The adsorption of CO,H2, H2, CO2 and H2O on carburized and graphitized Ni(110)

A study of the adsorption/desorption behavior of CO, H₂O, CO₂ and H₂ on Ni(110)(4 × 5)-C and Ni(110)-graphite was made in order to assess the importance of desorption as a rate-limiting step for the decomposition of formic acid and to identify available reaction channels for the decomposition. The carbide surface adsorbed CO and H₂O in amounts comparable to the clean surface, whereas this surface, unlike clean Ni(110), did not appreciably adsorb H₂. The binding energy of CO on the carbide was coverage sensitive, decreasing from 21 to 12 $\text{kcal}\text{mol}$ as the CO coverage approached 1.1 × 10¹⁵ molecules cm^?2 at 200K. The initial sticking probability and maximum coverage of CO on the carbide surface were close to that observed for clean Ni(110). The amount of H₂, CO, CO₂ and H₂O adsorbed on the graphitized surface was insignificant relative to the clean surface. The kinetics of adsorption/desorption of the states observed are discussed.     

Evidence for bicarbonate formation on vacuum annealed TiO2(110) resulting from a precursor-mediated interaction between CO2 and H2O

The reaction of CO₂ and H₂O to form bicarbonate (HCO⁻₃) was examined on the nearly perfect and vacuum annealed surfaces of TiO₂(110) with temperature programmed desorption (TPD), static secondary ion mass spectrometry (SSIMS) and high resolution electron energy loss spectrometry (HREELS). The vacuum annealed TiO₂(110) surface possesses oxygen vacancy sites that are manifested in electronic EELS by a loss feature at 0.75 V. These oxygen vacancy sites bind CO₂ only slightly more strongly (TPD peak at 166 K) than do the five-coordinated Ti⁴⁺ sites (TPD peak at 137 K) typical of the nearly perfect TiO₂(110) surface. Vibrational HREELS indicates that CO₂ is linearly bound at the latter sites with a ν_a(OCO) frequency similar to the gas phase value. In contrast, oxygen vacancies dissociate H₂O to bridging OH groups which recombine to liberate H₂O in TPD at 490 K. No evidence for a reaction between CO₂ and H₂O is detected on the nearly perfect surface. In sequentially dosed experiments on the vacuum annealed surface at 110 K, CO₂ adsorption is blocked by the presence of preadsorbed H₂O, adsorbed CO₂ is displaced by postdosed H₂O, and there is little or no evidence for bicarbonate formation in either case. However, when CO₂ and H₂O are simultaneously dosed, a new CO₂ TPD state is observed at 213 K, and the 166 K state associated with CO₂ at the vacancies is absent. SSIMS was used to tentatively assign the 213 K CO₂ TPD state to a bicarbonate species. The 213 K CO₂ TPD state is not formed if the vacancy sites are filled with OH groups prior to simultaneous CO₂+H₂O exposure. Sticking coefficient measurements suggest that CO₂ adsorption at 110 K is precursor-mediated, as is known to be the case for H₂O adsorption on TiO₂(110). A model explaining the circumstances under which the proposed bicarbonate species is formed involves the surface catalyzed conversion of a precursor-bound H₂O–CO₂ van der Waals complex to carbonic acid, which then reacts at unoccupied oxygen vacancies to generate bicarbonate, but falls apart to CO₂ and H₂O in the absence of these sites. This model is consistent with the conditions under which bicarbonate is formed on powdered TiO₂, and is similar to the mechanism by which water catalyzes carbonic acid formation in aqueous solution.     

O2、 CO2和H2O在UN(001)表面化学吸附的密度泛函理论研究

采用广义梯度近似GGA,修正Perdew-Burke-Ernzerhof交换-关联泛函,以及周期性切片模型对O₂、CO₂和H₂O在UN(001)表面的化学吸附行为进行非自旋极化水平的密度泛函理论计算. 在四个对称性化学位置条件下,对化学吸附能与分子和UN(001)表面之间距离的关系曲线进行优化. 结果表明O₂、CO₂和H₂O分子的最稳定吸附位置分别为桥式平行、空心平行和桥式H     

