Formaldehyde adsorption on the interior and exterior surfaces of CN nanotubes

Using density functional theory, we have investigated the adsorption of formaldehyde (H₂CO) on the interior and exterior walls of a carbon nitride nanotube (CNNT) in terms of energetic, geometric, and electronic properties. It was found that the adsorption is more preferential on the exterior surface of the tube with maximum adsorption energy of ?7.4 kcal/mol. It has also been found that the adsorption energy per molecule is increased by increasing the number of adsorbed molecules. The results reveal that the electronic properties of CNNT are very sensitive to the presence of formaldehyde so that the HOMO/LUMO gap is reduced from 4.02 eV in the free tube to 2.44 eV in the most stable configuration of 3H₂CO/CNNT complex. Also, we have showed that the response of the tube may depend on concentration of the H₂CO molecules, suggesting that the CNNT might produce an electrical signal in the presence of H₂CO molecules.     

A theoretical study of CO adsorption on aluminum nitride nanotubes

Adsorption of toxic CO molecule on single-walled aluminum nitride nanotubes (AlNNTs) was investigated using density functional theory calculations. A detailed analysis of the energetic, geometry, and electronic structure of various CO adsorptions on the tube exterior surface was performed. In contrast to carbon and BN nanotubes, our results indicated that AlNNTs can strongly interact with CO molecules. The adsorption energy of the most stable configuration was calculated to be about −0.25 eV. The Morokuma–Kitaura decomposition for molecular interaction energies was used to investigate the nature of C–Al bond in the most stable CO–AlNNT complex, demonstrating that electrostatic forces and polarization term are basic factors of attractive interaction between CO and AlNNT. They provide 37.9 and 40.4% of attractive interaction and charge transfer energies make a little contribution to the adsorption energy of CO.     

分形表面上CO氧化反应的蒙特卡罗模拟

众所周知,人们在理想完好的单晶表面上的动力学研究已取得了很大的成功[1],然而对许多实际催化剂来说,传统催化理论和实验之间不符的情况仍然俯拾皆是．现在人们对造成这种情况的原因已经有了更加深入的认识：大量的实验事实表明,在表面催化反应体系中,不但催化剂表面具有复杂的分形结构,而且催化剂表面上的活性中心分布也具有复杂的分形特性[2]．“分形”是指那些具有分数维数的几何对象．这些对象往往是不规则的,不能用通常的欧氏几何来描述[3]．将分形引入催化科学中最早的是Pfeifer和Avnir等[4]人,至今已有近二十年的历史,现…     

DFT study on the adsorption and dissociation of hydrogen sulfide on MgO nanotube

The adsorption of a H₂S molecule on the surface of an MgO nanotube was investigated using density functional theory. It was found that H₂S molecule can be associatively adsorbed on the tube surface without any energy barrier or it can be dissociated into –H and –SH species overcoming energy barrier of 4.03–7.77 kcal/mol. The associative adsorption is site selective so that the molecule is oriented in such a way that the sulfur atom was linked to an Mg atom. The HOMO–LUMO energy gap of the tube has slightly changed upon associative adsorption, while they were significantly influenced by dissociation process. Especially, the highest occupied molecular orbital of the tube shifts to higher energies which can facilitate electron emission current from the tube surface. Also, energy gap of the tube dramatically decreased by about 0.93–1.05 eV which influences the electrical conductivity of the tube.     

Oxygen gas-induced lip-lip interactions on a double-walled carbon nanotube edge

We have investigated adsorption of an O(2) molecule on a double-walled carbon nanotube (DWCNT) edge using density functional theory calculations. An O(2) molecule adsorbs exothermally without an adsorption barrier at open nanotube edges that are energetically favorable with a large adsorption energy of about -9 eV in most cases. Dissociative adsorption of an O(2) molecule induces various spontaneous lip-lip interactions via the bridged carbon atoms, generating the closed tube ends. This explains why the DWCNTs are chemically more stable than the single-walled nanotubes during observed field emission experiments. The field emission takes place via the localized states of the bridged carbon atoms, not via those of the adsorbed oxygen atoms particularly in the armchair nanotubes. We also find that some O(2) precursor states exist as a bridge between tube edges.     

CO分子在TiC(001)表面上的吸附构型与电子结构

采用第一性原理方法和平板模型对CO分子在TiC(001)表面的吸附构型和电子结构进行了详细研究. 结果表明, CO分子倾向于采用C端吸附在表层Ti原子上方. 对于该吸附方式, 计算得到的吸附能、CO各电子态所处能级位置以及C—O键伸缩振动频率的红移值均与实验观测结果相吻合. 由能带结构和Mvlliken布居分析结果可知, 当采用C端吸附时, CO的5σ和2π鄢态受到底物影响最为显著, 尤其是C端的桥位吸附方式. 此外, 还进一步对底物表面态在CO吸附过程中的作用进行了探讨.     

