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1.
In this study we have explored, by means of ab initio molecular dynamics, a subset of three different protic ionic liquids (ILs). We present both structural and dynamical information of the liquid state of these compounds as revealed by accurate ab initio computations of the interactions. Our analysis figures out the presence of a strong hydrogen bond network in the bulk state, that is more stable in those ILs characterised by a longer alkyl side chain. Indeed it becomes more long-lasting passing from ethyl ammonium to butyl ammonium, owing to the hydrophobic effects stemming from alkyl chain contacts. Furthermore, the relative free energy landscape of the cation–anion interaction exhibits a progressively deeper well as the side chain of the cation gets longer. The hydrogen bond interaction, as already mentioned in previous works, leads to loss of degeneracy of the asymmetric stretching vibrations of the nitrate anions. The resulting frequency splitting between the two normal modes is about 90 cm?1.  相似文献   

2.
Pristine and annealed multi-walled C nanotubes are preliminarily tested as catalysts towards the degradation of p-coumaric acid with better performances than the widely used activated carbon. In order to clarify the origin of their different catalytic efficiency, the samples are analysed by means of high-resolution transmission electron microscopy, X-ray photoemission, reflection electron energy loss and micro-Raman spectroscopy. Chemical composition, mass density, bonding configurations and threefold- to fourfold-coordinated carbon bonding ratios are determined. The comparative discussion of the results obtained leads to attribute the higher catalytic activity of the pristine nanotubes to their larger sp2/sp3 carbon bonding fraction and greater amount of oxygen containing functional groups.  相似文献   

3.
We investigated the effects of combination of noble metals M (Rh, Pd, Ir, Pt) and metal oxide supports S (Al2O3, SiO2, ZrO2, CeO2) on the NO + H2 reaction using planar catalysts with M/S two layered thin films on Si substrate. In this study, NO reduction ability per metal atom were evaluated with a specially designed apparatus employing pulse valves for the injection of reactant molecules onto catalysts and a time-of-flight mass spectrometer to measure multiple transient products: NH3, N2 and N2O simultaneously as well as with an atomic force microscopy to observe the surface area of metal particles. The catalytic performances of Rh and Ir catalysts were hardly affected by a choice of a metal oxide support, while Pd and Pt catalysts showed different catalytic activity and selectivity depending on the metal oxide supports. This assortment is consistent with ability to dissociate NO depending on metals without the effect of any support materials. There, the metals to the left of Rh and Ir on the periodic table favor dissociation of NO and those to the right of Pd and Pt tend to show molecular adsorption of NO. Therefore, the catalytic property of noble metals could be assorted into two groups, i.e. Rh and Ir group whose own property would mainly dominate the catalytic performance, and Pd and Pt group whose interaction with metal oxides supports would clearly contribute to the reaction of NO with H2. NO reduction activity of Pd and Pt was found to be promoted above that of Rh and Ir, provided that Pd and Pt were supported by CeO2 and ZrO2.  相似文献   

4.
It is important to study the interaction of ionic liquids (ILs) with protein for the applications of ILs in biochemical process, and help the researchers to choose and design the better ILs to serve as a solvent. In this work, the interaction between 1-alkyl-3-methylimidazolium bromide [Cnmim]Br (n=4, 6, 8, 10) and bovine serum albumin (BSA) was systematically investigated for the first time by multi-spectroscopic approach (fluorescence, UV–vis and FT-IR spectroscopy) and density functional theory (DFT). [Cnmim]Br (n=4, 6, 8, 10) can bind to BSA by H-bond interaction between their cationic headgroups and Asp/Glu amino acid residue at the surface of BSA, and hydrophobic interaction between their hydrocarbon chains and the hydrophobic amino acid residues in the interior of BSA. On the basis of thermodynamic parameters and the similar structure of [Cnmim]Br (n=4, 6, 8, 10), it can be inferred that the hydrophobic interaction plays a major role in the interaction of [C10mim]Br with BSA, while the hydrogen bond and van der Waals force play a major role in the interaction of [Cnmim]Br (n=4, 6, 8) with BSA. Synchronous fluorescence and FT-IR spectra indicate that [C10mim]Br could markedly change the secondary structure of BSA, while [Cnmim]Br (n=4, 6, 8) could slightly change the secondary structure of BSA. The results allowed us to understand (i) the effect of the alkyl chain length of the cation on the mechanism of ILs–protein interaction and (ii) the effect of the alkyl chain length of the cation on the protein secondary structure.  相似文献   

