Theoretical study of the adsorption of CO2 on tungsten carbide nanotubes

The adsorption of CO₂ on the single-walled tungsten carbide nanotubes has been investigated employing density functional theory method. The center of a hexagon of tungsten and carbon atoms in sites on tungsten carbide nanotube surfaces is the most stable adsorption site for CO₂ molecule, with a binding energy of −1.68 eV (−38.72 kcal/mol) and a WO binding distance of 1.95 Å. Furthermore, the adsorption of CO₂ on the single-walled carbon nanotubes has been investigated. Our first-principles calculations predict that the CO₂ adsorptive capacity of tungsten carbide nanotubes is about quadruple that of carbon nanotubes. This might have potential for greenhouse gas detection and bioremediation.     

Synthesis and CO2 capture property of high aspect-ratio Li2ZrO3 nanotubes arrays

High aspect-ratio Li₂ZrO₃ nanotubes were prepared by hydrothermal method using ZrO₂ nanotubes layers as templates. Characterizations of SEM, XRD, TEM and CO₂ adsorption were performed. The results showed that tetragonal Li₂ZrO₃ nanotubes arrays containing a little monoclinic ZrO₂ can be obtained using this simple method. The mean diameter of the nanotubes is approximately 150 nm and the corresponding specific surface area is 57.9 m² g⁻¹. Moreover, the obtained Li₂ZrO₃ nanotubes were thermally analyzed under a CO₂ flow to evaluate their CO₂ capture property. It was found that the as-prepared Li₂ZrO₃ nanotubes arrays would be an effective acceptor for CO₂ at high temperature.     

Sims studies of the adsorption of O2, CO and CO2 on titanium using low primary energies

The influence of the adsorption of O₂, CO and CO₂ on secondary ion yields from titanium has been examined using 500 eV primary argon ions. Secondary ion energy distributions were also measured. Electron-induced desorption was used as an auxiliary technique. For oxygen adsorption there is agreement with measurements using other techniques and the adsorption process is shown to occur in two stages, an initial rapid chemisorption regime followed by an oxide regime. For carbon monoxide adsorption, the measurements suggest that dissociation does not occur significantly at room temperature. For CO₂, the results are more complex. Complete dissociation seems unlikely but there may be partial dissociation. Some tentative generalizations are made concenrning the influence of adsorption on secondary ion yields.     

Adsorption of CO, CO2 and NO molecules on a BaTiO3 (0 0 1) surface

Since the development of Scanning Tunnelling Microscopy (STM) technique, considerable attention has been devoted to various molecules adsorbed on various surfaces. Also, a new concept emerged with molecules on surfaces considered as nano machines by themselves. In this context, a thorough knowledge of surfaces and adsorbed molecules at an atomic scale are thus particularly invaluable. The present work describes the first Density Functional Theory (DFT) study of adsorption of CO, CO₂ and NO molecules on a BaTiO₃ surface following a first preliminary calculation of O and O₂ adsorption on the same surface. In the previously considered work, we found that a (0 0 1) surface with BaO termination is more stable than the one with TiO₂-termination. Consequently, we extended our study to CO, CO₂ and NO molecules adsorbed on a (0 0 1) surface with BaO termination. The present calculation was performed on a (1 × 1) cell with one monolayer of adsorbed molecules. Especially, a series of cases implying CO molecules adsorbed in various geometrical configurations has been examined. The corresponding adsorption energy varies in the range of −0.17 to −0.10 eV. The adsorption energy of a CO₂ molecule directly located above an O surface atom (called O_s) is of the order of −0.18 eV. The O-C distance length is then 1.24 Å and the O-C-O and O-C-O_s angles are 134.0° and 113.0°, respectively. For NO adsorption, the most important induced structural changes are the followings: (i) the N-O bond is broken when a NO molecule is absorbed on a Ba-O_s bridge site. In that case, N and O atoms are located above an O and a Ba surface atom, respectively, whereas the O-Ba-O_s and N-O_s-Ba angles are 106.5° and 63.0°, respectively. The N-O distance is as large as 2.58 Å and the adsorption energy is as much as −2.28 eV. (ii) In the second stable position, the NO molecule has its N atom adsorbed above an O_s atom, the N-O axis being tilted toward the Ba atom. The N-O_s-Ba angle is then 41.1° while the adsorption energy is only −0.10 eV. At last, the local densities of states around C, O as well as N atoms of the considered adsorbed molecules have also been discussed.     

