Search Results (54)

Against the backdrop of global energy transition and strict environmental regulations, supercritical carbon dioxide (scCO₂) fracturing and oil displacement technologies have emerged as pivotal green approaches in shale gas exploitation, offering the dual advantages of zero water consumption and carbon sequestration. However, the inherent low viscosity of scCO₂ severely restricts its sand-carrying capacity, fracture propagation efficiency, and oil recovery rate, necessitating the urgent development of high-performance thickeners. The current research on scCO₂ thickeners faces a critical trade-off: traditional fluorinated polymers exhibit excellent philicity CO₂, but suffer from high costs and environmental hazards, while non-fluorinated systems often struggle to balance solubility and thickening performance. The development of new thickeners primarily involves two directions. On one hand, efforts focus on modifying non-fluorinated polymers, driven by environmental protection needs—traditional fluorinated thickeners may cause environmental pollution, and improving non-fluorinated polymers can maintain good thickening performance while reducing environmental impacts. On the other hand, there is a commitment to developing non-noble metal-catalyzed siloxane modification and synthesis processes, aiming to enhance the technical and economic feasibility of scCO₂ thickeners. Compared with noble metal catalysts like platinum, non-noble metal catalysts can reduce production costs, making the synthesis process more economically viable for large-scale industrial applications. These studies are crucial for promoting the practical application of scCO₂ technology in unconventional oil and gas development, including improving fracturing efficiency and oil displacement efficiency, and providing new technical support for the sustainable development of the energy industry. This study innovatively designed an amphiphilic modified amino silicone oil polymer (MA-co-MPEGA-AS) by combining maleic anhydride (MA), methoxy polyethylene glycol acrylate (MPEGA), and amino silicone oil (AS) through a molecular bridge strategy. The synthesis process involved three key steps: radical polymerization of MA and MPEGA, amidation with AS, and in situ network formation. Fourier transform infrared spectroscopy (FT-IR) confirmed the successful introduction of ether-based CO₂-philic groups. Rheological tests conducted under scCO₂ conditions demonstrated a 114-fold increase in viscosity for MA-co-MPEGA-AS. Mechanistic studies revealed that the ether oxygen atoms (Lewis base) in MPEGA formed dipole–quadrupole interactions with CO₂ (Lewis acid), enhancing solubility by 47%. Simultaneously, the self-assembly of siloxane chains into a three-dimensional network suppressed interlayer sliding in scCO₂ and maintained over 90% viscosity retention at 80 °C. This fluorine-free design eliminates the need for platinum-based catalysts and reduces production costs compared to fluorinated polymers. The hierarchical interactions (coordination bonds and hydrogen bonds) within the system provide a novel synthetic paradigm for scCO₂ thickeners. This research lays the foundation for green CO₂-based energy extraction technologies. Full article

Using anthropogenic carbon dioxide (CO₂) as a feedstock for the production of synthetic fuel has gained significant attention in recent years. Among the various CO₂ conversion pathways, the production of synthetic natural gas via CO₂ methanation holds promise because of its potential for both carbon recycling and renewable energy storage. Nickel (Ni) and ruthenium (Ru) are the dominant metals employed as catalysts in the CO₂ methanation reaction. This review summarizes the research landscape of Ni- and Ru-based catalysts over the last ten years. Bibliometric analysis revealed that China has the highest number of publications, the Chinese Academy of Sciences is the foremost academic institution, and the International Journal of Hydrogen Energy is the leading journal in this area of research. The publication trend revealed that research on Ni-based catalysts is published at almost four times the rate of Ru-based catalysts. Despite growth in research, problems with catalyst stability and kinetics still exist. The latest research on various catalytic systems, including supported, bimetallic, and single-atom catalysts and the fundamental challenges associated with the CO₂ methanation process are reviewed. This review provides a new angle for future studies on catalysts based on non-noble Ni and noble Ru metals and opens the way for additional research in this area. Full article

Recent progress in studies of Rydberg double-well electronic energy states of MeNg (Me = 12-group atom, Ng = noble gas atom) van der Waals (vdW) molecules is presented and analysed. The presentation covers approaches in experimental studies as well as ab initio-calculations of potential energy curves (PECs). The analysis is shown in a broader context of Rydberg states of hetero- and homo-diatomic molecules with PECs possessing complex ‘exotic’ structure. Laser induced fluorescence (LIF) excitation spectra and dispersed emission spectra employed in the spectroscopical characterization of Rydberg states are presented on the background of the diverse spectroscopic methods for their investigations such as laser vaporization–optical resonance (LV-OR), pump-and-probe methods, and polarization labelling spectroscopy. Important and current state-of-the-art applications of Rydberg states with irregular potentials in photoassociation (PA), vibrational and rotational cooling, molecular clocks, frequency standards, and molecular wave-packet interferometry are highlighted. Full article