H2/Air/CO2点火过程中的热辐射和化学反应效应

本文采用基于详细化学反应机理的化学反应流自适应数值模拟技术,研究了添加二氧化碳对氢气/空气预混气体点火的影响,获得了不同当量比下最小点火能随稀释率的变化情况。本文引入最小点火能的热辐射敏感度与化学反应敏感度,重点分析了CO₂的热辐射效应和化学反应效应对最小点火能的影响。研究结果表明二氧化碳的热辐射效应和化学反应效应只有在接近极限稀释率时才会导致最小点火能有显著升高。     

Some aspects of CO2 laser induced fluorescence in SF6−H2 mixtures

Measurements in SF₆?H₂ mixtures of HF¹ fluorescence at 2.8 μm induced by pulsed CO₂ laser radiation are reported. The dependence of fluorescence intensity on laser fluence is found to be strongly affected by the laser beam geometry in the interaction region. Our results show that the technique of HF¹ fluorescence intensity detection can be a sensitive and reliable single-shot measure of multiple-photon dissociation of SF₆ in a collisionless regime on condition that the laser fluence is uniform along the interaction region which is monitored.     

RHEED and Auger study of the MoO3(010) surface interaction with H2S/H2 mixture and pure H2S

Pure single crystals of MoO₃ were carefully grown by physical vapor transport. The initial stages of the interaction of H₂S with a MoO₃ (010) surface were studied by RHEED and AES at low pressure p <133 Pa and at T < 700 K. Three main stages were found: (a) The formation of either a completely disordered sulphur adiayer (with pure H₂S) or a superstructure MoO₃(010)-[2 × 1]S (with H₂S/H₂). (b) A reduction of MoO₃ producing oriented three-dimensional MoO₂ islands, (c) An epitaxial overgrowth of MoS₂ from the MoO₂ three-dimensional crystallites.     

Microwave linewidths of C2H4O perturbed by H2, N2, O2 and CO2

Microwave linewidths of C₂H₄O (κ = -0.41) broadened by H₂, N₂, O₂, and CO₂ and considering dipole-quadrupole interactions have been calculated using the Mehrotra-Boggs theory (1977). This theory accounts satisfactorily for observed linewidths     

Oxidation of H2/CO2 mixtures and effect of hydrogen initial concentration on the combustion of CH4 and CH4/CO2 mixtures: Experiments and modeling

An experimental investigation of the oxidation of hydrogen diluted by nitrogen in presence of CO₂ was performed in a fused silica jet-stirred reactor (JSR) over the temperature range 800-1050 K, from fuel-lean to fuel-rich conditions and at atmospheric pressure. The mean residence time was kept constant in the experiments: 120 ms at 1 atm and 250 ms at 10 atm. The effect of variable initial concentrations of hydrogen on the combustion of methane and methane/carbon dioxide mixtures diluted by nitrogen was also experimentally studied. Concentration profiles for O₂, H₂, H₂O, CO, CO₂, CH₂O, CH₄, C₂H₆, C₂H₄, and C₂H₂ were measured by sonic probe sampling followed by chemical analyses (FT-IR, gas chromatography). A detailed chemical kinetic modeling of the present experiments and of the literature data (flame speed and ignition delays) was performed using a recently proposed kinetic scheme showing good agreement between the data and this modeling, and providing further validation of the kinetic model (128 species and 924 reversible reactions). Sensitivity and reaction paths analyses were used to delineate the important reactions influencing the kinetic of oxidation of the fuels in absence and in presence of additives (CO₂ and H₂). The kinetic reaction scheme proposed helps understanding the inhibiting effect of CO₂ on the oxidation of hydrogen and methane and should be useful for gas turbine modeling.     

