库尔恰托夫研究所

Catalytic methane combustion is an efficient way to remove methane from the exhaust of natural gas vehicles and mine ventilation streams, thereby mitigating its strong greenhouse impact and reducing the fire and explosion hazards. The most widely used catalysts for methane combustion are high-surface-area oxide supports with palladium-based nanoparticles. The promotion of Pd by noble and transition metals is one of the most effective strategies to enhance long-term stability of the catalytic nanoparticles. Here, in search of a synthetic approach to localize promoters in the vicinity of active sites, we systematically compare ternary Pd-Pt-Ni/Al2O3 catalysts with simultaneous addition of Pt and Ni promoters prepared via wet impregnation and colloidal synthesis. The efficient incorporation of promoters into the active phase, Pd1_ xPtxO nanoparticles, is achieved only for the catalyst prepared via colloidal synthesis. Contrary, in addition to Pd1_ xPtxO nanoparticles, wet impregnation results in the growth of Pt-enriched metal nanoparticles, whereas Ni is distributed uniformly over the Al2O3 support with the formation of NiAl2O4 phase. An innovative microcalorimetric approach was used to evaluate catalytic performance. Microcalorimetry showed that the Pd-Pt-Ni/Al2O3 catalyst obtained by wet impregnation has higher initial methane combustion activity, owing to larger, more easily reducible Pd1_ xPtxO nanoparticles. By contrast, the Pd-Pt-Ni/Al2O3 catalyst prepared using colloidal synthesis exhibits significantly greater long-term stability, which is caused by the promotion effect of Pt and Ni. These findings highlight the high potential of colloidal nanoparticles containing one or more promoters for the preparation of highly stable and highly active methane combustion catalysts.

For improving functional and exploitation characteristics of the poly(phenylene oxide) (PPO) gas separation membrane, it was loaded with nitrogen-doped carbon quantum dots (CQDs) (0.5-1.5 wt%). The latter were synthesized from citric acid and L-phenylalanine via a one-step hydrothermal method. Both PPO and PPO/CQDs materials were studied with scanning electron microscopy; UV-vis, FTIR, and XPS spectroscopy techniques; and subjected to mechanical tests. The selectivity in the He/N2 and O2/N2 gas pair separation was shown to increase with increasing CQDs content in the PPO/CQDs membranes. Meanwhile the permeation of individual He, O2, and N2 gases through the PPO/CQDs membranes decreases with increasing CQDs content since the CQDs incorporation into the PPO matrix increases the density of the films and decreases their free volume.

Using DFT model chemistries, M06/def2TZVP and B3PW91/TZVP in combination with the D3 Grimme dispersion, the molecular structures of the coordination compounds of Si(II) and Ge(II) with the doubly deprotonated form of porphyrazine (H2P) having [SiP] and [GeP] composition, respectively, were calculated. The values of the most important bond lengths, valence and non-valence angles in these compounds, as well as the data of the NBO analysis, are presented. A very significant difference between their structures is noted: in the compound [SiP], both the chelate node MN4 and the group of four nitrogen atoms that make up it exhibit a rather noticeable deviation from coplanarity, whereas in the analogous compound [GeP], both are strictly planar. Based on the NBO analysis data, a conclusion has been drawn about a fairly high degree of delocalization of the electron density in these compounds and about the decisive role of p-orbitals in the formation of Si-N and Ge-N bonds. Standard enthalpy Delta fH0, entropy Sf 0, and Gibbs energy Delta fH0 of formation of these compounds were also calculated; all were found to be positive and quite significant in magnitude. Good agreement was also noted between the calculated data obtained using the two aforementioned DFT model chemistries.

Metals phytotoxicity assessment in soils is predominantly based on laboratory testing. In this paper, we evaluated the effect of the duration of laboratory testing on copper toxicity levels, in ryegrass (Lolium perenne L.) grown in soils polluted by copper mining. Laboratory testing was carried out according to the protocols of ISO 11269-2, 2012 (for 21 days) and ISO 22 030, 2005 (for 60 days). When tested for 21 days, the soil copper content had no statistically significant effect on plant growth or on the ryegrass shoot copper content. Conversely, when tested for 60 days, plant growth was inversely proportional to the total soil copper content and to the soil exchangeable copper concentration. Therefore, short-term testing underestimated copper phytotoxicity. The results of this study demonstrate that long-term laboratory testing is required to realistically predict metal toxicity in plants grown under the real conditions of natural and agricultural ecosystems.

In this work, we are the first, to our knowledge, to demonstrate both analytically and numerically that in the cross-section of a 2D paraxial accelerating Airy beam propagating on a parabolic trajectory, there are areas where a canonical energy backflow occurs. These areas arise in the far sidelobes of the Airy beam characterized by a subwavelength local period (superoscillation areas). At an arbitrary propagation distance from the initial plane, there is a threshold transverse coordinate, such that at all smaller negative values of the transverse coordinate, the longitudinal component of the canonical energy flow is negative. For a nonparaxial Airy beam, we derive an explicit analytical expression for the canonical energy flow near the initial plane. The energy backflow is revealed to occur near the intensity null, where a phase jump of π takes place. Near the intensity null, the phase derivative with respect to the longitudinal coordinate takes large negative values, leading to the longitudinal wavevector projection becoming larger than the wavenumber of light and directed oppositely. The maximum energy backflow is found to be about one-fifth of the direct maximum energy flow. Results of the numerical simulation for the paraxial and non-paraxial Airy beams are shown to agree with the theoretical prediction.