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1.
The electrochemical CO2 reduction reaction (CO2RR) on polycrystalline copper (Cu) electrode was performed in a CO2-saturated 0.10 M Na2CO3 aqueous solution at 278 K in the absence and presence of low-frequency high-power ultrasound (f = 24 kHz, PT ~ 1.23 kW/dm3) in a specially and well-characterized sonoelectrochemical reactor. It was found that in the presence of ultrasound, the cathodic current (Ic) for CO2 reduction increased significantly when compared to that in the absence of ultrasound (silent conditions). It was observed that ultrasound increased the faradaic efficiency of carbon monoxide (CO), methane (CH4) and ethylene (C2H4) formation and decreased the faradaic efficiency of molecular hydrogen (H2). Under ultrasonication, a ca. 40% increase in faradaic efficiency was obtained for methane formation through the CO2RR. In addition, and interestingly, water-soluble CO2 reduction products such as formic acid and ethanol were found under ultrasonic conditions whereas under silent conditions, these expected electrochemical CO2RR products were absent. It was also found that power ultrasound increases the formation of smaller hydrocarbons through the CO2RR and may initiate new chemical reaction pathways through the sonolytic di-hydrogen splitting yielding other products, and simultaneously reducing the overall molecular hydrogen gas formation.  相似文献   

2.
《Surface science》1986,166(1):L115-L118
Thermo-programmed heterogeneous catalytic oxidation of CO on Pd small particle/mica catalysts has been used to study the influence of the Pd particle number density on the catalytic turnover rate. Rapid increase is observed in the maximum CO2 turnover rate with decreasing particle density. This effect can be explained by the surface migration of gas molecules on the mica substrate. In previous papers devoted to CO oxidation on Pd particles we pointed out that both the initial sticking coefficient s0 of CO on Pd and the turnover rate rCO2 (for CO2 formation) increase when the particles size decreased. Measurements of the CO consumation rate Nc during an oxidation reaction have also demonstrated a similar particle size dependence for Nc. If the quantities s0 and rCO2 are calculated relative to the impinging flux of CO molecules Ji (Ji given by the kinetic theory of gases), the obtained values are always higher than unity for particle diameter smaller than 8 nm. In the light of these results it seems that the real CO flux should be higher than Ji. Ladas, Poppa and Boudart have suggested that the edge of the particles can receive more collisions than the face atoms, which could explain an increase of the mean CO flux with decreasing particle size.  相似文献   

3.
Epitaxial Si growth at low temperatures (500–800 °C) by atmospheric pressure plasma chemical vapor deposition has been investigated. Silicon films are deposited on (001) Si wafers using gas mixtures containing He, H2, and SiH4. The effects of deposition parameters (composition of reactive gases, very high frequency (VHF) power, and substrate temperature) on film properties are investigated by reflection high-energy electron diffraction, atomic force microscopy, cross-sectional transmission electron microscopy, and plasma emission spectroscopy. It is found that epitaxial temperature can be reduced by increasing VHF power, and that an optimum range of VHF power exists for Si epitaxy, depending on the substrate temperature and the composition of the reactive gases. The result of the H2 concentration dependence of Hα emission intensity, shows that hydrogen atoms generated in the atmospheric pressure plasma play an important role in Si epitaxial growth. Under the optimized growth conditions, defect-free epitaxial Si films (as observed by transmission electron microscopy) with excellent surface flatness are grown at 500 °C with an average growth rate of approximately 0.25 μm/min. PACS 81.05.Cy; 81.15.Gh; 68.55.Jk  相似文献   

4.
S. Jelvani  A.M. Koushki 《Optik》2012,123(16):1421-1424
In this paper, the laser output power of a fast-axial flow CO2 laser was optimized with gas pressures ratio of CO2:N2:He using a genetic algorithm technique. The power of laser was increased from 500 W (un-optimized case) to 2200 W (simulated case), also experimentally the power has achieved the value of 700 W (optimized case).  相似文献   

5.
The effect of CO on the gasification of a Polish coal-derived char was investigated in a fluidised bed from 1123 to 1248 K. Rate expressions developed from Ergun's mechanism or a modified three-step reaction mechanism, coupled with Cylindrical Pore Interpolation Model (CPIM) to account for the intra-particle mass transfer, were developed to predict gasification and the effect of CO. Compared to the Ergun's rate expression, the three-step expression has an extra term for pco, making the inhibition effect of CO more pronounced. The agreement between experimental and numerical results was satisfactory for both models simulating gasification by CO2/N2. Then, when CO (1% or 3%) was intentionally introduced in the feed gas (CO2/N2), the gasification rates significantly decreased. It was found that the model based on Ergun's mechanism over-estimated the gasification rate, while the results from the model with the three-step mechanism agreed with the experimental data.  相似文献   

