扫描速率(相对于扩散速率),可以得到电极表面的吸附/脱附过程的等温线. 本文将以醋酸根在酸性溶液中在Pt(111)上吸附作为例子,并将此方法扩展到复杂的甲酸氧化反应机理研究中.     

A quantum chemical study of ZrO2 atomic layer deposition growth reactions on the SiO2 surface

Zirconium oxide (ZrO₂) is one of the leading candidates to replace silicon oxide (SiO₂) as the gate dielectric for future generation metal-oxide-semiconductor (MOS) based nanoelectronic devices. Experimental studies have shown that a 1–3 monolayer SiO₂ film between the high permittivity metal oxide and the substrate silicon is needed to minimize electrical degradation. This study uses density functional theory (DFT) to investigate the initial growth reactions of ZrO₂ on hydroxylated SiO₂ by atomic layer deposition (ALD). The reactants investigated in this study are zirconium tetrachloride (ZrCl₄) and water (H₂O). Exchange reaction mechanisms for the two reaction half-cycles were investigated. For the first half-reaction, reaction of gaseous ZrCl₄ with the hydroxylated SiO₂ surface was studied. Upon adsorption, ZrCl₄ forms a stable intermediate complex with the surface SiO₂–OH^* site, followed by formation of SiO₂–O–Zr–Cl^* surface sites and HCl. For the second half-reaction, reaction of H₂O on SiO₂–O–Zr–Cl^* surface sites was investigated. The reaction pathway is analogous to that of the first half-reaction; water first forms a stable intermediate complex followed by evolution of HCl through combination of a Cl atom from the surface site and an H atom from H₂O. The results reveal that the stable intermediate complexes formed in both half-reactions can lead to a slow film growth rate unless process parameters are adjusted to lower the stability of the complex. The energetics of the two half-reactions are similar to those of ZrO₂ ALD on ZrO₂ and as well as the energetics of ZrO₂ ALD on hydroxylated silicon. The energetics of the growth reactions with two surface hydroxyl sites are also described.     

Structural modifications in metal complexes of a plant metallothionein caused by reductive radical stress: a Raman study

The effect of radical stress in the biological environment is a very active field of research connecting various disciplines of life science. Thus, a comprehensive vision of all possible reactive species is necessary for contributing to the solution of puzzling questions on free radicals. In this contest, damages to Zn(II) and Cd(II) complexes of a plant metallothionein (Quercus suber—QsMT), because of reductive radical stress, were investigated by Raman spectroscopy. QsMT is a low‐molecular‐weight cysteine‐rich protein obtained by in vivo synthesis to have a physiologically representative model. Gamma‐irradiation was used to simulate the endogenous formation of reductive species. By changing the appropriate conditions of irradiation, a selection of the reacting radical species (hydrogen atom and hydrated electron) was carried out. Specific damages occur at sensitive amino acid sites, selectively, rather than indiscriminately. In particular, Cys resulted to be among the most sensitive residues toward radical attack, suggesting that the thiolate clusters of both metal and QsMTs act as efficient interceptors of reducing species. Under reductive stress, Zn–QsMT undergoes a significant thiolate group oxidation and the participation of ligands other than the cysteine‐derived thiolate bonds (i.e. His) in zinc coordination becomes necessary for the protein stabilization. Regarding Met residues, they resulted to be more sensitive to the reductive radical attack when the protein binds Cd(II) ions, indicating that the protein structure can play a significant role in blocking the ready access of free radicals to the sulfur‐containing residues, so strongly affecting the radiosensitivity of the protein. In conclusion, the results obtained from γ‐irradiation experiments indicate that reductive stress causes changes in the primary QsMT structure and in the secondary and tertiary structures, and the radical‐induced effects are dependent on the metal bound. Copyright © 2009 John Wiley & Sons, Ltd.     

Potential Images of Ferroelectric Domain Structures Formed by Electron Beam in Lithium Niobate Crystals

Ferroelectric domain structures formed by an electron beam in lithium niobate crystals are studied using low-voltage SEM microscopy. The structures are formed in crystals with different conductivity, including samples with high-resistance congruent composition (CLN) and samples with conductivity increased by reductive annealing (RLN). The potential nature of the contrast of the domain structures observed in the secondary electron mode depending on the conductivity of the samples and the direction of spontaneous polarization of the domains is analyzed. It is assumed that the domain contrast in CLN crystals is associated with long-lived charges localized near domain walls and in the irradiated areas. The recorded domain structures in the CLN crystals are visualized on polar and nonpolar cuts. In the RLN crystals with improved conductivity compared to CLN, the potential contrast of the periodic domain structures is found only on the polar cuts, where vector P_s of the domains is perpendicular to the irradiated surface. This contrast is likely because the field of the spontaneous electric polarization charges influences the secondary electrons.