Study on gas adsorption and desorption characteristics on water injection coal

To study the desorption mechanism of methane in coal by H₂O injection and establish the Wiser molecular structure model of bituminous coal, the Grand Canonical Monte Carlo method was used to study the desorption behavior of CH₄ in coal with different amounts of H₂O injection at molecular scale. The results showed that at 293 K, the maximum adsorption capacity of H₂O was about 16 mmol/g, and that of CH₄ was about 8 mmol/g, which was about twice that of CH₄. This indicates that H₂O has a stronger adsorption capacity than CH₄. For methane-bearing coal, when the amount of water injected is 100, the average relative concentration of CH₄ is 0.5446, and the average relative concentration of CH₄ decreases by 33.77% compared to the water content of 20. Under the same time conditions, the root mean square displacement and diffusion coefficient of CH₄ decrease with the increase of H₂O injection quantity. With the increase of H₂O injection, the motion velocity of CH₄ in vacuum layer decreased. When water was injected, methane was trapped in the coal by water. The more H₂O injected, the more methane trapped in the coal, and the less methane desorption. This research lays a theoretical foundation for further research involving coal-water interaction.     

铁脂质体/水分配系数测定及影响因素考察

基于PAF-301分子模型通过Li 掺杂或B取代等模式设计了几种新型多孔芳香骨架(PAFs)材料, 采用量子力学和分子力学方法对新材料的储氢性能进行研究. 由量子力学计算得到了不同分子片段与H₂之间的结合能, 并结合DDEC方法计算了各分子片段的原子电荷分布. 利用巨正则蒙特卡洛(GCMC)模拟方法计算了77和298 K下H₂在不同PAFs材料中的吸附平衡性质. 结果表明, H₂直接与苯环的结合能较低, 但掺杂Li 原子能够提高H₂与六元环的结合能, 同时Li 原子体现出较高的正电性质, B原子取代苯环中的两个C原子后, 使得原有C原子电负性增强; 77 K下PAF-301Li 具有最高的储氢性能, 而PAF-C₄B₂H₄-Li₂-Si 和PAF-C₄B₂H₄-Li₂-Ge体现出较好的常温储氢性能, 各种材料的常温储氢性能远低于其低温储氢性能. 通过77 K下H₂在PAFs材料中的等位能面分布和吸附平衡质心密度分布对H₂在PAFs 材料中的优先吸附位置进行分析, 发现在PAF-301 和PAF-301Li 骨架中, 由于中心能量较低的等位能区域范围较宽, H₂在其中存在四个明显的吸附高密度分布区域, 而其它三种PAFs晶胞中心能量较低的等位能区域范围较窄, 使得H₂在其中只存在两个明显的吸附高密度分布区域.     

The molecular and electronic structure of the Mo12S24 macromolecule as a model of the active component of a hydrodesulfurization catalyst

The density functional theory (DFT) with the B3P86 hybrid exchange-correlation functional was used to calculate the molecular and electronic structure of the Mo₁₂S₂₄ macromolecule as a single MoS₂ layered structure slab. Calculations with geometry optimization are indicative of insignificant relaxation of the coordinatively unsaturated Mo and S atoms, which corresponds with the literature DFT data on the MoS₂ single slab obtained with periodic boundary conditions. The calculated forbidden band width (0.85–0.98 eV) is comparable with its experimental value (1.30 eV) and the results of DFT calculations of MoS₂ with periodic boundary conditions (0.89 eV). An analysis of the electronic state of the surface Mo centers in the Mo₁₂S₂₄ macromolecule showed that these centers were reduced to a greater degree than the Mo(IV) atoms in the bulk. The adsorption complex between the Mo₁₂S₂₄ macromolecule and six H₂S molecules was calculated to characterize the adsorption ability of the coordinatively unsaturated Mo centers. The structure and energy characteristics of the adsorption complex corresponded to weak donor-acceptor interaction between the π lone pair of H₂S and the surface (reduced) Mo centers. The suggestion was made that the active center of the catalytic cycle of thiophene hydrodesulfurization should induce the oxidative addition of H₂ followed by the occlusion of hydrogen into the MoS₂ matrix.     