5.
Commercial and home-made Ce-Zr catalysts prepared by co-precipitation were characterised by XRD, Raman spectroscopy, N2 adsorption at −196 °C and XPS, and were tested for NO oxidation to NO2. Among the different physico-chemical properties characterised, the surface composition seems to be the most relevant one in order to explain the NO oxidation capacity of these Ce-Zr catalysts. As a general trend, Ce-Zr catalysts with a cerium-rich surface, that is, high XPS-measured Ce/Zr atomic surface ratios, are more active than those with a Zr-enriched surface. The decrease in catalytic activity of the Ce-Zr mixed oxided upon calcinations at 800 °C with regard to 500 °C is mainly attributed to the decrease in Ce/Zr surface ratio, that is, to the surface segregation of Zr. The phase composition (cubic or t′′ for Ce-rich compositions) seems not to be a direct effect on the catalytic activity for NO oxidation in the range of compositions tested. However, the formation of a proper solid solution prevents important surface segregation of Zr upon calcinations at high temperature. The effect of the BET surface area in the catalytic activity for NO oxidation of Ce-Zr mixed oxides is minor in comparison with the effect of the Ce/Zr surface ratio.  相似文献   

6.
Poly(4vinylpyridine-co-styrene) (P(4VP-co-St)) was grafted on silica gel particles in the manner of “grafting from”, and the grafting particle P(4VP-co-St)/SiO2 was gained. The chloromethylation reaction for the tetraphenylporphyrin (TPP) was performed using a chloromethylation reagent, 1,4-bis(chloromethyoxy)butane which was uncarcinogenic, and the tetra-chloromethylphenyl-porphyrin (TMCPP) was prepared. Then, the quaternization reaction between the benzyl chloride groups on TMCPP and pyridine groups of the grafted P(4VP-co-St) macromolecules occurred and the bonding of TMCPP on the particles P(4VP-co-St)/SiO2 was realized, resulting in the functional composite-type particles TMCPP-P(4VP-co-St)/SiO2. Subsequently, the metallation of the bonded particles TMCPP-P(4VP-co-St)/SiO2 was carried out via the coordination reaction between TMCPP-P(4VP-co-St)/SiO2 and metal salt, resulting in the supported metalloporphyrin (MP) catalysts MP-P(4VP-co-St)/SiO2. The supported catalysts were characterized by UV-Vis spectra. The effects of various factors on the bonding process of TMCPP on P(4VP-co-St)/SiO2 were studied in detail. In addition, the catalytic activity of the supported catalysts MP-P(4VP-co-St)/SiO2 have been studied in oxidation process of ethyl benzene with molecular oxygen to acetophenone without the use of sacrificial co-reductant. The experimental results showed that the tetra-chloromethylphenyl-porphyrin (TMCPP) could be successfully bonded onto the P(4VP-co-St)/SiO2 surfaces by means of the quaternization reaction between TMCPP and the pyridine groups on grafted P(4VP-co-St) macromolecules. The supported catalysts MP-P(4VP-co-St)/SiO2 exhibited the fine catalytic activity. Moreover, the supported cobalt porphyrin was more active than the supported iron and manganese porphyrins.  相似文献   

7.
采用共沉淀法制备不同组分类水滑石前驱体Co-M-Al和Co-M-Ce-Al (M=Zn, Ni, Cu)复合氧化物催化剂催化分解N2O. 结果表明,Co-M-Al系列氧化物催化剂的催化活性Co-Ni-Al系列>Co-Zn-Al系列>Co-Cu-Al系列;CeO2添加使得催化剂催化活性进一步提高,N2O分解温度T50和T90均下降80 oC;继续负载碱金属K也使氧化物催化剂催化活性提高,N2O分解温度T50和T90下降约50 oC.  相似文献   