First-principles study on the catalytic role of Ag in the oxygen adsorption of LaMnO3(0 0 1) surface

In the present paper, the catalytic role of Ag in the oxygen adsorption of LaMnO₃(0 0 1) surface has been theoretically investigated using first-principles calculations based on the density functional theory (DFT) and pseudopotential method. The O₂ adsorption energy is larger for the vertical adsorption and the covalent bond was formed between O₂ molecule and surface Mn. The calculation of electronic properties of interaction between Ag atom and LaMnO₃(0 0 1) surface demonstrates that the most stable position for Ag adsorption is hollow site. The O₂ adsorption energy dramatically increased from 0.298 eV to 1.108 eV due to Ag pre-adsorbed. It is Ag pre-adsorbed that facilitates O₂ adsorption on surface. The bond length and bond population of O₂ molecule indicate that Ag atom facilitates O₂ molecule dissociative adsorption. The Ag atom strengthens LaMnO₃(0 0 1) substrate activity and activity center was formed on surface, which enhances the electrocatalytic activity of LaMnO₃ as solid oxide fuel cells cathode material at low temperature.     

Particle imaging of ignition and devolatilization of pulverized coal during oxy-fuel combustion

Oxy-fuel combustion of coal is a promising technology for cost-effective power production with carbon capture and sequestration that has ancillary benefits of emission reductions and lower flue gas cleanup costs. To fully understand the results of pilot-scale tests of oxy-fuel combustion and to accurately predict scale-up performance through CFD modeling, fundamental data are needed concerning coal and coal char combustion properties under these unconventional conditions. In the work reported here, the ignition and devolatilization characteristics of both a high-volatile bituminous coal and a Powder River Basin subbituminous coal were analyzed in detail through single-particle imaging at a gas temperature of 1700 K over a range of 12–36 vol % O₂ in both N₂ and CO₂ diluent gases. The bituminous coal images show large, hot soot cloud radiation whose size and shape vary with oxygen concentration and, to a lesser extent, with the use of N₂ versus CO₂ diluent gas. Subbituminous coal images show cooler, smaller emission signals during devolatilization that have the same characteristic size as the coal particles introduced into the flow (nominally 100 μm). The measurements also demonstrate that the use of CO₂ diluent retards the onset of ignition and increases the duration of devolatilization, once initiated. For a given diluent gas, a higher oxygen concentration yields shorter ignition delay and devolatilization times. The effect of CO₂ on coal particle ignition is explained by its higher molar specific heat and its tendency to reduce the local radical pool. The effect of O₂ on coal particle ignition results from its effect on the local mixture reactivity. CO₂ decreases the rate of devolatilization because of the lower mass diffusivity of volatiles in CO₂ mixtures, whereas higher O₂ concentrations increase the mass flux of oxygen to the volatiles flame and thereby increase the rate of devolatilization.     

Ammonia modification of activated carbon to enhance carbon dioxide adsorption: Effect of pre-oxidation

A commercial granular activated carbon (GAC) was subjected to thermal treatment with ammonia for obtaining an efficient carbon dioxide (CO₂) adsorbent. In general, CO₂ adsorption capacity of activated carbon can be increased by introduction of basic nitrogen functionalities onto the carbon surface. In this work, the effect of oxygen surface groups before introduction of basic nitrogen functionalities to the carbon surface on CO₂ adsorption capacity was investigated. For this purpose two different approaches of ammonia treatment without preliminary oxidation and amination of oxidized samples were studied. Modified carbons were characterized by elemental analysis and Fourier Transform Infrared spectroscopy (FT-IR) to study the impact of changes in surface chemistry and formation of specific surface groups on adsorption properties. The texture of the samples was characterized by conducting N₂ adsorption/desorption at −196 °C. CO₂ capture performance of the samples was investigated using a thermogravimetric analysis (TGA). It was found that in both modification techniques, the presence of nitrogen functionalities on carbon surface generally increased the CO₂ adsorption capacity. The results indicated that oxidation followed by high temperature ammonia treatment (800 °C) considerably enhanced the CO₂ uptake at higher temperatures.     