Gas chromatographic investigation of adsorption equilibria on graphitized thermal carbon black

Summary Retention volumes and heats of adsorption at low surface coverages of graphitized thermal carbon black (GTCB) for C₆–C₁₄ aromatic hydrocarbons have been determined. The dependence of heats of adsorption of these molecules on their structure and the number of carbon atoms in the molecule have been investigated. Substitution in the ring in methylbenzenes is not equivalent to the lengthening of the side-chain in the isomers of n-alkylbenzenes and gives rise to a much greater increase in the retention volumes and heats of adsorption.     

Effects of inert gas CO2/N2 injection on coal low-temperature oxidation characteristic: Experiments and simulations

To deeply understand the mechanism of inert gases in inhibiting coal spontaneous combustion, the effects of dry air, CO₂, and N₂ on coal spontaneous combustion were analyzed experimentally. To this end, bituminous coal prepared from Dongrong No. 2 Coal Mine was considered the research object. Based on the adsorption configuration of the oxygen-containing coal, the displacement behavior of O₂ by CO₂ /N₂ was studied using the grand canonical Monte-Carlo (GCMC) and molecular dynamics (MD) methods. The obtained results show that the injection of CO₂ and N₂ reduces the ability of spontaneous combustion of coal. It is found that among the studied gases, CO₂ has a stronger inhibition effect on coal spontaneous combustion, which increases the temperature of CO occurrence by 5℃, decreases the concentration of CO by 29.91%, and inhibits low-temperature oxidation of coal. From the microscopic point of view, CO₂ /N₂ gases can effectively displace O₂ by diffusion and occupying adsorption sites. It is found that after the injection of CO₂, the concentration of O₂ molecules increases significantly in the vacuum layer. Compared with N₂, injection of CO₂ increases the diffusion activation of O₂ by 5.89%. This indicates that the injection of an inert gas significantly reduces the oxygen absorption capacity of coal, thereby decreasing the coal-oxygen combination reaction and preventing the spontaneous combustion of coal. The performed analyses demonstrate that CO₂ outperforms N₂ in restraining the spontaneous combustion of coal.     

Assessment of the Strength of Energetic Compounds Through the Trauzl Lead Block Expansions Using Their Molecular Structures

The strength of energetic materials can be expressed as the expansion of the cavity of a standard lead block through explosion of the sample. A new method is introduced for prediction of the Trauzl lead block expansions for some of the important classes of pure and mixture of energetic compounds, with the general formula of C_aH_bN_cO_d. This model needs only the molecular structure of the energetic materials without using the detonation characteristics of different explosives. The model uses the ratios of the number of carbon to oxygen (a/d) and hydrogen to oxygen atoms (b/d). The effects of intra‐ and intermolecular interactions are applied to the model by assignment of some correcting parameters upon considering certain molecular fragments. This model gives more reliable results with respect to three of the best available methods.     