Experimental and numerical investigation of hetero-/homogeneous combustion of CO/H2/O2/N2 mixtures over platinum at pressures up to 5 bar

The hetero-/homogeneous combustion of fuel-lean CO/H₂/O₂/N₂ mixtures over platinum is investigated at pressures up to 5 bar, inlet temperatures (T_IN) up to 874 K, and a constant CO:H₂ molar ratio of 2:1. Experiments are performed in an optically accessible channel-flow catalytic reactor and involve planar laser induced fluorescence (LIF) of the OH radical for the assessment of homogeneous (gas-phase) ignition and 1-D Raman measurements of major gas-phase species concentrations over the catalyst boundary layer for the evaluation of the heterogeneous (catalytic) processes. Simulations are carried out with an elliptic 2-D model that includes detailed heterogeneous and homogeneous chemical reaction schemes. The predictions reproduce the Raman-measured catalytic CO and H₂ consumption, and it is further shown that for wall temperatures in the range 975 ? T_w ? 1165 K the heterogeneous pathways of CO and H₂ are largely decoupled. However, for wall temperatures below a limiting value of 710–720 K and for the range of pressures and mixture preheats investigated, CO(s) blockage of the surface inhibits the catalytic conversion of both fuel components. The homogeneous ignition distance is well-reproduced by the model for T_IN > 426 K, but it is modestly overpredicted at lower T_IN. Possible reasons for these modest differences can be the values of third body efficiencies in the gas-phase reaction mechanism. The sensitivity of homogeneous ignition distance on the catalytic reactions is weak, while the H₂/O₂ subset of the CO/H₂/O₂ gaseous reaction mechanism controls the onset of homogeneous ignition. Pure hydrogen hetero-/homogeneous combustion results in flames established very close to the catalytic walls. However, in the presence of CO the gaseous combustion of hydrogen extends well-inside the channel core, thus allowing homogeneous consumption of H₂ at considerably shorter reactor lengths. Finally, implications of the above findings for the design of syngas-based catalytic reactors for power generation systems are discussed.     

Reduced Brillouin backscatter in CO2 laser-target interaction

Substantially reduced Brillouin reflection has been found for CO₂ laser irradiated high density gas targets. In contrast to high reflectivity (60%) previously observed for underdense hydrogen plasma, total backscatter (stimulated plus specular) is found to peak at 30% for incident intensity 5 × 10¹² W/cm² and decrease thereafter to 18% at 10¹³ W/cm². Ponderomative effects are postulated to account for these observations.     

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.     

Total cross sections for scattering of electrons from O2, H2O, H2, O3, CO and CO2 at 100－2000eV

A complex optical model potential rewritten by the concept of bonded atom, which considers the overlap of electron clouds, is employed to calculate the total cross sections for electron scattering from several simple molecules (O_2, H_2O, H_2, O_3, CO and CO_2) consisting of C, H and O atoms in an incident energy range of 100－2000eV by the use of the additivity rule at Hartree－Fock level. In the study, the complex optical potential composed of static, exchange, correlation polarization plus absorption contributions firstly uses the bonded-atom concept. The quantitative molecular total cross section results are compared with experimental data and with the other calculations wherever available and good agreement is obtained. It is shown that the additivity rule along with the complex optical model potential rewritten by the concept of bonded atom can be used successfully to calculate the total cross section of electron－molecule scattering above 100eV, whereas the rule together with the complex optical model potential not rewritten by the concept of bonded atom is only successfully used above 300－500eV. So, the introduction of the bonded-atom concept in the complex optical potential can improve the accuracy of the total cross section calculations.     

The fluorescence and IR energy deposition from from CO2 laser irradiation of SF6−H2 mixtures

The multiple photon excitation and dissociation of SF₆ and hydrogen mixtures is measured by using simultaneously pulsed optoacoustic detection to monitor the energy deposition and time resolved HF fluorescence to monitor the production of vibrationally hot HF. From these studies we deduce that at least three mechanisms lead to production of vibrationally excited HF. One mechanism produces free F from the unimolecular laser-induced decomposition of SF₆. The second mechanism involves the reaction between two vibrationally hot SF₆ molecules to produce free F. In both of these cases the F atom subsequently react with H₂ to produce vibrationally hot HF. The third involves the reaction between a vibrationally hot SF₆ molecule and a hydrogen molecule producing vibrationally hot HF directly.     

Collision-induced simultaneous transitions in H2+CF4 and H2+SF6 mixtures

The simultaneous transitions of the v₃ fundamental vibrations of CF₄ and SF₆ with the fundamental Q branch and S(1) line of H₂ have been studied for various H₂+CF₄ and H₂+SF₆ mixtures at total pressures up to 185 bars. The integrated intensities are found to be proportional to the partial densities of the gas mixture components. The agreement between experimental and calculated intensities is generally better for the Kihara potential than for the Lennard-Jones potential.     