8.
Ionic liquids (ILs) are expected to be used as readily available “designer” solvents, characterized by a number of tunable properties that can be obtained by modulating anion and cation combinations and ion chain lengths. Among them, its high ionicity is outstanding in the preparation and property modulation of two-dimensional (2D) materials. In this review, we mainly focus on the ILs-assisted exfoliation of 2D materials towards large-scale as well as functionalization. Meanwhile, electric-field controlled ILs-gating of 2D material systems have shown novel electronic, magnetic, optical and superconducting properties, attracting a broad range of scientific research activities. Moreover, ILs have also been extensively applied in various field practically. We summarize the recent developments of ILs modified 2D material systems from the electrochemical, solar cells and photocatalysis aspects, discuss their advantages and possibilities as “designer solvent”. It is believed that the design of ILs accompanying with diverse 2D materials will not only solve several scientific problems but also enrich materials design and engineer of 2D materials.  相似文献   

9.
二噁英是一类含氯挥发性有机污染物,具有环境持久性、生物蓄积性和长期残留性等特性,可造成致畸、致癌和致突变等危害。铁矿烧结过程中含氯前驱物在碱性环境下通过Ullman反应或经飞灰中某些催化性成分催化生成二噁英;碳、氢、氧和氯等元素可通过基元反应“从头合成”(de novo)二噁英,是二噁英最主要的排放源之一。物理吸附技术仅能实现污染物由气相向固相转移,加重了飞灰处理负担,并存在特定温度条件下(250~350 ℃)二噁英再生风险。催化降解技术能彻底矿化有机污染物,生成CO2,H2O和HCl/Cl2,是一种避免二次污染高效节能、成本较低的方法。但由于传统催化剂活性温度区间较高,无法达到烧结烟气末端温度。选择合适的催化剂,提高催化剂低温降解活性,能实现低温、高效催化降解烧结烟气中有机污染物的目标。过渡金属Ce具有稀土金属的4f轨道配位效应和路易斯酸活性位点,对有机污染物C-H和C-Cl键活化起到至关重要的作用,掺杂过渡金属、调整活性组分比例可进一步提高铈基催化剂的抗中毒性能和降解活性。因此,本文采用溶胶凝胶法制备Ce-V-Ti复合催化剂,以氯苯为二噁英模型分子,研究了不同活性组分比例对铈基催化剂降解烧结烟气中二噁英活性影响。利用X射线衍射仪、比表面积及孔径测定仪和拉曼光谱仪对催化剂进行表征,研究Ce-V-Ti催化剂的相组成、比表面积和分子结构,并推测铈基催化剂的降解机理。结果表明,在实验室模拟烧结烟气气氛下,反应条件为GHSV=30 000 h-1、20%O2和100 ppm CB,当Ce质量分数为15%、V质量分数为2.5%时,Ce-V-Ti催化降解氯苯活性最高,150 ℃能达到约60%转换率,300 ℃能实现95%降解率。催化剂载体与活性组分之间化学交互作用,影响催化剂的降解活性。通过光谱学分析发现,Ce-V-Ti催化剂XRD图谱主要为锐钛矿相的TiO2,比表面积为95.53 m2·g-1,孔容0.29 cm3·g-1,孔径6.5 nm。表面官能团主要为C-H基团和H-O官能团。引入V作为Ce-Ti催化剂助剂,促进了Ce元素固溶,增加了催化剂表面氧空位,有利于提升催化剂降解活性。通过对催化剂机理分析,认为反应物首先通过发生亲核取代而垂直吸附于催化剂表面,再被活性组分Ce活化,活化后氯苯分子被表面活性氧分解矿化。同时,过渡金属V的低价态氧化物发生氧化反应,促进Ce的还原反应。  相似文献   

10.
Density functional theory (DFT) calculations at ωB97XD/SDD level have been conducted to study the differences between the insertions of ethylene into the non‐metallocene octahedral group 4 catalysts and those into metallocene group 4 catalysts. The study shows that both can be described by the Cossess mechanim, but are different energetically. The latter have energy profiles involving stable π complexes between ethylene and catalysts prior to insertion and the insertion transition states (TSs) being lower than reactants, whereas the π complexes involved in the former are significantly less stable than their counterparts in the latter, and the insertion TSs are higher than or close to the reactants. The energy decomposition analyses on the activation energies indicate that the octahedral catalysts exert more significant steric effects than the metallocene catalysts, which are responsible for the differences. The cis arrangements of two chloride atoms in the precursors of metallocene catalysts were considered to be crucial for their catalytic activity, but the precursors of octahedral catalysts with either cis or trans arrangements of two chloride atoms exhibit activity. Nevertheless, the effective catalysts generated from octahedral precursors with cis chloride atoms have lower activation barriers than those from precursors with trans chloride atoms. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

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