内蒙五牧场矿区11号煤层原煤大分子结构特征及其形成机制

在对内蒙古自治区呼伦贝尔市伊敏盆地五牧场区11号煤层原煤工业分析、元素分析、¹³C-NMR、FT-IR、XPS等分析基础上,获得了煤大分子结构中碳骨架信息、脂肪结构以及含氧官能团类型及比例、氮原子的存在形式和比例等结构信息。以此为基础,构建了煤的大分子结构模型,并应用 ¹³C-NMR预测软件ACD/CNMR predictor 对其进行了修正, 获得与实验核磁共振谱图吻合较好的大分子结构模型。大分子结构的芳香结构单元以苯、萘、蒽、菲为芳香结构单元,数量分别是1、2、2、1,醚键、氢化芳环以及邻位亚甲基作为连接芳香结构的主要桥键;氧原子以酚羟基、羰基、羧基的形式存在,数量分别是7、3、2;氮原子分别以吡啶和吡咯的形式存在,甲基和脂肪短链分布在芳香单元的边缘。与相邻矿区的褐煤及相近变质程度的神东长焰煤的比较发现,其形成机制主要是在高温低压环境下,热演化过程中快速失去各种含氧官能团,导致短链脂肪类物质的形成,而低压环境则有利于热演化过程中形成的各种小分子物质逸散导致自由基的缩聚,形成较大的芳香结构单元,但是直链脂肪类物质的存在具有位阻效应,不利于芳香结构单元的定向排列,导致所谓的"化学成分成熟超前于其结构成熟"现象。     

柳林3#镜煤吡啶残煤大分子结构模型及分子模拟

对柳林3^#镜煤吡啶抽提残煤(LLR)进行了¹³C CP/MAS NMR和XPS分析,结合元素分析和工业分析,构建了其大分子模型。LLR结构中芳香部分以蒽为主,脂肪结构主要以脂肪侧链的形式存在,氧原子分别以醚键、羟基和羰基形式存在,氮原子以吡咯和吡啶的形式存在。运用¹³C NMR预测软件ACD/CNMR predictor计算了大分子结构模型的¹³C化学位移。与实验¹³C NMR谱图相比较,对LLR的大分子结构模型进行了修正,获得了¹³C NMR计算谱能和实验谱图吻合较好的大分子结构模型。采用分子模拟对LLR化学结构模型进行能量优化,结果表明,大分子结构的能量按其大小排序主要为范德华能、键扭转能、键角能与键伸缩能。芳环之间的平行排列在该结构模型中占有很小的比例。最后通过添加周期性边界条件得到该煤的密度为1.22 g/cm³。量子化学半经验方法(PM 3)模拟结构表明,脂肪侧链中的C-C键较长,因而活性较高;边缘碳原子带有较多的负电荷,易于发生氧化反应;芳香碳原子所带电荷较少,稳定性很高。     

MoS<Subscript>2</Subscript> single slab as a model for active component of hydrodesulfuration catalyst: a quantum chemical study 1. Molecular and electronic structure of Mo<Subscript>12</Subscript>S<Subscript>24</Subscript> macromolecule and its adsorption complex with H<Subscript>2</Subscript>S

The molecular and electronic structure of Mo₁₂S₂₄ macromolecule as the MoS₂ single slab structure was calculated by the density functional theory (DFT) method with the B3P86 hybrid exchange-correlation functional. The results of calculations point to slight relaxation of coordinatively unsaturated Mo and S atoms, which is consistent with the published data. The calculated width of the forbidden band (0.85–0.98 eV) is comparable with the experimental value (1.30 eV) and similar to that obtained from DFT calculations with periodic boundary conditions (0.89 eV). The surface Mo centers in the Mo₁₂S₂₄ macromolecule are more reduced than the internal (Mo^IV) atoms. In order to characterize the adsorption capacity of coordinatively unsaturated Mo centers, a Mo₁₂S₂₄·6H₂S adsorption complex was calculated. The structure and energy characteristics of the adsorption complex point to a weak donor-acceptor interaction of the π-lone pair of H₂S molecule with the surface (reduced) Mo centers. The active center of thiophene hydrodesulfuration catalysts is formed as a result of the oxidative addition of hydrogen followed by occlusion of hydrogen into the MoS₂ matrix. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2189–2193, October, 2005.     