The mapping relation between the emission angle of the photoelectron and its ionization time (i.e., the angle–time mapping) is important for the attoclock measurement. For a long time, the angle–time mapping was assumed to be angularly uniform. Recent investigations have demonstrated that the angle–time mapping is discontinuous for the low-energy electron at the angle for the minimum yield. However, the previous results were interpreted based on the assumption of s-electron initial states for noble-gas atoms, and the effect of the initial orbital symmetry on the angle–time mapping has been rarely investigated. In this work, we investigate the influence of the initial orbital symmetry on time–energy distribution using F⁻ ions as a specific example. We demonstrate that the initial orbital symmetry significantly impacts the time–energy distribution. This behavior can be well explained by the saddle-point method. More interestingly, it is found that the angle–time mapping is strongly dependent on the initial orbital symmetry in the elliptically polarized laser field, especially for the low-energy electrons. Our work holds great significance for further developing the attoclock scheme. Full article

We present a classical treatment of the ionization and electron-capture processes in the interaction of protons with neutral noble-gas atoms, namely, Ne, Ar, Kr, and Xe. We used a three-body classical-trajectory Monte Carlo (CTMC) method to calculate the total (TCS) and differential (DCS) cross sections of single-electron processes. The Garvey-type model potential was employed in the CTMC model to describe the collision between the projectile and the target, accounting for the screening effect of the inactive electrons. The TCSs are evaluated for impact energies in the energy range between 0.2 keV and 50 MeV for a number of sub-shells of the targets. The ionization DCS are evaluated for an impact energy of 35 keV, focusing on the outer sub-shells only. We found that our ionization and electron-capture TCSs are in very good agreement with the previous theoretical and experimental data for all targets. Moreover, we presented single (SDCS)- and double (DDCS)-differential cross sections as a function of the energy and ejection angle of the ionized electron for all collision systems. Full article

Bioethanol, which is currently produced commercially from a growing variety of renewable biomass and waste sources, is an appealing feedstock for the production of fuels and chemicals. The literature clearly shows that bioethanol is a versatile building block to be used in biorefineries. The ethanol conversion using several catalysts with acidic, basic, and redox characteristics results in a diverse assortment of high-value bioproducts. High-acidity tungsten zirconia-based catalysts are stated to compete with traditional zeolitic catalysts and can be employed in the dehydration of ethanol to ethylene, but for a low reaction temperature acetic acid is formed, which causes corrosion issues. WO₃-ZrO₂ (W/Zr = 1, atomic) catalysts modified with MoO₃ were prepared by a sol-gel-like procedure and tested in a gas phase ethanol conversion in the presence of air. The citrate derived xerogels were annealed at 853 K for 12 h, allowing low surface area (<10 m²/g) materials with a Mo-W mixed-oxide-rich surface over tetragonal nanostructured zirconia. Catalysts with MoO3-loading produced mainly acetaldehyde, instead of ethylene, as a result of the high reducibility of Mo⁶⁺ when compared to W⁶⁺. During the reaction, the Mo⁶⁺ becomes partially reduced, but Mo⁶⁺/Mo⁵⁺ species are still active for methanol conversion with increased ethylene selectivity due to the high acidity of tetrahedral MO_X species formed during the reaction. Adding water to ethanol, to simulate bioethanol, only leads to a slight inhibition in ethanol conversion over the MoO₃/(WO₃-ZrO₂) catalysts. The results show that molybdenum oxide deposited on tungstated zirconia catalyst is active, with low sensitivity to water, for the valorization of bioethanol into high-value chemicals, such as ethylene and acetaldehyde, and whose selectivity can be tuned by changing the amount of MoO₃ that is loaded. The MoO₃/(WO₃-ZrO₂) catalysts prepared show catalytic behavior similar to that of noble metal-based catalysts reported in the literature for the dehydrogenation of bioethanol in high-value chemicals. Full article