Auger electron spectroscopic study of CO2 adsorption on Zircaloy-4 surfaces

We investigate the adsorption of CO₂ onto Zircaloy-4 (Zry-4) surfaces at 150, 300 and 600 K using Auger electron spectroscopy (AES). Following CO₂ adsorption at 150 K the graphitic form of carbon is detected, whereas upon chemisorption at 300 and 600 K we detect the carbidic phase. As the adsorption temperature is increased, the carbon Auger signal increases, whereas the oxygen signal decreases. Adsorption at all three temperatures results in a shift of the Zr Auger features, indicating surface oxidation. The effect of adsorbed CO₂ on the Zr(MVV) and Zr(MNV) transitions depends on adsorption temperature and is less pronounced at higher temperatures. On the other hand, changes in the Zr(MNN) feature are similar for all three adsorption temperatures. The changes in the Zr Auger peak shapes and positions are attributed to oxygen from dissociated CO₂, with the differences observed at various temperatures indicative of the diffusion of oxygen into the subsurface region.     

B12N12纳米笼：潜在的二氧化氮检测传感器

利用密度泛函理论通过计算吸附能量、HOMO/LUMO能隙变化、电荷转移、结构扭曲等研究二氧化氮分子在B12N12纳米笼的吸附．此外,通过计算B₁₂N₁₂的电子结合能、Gibbs自由能、态密度和分子表面的静电势研究其稳定性和其它特性．B₁₂N₁₂纳米笼吸附二氧化氮显示三种构型．B₁₂N₁₂团簇的HOMO/LUMO能隙变化对二氧化氮分子的存在非常敏感,从自由团簇的6.84 eV降为NO₂/团簇稳定团簇的3.23 eV．团簇的导电性被极大地提高,表明B₁₂N₁₂纳米簇可能是潜在的二氧化氮气体分子检测传感器.     

Nitrogen release during reaction of coal char with O2, CO2, and H2O

The chemistry of char-N release and conversion to nitrogen-containing products has been probed by studying its release and reactions with O₂, CO₂, and H₂O. The experiments were performed in a fixed bed flow reactor at pressures of up to 1.0 MPa. The results show that the major nitrogen-containing products observed depend on the reactant gas; with O₂, NO, and N₂ being the major species observed. Char-N reaction with CO₂ produces N₂ with very high selectivity over a broad range of pressures and CO₂ concentrations, and reaction with H₂O gives rise to HCN, NH₃, and N₂. Observed distributions of nitrogen-containing products are little affected by pressure when O₂ and CO₂ are the reactant gases, but increasing pressures in the reaction with H₂O results in the formation of increasing proportions of NH₃. Formation of NH₃ is also promoted by increasing concentrations of H₂O in the feed gas. The results suggest that NO and HCN are primary products when O₂ and H₂O, respectively, are used as the reactant gases, and that the other observed products arise from interactions of these primary products with the char surface.     

Ignition and devolatilization of pulverized bituminous coal particles during oxygen/carbon dioxide coal combustion

Oxygen/carbon dioxide recycle coal combustion is actively being investigated because of its potential to facilitate CO₂ sequestration and to achieve emission reductions. In the work reported here, the effect of enhanced oxygen levels and CO₂ bath gas is independently analyzed for their influence on single-particle pulverized coal ignition of a U.S. eastern bituminous coal. The experiments show that the presence of CO₂ and a lower O₂ concentration increase the ignition delay time but have no measurable effect on the time required to complete volatile combustion, once initiated. For the ignition process observed in the experiments, the CO₂ results are explained by its higher molar specific heat and the O₂ results are explained by the effect of O₂ concentration on the local mixture reactivity. Particle ignition and devolatilization properties in a mixture of 30% O₂ in CO₂ are very similar to those in air.     

DC discharge experiment in an Ar/N2/CO2 ternary mixture: A laboratory simulation of the Martian ionosphere's plasma environment

A low-pressure DC plasma discharge sustained in a 1.6%Ar–2.7%N₂–95.3%CO₂ ternary mixture is studied. This plasma was generated in a total pressure range from 1.0 to 4.0 Torr, a power of 6.3 W and a 12 l/min flow rate of gases. The electron temperature was found to be 8.41 eV and the ion density, in the order of 10⁹ cm⁻³. The species observed in the plasma mixture were CO₂, CO₂⁺, CN, CO, CO⁺, O₂, O₂⁺, N₂, N₂⁺, NO, C⁺, Ar and Ar⁺. At the pressure range in the present study, the species observed do not change their intensity due to an increase in the pressure and they separate in two groups according to their emission intensity: the band of the first group (CO₂, CO₂⁺ and CN) is approximately a factor of 3 more intense than that of the second group (CO, CO⁺, O₂, O₂⁺, N₂, N₂⁺, NO, C⁺, Ar and Ar⁺). The behavior of the emission intensities may be correlated to the constant ion density and electron temperature measured. Also, we observed the same constant behavior in the ratios of the neutral and positive species intensities to that of the N₂ intensity, as a function of pressure. This may suggest that the different rate coefficients and cross sections of elastic collision, excitation and de-excitation of electronic or vibrational levels, inelastic and superelastic collisions of electrons with the gas phase and products, neutral–neutral interactions, resonant charged transfer processes, recombination, to mention some, to produce these species change in the same proportion, as a function of the pressure to keep the relative ratios of the species almost constant.     