含Cu复合氧化物对NO和CO吸附和活化的TPSR研究

利用MS－TPD法并结合XRD、化学分析等对催化剂进行了表征，探讨了K2NiF4结构La2-x(Sr，Th)xCuO4±λ系催化剂中三个典型样品LaSrCuO4、La2CuO4和La1.7Th0．3CuO4对NO、CO及CO＋NO等小分子的吸附性能和活化规律。结果表明：NO吸附量的大小与催化剂中氧空位含量有关，吸附强度和脱附峰种类与金属离子氧化态有关。CO在氧缺陷复合氧化物催化剂上的吸附是首先变为碳酸根，并在高温以CO2物种脱出．在NO和CO的共吸附过程中，有关NO的吸、脱性能与单独NO－TPD中NO的吸脱附规律相似，表明NO在NO＋CO共吸附的竞争吸附过程中，优先吸附起决定作用，而受CO的影响较小．NO的吸附是NO活化分解的必要条件．     

CO氢化合成乙醇反应的过渡应答研究——改性Rh/Al2O3催化剂的吸附特性

本文以四极质谱作为过渡应答测量中的分析手段, 连续快速跟踪和分析被测物种, 测量了H_2和CO在改性Rh/Al_2O_3催化剂上的吸附和脱附性能。结果发现, 507 K时H_2或CO的吸附中存在着部份不可逆吸附。CO和H_2吸附在相同的活性位上, 存在竞争吸附。CO的吸附作用略强於H_2。钾元素的改性使催化剂对H_2或CO的吸附量均减少, 然而相对于H_2而言, CO的吸附作用更强了。     

Determination of adsorption heats of individual adsorption complex by combination of microcalorimetry and FTIR spectroscopy

Adsorption of CO as a probe molecule on K-FER zeolites differing in Si/Al ratio was investigated. Successful determination of adsorption heats of individual adsorption complexes formed upon adsorption of CO molecules on K-FER zeolites at 300 K by combination of IR spectroscopy with adsorption microcalorimetry is reported. Adsorption heat of bridged carbonyl complexes, where CO molecule interacts with two nearby extraframework K⁺ cations, was experimentally determined for the first time. It was found that bridged complexes on dual cationic sites exhibit adsorption heat of 34.8 kJ mol^?1, whereas monodentate carbonyls on single isolated K⁺ cation exhibit adsorption heat of only 26.2 kJ mol^?1 and adsorption heat of isocarbonyls was 21.5 kJ mol^?1.     

CO在Cs/Ru(1010)表面上吸附的ARUPS研究

CO adsorption on Ru(100) and Cs/Ru(10O) surfaces has been investigated using ARUPS, at low temperature 150K. The 5σ+1π and 4σ levels of CO molecule were　found in angle-rcsolved UP spectra showing that CO is in molecular adsorption states on clean and Cs precovercd Ru(1010). The dependence of CO 4σ intensity on incident angle suggests that adsorbed CO stands upright on clean Ru(1010) surface; But adsorbed CO, with a short-range interaction with Cs atom [15], does not stand upright and tilts in <1210> azimuth on a Cs-precovered Ru(1010) surface.     

NiO(001)表面吸附CO的从头算研究

用量子化学B3LYP方法,以外加点电荷来封闭边界效应的簇为模型,计算了CO在NiO(001)面上不同吸附位置的吸附情况,并计算了振动频率。结果表明:1) CO的最佳吸附方式为C端垂直吸附在Ni位;2)吸附后CO间的振动频率蓝移13 cm-1;3)在O空缺、边和角等位置的吸附不如在完整表面的吸附稳定,这些均与实验结果一致。吸附后CO把主要起反键作用的C2s电子给予簇表面,使得吸附后CO键级加大,导致吸附后振动频率蓝移。并比较了Gaussian98 和Crystal98的计算结果,两者的结果能较好地符合。     

Dispersion-corrected DFT study on the carbon monoxide sensing by B<Subscript>2</Subscript>C nanotubes: effects of dopant and interferences

Electrical sensitivity of a boron carbon nanotube (B₂CNT) was examined toward carbon monoxide (CO) molecule by using dispersion-corrected density functional theory calculations. It was found that CO is weakly adsorbed on the tube, releasing energy of 3.5–4.1 kcal/mol, and electronic properties of the tube are not significantly changed. To overcome this problem, boron and carbon atoms of the tube were substituted by aluminum and silicon atoms, respectively. Although both Al and Si doping make the tube more reactive and sensitive to CO, Si doping seems to be a better strategy to manufacture CO chemical sensors due to the higher sensitivity without deformation of nanotube structure after adsorption procedure. Moreover, it was shown that some interference molecules such as H₂O, H₂S and NH₃ cannot significantly change the electronic properties of B₂CNT. Therefore, the Si-doped tube might convert the presence of CO molecules to electrical signal.     