Chemical looping combustion characteristics of coal with Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> oxygen carrier

Chemical looping combustion (CLC) by direct use of coal as fuel is promising with its prominent advantages, but insufficient conversion of coal in the CLC system is a great limitation. In this research, in order to explore the limiting factor inherent for coal conversion in the CLC system, from the perspective of chemical structure of coal, reaction of a selected Chinese typical coal (designated as LZ) with Fe₂O₃ was systematically investigated. Thermogravimetric investigation of LZ coal reaction with Fe₂O₃ at the oxygen excess number Φ = 1.0 indicated that after dehydration, there existed three discernible reaction stages as observed, which were attributed to the combined reactions of Fe₂O₃ with the primary and secondary gaseous products evolved from LZ coal. Meanwhile, the Fe₂O₃ provided should be controlled around Φ = 1.0 aiming at effective conversion of LZ coal and simultaneous proper utilization of Fe₂O₃. And then, both gaseous Fourier transform infrared spectroscopy and energy-dispersive X-ray spectroscopy analysis of the gaseous and solid products formed from reaction of LZ coal with Fe₂O₃ at Φ = 1.0 indicated that full conversion of LZ coal was not reached with a little unconverted CO occurring, though partial Fe₂O₃ was over reduced to lower valence of oxides than Fe₃O₄. Furthermore, in order to explore the insufficient conversion of LZ coal at the molecular scale, X-ray photoelectron spectroscopy analysis revealed the distribution and evolution of the carbon functional groups involved in LZ coal after its reaction with Fe₂O₃ and further found that effective conversion of the aromatic/aliphatic C=C/C–H groups in LZ coal was the rate-limited step at the molecular scale with the relative content of these groups still dominated around 59% after LZ coal reaction with Fe₂O₃. Finally, solid IR (infrared) analysis and quantitative evaluation of the solid products of LZ coal reaction with Fe₂O₃ indicated that the length of aliphatic C–H groups decreased due to its partial disintegration, while the aromatization of the residual char was aggravated with the higher relative IR intensity ratio of the aromatic C=C groups, which reduced the reactivity of LZ residual char and hindered the full conversion of LZ coal.     

兖州煤大分子结构模型构建及其分子模拟

结合兖州煤的工业分析与元素分析及¹³C CP/MAS NMR实验结果构建了其大分子结构模型;芳香化合物以苯为主;脂肪结构以脂肪侧链、环烷烃和氢化芳环的形式存在,且甲基、亚甲基和次甲基的含量相当;17个氧原子分别以羧基、羰基与羟基型式存在;三个氮原子分别以吡啶与吡咯的形式存在;五个硫原子以噻吩型硫的型式存在。采用分子力学（MM）和分子动力学（MD）对兖州原煤化学结构模型进行能量最小化模拟,显示稳定大分子结构的主要能量按大小排序依次为范德华能、键扭转能、键角能与键伸缩能;分子内芳香层片之间的π－π相互作用,使其以近似平行的方式排列。量子化学半经验方法（AM1）模拟结果表明,羰基碳原子相连的C－C键的活性比较高;模型中与S相连的C原子、边缘C原子都有较多的负电荷,易于发生氧化反应,而芳香碳原子所带电荷较少,稳定性很高。
     

NMR 13C study of the structure of polyethyleneimine

The NMR ¹³C (CMR) spectrum of high molecular weight (M = 20,000) branched polyethyleneimine (PEI) obtained by polymerization of ethyleneimine (EI) in aqueous and alcoholic solutions at 50° with 1,3-dichloropropanol as initiator, contains 8 lines. The lines were identified using CMR spectra of model compounds, i.e. linear PEI, regularly branched PEI, diethylenetriamine and ethyleneimine pentamer. It has been shown that the deshielding effect of the nitrogen atoms on the α-atoms of carbon decreases in the folowing order: N_tert > N_sec > N_prim; with the atoms of carbon in the β-position, the effect increases in the opposite order.A quantitative estimation has been made of the distribution of the diads of elementary units containing the same and different nitrogen atoms. The data have been used to draw some conclusions about the structure of the PEI macromolecule.     