6.
The interaction of NO with CO and with H2 on Pt(100) was studied by temperature programmed desorption (TPD), isothermal desorption mass spectrometry, and low energy electron diffraction (LEED), TPD of NO and CO coadsorbed at 120 K yields almost complete reaction with both N2 and CO2 products desorbing as sharp, simultaneous peaks at ≈ 410 K. with full widths at half maximum as narrow as 3 K. Isothermal desorption mass spectrometry yields N2 and CO2 rates that exhibit a maximum with time. Both experiments indicate that the reaction mechanism is autocatalytic. Annealing NO-CO adlayers formed at 120 K to temperatures above 300 K causes the subsequent N2 and CO2 TPD peaks to broaden.'TPD of NO coadsorbed with H2 yields sharp N2 and H2O product peaks that closely resemble the N2 and CO2 peaks observed in the NO + CO reaction. LEED experiments during TPD and isothermal desorption showed that the (1 × 1) → hex substrate phase transformation sometimes accompanies desorption of N2 and CO2. The TPD and isothermal desorption results can be fit by two simple models: chemical autocatalysis, in which an intermediate chemical species participates in a “chain propagation” reaction, and structural autocatalysis, which involves the formation of a reactive intermediate structure involving Pt atom displacements.  相似文献   

7.
We find that inward diffusion of network-modifying cations can occur in an iron-containing silicate glass when it is heat-treated in CO/CO2 (98/2 v/v) or H2/N2 (1/99 v/v) gases at temperatures around the glass transition temperature. The inward diffusion is caused by the reduction of ferric to ferrous ions and this diffusion leads to formation of a silica-rich surface layer with a thickness of 200–600 nm. The diffusion coefficients of the network-modifying divalent cations are calculated and they are different for the glasses treated in the CO and H2 gases. At the applied partial pressures of CO and H2, the H2-bearing gas creates the silica-rich layer more effectively than the CO-bearing gas. The layer increases the hardness and chemical durability of the glass due to the silica network structure in the surface layer.  相似文献   

8.
《Current Applied Physics》2014,14(3):451-454
Taking advantages of the special characteristics of a transversely excited atmospheric (TEA) CO2 laser, the analysis of sodium aerosol has been successfully conducted by using laser-induced gas plasma spectroscopy (LIGPS) method. In this study, the sodium aerosol was deposited on a nickel metal plate; the metal plate functions as a subtarget to initiate a gas plasma. When a pulsed TEA CO2 laser was focused on the metal surface, a large-volume and high-temperature gas plasma was induced. The fine particles of sodium then entered into the gas plasma region to be dissociated and excited. By using this technique, a semi quantitative analysis of sodium aerosol was made. The detection limit of sodium was approximately 200 ppb.  相似文献   

9.
The use of natural-gas-fueled combustion engines at unusual operating conditions to provide electrical and/or chemical energy on demand emphasizes the need for fundamental research on decomposition and formation of base chemicals at these conditions. In this work, the CO formation behind reflected shock waves from the pyrolysis of CO2/CH4 mixtures was investigated for the first time in the context of engine-based dry methane reforming, to understand the interaction of CO2 and CH4 at high temperatures and to test the validity of literature reaction mechanisms. Different CO2/CH4 mixtures at atmospheric pressure and temperatures between 1900 K and 2700 K were investigated. Time-resolved CO measurements were performed by laser absorption using a quantum cascade laser.With increasing CO2 addition later reaction onset was observed, showing a reduction in the overall reactivity. Rate of production and sensitivity analyses highlight competing reactions in the pyrolysis and oxidation pathways and that the number of available H radicals is limited, which is attributed to the reduced reactivity. However, the analysis shows that CO2 is also a source for OH radicals (via CO2 + H ⇌ CO + OH), which enhance methane decomposition. The comparison with literature reaction mechanisms showed that none of the tested mechanisms can perfectly predict the time-resolved CO formation, highlighting the need for the validation of detailed kinetics models under nontypical conditions.  相似文献   