Density-functional study of CO adsorbed on RhN （N = 2-19） clusters

We investigate the structural, electronic and adsorption properties of one single CO molecule adsorbed on Rh_N (N = 2-19) clusters, using the density-functional theory in the spin-polarized generalized gradient approximation. It is found that the structural growth model of the Rh_N clusters transforms from double layers (N = 12-16) to three layers (N = 17-19). Three different adsorption types are the atop site adsorption for N = 6, 8, 9, 11, 12, the bridge site adsorption for N = 2-5, 7, 10, 13-15, 17 and the face adsorption for N = 16, 18, 19. The adsorption abilities of Rh_N clusters are related to C-O bond length, vibrational frequency, adsorption energy and the charge transfer between CO and Rh clusters as well as the electronic density of state. With the increase of Rh cluster size, the adsorption energy of CO adsorbed on Rh_N clusters tends to be 2.2 eV-2.3 eV, which is 0.2 eV-0.3 eV larger than the theoretical value (about 2.0 eV) of CO molecule adsorption on clean Rh (111) surface.     

H2O2 adsorption on the BN and SiC nanotubes: A DFT study

We have performed a comparative density functional theory study on adsorption of hydrogen peroxide (H₂O₂) on the boron nitride and silicon carbide nanotubes (BNNT and SiCNT) in terms of energetic, geometric, and electronic properties. It has been found that the molecule is chemically adsorbed on both of the tubes so that its interaction with SiCNT (adsorption energy ∼−0.97 eV) is much stronger than that with BNNT (adsorption energy ∼−0.47 eV). The H₂O₂ adsorption on BNNT slightly decreases its work function, increasing the field electron emission from the BNNT surface while it may not affect that of the SiCNT. In addition, the adsorption process may increase the electrical conductivity of SiCNT while does not affect that of the BNNT, significantly. We believe that the SiCNT may be a potential candidate for detection of H₂O₂.     

Line-mixing and collision induced absorption for O2–CO2 mixtures in the oxygen A-band region

The absorption by O₂–CO₂ mixtures in the region of the oxygen A-band near 760 nm has been measured in the laboratory at room temperature and for total pressures up to about 80 atm. As done in our previous studies for O₂–N₂ mixtures the contribution of the “allowed” A-band transitions have been calculated both accounting for line-mixing effects and disregarding this process. The differences between computed spectra and measured values enable extraction of the collision induced absorption (CIA) contribution, which, after removal of the O₂–O₂ contribution, provides, for the first time, the O₂–CO₂ CIA. It is shown that neglecting line-mixing overestimates absorption in the wings and underestimates absorption at the P and R branch peaks, and that the O₂–CO₂ CIA has an integrated intensity, in the A-band region, about 1.5 times larger than that of for pure O₂ and almost 10 times greater than for O₂–N₂.     

Selectively strong molecular adsorption on boron nitride monolayer induced by transition metal substrate

We studied adsorption of several molecules (CO, CO₂, H₂O, N₂O, NO, NO₂, and O₂) on hexagonal boron nitride (h-BN) monolayers supported on transition metal (TM) surfaces, using density functional calculations. We observed that all the molecules bind very weakly on the pristine h-BN, with binding energies in the range of 0.02–0.03 eV. Interestingly, however, when h-BN is supported on the TM surface, NO₂ and O₂ become strongly chemisorbed on h-BN, with binding energies of >1 eV, whereas other molecules still physisorbed, with binding energies of ～0.1 eV at most. The electron transfer from TM to p_z states of h-BN played a substantial role in such strong bindings of NO₂ and O₂ on h-BN, as these molecules possess unpaired electrons that can interact with p_z states of h-BN. Such selective molecular binding on h-BN/TM originates from the peculiar distribution of the spin-polarized highest occupied and lowest unoccupied molecular orbitals of NO₂ and O₂. Strong molecular adsorption and high selectivity would make the h-BN/TM system possible for a variety of applications such as catalysts and gas sensors.     