504—Interfacial behaviour of p-aminobenzoic acid (PABA) at the mercury/solution interface: A possible role of adsorption in the bacteriostatic action of PABA antimetabolites

The interfacial behaviour of p-aminobenzoic acid (PABA) at the mercury/aqueous solution interface was examined and compared with that of its antimetabolites (sulpha drugs). On qualitative grounds the adsorption process of PABA is quite similar to that of its antimetabolites. It was shown that the common framework of the molecule, p-NH₂φ-XO₂- (XC or S), is adsorbed flat on the electrode surface and that the two groups of atoms always present in the different compounds, i.e. the p-amino group and the two oxygen atoms, are directly involved in the interaction with the charged surface.These results imply a possible role of an adsorption step in the mechanism of action of the sulpha drugs at the biological level.     

Chemisorption of NH3 at the open ends of boron nitride nanotubes: a DFT study

Considering the thermodynamic aspects and reaction pathways of chemical adsorption of NH₃ molecule at the open ends of boron nitride nanotubes (BNNTs), theoretically, it was found that the open-ended BNNTs are able to cleave the N–H bond of NH₃ via a one- or two-stepwise mechanism. The N-enriched and B-enriched open-ended BNNTs show a nucleophilic and electrophilic behavior toward the NH₃, respectively. Besides, some effects of this chemical adsorption on the electronic properties of BNNTs were explored.     

NiO表面磁性对分子吸附的影响的第一性原理研究

过渡金属氧化物广泛应用在当今能源与环境相关的催化领域,理解其表面化学性质以及结构-反应活性之间的关系对于先进催化材料的进一步发展以至理性设计至关重要.3d后过渡系金属(Mn,Fe,Co,Ni)的氧化物以其中金属离子独特的自旋状态和由此产生的铁磁/反铁磁性为典型特征.研究过渡金属氧化物的自旋状态以及磁性对表面化学的影响将使我们更加完整了解这些材料的表面化学.以NiO为代表的后过渡系金属岩盐结构一元氧化物具有反铁磁性,被经常作为反铁磁研究的模型体系.尽管在低温(低于其Neel温度)下NiO体相的完整晶体具有确定的反铁磁序,但是一系列最新研究表明,在条件变化时NiO表面的Ni离子可以产生不同的磁序.以此为背景,本工作以NiO为模型体系,采用DFT+U的第一性原理方法研究了NiO表面磁序对表面的小分子吸附活性的影响,包括表面吸附活性对各磁性相的表面取向以及吸附物种磁性的依赖关系.我们考察了NiO的5种反铁磁相和一种铁磁相,两个晶面NiO(001)和NiO(011),顺磁性分子NO和非顺磁性分子CO.我们发现表面能受磁性的影响较轻微,NiO(001)面上从49到54 meV/?2,NiO(011)面上从162到172 meV/?2.在NiO(001)面上,CO与NO都倾向于在Ni离子的顶位吸附.对于不同的体相磁序与表面取向,CO吸附能的变化范围为-0.33~-0.37 eV,NO吸附能的变化范围为-0.42~-0.46 eV.在NiO(011)表面,两种分子都倾向于吸附在由两个Ni离子构成的桥位.我们发现相对于NiO不同磁性相的体相长程磁序,吸附位点处构成桥位的两个Ni离子的局部磁矩相对取向对于分子的吸附具有更加显著的影响.计算得到NO在局部磁矩相对取向反平行(↑↓)吸附位点处的吸附能为-0.99~-1.05 eV,在局部磁矩相对取向平行(↑↑)吸附位点处吸附会增强,吸附能为-1.21~-1.30 eV.对于CO,尽管计算的吸附能在(↑↓)吸附位点(-0.73~-0.75 eV)与在(↑↑)吸附位点(-0.71~-0.72 eV)非常接近,两种吸附位点处的CO吸附时分子轨道杂化方式以及吸附后CO的局域电子态密度却具有明显不同的特征.本工作突出揭示了分子在过渡金属氧化物表面的多重吸附位点上吸附时吸附位点的局域磁矩相对取向对吸附性能的影响.     

