NO--CO--O2 Reaction on a Metal Catalytic Surface using Eley--Rideal Mechanism

Interactions among the reacting species NO, CO and O2 on metal catalytic surfaces are studied by means of Monte Carlo simulation using the Eley-Rideal （ER） mechanism. The study of this three-component system is important for understanding of the reaction kinetics by varying the relative ratios of the reactants. It is found that contrary to the conventional Langmuir-Hinshelwood （LFI） thermal mechanism in which two irreversible phase transitions are obtained between active states and poisoned states, a single phase transition is observed when the ER mechanism is combined with the LH mechanism. The phase diagrams of the surface coverage and the steady state production of CO2, N2 and N2O are evaluated as a function of the partial pressures of the reactants in the gas phase. The continuous production of CO2 starts as soon as the CO pressure is switched on and the second order phase transition at the first critical point is eliminated, which is in agreement with the experimental findings.     

The effect of NO/O2 ratio in NO-CO-O2 reaction on a catalytic surface: A computer simulation study

The interaction among the reacting species in the NO-CO-O₂ reaction on a metal catalytic surface that proceeds according to the Langmuir-Hinshelwood mechanism is studied by means of Monte Carlo simulation. The study of this three-component system is essential for the understanding of the influence of NO/O₂ ratio on the catalytic reduction of NO into N & O and oxidation of CO to CO₂. It is found that this complex system, which has not been studied on these lines before, exhibits irreversible phase transitions between active states with sustained reaction and poisoned states with the catalytic surface fully covered by the reactants. The phase diagrams of the surface coverage with CO, N or O and the steady state production of CO₂ are evaluated as a function of the partial pressure of CO in the gas phase. From this study, it is observed that with the addition of NO in the CO-O₂ reaction, the critical points in the phase diagram move towards lower values of CO partial pressure but the width of reaction window remains almost the same. However, the maximum production rate of CO₂ decreases continuously. On the other hand, the addition of O₂ in the NO-CO reaction shifts the critical points towards higher values of CO pressure. Moreover, the width of reaction window as well as the production rate of CO₂ increases with the increase in O₂ concentration.     

Adsorption and Reaction of CO on （100） Surface of SrTiO3 by Density Function Theory Calculation

Adsorption and reaction of CO on two possible terminations of SrTiO3 （100） surface are investigated by the first-principles calculation of plane wave ultrasoft pseudopotentiai based on the density function theory. The adsorption energy, Mulliken population analysis, density of states （DOS） and electronic density difference of CO on SrTiO3 （100） surface, which have never been investigated before as far as we know are performed. The calculated results reveal that the Ti-CO orientation is the most stable configuration and the adsorption energy （0.449eV） is quite small. CO molecules adsorb weakly on the SrTiO3 （100） surface, there is predominantly electrostatic attraction between CO and the surface rather than a chemical bonding mechanism.     

The effect of inactive impurities on a surface in NO-CO reaction: A Monte Carlo simulation

The interaction among the reacting species in the NO-CO reaction on a metal catalytic surface that proceeds according to the Langmuir-Hinshelwood thermal mechanism is studied by means of Monte Carlo simulations. The study of this system is essential for the understanding of the influence of impurities on the catalytic oxidation of NO by CO. It is found that this complex system exhibits irreversible phase transitions between active states with sustained reaction and poisoned states without reaction. The same system has also been investigated by non-thermal (Eley-Rideal) mechanism. Both the phase diagrams of the surface coverage and the steady state production of CO₂ and N₂ are evaluated as a function of the partial pressures of the reactants in the gas phase. From this study, it is observed that with the increase of impurities, the production rate reduces and the reaction stops at a certain point. Moreover, the first order transition in the phase diagram converts into second order phase transition that is in accordance with the experimental findings. Therefore, the first order phase transition, which is a characteristic of such catalytic reactions, is eliminated.     

CO-H2-O2 reaction on a catalytic surface: A computer simulation study

The oxidation of carbon monoxide to form carbon dioxide and the oxidation of hydrogen to form water are the reactions of environmental and industrial importance. These two reactions have been studied independently by Monte Carlo computer simulation using Langmuir-Hinshelwood mechanism but no effort has been made to study the combined CO-H₂-O₂ reaction on these lines. Keeping in view the importance of this 3-component system, the surface coverages and production rates are studied as a function of CO partial pressure for different ratios of H₂ and O₂. The diffusion of reacting species on the surface as well as their desorption from the surface is also introduced to include temperature effects. The phase diagrams of the system are drawn to observe the behavior of these atoms/molecules on the surface and the production of CO₂ and H₂O are determined at different concentrations of H₂. The results are compared with 2-component systems.     

