Dmitry A. Svintsitskiy

Highly Oxidized Platinum Nanoparticles Prepared through Radio‐Frequency Sputtering: Thermal Stability and Reaction Probability towards CO

Platinum-oxide nanoparticles were prepared through the radio-frequency (RF) discharge sputtering of a Pt electrode in an oxygen atmosphere. The structure, particles size, electronic properties, and surface composition of the RF-sputtered particles were studied by using transmission electron microscopy and X-ray photoelectron spectroscopy. The application of the RF discharge method resulted in the formation of highly oxidized Pt(4+) species that were stable under ultrahigh vacuum conditions up to 100 °C, indicating the capability of Pt(4+) -O species to play an important role in the oxidation catalysis under real conditions. The thermal stability and reaction probability of Pt(4+) oxide species were analyzed and compared with those of Pt(2+) species. The reaction probability of PtO2 nanoparticles at 90 °C was found to be about ten times higher than that of PtO-like structures.

Observation of the superstructural diffraction peak in the nitrogen doped carbon nanotubes: Simulation of the structure

ABSTRACT A superstructural peak at ∼12° in X-ray diffraction patterns of nitrogen-doped carbon nanotubes compared to the undoped carbon nanotubes was observed and assigned to the formation of spatially ordered defects. The simulation of the N-CNT structure using the graphitic g-C3N4 phase and turbostratic ordering made it possible to propose a new model of the spatially ordered defects in the N-CNT layer, which consist of clusters of carbon vacancies and pyridine-like nitrogen. A correlation between this type of defects and electrical conductivity of the N-CNTs is defined.

The influence of CuO dispersion on catalytic properties in the CO oxidation: a comparative studies in two types of catalytic reactors

The catalytic properties of copper(II) oxide powders were studied in the CO oxidation reaction by using plug‐flow and flow‐circulation reactors. Data obtained from different catalytic experiments were in good agreement with each other. The specific catalytic rate [molecules cm−2 s−1] increased by a factor of approximately four if the surface area of the CuO powder was reduced from 90 to 8 m2 g−1. A further decrease in the CuO surface area to 1 m2 g−1 resulted in the decrease of the specific CO oxidation rate by more than 20‐fold. These results indicate that CO oxidation is sensitive to the structure of the copper(II) oxide catalyst. The structural sensitivity of CuO powders was discussed in terms of its defect structure and particle morphology.

The evolution of the M1 local structure during preparation of VMoNbTeO catalysts for ethane oxidative dehydrogenation to ethylene

The so-called M1 phase (the common formula (TeO)x(Mo, V, Nb)5O14) is a very promising catalyst for ethane oxidative dehydrogenation (ODE). It shows 90% selectivity to ethylene at 78% ethane conversion (400 °C, contact time – 5.5 s). The active crystal structure is formed under certain synthetic conditions in VMoNbTe mixed oxides. This paper is devoted to the analysis of how the local and average structure of the M1 phase is developed during the synthesis and what happens at particular synthetic steps. The analysis of the local structure was performed using the EXAFS and pair distribution function (PDF) methods. The EXAFS analysis of the initial VMoTe water solution and VMoNbTe slurry showed that Anderson-type heteropoly anions are formed in the solution and are preserved after fast spray-drying of the slurry. Nb cations do not enter the structure of the polyanions, but form an extended hydrated oxide matrix, where distorted NbO6 and NbO7 polyhedrons are connected to each other. The hydrated oxide matrix with captured polyanions provides the compositional homogeneity of the precursor. The distances in the second coordination shell are redistributed after thermal treatment at 310 °C. After being heated at T > 350°, the local structure of the M1 phase is organized and pentagonal domains are formed. These domains consist of a NbO7 pentagonal bipyramid and five MeO6 adjacent octahedra (Me = Mo, V). In the first stages, the building blocks are stacked along the [001] direction. The crystallization process results in the connection of the pentagonal domains to the extended polygonal grid. The formation of the regular grid with TeOx containing channels is accompanied by the increase in ethane conversion and ethylene selectivity of the catalysts.

Highly Stable Single-Atom Catalyst with Ionic Pd Active Sites Supported on N-Doped Carbon Nanotubes for Formic Acid Decomposition

Single-atom catalysts with ionic Pd active sites supported on nitrogen-doped carbon nanotubes have been synthesized with a palladium content of 0.2-0.5 wt %. The Pd sites exhibited unexpectedly high stability up to 500 °C in a hydrogen atmosphere which was explained by coordination of the Pd ions by nitrogen-containing fragments of graphene layers. The active sites showed a high rate of gas-phase formic acid decomposition yielding hydrogen. An increase in Pd content was accompanied by the formation of metallic nanoparticles with a size of 1.2-1.4 nm and by a decrease in the catalytic activity. The high stability of the single-atom Pd sites opens possibilities for using such catalysts in high-temperature reactions.

Application of RF discharge in oxygen to create highly oxidized metal layers

ABSTRACT The radio frequency (RF) discharge in an oxygen atmosphere was used to produce metal oxide films. The high efficiency of the RF discharge technique for metal oxidation at room temperature was demonstrated for gold, silver and copper foils. Oxide films up to 10 nm in thickness were obtained. The produced oxide films were studied by X-ray photoelectron spectroscopy (XPS). The XPS data showed the formation of oxidised species: Cu2+, Ag1+ and Au3+. Analysis of the oxygen species was performed using O1s spectra. For copper and silver foils, the formation of additional oxygen species apart from oxygen in the structure of oxides was shown. The reaction probability toward oxidation of carbon monoxide (CO) was estimated for all oxidised layers. It was established that gold and silver oxide films interacted with CO at room temperature, while cupric oxide showed high activity at temperature >353 K.