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.

Chiral optical cavities are crucial for the development of nonequilibrium quantum materials by discriminating and selectively coupling to light of a specific circular polarization, but fundamentally cannot be realized with conventional mirror cavities. Here, we demonstrate this unique functionality by developing a monolithic transition metal dichalcogenide (TMDC) metasurface with broken out-of-plane symmetry, allowing for the selective formation of self-hybridized chiral exciton-polaritons. Our metasurface maintains maximal chirality for oblique incidence up to 20°, thereby outperforming all previously known designs. Moreover, we study the chiral strong-coupling regime in nonlinear experiments and reveal polaritonic signatures in chiral third-harmonic generation. Our results position maximally chiral van der Waals (vdW) metasurfaces as a versatile platform for tunable chiral polaritonics with applications in nonreciprocal photonic devices and valleytronics.

Abstract In the recent years, argon-based experiments looking for Dark Matter in the Universe have explored the non-standard scenario in which Dark Matter is made by low-mass Weakly Interacting Massive Particles, of mass in the range of 1–10 GeV instead of the canonical hundreds of GeV. Detecting such particles is challenging, as their expected signatures are nuclear recoils with energies below 10 keV, observable solely via ionization. This necessitates a precise understanding of the detector response in this energy regime, which remains incomplete for argon. To address this, the ReD experiment was developed within the framework of the DarkSide-20k Collaboration to produce and characterize few-keV nuclear recoils. A compact dual-phase argon Time Projection Chamber (TPC) was irradiated with neutrons from a $$^{252}$$ 252 Cf source, to produce Ar recoils in the energy range of interest via (n,n’) elastic scattering. A downstream spectrometer composed of 18 plastic scintillators detected the neutrons scattered off Ar nuclei, enabling recoil energy reconstruction via two-body kinematics. The ionization yield $$Q_{y}$$ Q y of argon, defined as the number of electrons produced per unit energy deposit, was measured in a model-independent way between 2 and 10 keV. These measurements extend direct experimental coverage well below the previous limit of approximately 7 keV. The results are consistent with existing data above 7 keV, while they indicate a higher $$Q_{y}$$ Q y at lower energies.