The co-adsorption of H2 and CO on Ni(110)

The effect of co-adsorption of hydrogen and CO on Ni(110) has been examined with HREELS. In the mixed adlayer at low CO and hydrogen coverage, the spectra indicate that no strong interaction between H_(a) and CO_(a) occurs. At high hydrogen coverage the surface reconstructs and consequently the adsorption site for the CO is modified. The reconstruction and site modification is reversible and depends on the hydrogen coverage.     

The temperature dependence of the interaction of NO + CO on Pt{1 0 0}

Infrared reflection absorption spectroscopy together with mass spectrometry has been used to investigate the interaction of NO and CO on Pt{1 0 0}, initially prepared in the reconstructed ‘hex’ phase, under ambient pressures of these gases, in the temperature range 300-500 K. The results allow the local and total coverages of adsorbed CO and NO to be related to the rate of reaction to produce gas phase CO₂, and provide insight into the species present on the surface during the so-called low temperature oscillatory reaction regime of this process. At temperatures below that at which NO dissociation occurs (approximately 390-400 K) adsorption is controlled by the non-reactive displacement of NO by CO and results in a CO-poisoned surface. Above 400 K when significant CO₂ production occurs, the NO coverage increases to produce a surface with NO and CO fully intermixed; the increase in NO coverage is attributed to the higher rate of NO arrival from the gas phase (with a partial pressure ratio of P_NO:P_CO>1) at free surface sites created by NO dissociation and subsequent reaction with CO. The competition between these two processes of non-reactive NO displacement by CO and reactive displacement of CO by NO is proposed to determine the parameter space of the low temperature oscillatory regime. Rapid equilibration between bridged and atop CO species leads to them appearing to exhibit identical reaction behaviour. Particularly at the lowest reaction temperatures (around 400 K), islands of pure CO may coexist on the surface but not participate in the reaction. Under conditions corresponding to the high temperature oscillatory regime, small quantities of absorbed CO, but no NO, are seen on the surface.     

Explosive production of CO2 from (NO + CO)/Pd(100)

Explosive CO₂ production followed by the gradual N₂ production has been observed by TDS as a result of the NO-CO reaction on the Pd(100) surface which does not reconstruct. The location and width of the CO₂ desorption peak have been found to be almost independent of the total coverage. For this autocatalytic reaction, the vacancy requirement model is considered to be valid. Change in the CO₂ production by varying the NO coverage (with the CO coverage fixed) has been also studied, from which information on the island formation is derived.     

硅在cBN单晶合成中的行为

 实验制备了复合氮化物Li₈SiN₄，并对合成温度、合成时间、气流量等因素的影响以及产物的稳定性进行了讨论。研究了Li₈SiN₄作为触媒添加剂时硅在cBN单晶合成中的作用。结果表明：cBN晶体多为截角八面体，晶面致密光滑；硅参与cBN的合成反应，并以SiO₂的形式沉积在cBN表面。     

A mechanistic char oxidation model consistent with observed CO2/CO production ratios

Reliable prediction of char conversion, heat release, and particle temperature during heterogeneous char oxidation relies upon quantitative calculation of the CO₂/CO production ratio. This ratio depends strongly on the surface temperature, but also on the local partial pressure of oxygen and thus becomes more important in simulations of oxy-fuel or pressurized combustion systems. Existing semi-empirical intrinsic kinetic models of char combustion have been calibrated against the temperature-dependence of the CO₂/CO production ratio, but have neglected the effect of the local oxygen concentration. In this study we employ steady-state analysis to demonstrate the limitations of the existing 3-step semi-global kinetics models and to show the necessity of using a 5-step model to adequately capture the temperature- and oxygen-dependence of the CO₂/CO production ratio. A suitable 5-step heterogeneous reaction mechanism is developed and its rate parameters fit to match CO₂/CO production data, global reaction orders, and activation energies reported in the literature. The model predictions are interrogated for a broad range of conditions characteristic of pressurized, oxy-fuel, and conventional high-temperature char combustion, for which essentially no experimental information on the CO₂/CO production ratio is available. The results suggest that the CO₂/CO production ratio may be considerably lower than that estimated with existing power-law correlations for oxygen partial pressures less than 10 kPa and surface temperatures higher than 1600 K. To assist with implementation of the mechanistic CO₂/CO production ratio results, an analytical procedure for calculating the CO₂/CO production ratio is presented.     

