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1986 Volume 2 Issue 1
The adsorption of oxygen on silver has been studied by XPS. The results indicate that the surface pretreatment method may effect the adsorption ability of oxygen on silver.It is shown that at room temperature and low p_(O_2)(≤10~(-5)Pa) three adsorption states of oxygen have existed on surface and their Ols binding energies are 528.2, 529.7 and 532.2 eV respectively, corresponding to two different atomic and one molecular adsorption species. We find that one of the atomic oxygen species (E_BCOls=528.2 eV) may transform to another one (E_B=529.7 eV) when the exposure of oxygen increases. At larger exposure, some oxygen atoms have entered the bulk of silver and its E_B(O1s)=530.2 eV. According to the XPS difference spectra of valence band, the resonance of the adsorbate appears at 2.8—3.0 eV and 9.0 eV bolow E_F, which are similar to the results of UPS. It is suggested that the atomic and molecular adsorption species of oxygen coexist on silver surface.
Electric property across the Pt film-TiO_2 and Pt film-ZnO interface was characterized by the Ⅰ-Ⅴ curves. It was seen clearly that by H_2 treatment at high temperature the original rectifying property of the metal-semiconductor junction was changed into ohmic resistance contact.
Electron exchange capability at the Pt film-TiO_2 and Pt-ZnO surface was measured electrochemically by making contact with a solution of Fe(CN)_6~(4-)/Fe(CN)_6~(3-). It was illustrated that the H_2 treated SMSI sample was much more feasible to charge transfer than the non-SMSI ones and it worked well either anodically or cathodically, analo us to the metallic Pt.
By Auger depth profiling it was demonstrated that by heating Pt film-TiO_2 in H_2 interdiffusion at the metal-semiconductor interface happened, as a consequence the interfacial energy barrier for electron transfer was diminished and the charge transfer process greatly enhanced.
Under linear temperature increase condition thermal behaviors, mechanismfunction and kinetic parameters of thermal decomposition of 2,6-dinitrophenol obtained with a model CDR-1 instrument with the sealed cell of stainless steel are reported. The data are fitted to the integral, differential and exothermic rate equations by linear least-squares, iterative, combined dichotomous and leastsquares methods, respectively. The apparent activation energy, pre-exponential constant, reaction order and probable mechanism function (integral form) of thermal decomposition reaction of 2,6-dinitrophenol obtained by the logical choice method are 134±9 kJ mol~(-1), 10~(9.17±0.77)s~(-1), 0, and a respectively.
A.C. impedance is an extremely valuable tool for the interpretation of electrochemical reaction mechanisms and
cell characteristics.
We describe here instrumentation capable of measuring the capacitance and resistance of electrochemical cells under
conditions of varying cell voltage and/or measuring frequency.
Circuit
The principle on which the circuit is based (Figure 1) is that of phase-sensitive detection and is similar to methods
described previously [1] with two exceptions. In most impedance measurement circuits, the cell voltage is modulated and the
corresponding response of the cell current monitored. This sometimes presents aproblem in separating the cell response from
that of the control circuit and generally requires larger perturbation signals. In this case, a small (<10 μA) current
signal is applied with the control circuit isolated through L. Second, in this system, the measuuring frequency can be varied
using a ramp generator coupled to a voltage-controlled frequency oscillator.
The lock-in amplifier that was used (PAR Model 5204) contains two phasesensitive detectors that are driven by ortho nal
reference signals. Both cell resistance (in phase) and cell reactance (-1/ωC, quadrature) can be monitored simultaneously.
Any phase shift caused by the measurement circuit can be offset by substituting a standard resistor for the electrochemical
cell and adjusting the phase control of the lock-in amplifier. In all cases tested, this adjustment was less than ±2°.