一氧化碳共吸附法确定叔丁胺分子在Cu(111)表面的吸附位

采用扫描隧道显微镜(STM)和密度泛函理论(DFT)研究了78 K时单个叔丁胺分子在Cu(111)表面的吸附位. 我们提出以共吸附的一氧化碳√3 ×√3 超结构为基底铜原子的标识方法, 确定了低覆盖度的叔丁胺分子在Cu(111)表面的吸附位为顶位. 而采用单个一氧化碳分子标识基底铜原子的位置, 同样得出了叔丁胺分子的吸附位为顶位. 此外, 还采用DFT计算叔丁胺分子在Cu(111)表面的优势吸附构型. 理论计算结果表明顶位吸附构型为能量最稳定的构型, 与实验结果相吻合.     

A DFT study of the adsorption and dissociation of CO on Fe(100): influence of surface coverage on the nature of accessible adsorption states.

In the present article, we report adsorption energies, structures, and vibrational frequencies of CO on Fe(100) for several adsorption states and at three surface coverages. We have performed a full analysis of the vibrational frequencies of CO, thus determining what structures are stable adsorption states and characterizing the transition-state structure for CO dissociation. We have calculated the activation energy of dissociation of CO at 0.25 ML (ML = monolayers) as well as at 0.5 ML; we have studied the dissociation at 0.5 ML to quantify the destabilization effect on the CO(alpha3) molecules when a neighboring CO molecule dissociates. In addition, it is shown that the number and nature of likely adsorption states is coverage dependent. Evidence is presented that shows that the CO molecule adsorbs on Fe(100) at fourfold hollow sites with the molecular axis tilted away from the surface normal by 51.0 degrees. The asorprton energy of the CO molecule is -2.54 eV and the C-O stretching frequency is 1156 cm(-1). This adsorption state corresponds to the alpha3 molecular desorption state reported in temperature programmed desorption (TPD) experiments. However, the activation energy of dissociation of CO(alpha3) molecules at 0.25 ML is only 1.11 eV (approximately 25.60 kcal mol(-1)) and the gain in energy is -1.17 eV; thus, the dissociation of CO is largely favored at low coverages. The activation energy of dissociation of CO at 0.5 ML is 1.18 eV (approximately 27.21 kcal mol(-1)), very similar to that calculated at 0.25 ML. However, the dissociation reaction at 0.5 ML is slightly endothermic, with a total change in energy of 0.10 eV Consequently, molecular adsorption is stabilized with respect to CO dissociation when the CO coverage is increased from 0.25 to 0.5 ML.     

An ab initio study of CO adsorption on ceria(1 1 0)

Hartree–Fock and DFT calculations are reported for the CO/CeO₂(1 1 0) surface system. The electron density, electrostatic potential, atomic charges and projected electronic density of states have been calculated from an ECP-and-point-charge-embedded cluster model and is compared with periodic calculations. The agreement between the two surface models is reasonably good. A number of weakly bonding CO adsorption sites were found, with E_ads (BSSE-corrected) ranging from 0.01 to 0.22 eV per adsorbed molecule. The two most favourable sites are found in the vicinity of surface cerium ions, with the CO molecule oriented in a tilted fashion, C-end down. The surface-induced CO stretching vibrational frequency shifts on these sites are a redshift of ≈−30 cm⁻¹ and a blueshift of ≈25 cm⁻¹, respectively.     

Pd(Cu)在MgO(100)表面吸附CO和O2的理论研究

采用固体镶嵌势能模型和DFT/B3LYP方法研究了在Pd/MgO和Cu/MgO表面吸附CO和O₂分子的电子性质. 计算结果表明, 在完美MgO(100)表面Pd原子对CO和O₂的吸附能分别为206.5和84.8 kJ/mol, 因此可知Pd原子更容易吸附CO分子; 而当Pd原子附着于有氧缺陷的MgO表面时, 它对两种分子的吸附都非常弱. 相反, 附着于MgO表面的Cu原子对O₂分子的吸附更为有利, 其吸附能在140～155 kJ/mol之间. 研究结果还表明, 对于双分子吸附体系, 即CO＋CO, CO＋O₂, O₂＋O₂体系, 双分子之间的结合力可减小完美MgO表面上Pd原子与被吸附分子的相互作用, 使吸附能减少了46～96 kJ/mol. 而对于在MgO表面上的Cu原子, 只有O₂＋O₂ 体系使吸附能减少了大约50～71 kJ/mol.