Reactive Ion Etching as Cleaning Method Post Chemical Mechanical Polishing for Phase Change Memory Device

In order to improve nano-scale phase change memory performance, a super-clean interface should be obtained after chemical mechanical polishing （CMP） of Ge2Sb2Te5 phase change films. We use reactive ion etching （RIE） as the cleaning method. The cleaning effect is analysed by scanning electron microscopy and an energy dispersive spectrometer. The results show that particle residue on the surface has been removed. Meanwhile, Ge2Sb2Te5 material stoichiometric content ratios are unchanged. After the top electrode is deposited, currentvoltage characteristics test demonstrates that the set threshold voltage is reduced from 13 V to 2.7V and the threshold current from 0.1 mA to 0.025 mA. Furthermore, we analyse the RIE cleaning principle and compare it with the ultrasonic method.     

A New Method for Generating Hydrogen from Water

A new method for generating hydrogen by the reaction of Al powder with water using iodine as additive is developed. 12 can penetrate through the surface oxide layer on aluminium to form AlI3. High solubility of AlI3 in water is benefited to activate Al surface. It is found that the production of hydrogen becomes significant above 60℃ and obeys a logarithm rule. The pH value which is determined mainly by the kinetics of hydration spontaneously. varies from 5 to 3 then back to 4.5 during the reaction, reaction of AlI3 and the reaction of Al and HI produced     

冲击波作用下碳水混合物发射光谱研究

 利用二级轻气炮和OMA-Ⅲ光多通道系统,分别研究金刚石与水、石墨与水两种碳水混合物在冲击波作用下的发射光谱。冲击压力高于16.41 GPa时,观测到350～750 nm波段内叠加在连续辐射背景上的发射谱;当冲击压力高于33.95 GPa时,C₂、CO、CO₂的谱线辐射明显,表明碳和水发生了化学反应。     

Adsorption and interaction of CO and NO on Pt(410): I. TPD studies

NO and CO adsorption and the NO/CO reaction on Pt(410) are studied by TPD. NO is found to dissociate on Pt(410) at 120 K, but it reacts to form N₂O at higher exposures. The N₂O desorbs in two peaks at 135 and 150 K. CO adsorbs molecularly, and desorbs in 5 peaks at 550, 500, 450, 380 and about 130 K. CO is also found to dissociate upon heating, leaving a carbon residue on the surface which changes the TPD spectra. The NO/CO reaction shows a surface explosion at 360 K. These results provide additional evidence that Pt(410) has unusual reactivity, as predicted by Banholzer, Park, Mak and Masel, Surface Sci. 128 (1983) 176.     

Compatibility of field emitter studies of oscillating surface reactions with single crystal measurements: catalytic CO oxidation on Pt

Kinetic oscillations in catalytic CO oxidation on Pt have been studied on large (millimeter size) single crystal planes of Pt as well as on a Pt field emitter tip that exposes different crystal facets of nanometer size. In order to examine the compatibility of results from the two types of experiments, the regions of different dynamical behavior (bifurcation diagram) have been mapped out in p_CO,T-parameter space using a field electron microscope (FEM) and a field ion microscope (FIM). The comparison with the results of single crystal measurements shows that in the case of applied electrostatic fields less than 5 V nm⁻¹ (FEM), the field-induced effects are negligible, but they are significant for fields exceeding 12 V nm⁻¹ (FIM). The field-induced shift of the bifurcation diagram toward lower p_CO values, observed with FIM, is explained in terms of a field-modified interaction of CO and O₂ with Pt studied here with field ion appearance energy spectroscopy. With coadsorbed lithium (submonolayer coverage), the existence range for rate oscillations is shifted toward higher p_CO values. This shift is attributed to a redistribution of the electron density at the surface induced by alkali metal co-adsorption.     