利用电化学微分质谱在燃料电池的阴极研究碳载体的氧化

利用电化学微分质谱,在双薄层流动电解池中,通过检测二氧化碳产物的信号研究氧气与铂纳米粒子对碳载体氧化机理与动力学的影响．研究发现,碳载体可以在不同的电位区间内被氧化;氧气可以加速碳的氧化,在相同的电位下碳氧化生成二氧化碳产物的速率在氧气饱和溶液中是在氮气饱和溶液中的两倍;铂纳米粒子可以催化碳的氧化,在碳电极上,担载的铂纳米粒子可以大大降低碳氧化的过电势．讨论了铂与氧气促进碳氧化的机理．     

A density functional theory study on the adsorption of CO and O2 on Cu-terminated Cu2O （111） surface

The adsorptions of CO and 02 molecules individually on the stoichiometric Cu-terminatcd Cu20 （111） surface are investigated by first-principles calculations on the basis of the density functional theory. The calculated results indicate that the CO molecule preferably coordinates to the Cu2 site through its C atom with an adsorption energy of-1.69 eV, whereas the 02 molecule is most stably adsorbed in a tilt type with one O atom coordinating to the Cu2 site and the other O atom coordinating to the Cul site, and has an adsorption energy of -1.97 eV. From the analysis of density of states, it is observed that Cu 3d transfers electrons to 2π orbital of the CO molecule and the highest occupied 5σ orbital of the CO molecule transfers electrons to the substrate. The sharp band of Cu 4s is delocalized when compared to that before the CO molecule adsorption, and overlaps substantially with bands of the adsorbed CO molecule. There is a broadening of the 2π orbital of the 02 molecule because of its overlapping with the Cu 3d orbital, indicating that strong 3d-2π interactions are involved in the chemisorption of the 02 molecule on the surface.     

微弧等离子喷涂碳纳米管/纳米Al2O3-TiO2复合涂层的吸波性能研究

将碳纳米管与纳米Al₂O₃-TiO₂陶瓷粉末超声共混制备了碳纳米管/纳米Al₂O₃-TiO₂复合粉末,测试了复合粉末在2—18GHz波段的电磁参数.研究表明：随着碳纳米管质量分数的增加,碳纳米管/纳米Al₂O₃-TiO₂复合粉末的复介电常数和损耗角不断增大.当碳纳米管质量分数和厚度增加时,复合粉末对电磁波的反射率峰值先增加后减小,而谐振频率不断向低频移动.采用微弧等离子喷涂制备了7wt%碳纳米管/纳米Al₂O₃-TiO₂复合吸波涂层,当厚度为1.5mm时,涂层最小反射率为-24.0dB,当厚度为2.0mm时,涂层小于-10dB的频带宽为3.60GHz,当温度为500℃高温时,1.0mm厚的涂层最小高温反射率为-12.2dB,小于-10dB频带宽为2.0GHz.复合涂层的实际厚度D与理论厚度d呈线关系：d=0.898D+0.515. 关键词： 等离子喷涂 碳纳米管 2O₃-TiO₂')" href="#">纳米Al₂O₃-TiO₂ 吸波性能     

Adsorption of small molecules on transition metal doped rhodium clusters Rh3X (X = 3d, 4d atom): a first-principles investigation

The adsorption behaviours of seven molecules (CO, CO₂, N₂, NO, O₂, N₂O and NO₂) on Rh₃X (X?=Sc-Zn, Y-Cd) clusters are systematically investigated by density-functional calculations. Rh₃X clusters exhibit physical adsorption when interacting with CO₂, CO, N₂ and NO. The adsorption energies (E_ads) can be ranked as follows: NO?>?CO?>?CO_2?≥?N₂. Compared with pure Rh₄ cluster, the adsorption capacity changes with the doping element. Chemical adsorption can be obtained for Rh₃X when adsorbing O₂, N₂O and NO₂. E_ads shows an order of E_ads(O₂)?>?E_ads(NO₂)?>?E_ads(N₂O). When O₂ is adsorbed, energy barrier with doping Tc or Cr atom is substantially reduced, which indicates that chemical reactivity of O₂ on Rh₄ can be significantly enhanced. The doped rhodium clusters can be viewed as good candidates in the discrimination between different gas molecules.