Applications
The response of the measuring system to a dummy cell consisting of a 50 Ω resistor in series with a 50 Ω resistor and 1 μF
capacitor in parallel gave a spectrum that agreed with the theoretical prediction within 2%. In Figure 2, the differential
capacitance of a dropping mercury electrode in 1 molL~(-1) Na_2SO_4 solution obtained using the system under discussion is
compared with Grahame′s original data [2,3]. Curve b is for a solution saturated with N-heptyl alcohol. The agreement is
quite od with the exception of the adsorption peaks. The peak heights should be sensitive to the perturbation signal
magnitude in that higher amplitude perturbations tend to “average out” sharp peaks. The small current signal that was used
in the present case seems to improve the resolution of the capacitance peaks.
There an error in the original report by Grahame(2). The abscissas in Figures 20 and 21 should read, “E relative to the
normal mercury/mercurous sulfate electrode” instead of “E relative to the normal calomel electrode”. The reasons are as
follows:
1) Our numerous experiments using SCE reference electrode and normal mercury/mercurous sulfate reference electrode show
Grahame′s abscissa (in fig.21) is incorrect.
2) The related fig.20 of Grahame′s paper was quoted from uy (Ann. Chim. Phys. 8, 291). However, we found out in this
original paper uy used a large mercury pool asreference electrode. Since it is a normal sulfate solution, the
electrodepotential should related to mercury/mercurous sulfate electrode but not to NCE electrode.
3) From table 1 on page 451 in Grahame′s paper, the E~(MAX) (potential of the electrocapillary maximum) in Na_2SO_4 solution
is -0.48 V versus NCE. It agrees well with Frumkin′s data -0.47 V versus NCE (A.H.фрумкин et.al. КИНЕТИКА Э
ЛЕКТРОДНЫХ ПРОЦЕССОВ. 1952, p.31, table 1). If in fig.20 the maximum is -0.85 V “relative to normal
mercury/mercurous sulfate electrode”, since N-mercury/mercurous electrode is 0.335 V more positive that NCE, now the maximum
appears at -0.515 V releative to NCE electrode. It agrees well with other data.
Our intention of pointing out this minor error in Grahame′s paper is merely because this paper is generally accepted as the
classical paper with most authority in its own field and Figure 21 is widely quoted in numerous papers and text-books (e. g.
A. J. Bard, L. R. Faulkner, “Electrochemical Methods, fundamentals and Applications.” 1980. p.550, 551).
The performance of silver oxide electrodes is knowng to be sensitive to the magnitude of the charging current (4). Upon
chargin at 17 mA/cm~2 (Curve a, Figure 3), potential plateaux corresponding to
2Ag+2OH~-→Ag_2O+H_2O+2e~-
and
Ag_2+4OH~-→Ag_2O_3+2H_2O+4e~-
are observed prior to oxygen evolution (highest plateau). The potential decay curve displays three plateaux corresponding to
the reverse reactions
Ag_2O_3→A →Ag_2O→Ag
In concentrated electrolyte, the cell resistance reflects primarily the resistance of the surface layer. Verification of this
fact was achieved by measurement of the resistance during potential decay. The initial decay of Ag_2O_3 to A proceeds at
low resistance in accordance with the relatively high conductance of these compounds Ag_2O_3, 2×10~2 Ω~(-1)cm~(-1); A ,
10~(-1) Ω~(-1)cm~(-1)). The transformation of the surface layer from A to Ag_2O proceeded concurrently with an increase in
resistance (Ag_2O3, 10~(-8) Ω~(-1)cm~(-1)). The resistance diminished upon discharge of Ag_2O to Ag. Rapid measurements of
this type facilitate successfull evaluation of Ag battery characteristics.
Complex plane spectra of iron oxide electrodes (s) were generated by continuous variation of measurement frequency during
experiments with both illuminated and non-illuminated electlodes. Analysis of the curves (Figure 4) provided an equivalent
circuit that explained the observed results. It was found that the internal resistance of the semiconducting oxide (R_(SC))
diminished under illumination simultaneousry with an increase in space charge capacitance. The capacitance and resistance
data obtained show promise toward routine evaluation of semiconducting materials and may facilitate optimization of
photoelectrochemical devices.
