XPS/ToF-SIMS Characterization of TiO₂ Supported Au Nanoparticles: Effect of Catalytic CO Oxidation

С помощью рентгеновской фотоэлектронной спектроскопии (РФЭС) и времяпролётной вторично-ионной масс-спектрометрии (ВП-ВИМС) проведено сравнительное исследование состава поверхности и электронной структуры катализатора Au/TiO₂ в свежеприготовленном состоянии и после его использования в реакции окисления CO при комнатной температуре.За допомогою рентґенівської фотоелектронної спектроскопії (РФЕС) та часопролітної вторинно-іонної мас-спектрометрії (ЧП-ВІМС) проведено порівняльне дослідження складу поверхні й електронної структури каталізатора Au/TiO₂ у свіжоприготованому стані та після його використання у реакції окиснення CO за кімнатної температури.X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) are employed for a comparative study of the surface composition and electronic structure of an Au/TiO₂ catalyst in the asprepared state and after using it in the reaction of CO oxidation at room temperature

XPS-SIMS surface characterization of aluminovanadate oxide catalyst precursors: Effect of precipitation pH

X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF SIMS) are used to study the surface physical and chemical state of aluminovanadate oxide catalyst precursors (V-Al-O) precipitated at different pH within the range from 5.5 to 10. For comparison, the reference V 2O 5 and Al 2O 3 oxides are also investigated. Using XPS, the core-level photoelectron spectra, x-ray induced Auger spectra, and the valence- band spectra of the samples are obtained, and the surface concentration of components of the catalyst is quantitatively evaluated. Auger parameters for Al and O in V-Al-O, V 2O 5 and Al 2O 3 are measured, and the chemical Wagner diagrams are plotted. The O 2p-2p hole repulsion energy for all the samples is estimated. The binding-energy shifts of the O I s, V 2p and Al 2p lines are determined as a function of pH and analysed in terms of the initial-state effect related to the atomic charge as well as the Madelung potential and of the final-state relaxation effect. Increasing of pH is found to result in the monotonic variation of the surface composition with the V/Al ratio decreasing by a factor of ≅ 2.6, in the modification of the valence band, progressive hydration of the surface, and increasing dispersion of vanadium-oxide particles. In V-Al-O catalysts, the fraction of reduced V 4+ ions revealed by XPS is increasing with increasing pH, so, the average vanadium oxidation state is changed from ≅+4.8 to +4.6. The enhancement of catalytic activity for propane oxidative dehydrogenation demonstrated by V-Al-O at high precipitation pH is in a good correlation with decreasing surface V/Al ratio, growing population of the V 4+ states, and increasing nucleophilicity of oxygen atoms

X-ray induced surface modification of aluminovanadate oxide

Aluminovanadate oxide, ‘‘V–Al–O’’, has been studied by X-ray photoelectron spectroscopy (XPS) with the emphasis to reveal chemical modifications as a function of the X-irradiation time. Considerable damage was found for V–Al–O and less so for vanadium pentoxide, V2O5, and sapphire, a-Al2O3, both serving as reference samples. Modifications in V–Al–O were seen even at low radiation doses. Absolute and relative shifts in binding energies along with changes of peak intensities and widths demonstrate that an appreciable amount of V5+ is reduced to lower oxidation states. X-ray induced chemical modifications extend at least to the depth sampled by the V3p electrons. It is suggested that the damage is caused by electron-hole pair generation and Auger decay. Al–O–H in V–Al–O is also affected by X-rays. This causes O2 and water desorption as followed by mass spectrometry of the residual gas.info:eu-repo/semantics/publishe

Interaction of low energy protons, deuterons,

We have performed measurements of energy-angle distributions for low energy (E ≲ 10 keV) hydrogen ions transmitted through thin amorphous carbon foils. The applicability of standard potentials for the description of the multiple scattering is tested by making comparisons of the experimental results with theoretical calculations using the model of Sigmund and Winterbon on a broad angular scale. The angular dependence of the energy loss for protons and deuterons is analyzed using the three-components model of Famá et al., that separately considers the contribution of elastic and inelastic mechanisms and the roughness effect. Additionally, the velocity dependence of the stopping power and the possible existence of isotopic and molecular effects in the energy loss is investigated by measurements with H+, D+, \hbox{${\rm H}_2^+$} and \hbox{${\rm D}_2^+$} beams of velocities between 0.15 and 0.6 a.u