P. Stefanov

X-ray photoelectron spectroscopy, temperature-programmed desorption and temperature-programmed reduction study of LaNiO3 and La2NiO4 +δ catalysts for methanol oxidation

An X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD) and reduction (TPR) study of LaNiO3 and La2NiO4+δ perovskites has been carried out. The existence of at least two different forms of oxygen in these compounds is shown by both oxygen reactivity (TPD and TPR) and XPS characterisation. XP spectra have also revealed a surface enrichment in lanthanum and oxygen. TPR profiles have shown a reduction of LaNiO3 through the formation of La2Ni2O5 as an intermediate compound. Above 450 °C, LaNiO3 and intergrowth nickelates (La2NiO4 and La2NiO4 +δ) undergo a final reduction to metallic Ni and La2O3. Between 200 and 400 °C all three compounds exhibit a high catalytic activity in the total catalytic oxidation of methanol.

Chemical composition and corrosion resistance of passive chromate films formed on stainless steels 316 L and 1.4301

Abstract The chemical composition and corrosion behavior of the natural and formed by chemical treatment in chromium-containing solution passive films on 316 L and 1.4301 stainless steel surfaces have been investigated by means of X-ray photoelectron spectroscopy and electrochemical in situ method of anodic polarization curves. It have been established that the oxide films formed by the chemical treatment have different chemical composition (Cr-enriched), color and reduced corrosion resistance compared to the natural passive films on both steels. The results have shown that the lower part of the oxide layer represents a uniform modified passive film and the upper one is a porous Cr3+-enriched film with an island-like structure. The latter permits a direct contact of the solution with the modified passive film which controls the corrosion resistance by the dissolution of the Fe3+ oxides present in the lower thinner layer.

Electrochemical growth of thin La2O3 films on oxide and metal surfaces

This work presents a new electrochemical method (i.e. new electrolyte composition and electrolysis regime) for direct formation of La2O3 on ZrO2 and other oxide and metal substrates from nonaqueous electrolytes, data on the kinetics of the electrochemical processes and scanning electron microscopy (SEM) and XPS studies of the morphology, structure, dispersion and chemical composition of La2O3.

Surface segregation and preferential sputtering in thin Al–Ni alloy films

Abstract The surface composition of AlxNi1−x alloy films was studied by X-ray electron spectroscopy (XPS) after various surface treatments and oxidation at room temperature. Ion etching caused a marked enrichment in Ni of the altered surface layer. After extensive sputtering, bombardment-induced segregation of Al at the outermost surface layer of the films was established. Al segregation to the surface was observed during annealing up to 1200 K. The interaction of oxygen with the surface of the alloy films caused surface segregation of Al, accompanied by preferential oxidation of Al.

Characterization of the surface structure and composition of stainless steel 316 L after electrochemical roughening

SUMMARY The changes in morphology, structure and chemical composition of the surface of stainless steel 316 L roughened by an electrochemical treatment have been studied by means of profilometry, SEM and XPS methods. The steel was subjected to a two-stage electrochemical anodic treatment based on the use of electrolytes containing an organic acid and a mixture of inorganic acids, respectively. The anodic treatment caused an essential change in surface morphology and structure, this resulting in an increase of the averaged surface depth Rz from 0.28 to 2.58 μm. XPS depth profiling has shown that the iron and nickel concentrations in the surface layer of the roughened steel are slightly reduced.

Lithium-promoted V2O5−TiO2 catalysts for o-xylene oxidation to phthalic anhydride

A V2O5−Li2O−TiO2 (a) based catalyst for o-xylene oxidation to phthalic anhydride has been synthesized. The activity and selectivity of the specimen obtained are comparable with those of industrial catalysts.