(This paper has been presented on 161st meeting of the Electrochemical Society, 1982, Montreal, Canada)
Mean activity Coefficients of HCl in concentrated hydrochloric acid solutions are determined by measuring emf′s of following cells (A). Ag-AgCl/HCl(m)/H_2(P)/Pt(black) (B). Ag-AgCl/HCl(m)/pH-glass electrode for HCl molalities from 0.01844 to 15.02 tool kg~(-1) at 25 ℃. Using observed emf data of ceils (A) and (B), mean activity coefficients of HCl are calculated, and their deviations are less than 1.2%. Within this molality range, “standard potential” E_G~0 of pH-glass electrode is a constant and its standard deviation is equal to 0.016%. The pH-glass electrode used has od reproducibility. Therefore, it is possible to determine the activity coefficients in high concentrated hydrochloric acid solution by using pH-glass electrode.
For concentrated hydrochloric acid in molality range 0.1844—15.02 mol kg~(-1) at 25 ℃, the lograrithm of activity coefficients of HCl can be expressed adquately by the equation:
logγ±=-0.5115/(1+1.471)+0.1069 m+7.412×10~(-3) m-6.637×10~(-4) m~3
+1.586×10~(-5) m~4
where m is the HCl concentration in molality, γ± is its activity coefficients. Using this equation, activities of solvent H_2O have been calculated.
La_(1-x)Sr_xCoO_3 has been studied by XPS. It is showed that the La 3d_(5/2) spectrum is a doublet. The peak of higher one of BE is assigned to a shake-up satellite, which results from that 2p electrons of oxygen transfer to the empty 4f orbital of lanthanum. The ratio R of the intensity of shake-up satellite to parent peak is a measure of covalency of La—O.R, and hence the covalency of La—O increases with the increasing stronium content, The R is called COVALENT FACTOR. It was found that if stronium was partly substituted for the place of lanthanum, it would influence the covalency of La—O. The covalency of Co—O decreases with the increase of stronium content, while ionicity of Co—O increases, which results in a change of reducing temperature of cobalt in La_(1-x)Sr_xCoO_3.
We succeeded in explaining the reasons of both segregation of lanthanum of LaCoO_3 and no segregation when stronium was partly substituted for the place of lanthanum.
Five adsorbed systems have been studied by using exponential heating desorption. Those are benzene/zeolite HZSM-5, benzene/zeolite NaY, benzene/zeolite rare-earthe-Y, benzene/mordenite and n-hexane/mordenite. The experiments proved that the relation between activation energy of desorption and temperature of most desorption rate is linear, i.e. E_d=KT_m.
The data of exponential temperature programmed were analysed and compared with those of linear temperature programmed. The values of various kinetics parameter are coincided. Their activation energies are shown in Table.
The following kinetics parameter equation of exponential temperature programmed has been derived:
lnT_m/a=E_d/RT_m+lnE_d/ARnθ_m~(n-1).
and the equation has compared with that of linear temperature programmed:
lnT_m~2/β=E_d/RT_m+lnE_d/ARnθ_m~(n-1).| It is found that the effect of temperature deviation, ΔT, on all parameter is less (2T+ΔT) times by using equation of exponential temperature programmed than that of linear temperature programmed.
Through these experiments we found that the temperature control of exponential temperature programmed is easier than that of linear temperature programmed.