10.
OH radical number density in multiple atmospheric pressure microwave plasma jets is measured using UV cavity ringdown spectroscopy of the OH (A–X) (0–0) band at 308 nm. The plasma cavity was excited by a 2.45 GHz microwave plasma source and plasma jets of 2–12 mm long were generated by using three different plasma gases, argon (Ar), Ar/N2, and Ar/O2. Comparative characterization of the plasma jets in terms of plasma shape, stability, gas temperature, emission intensities of OH, NO, and N2, and absolute number density of the OH radical was carried out under different plasma gas flow rates and powers at various locations along the plasma jet axis. With three different operating gases, the presence of OH radicals in all of the plasma jets extended to the far downstream. As compared to the argon plasma jets, the plasma jets formed with Ar/N2 and Ar/O2 are more diffuse and less stable. Plasma gas temperatures along the jet axis were measured to be in the range of 470–800 K for all of the jets formed in the different gas mixtures. In each plasma jet, OH number density decreases along the jet axis from the highest OH density in the vicinity of the jet tip to the lowest in the far downstream. OH density ranges from 1.3 × 1012 to 1.1 × 1016, 4.1 × 1013 to 3.9 × 1015, and 7.0 × 1012 to 4.6 × 1016 molecule/cm3 in the Ar, Ar/N2, and Ar/O2 plasma jets, respectively. The OH density dependence on plasma power and gas flow rate in the three plasma jets is also investigated.  相似文献   

11.
The operation of a continuous CO2 waveguide laser at nearly atmospheric pressure is reported. A plasma injection technique is used to produce a uniform discharge at atmospheric pressure. Continuous output power of 0.6 W was obtained at the inlet pressure of 800 torr. Corresponding outlet pressure was 340 torr. While the maximum output power was 1.4 W at the inlet pressure of 600 torr. The gas mix ratio was CO2 : N2 : He = 1 : 1 : 6.  相似文献   

12.
I. Nakamura 《Surface science》2006,600(16):3235-3242
Reactions between NO and CO on Rh(1 1 1) surfaces were investigated using infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed desorption. NO adsorbed on the fcc, atop, and hcp sites in that order, whereas CO adsorbed initially on the atop sites and then on the hollow (fcc + hcp) sites. The results of experiments with NO exposure on CO-preadsorbed Rh(1 1 1) surfaces indicated that the adsorption of NO on the hcp sites was inhibited by preadsorption of CO on the atop sites, and NO adsorption on the atop and fcc sites was inhibited by CO preadsorbed on each type of site, which indicates that NO and CO competitively adsorbed on Rh(1 1 1). From a Rh(1 1 1) surface with coadsorbed NO and CO, N2 was produced from the dissociation of fcc-NO, and CO2 was formed by the reaction of adsorbed CO with atomic oxygen from dissociated fcc-NO. The CO2 production increased remarkably in the presence of hollow-CO. Coverage of fcc-NO and hollow-CO on Rh(1 1 1) depended on the composition ratio of the NO/CO gas mixture, and a gas mixture with NO/CO ? 1/2 was required for the co-existence of fcc-NO and hollow-CO at 273 K.  相似文献   

13.
《Surface science》1987,179(1):59-89
Molecular adsorption is observed on a Ni(110) surface at 80 K. The relative binding energies of the valence ion states as determined by ARUPS are consistent with those in the gas as well as in the condensed phase, and indicate that the electronic structure of the adsorbed molecule is only slightly distorted upon adsorption at this temperature. The adsorbate spectra show E versus k dispersions indicating some long-range order in the adsorbate. The variations in relative ionisation probabilities of the ion states as a function of electron emission angle suggest that the molecular axis is oriented parallel to the surface within ± 20°. Upon heating the adsorbate to above 100 K. (i.e. 140 K) the spectrum changes. A new species causing an increase in work function by 1 eV can be identified. Comparison with calculations suggests that it is an anionic bent CO; molecule. Electron energy loss studies on this intermediate species support the proposed bent CO2 geometry and favour a coordination site with C2v symmetry. The bent CO2 moiety is stable up to 230 K. Further heating to room temperature leads to dissociation of the bent CO2 molecule into adsorbed CO and O. The CO molecule is oriented with its axis perpendicular to the surface. The bent CO2 species appears to be a precursor to dissociation. Results on CO2 adsorption on an oxygen precovered surface show that CO2 interacts with oxygen at 85 K. Upon heating the co-adsorbate to near room temperature a reaction product is formed the nature of which cannot yet be clearly identified.  相似文献   