A first principles study of the adsorption and dissociation of CO<Subscript>2</Subscript> on the δ-Pu (111) surface

A complete understanding of the nature of the 5f electrons has been and continues to be a major scientific problem in condensed matter physics. Bulk and surface electronic structure studies of the actinides as also atomic and molecular adsorptions on the actinide surfaces provide a path towards this understanding. In this work, ab initio calculations within the framework of density functional theory have been used to study the adsorption of molecular CO₂ and the corresponding partially dissociated (CO + O) and completely dissociated (C + O + O) products on the δ-Pu (111) surface. The completely dissociated C + O + O configurations exhibit the strongest binding with the surface (7.92 eV), followed by partially dissociated products CO + O (5.08 eV), with molecular CO₂ adsorption having the lowest binding energies (2.35 eV). For all initial vertically upright orientations, the CO₂ molecule physisorbs or do not bind to the surface and the geometry and orientation do not change. For all initial flat lying orientations chemisorption occurs, with the final state corresponding to a bent CO₂ molecule with bond angles of 117°–130° and the elongation of the CO bond. For CO + O co-adsorption, the stable configurations corresponded to CO dipole moment orientations of 100°–172° with respect to the surface normal and the elongation of the CO bond. The most stable chemisorption cases correspond to anomalously large rumpling of the top Pu layer. The interactions of the CO₂ and CO with the Pu surface have been analyzed using the energy density of states and difference charge density distributions. The nature and the behavior of the 5f electrons have also been discussed in detail in the context of this study.     

Additivity Rule for Electron-Molecule Total Cross Section Calculations at 50-5000 eV： A Geometrical Approach

To quantify the changes of the geometric shielding effect in a molecule as the incident electron energy varies, we present an empirical fraction, which represents the total cross section （TCS） contributions of shielded atoms in a molecule at different energies. Using this empirical fraction, a new formulation of the additivity rule is proposed. Using this new additivity rule, the TCSs for electron scattering by CO2, C2H2, C6H12 （cyclo-hexane） and CsH16 （cyclo-octane） are calculated in the range 50-5000 e V. Here the atomic cross sections are derived from the experimental TCS results of simple molecules （H2, O2, CO）. The quantitative TCSs are compared with those obtained by experiments and other theories, and good agreement is attained over a wide energy range.     

Spectral Study of Effects of Aluminium Nanoparticles on Fast Reaction of Nitromethane

Fast reactions between nitromethane and aluminium nanoparticles are studied using transient spectral methods. In comparison with species produced by pure nitromethane, the emergence time for species produced by nitromethane after addition of 1 g of aluminium nanoparticles decreases by 46-58% and the emission intensity increases by 13-100%. The results demonstrate that aluminium nanoparticles have positive effect on accelerating the decomposition rate of nitromethane and that the explosion efficiency of nitromethane is greatly improved. Fast reactions carried out between nitromethane and aluminium nanoparticles in different environments （CO2, H2O and O2） reveal that O2 and an appropriate amount of H2O improve the explosion efficieney of nitrornethane, whereas CO2 has the weakest effect on improving this parameter. The investigations provide insights into the process occurring in actual systems involving propellants and fuel-air explosives.     

Structural Deformation of CO22+ in Intense Femtosecond Laser Fields

The angular distributions of CO^＋ from the dissociation of CO2^2＋ and CO2^＋ in intense femtosecond laser fields （45 fs, about 5 × 10^15 W/cm^2） are studied at a laser wavelength of 800nm based on the time-of-flight mass spectra of CO^＋ fragment ions. The experimental results show that structural deformation occurs in the charge state of CO2^2＋ and the CO^＋ maintains linear geometrical structure.     

In-situ study of the catalytic oxidation of CO on a Pt(1 1 0) surface using ambient pressure X-ray photoelectron spectroscopy

CO and O₂ co-adsorption and the catalytic oxidation of CO on a Pt(1 1 0) surface under various pressures of CO and O₂ (up to 250 mTorr) are studied using ambient pressure X-ray photoelectron spectroscopy (APXPS) and mass spectrometry. There is no surface oxide formation on Pt under our reaction conditions. CO oxidation in this pressure (<500 mTorr), O₂ to CO ratio (<10), and temperature (150 °C) regime is consistent with the Langmuir-Hinshelwood reaction mechanism. Our findings provide in-situ surface chemical composition data of the catalytic oxidation of CO on Pt(1 1 0) at total pressures below 1 Torr.