Ni/γ-Al_2O_3, Ni/γ-Al_2O_3-La_2O_3 (La_2O_3 6.7%)and Ni/γ-Al_2O_3-La_2O_3 (La_2O_3 11.7%) catalysts were prepared by incipient wetness technique. The particle size distribution (Fig.9) and the average size of nickel in these catalysts were determined by Transmission Electron Microscopy (TEM). Average particle size could be compared with the data determined by X-Ray Diffraction (XRD)(see Table 3). It has been found that the particle size of nickel in catalysts is decreasing (Table 1) and activity of methanation is increasing (Fig.2) as adding La_2O_3 to Nicatalyst. Results of TEM and XRD in this paper support the model suggested by Xie Youchang et. al., of close-packed monolayer La_2O_3 dispersed on γ-Al_2O_3 surface, if the amount of La_2O_3 is less than the threshold value (0.28 La_2O_3/100 m~2 γ-Al_2O_3). X-Ray line broaden of γ-Al_2O_3 lattice, due to La_2O_3 highly dispersed on the surface of alumina.
Fe K absorption spectra of an electrically conductive polymer——FeCl_3-doped polythiophene and model compound [N(C_2H_5)_4][FeCl_4] were measured with a laboratory EXAFS system, which utilizes a high power rotating-anode X-ray generator (Rigaku model RU-1000) as a X-ray source. The analysis of observed EXAFS data shows that Fe atom is surrounded by four Cl atoms with Fe-Cl distance of 2.19. It is concluded that the dopant exists mainly in the form of FeCl_4~-. The result provides a direct structural information that strongly supports the proposition: the doping process is as follows
2FeCl_3+e~-→FeCl_4~-+FeCl_2
The kinetic behaviors of schlögl's model A+2X<=>3X and X<=>B has been studied under the continuous flow stirred reaetor(CSTR)conditions. The parameters' regions, in which the reaction system exhibits all kinds of different kinetic behaviors e.g. bistability and limit cycle oscillation, can be divided by the phase plane method. The system may exhibit oscillation or bistability for some range of flow rates under the constraints of all other parameters being fixed. This method, with advantages of simplicity in calculation and explicitness in physical background, offers an effective path for designing chemical oscillation and predicting other kinetic phenomena.
The crystal and molecular structure of the title compound was determined by X-ray analysis. The intensities of 2991 independent reflections with I>2σ were measured by an Enraf-Nonius CAD_4 diffractometer with Mo-K_α radiation.
The crystal belongs to space group P21/c with cell dimensions a=1.8807(3), b=0.5786(1)。c=2.0557(6) nm, β=116.86(1)°and z=8.
The structure was solved by Patterson function and direct method, and refined by full matrix least squares with 2991 (I>2σ) reflections. The refinement converged at R=0.035.
There are two acetyl ferrocene molecules in an asymmetric unit. The geometrical features of the molecules as well as the characteristics of molecular packing in the unit cells are considerd.
Two 1,1'-disubstituted ferrocene organometallic compounds 1,1'-dihydroxy-methylferrocene (Ⅰ) and 1,1'-diformylferrocene (Ⅱ) have been synthesised. The ~(13)C NMR spectra in CDCl_3 solution have been determined and assigned. A theoritical calculation of ~(13)C NMR chemical shift based on our INDO/σ program has been applied to these two compounds which included d orbitals. These are the most complicated compounds up to now for the chemical shift calculation, It is satisfied for the trend between the theoritical calculation and experiment.
A propylene hydroformylation system in presence of the rhodium-phosphine catalyst has been monitored with a gas-liquid chromatograph. It has been proved that the system is a chemical oscillation system in certain conditions.
The experiment has shown that the oscillation of this system requests[C_3H_6]/[H_2+CO]>1 in gas phase.
The action of the solvent is quite special, i.e.a suitable quantity of tripolymer of n-butyladehyde has to exist. The hydroformylation reaction will not on if the content of the tripolymer is too high, and the oscillation phenomenon will not occur if its content is too low.
Since until now there are no reports about the effect of butyladehyde properties on this catalytic reaction and about the concentration oscillation phenomenon of the rhodium-phosphine catalyst system, the progressive study of this system will be ver yinteresting.
