Ren I. Kvon

Study of reactivity of oxygen states adsorbed at a silver surface towards C2H4 by XPS, TPD and TPR

Reactivity of oxygen states absorbed at the surface of a silver foil towards ethylene has been studied by XPS, TPD and TPR. Isotope experiments with “ionic” oxygen (BE9(C 1s)=528.4 eV) labelled by 18O2 and the “covalent” oxygen (BE(O 1s)=530.5 eV) labelled by 16O2 have been carried out. It has been revealed that both oxygen states are desorbed separately. Following the ethylene experiment indicated that the “ionic” oxygen is active in total oxidation only, while the “covalent” oxygen takes part in the ethylene epoxidation.

XPS STUDY OF THE SIZE EFFECT IN ETHENE EPOXIDATION ON SUPPORTED SILVER CATALYSTS

Supported silver catalysts (Ag/α-Al 2 O 3 ) with different particle sizes (100–1000 A) have been prepared and studied by XPS. It has been shown that the increase in the ethene epoxidation rate with silver particle size (size effect) is accompanied by a decrease in the Ag 3d 5/2 binding energy value. The variation in E b (Ag 3d 5/2 ) cannot be explained in terms of a change in the metallic character of the silver (initial state effect), but seems to be determined by the differential charging of the supported silver. The latter effect originates from the easier screening of surface charge induced by photoemission on the silver particles owing to their internal conductivity, rather than that on the dielectric support. The correlation between the internal conductivity of supported silver particles and their catalytic activity is discussed in the context of possible mechanisms for ethene epoxidation.

Identification of nitrogen-containing species obtained by nitric oxide adsorption on the surface of model gold catalysts

Nitric oxide adsorption at 300–500 K on gold particles supported on an alumina film has been investigated for the first time by in situ X-ray photoelectron spectroscopy. Two nitrogen-containing adsorption species can form on the surface of gold particles. By test experiments on NO adsorption on the stepped face (533) of a gold single crystal, these species have been identified as adsorbed nitrogen atoms (which are detected throughout the temperature range examined) and a surface complex with N2O stoichiometry (which is stable in a narrow temperature range of 325–425 K).

On the effect of Cu on the activity of carbon supported Ni nanoparticles for hydrogen electrode reactions in alkaline medium

Effects of adding varied amounts of copper to carbon-supported nickel particles on their structure, composition and electrocatalytic activity for the hydrogen oxidation and evolution reactions in alkaline medium have been explored. Ni1-xCux/C catalysts were prepared by the incipient wetness impregnation. Comprehensive characterization of the catalysts included X-ray powder diffraction, X-ray photoelectron spectroscopic, transmission electron microscopic and cyclic voltammetric analyses, while atomistic Monte Carlo simulations have been undertaken to obtain further insights into the structure of the bimetallic NiCu nanoparticles. We found that compared to monometallic Ni, NiCu nanoparticles show lower propensity towards oxidation under ambient conditions. Furthermore, we report that adding Cu allows increasing the surface-weighted electrocatalytic activity, and the specific surface area of Ni1-xCux/C electrodes, both contributing to a ca four-fold enhancement of the mass-weighted activity. The nature of the synergistic interactions between Ni and Cu is proposed on the basis of the analysis of experimental data and Monte Carlo structural modelling results.

The study of the surface layer of 3D-matrices for tissue engineering

Matrices fabricated by electrospinning from polycaprolactone solutions with human albumin or gelatin to 1,1,1,3,3,3-hexafluoroisopropanol have been investigated. Microstructure of matriх surface was analyzed using scanning electron microscopy. Protein distribution in the surface layer was studied by modification with N-(2-hydroxyethyl)phenazine and X-ray photoelectron spectroscopy. The protein concentration in the surface layer of matrices was up to 12 times higher than in the initial solution, and the lower the protein concentration in the solution, the higher the relative protein content is on the surface of matrices. During incubation of matrices in aqueous solutions protein concentration in the surface layer decreased by less than 10% during the first 30–60 min and remained at this level for a long time (seven days). Treatment with proteinase K resulted in about one-third decrease in protein concentration in the surface layer. Thus, both methods used in this study are applicable for analysis of the surface layer of materials fabricated by electrospinning from mixtures of synthetic and natural polymers; however, X-ray photoelectron spectroscopy appears to be a more informative and convenient method.