Reduction of CeO2 in composites with transition metal complex oxides under hydrogen containing atmosphere and its correlation with catalytic activity

Reduction behavior of pure and doped CeO2, the multi-phase La0.6Sr0.4CoO3.xCeO2, La0.sSr0.2MnO3 . xCeO2, and La0.95Ni0.6Fe0.4O3.xCeO2 composites, was studied under hydrogen containing atmosphere to address issues related to the improvement of electrochemical and catalytic performance of electrodes in fuel cells. The enhanced reduction of cerium oxide was observed initially at 800~C in all composites in spite of the presence of highly reducible transition metal cations that could lead to the increase in surface concentration of oxygen vacancies and generation of the electron enriched surface. Due to continuous reduction of cerium oxide in La0.6Sr0.4CoO3 ＂x- CeO2 and La0.sSr0.zMnO3 ＂xCeO2 （up to 10 h） composites the redox activity of the Ce4＋/Ce3＋ pair could be suppressed and additional measures are required for reversible spontaneous regeneration of Ce4＋. After 3 h exposure to H2-Ar at 800~C the reduction of cerium oxides and perovskite phases in La0.95Ni0.6Fe0.403 ＂xCeO2 com- posites was diminished. The extent of cerium oxide involvement in the reduction process varies with time, and depends on its initial deviation from oxygen stoichiometry （that results in the larger lattice parameter and the longer pathway for O2 transport through the fluorite lattice）, chemical origin of transition metal cations in the perovskite, and phase diversity in multi-phase composites.

Effect of 2-mercaptobenzothiazole concentration on sour-corrosion behavior of API X60 pipeline steel:Electrochemical parameters and adsorption mechanism

We investigated the effect of the 2-mercaptobenzothiazole concentration on the sour-corrosion behavior of API X60 pipeline steel in an environment containing H_(2)S at 25°C and in the presence of 0,2.5,5.0,7.5,and 10.0 g/L of 2-mercaptobenzothiazole inhibitor.To examine this behavior,we conducted open-circuit potential(OCP),potentiodynamic polarization,and electrochemical impedance spectroscopy(EIS)tests.Energy dispersive spectroscopy and scanning electron microscopy were also used to analyze the corrosion products.The results of the OCP and potentiodynamic polarization tests revealed that 2-mercaptobenzothiazole reduces the speed of both the anodic and cathodic reactions.An assessment of the Gibbs free energy of the inhibitor(△G_(ads)^(■))indicated that its value was less than-20 kJ·mol^(-1)and greater than-40 k J·mol^(-1).Therefore,the adsorption of 2-mercaptobenzothiazole onto the surface of the API X60 pipeline steel occurs both physically and chemically,the latter of which is particularly intentional.In addition,as the△G_(ads)^(■)dsvalue was negative,we could conclude that the adsorption of 2-mercaptobenzothiazole onto the surface of the pipeline steel occurs spontaneously.The EIS results indicate that with the increase in the 2-mercaptobenzothiazole inhibitor concentration,the corrosion resistance of API X60 steel increases.An analysis of the corrosion products revealed that iron sulfide compounds form on the surface.In summary,the results showed that an increase in the inhibitor concentration results in a decrease in the corrosion rate and an increase in inhibitory efficiency.Additionally,we found that the 2-mercaptobenzothiazole adsorption process on the API X60 steel surfaces in an H2 S-containing environment follows the Langmuir adsorption isotherm and occurs spontaneously.

THEORETICAL STUDIES OF THE NATURE OF THE 2210 cm^(-1) IR ABSORPTION PEAK IN SILICON CRYSTAL CONTAINING HYDROGEN (Ⅲ)——TEMPERATURE EFFECTS OF THE PEAK SHAPEAND THE SYMMETRIC BREAKING OF DEFECT COMPLEX

It is verified that the phonon scattering process and the residual linewidthare the dominant factors of the linewidth of 2210 cm^(-1) IR absorption peak except the anomalous linewidth at 200 K. By investigating the anomalities of the peak shape and thelinewidth of the peak at 200 K, we put forward a mechanism that the T_d symmetry of defect-complex corresponding to the 2210 cm^(-1) peak can he transferred into the D_(2d) symmetry as temperature rises to above 200 K. The quantitative analysis shows that the V+4H-model is indeed of two states: The T_d configuration is stable at temperature lower than 200 K, while the D_(2d) one is stable at temperature higher than 200 K. We can draw the conclusion that the V +4H-model corresponds to the 2210 cm^(-1) IR absorption peak from the symmetric breaking mechanism, which can quantitatively fit the experimental results.