Two-dimensional molecular pattern in the structure of a calcium(II) complex with pyrazine-2,3-dicarboxylate and water ligands

The structure of di(aquo-O)(pyrazine-2,3-dicarboxylato-N,O; -O′,O′′) calcium(II) hydrate [Ca(2,3-PZDC)(H₂O)₂·;H₂O] contains molecular sheets in which Ca(II) ions are bridged by the carboxylate groups of the ligand molecules. Two bridging paths are evident. In the first, an N,O-bonding moiety formed by a hetero-ring nitrogen atom and the carboxylate oxygen atom nearest to it and both oxygen atoms of the second carboxylic group are active. The second path is formed by the other oxygen atom from the carboxylic group involved in the N,O-bonding moiety and an oxygen atom from the second carboxylic group. The latter atom is bidentate. A two-dimensional molecular pattern is formed. Each Ca(II) ion is also coordinated by two water oxygen atoms, making the number of coordinated atoms eight. The coordination polyhedron is a distorted pentagonal bipyramid with an oxygen atom at the apex on one side of the equatorial plane and two oxygen atoms forming the apices on the other side.     

Density-functional theory calculation on the nitrogen oxide reduction reaction with carbon monoxide on a titanium dioxide nanocluster

The density functional theory was used for simulation of the NO reduction reaction with carbon monoxide on a reduced Ti₈O₁₅ nanocluster. The reaction proceeds on oxygen vacancies formed via the removal of terminal or bridging O atoms. In the case of adsorption of two NO molecules of such sites, a stable adsorption complex with the bidentate ligand ‥ONNO is produced. When a CO molecule approaches one of the O atoms of this cycle, the following exothermic reaction yielding N₂ and CO₂ adsorbed on the Ti₈O₁₆ cluster takes place: 2NO+ CO + Ti₈O₁₅ → N₂+ Ti₈O₁₆ · CO₂. The proposed model of the reaction agrees well with experimental data.     

Surface Modification of Bituminous Coal and Its Effects on Methane Adsorption

This paper studied the role of O‐containing groups over the coal surface in methane adsorption. The coal was modified with H₂SO₄, (NH₄)₂S₂O₈ or H₂SO₄/(NH₄)₂S₂O₈), respectively, to introduce O‐containing functional groups, and characterized by proximate analysis, ultimate analysis, Boehm titration, X‐ray photoelectron spectroscopy (XPS) and nitrogen adsorption. The results of ultimate analysis, Boehm titration and XPS indicate that there were increases in terms of both the content of oxygen and the quantities of O‐containing groups over the modified coals surface, especially for the carboxyl. Nitrogen adsorption shows that the modified coals possessed higher surface area and pore volume than that of 0‐XQ. The methane adsorption data were measured at 298 K at pressures up to 4.0 MPa by the volumetric method and fitted well by Langmuir model. Experimental results implied that O‐containing groups and pore structure affected methane adsorption. The adsorption capacities decreased as increasing quantities of O‐containing groups.     

Structure of adsorption layers and conformation transformations of ethylhydroxyethylcellulose on surfaces of titanium and iron oxides

Regularities of the adsorption of ethylhydroxyethylcellulose (EHEC) hydrophilic polymer on a surface of inorganic pigments of TiO₂ and Fe₂O₃ were investigated by infrared spectroscopy. It was found that the adsorption interaction between EHEC and a surface of oxides is accompanied by conformation transformations of the adsorbed molecules of EHEC. The means by which macromolecules bind with active centers on a surface of metal oxides and the influence of the oxides’ nature on the EHEC macromolecule conformation transformations determining the structure of the adsorption layer upon adsorption were established.     