14.
We have studied desorption of 13CO and H2O and desorption and reaction of coadsorbed, 13CO and H2O on Au(310). From the clean surface, CO desorbs mainly in, two peaks centered near 140 and 200 K. A complete analysis of desorption spectra, yields average binding energies of 21 ± 2 and 37 ± 4 kJ/mol, respectively. Additional desorption states are observed near 95 K and 110 K. Post-adsorption of H2O displaces part of CO pre-adsorbed at step sites, but does not lead to CO oxidation or significant shifts in binding energies. However, in combination with electron irradiation, 13CO2 is formed during H2O desorption. Results suggest that electron-induced decomposition products of H2O are sheltered by hydration from direct reaction with CO.  相似文献   

15.
Electron energy loss spectra of CO, N2 and O2 have been recorded in the regions of carbon, nitrogen and oxygen K-shell excitation and ionisation. These results are compared to previous energy loss, photoabsorption and theoretical studies of the same spectral regions. Several inconsistencies in the published spectra are clarified in the present work. Comparisons with recent calculations of the K-shell continua of these molecules are presented. Vibrational structure in the K → π * transitions of CO (C 1s) and N2 (N 1s) has been resolved in high-resolution studies (< 0.1 eV FWHM) of these species.  相似文献   

16.
《Surface science》1995,341(3):L1096-L1100
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.  相似文献   

17.
Bulk Pt/ZnO Schottky rectifiers show gas sensitivities for CO of 4% and 8%, respectively, at 150 °C for 1 and 10% CO in N2. The current or voltage changes are time dependent, with an activation energy of 40.7 kJmol-1. Over a limited range of partial pressures of CO (PCO) in the ambient gas, the on-state resistance R of the sensor at fixed bias voltage decreased according to R=(RO+A(PCO)0.5)-1, where A is a constant and RO is the resistance in N2. Since these devices are also sensitive to H2 and C2H4, the ZnO rectifiers appear promising for a range of gas-sensing applications. PACS 81.05.Dz; 73.61.Ga; 72.80.Ey  相似文献   

18.
A kinetic model has been developed for the investigation of the novel performance of a CO laser, on which efficient extraction of laser power was obtained by exciting a subsonic gas mixture of CO/N2/He/O2 through transverse dc discharge. Kinetic equations for direct excitation by electron impact, V-V and V-R/T energy transfer, and stimulated emission are coupled with a semi-one-dimensional flow model. Careful consideration is devoted especially to the V-V transfer process of CO–N2 and N2–N2. The laser power was calculated by a constant gain method. The laser output performance, examined as a function of gas mixture ratio, temperature, flow velocity, and discharge current, was in good agreement with the experiment.  相似文献   

19.
Among the possible products of CO2 electrochemical reduction, CO plays a unique and vital role, which can be an ideal feedstock for further reduction to C2+ products, and also the important component of syngas that can be used as feedstock for value-added chemicals and fuels. However, it is still a challenge to tune the CO selectivity on Cu electrode. Here we newly construct an ultrasound-assisted electrochemical method for CO2 reduction, which can tune the selectivity of CO2 to CO from less than 10% to >80% at −1.18 V versus (vs.) reversible hydrogen electrode (RHE). The partial current density of CO production is significantly improved by 15 times. By in-situ Raman study, the dominating factor for the improved CO production is attributed to the accelerated desorption of *CO intermediate. This work provides a facile method to tune the product selectivity in CO2 electrochemical reduction.  相似文献   

20.
The rate constants of intramolecular intermode relaxation of the CO2 molecule (0001) in pure CO2 and in binary mixtures with He, Ar, H2, O2, N2, CO, NO, N2O, and H2O were measured in the temperature range 300–1000 K by means of a laser-induced luminescence method. It is shown that these relaxation rate constants K for all the gas mixtures investigated increase with increase in the gas temperature in this range; the most efficient in deactivation of the 0001 level are the collisions of CO2 molecules with H2O molecules; the mechanisms of relaxation of the 0001 level of CO2 and their channels depend not only on the temperature but also on the parameters of colliding particles; for each of the colliding partners of the CO2 molecules there is a certain temperature T c above which the temperature dependence of K is coordinated with the Landau–Teller dependence, and, moreover, the simpler the structure of the colliding partner of the CO2 molecule, the higher the temperature T c. Deviations from these dependences at temperatures T < T c are attributed to the influence of intermolecular forces of attraction, change of relaxation channels, and formation of molecular clusters. For all the colliding partners of the CO2 molecules, the interaction radii are determined from the intermolecular potentials of interaction used in the theoretical model.  相似文献   

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