CO2/H2O混合气体在水平管外凝结换热与分离特性研究

本文通过实验研究了CO₂质量分数为11.39%~70.95%,壁面过冷度为5~25 K,总压力为5~15 kPa的CO₂/H₂O混合气体自然对流条件下在水平管外的凝结换热规律,结果表明CO₂/H₂O的凝结换热系数随CO₂含量和壁面过冷度的增大而降低,但随总压力的增大而增大。根据实验结果建立了新关联式,将关联式应用到凝汽器的设计计算与分析,且对凝汽器进行了分离特性和经济性分析。     

Linewidths of HCl broadened by CO2 and N2 and CO broadened by CO2

High resolution measurement of the linewidths of HCl broadened by CO₂ and N₂ and CO broadened by CO₂ have been performed in both the 1-0 and 2-0 bands of HCl and the 2-0 band of CO. The data were analyzed by the direct and the peak absorption methods. Values of the linewidths obtained by the two methods are in good agreement. For |m| ≤ 3, for the case of HCl + CO₂, the agreement is good for the values obtained in both bands of HCl. However for |m| > 3, the HCl + CO₂ linewidths in the 1-0 band are smaller than the corresponding lines in the 2-0 band by as much as 11% for |m| = 9. Lines (|m| ≤ 3) of the 1-0 and 2-0 bands of HCl broadened by CO₂ were also analyzed in terms of the super-Lorentzian line profile proposed by Varanasi, S. K. Sarangi, and G. D. T. Tejwani (J. Quan. Spectr. Radiative Transfer12, 857 (1972)) and the Lorentzian profile. The results indicate that near the line center (within 3γ), the shape of HCl + CO₂ lines are Lorentzian.     

Co-electrolysis of CO2 and H2O in solid oxide cells: Performance and durability

This study examines the initial performance and durability of a solid oxide cell applied for co-electrolysis of CO₂ and H₂O. Such a cell, when powered by renewable/nuclear energy, could be used to recycle CO₂ into sustainable hydrocarbon fuels. Polarization curves and electrochemical impedance spectroscopy were employed to characterize the initial performance and to break down the cell resistance into the resistance for the specific processes occurring during operation. Transformation of the impedance data to the distribution of relaxation times (DRT) and comparison of measurements taken under systematically varied test conditions enabled clear visual identification of five electrode processes that contribute to the cell resistance. The processes could be assigned to each electrode and to gas concentration effects by examining their dependence on gas composition changes and temperature.This study also introduces the use of the DRT to study cell degradation without relying on a model. The durability was tested at consecutively higher current densities (and corresponding overpotentials). By analyzing the impedance spectra before and after each segment, it was found that at low current density operation (− 0.25 A/cm² segment) degradation at the Ni/YSZ electrode was dominant, whereas at higher current densities (− 0.5 A/cm² and − 1.0 A/cm²), the Ni/YSZ electrode continued to degrade but the serial resistance and degradation at the LSM/YSZ electrode began to also play a major role in the total loss in cell performance. This suggests different degradation mechanisms for high and low current density operation.     

Characterization of nanoporous carbons by combining CO2 and H2 sorption data with the Monte Carlo simulations

The Monte Carlo method in its grand ensemble variant (GCMC) is used in combination with experimental data in order to characterize microporous carbons and obtain the optimal pore size distribution (PSD). In particular, the method is applied in the case of AX-21 carbon. Adsorption isotherms of CO₂ (253 and 298 K) and H₂ (77 K) up to 20 bar have been measured, while the computed isotherms resulted from the GCMC simulations for several pore widths up to 3.0 nm. For the case of H₂ at 77 K quantum corrections were introduced with the application of the Feynman-Hibbs (FH) effective potential. The adsorption isotherms were used either individually or in a combined manner in order to deduce PSDs and their reliability was examined by the ability to predict the experimental adsorption isotherms. The combined approach was found to be capable of reproducing more accurately all the available experimental isotherms.