Estimation of Adsorption Capacity for Dissociating and Non Dissociating Aromatic Compounds on Activated Carbon with Different Models

The process of adsorption of two dissociating and two non-dissociating aromatic compounds from dilute aqueous solutions on an untreated commercially available activated carbon (B.D.H.) was investigated systematically. All adsorption experiments were carried out in pH controlled aqueous solutions. The experimental isotherms were fitted into four different models (Langmuir homogenous Models, Langmuir binary Model, Langmuir-Freundlich single model and Langmuir-Freundlich double model). Variation of the model parameters with the solution pH was studied and used to gain further insight into the adsorption process. The relationship between the model parameters and the solution pH and pK_a was used to predict the adsorption capacity in molecular and ionic form of solutes in other solution.A relationship was sought to predict the effect of pH on the adsorption systems and for estimating the maximum adsorption capacity of carbon at any pH where the solute is ionized reasonably well.N₂ and CO₂ adsorption were used to characterize the carbon. X-ray Photoelectron Spectroscopy (XPS) measurement was used for surface elemental analysis of the activated carbon.     

DFT and kinetics study of O/O2 mixtures reacting over a graphite (0001) basal surface

Spin-polarized density functional calculations were used to investigate the interaction of atomic and molecular oxygen on the basal graphite surface at several atomic coverages. Two carbon layers were enough to represent the graphite surface. Oxygen atoms bind mainly over C?CC bridge sites forming an epoxide-like structure with a two carbon puckering and with adsorption energies in the 0.95?C1.28?eV range, depending on the atomic coverage. Molecular oxygen only shows a very weak physisorption. Atomic adsorption and diffusion along with atomic recombination via Eley?CRideal and Langmuir?CHinshelwood mechanisms were studied. All surfaces processes were activated with energy barriers that decreased for lower atomic coverages. Relaxation effects were non-negligible. A microkinetic model with six elementary surface processes was proposed to see the overall behaviour of several initial O/O₂ mixtures flowing over a graphite surface at 300?C1,000?K. Thermal rate constants were derived from Density Functional Theory data and standard Transition State Theory. A very low steady-state atomic coverage (??_???<?0.5%) was predicted, and also very low atomic recombination coefficients were observed (??_O?<?5?×?10^?4). The Eley?CRideal together with the adsorption and desorption processes was much more important than the Langmuir?CHinshelwood reaction.     

Singlet Oxygen Induced Site-Specific Etching Boosts Nitrogen-Carbon Sites for High-Efficiency Oxygen Reduction

Targeted construction of carbon defects near the N dopants is an intriguing but challenging way to boost the electrocatalytic activity of N-doped carbon toward oxygen reduction reaction (ORR). Here, we report a novel site-specific etching strategy that features targeted anchoring of singlet oxygen (¹O₂) on the N-adjacent atoms to directionally construct topological carbon defects neighboring the N dopants in N-doped carbon (¹O₂−N/C). This ¹O₂−N/C exhibits the highest ORR half-wave potential of 0.915 V_RHE among all the reported metal-free carbon catalysts. Pyridinic-N bonded with a carbon pentagon of the neighboring topological carbon defects is identified as the primary active configuration, rendering enhanced adsorption of O₂, optimized adsorption energy of the ORR intermediates, and a significantly decreased total energy barrier for ORR. This ¹O₂-induced site-specific etching strategy is also applicable to different precursors, showing a tremendous potential for targeted construction of high-efficiency active sites in carbon-based materials.     

Molecular Dissociation on the SiC(0001) 3×3 Surface

In the framework of density functional theory, the adsorption of the halogenated polycyclic aromatic hydrocarbon 2,11‐diiodohexabenzocoronene (HBC‐I₂) on the SiC(0001) 3×3 surface has been investigated. Nondissociative and dissociative molecular adsorption is considered, and simulated scanning tunneling microscopy (STM) images are compared with the corresponding experimental observations. Calculations show that dissociative adsorption is favorable and reveal the crucial importance of the extended flat carbon core on molecule–surface interactions in dissociative adsorption; the iodine atom–surface interaction is of minor importance. Indeed, removing iodine atoms does not significantly affect the STM images of the central part of the molecule. This study shows that the dissociation of large halogenated polycyclic aromatic hydrocarbon molecules can occur on the SiC surface. This opens up interesting perspectives in the chemical reactivity and functionalization of wide band gap semiconductors.