The K-Rb-²¹Ne co-magnetometer exhibits poorer dynamic performance due to the larger equivalent magnetic field generated by alkali metal atoms. In this study, the impact of the atomic number density of alkali metal atoms and noble gas atoms in the cell on the dynamic performance of the atomic ensemble is investigated quantitatively. Relationships between the slow-decay term in the transient response attenuation of the Spin-Exchange Relaxation-Free (SERF) co-magnetometer to interference magnetic fields and the number densities of noble gas atoms as well as alkali metal atoms are established. Based on the established model, the relationship between the number density of ²¹Ne atoms and dynamic performance is investigated using cells with five different noble gas pressures. Then, we investigate the impact of the number density of alkali metal atoms using a cell with a pressure of 2.1 atm at different temperatures. The results indicate that, as the number density of alkali metal atoms or noble gas atoms in the cell increases, the dynamic performance of the system improves, which provides a theoretical basis for the design of cell parameters for SERF co-magnetometers. Full article

The development of catalysts for low-temperature methane combustion is crucial in addressing the greenhouse effect. An effective industrial catalyst strategy involves optimizing noble metal utilization and boosting metal–metal interaction. Here, the PdNi-H catalyst was synthesized using the self-assembly method, achieving the high dispersion and close proximity of Pd and Ni atoms compared to the counterparts prepared by the impregnation method, as confirmed by EDS mapping. The XRD and TEM results revealed Pd²⁺ and Ni²⁺ doping within the CeO₂ lattice, causing distortions and forming Pd-O-Ce or Ni-O-Ce structures. These structures promoted oxygen vacancy formation in CeO₂, and this was further confirmed by the Raman and XPS results. Consequently, the PdNi-H catalyst demonstrated an excellent redox ability and catalytic activity, achieving lower ignition and complete methane burning temperatures at 282 and 387 °C, respectively. The highly dispersed PdNi species played a pivotal role in activating methane for enhanced redox ability. Additionally, the narrow size distribution range contributed to more vacancies on the surface of CeO₂, as confirmed by the XPS results, thereby facilitating the activation of gas phase oxygen to form oxygen species (O₂⁻). This collaborative catalytic approach presents a promising strategy for developing efficient and stable methane combustion catalysts at low temperatures. Full article

Highly aligned multi-wall carbon nanotubes were investigated with scanning electron microscopy (SEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) before and after bombardment performed using noble gas ions of different masses (argon, neon and helium), in an ultra-high-vacuum (UHV) environment. Ion irradiation leads to change in morphology, deformation of the carbon (C) honeycomb lattice and different structural defects in multi-wall carbon nanotubes. One of the major effects is the production of bond distortions, as determined by micro-Raman and micro-X-ray photoelectron spectroscopy. We observe an increase in sp${}^3$ distorted bonds at higher binding energy with respect to the expected sp${}^2$ associated signal of the carbon 1s core level, and increase in dangling bonds. Furthermore, the surface damage as determined by the X-ray photoelectron spectroscopy carbon 1s core level is equivalent upon bombarding with ions of different masses, while the impact and density of defects in the lattice of the MWCNTs as determined by micro-Raman are dependent on the bombarding ion mass; heavier for helium ions, lighter for argon ions. These results on the controlled increase in sp${}^3$ distorted bonds, as created on the multi-wall carbon nanotubes, open new functionalization prospects to improve and increase atomic hydrogen uptake on ion-bombarded multi-wall carbon nanotubes. Full article

With the advances in engine technology, the exhaust gas temperature of automobiles has further reduced, which in turn leads to an increase in the emissions of carbon monoxide (CO) and hydrocarbons (HCs). In order to understand the influence of CeO₂-based catalysts loaded with different noble metals on the catalytic oxidation activity of CO and HCs, this study constructed catalyst models of Ce_0.875Zr_0.125O₂ (100) surfaces loaded with Pt, Pd, Ag, and Au. The electronic density and state density structures of the catalysts were analyzed, and the reaction energy barriers for CO oxidation and C₃H₆ dehydrogenation oxidation on the catalyst surfaces were also calculated. Furthermore, the activity sequences of the catalysts were explored. The results revealed that after loading Pt, Pd, Ag, and Au atoms onto the catalyst surfaces, these noble metal atoms exhibited strong interactions with the catalyst surfaces, and electron transfer occurred between the noble metal atoms and the catalyst surfaces. Loading with noble metals can enhance the catalytic activity of CO oxidation, but it has little effect on the dehydrogenation oxidation of C₃H₆. Of the different noble metals, loading with Pd exhibits the best catalytic activity for both CO and C₃H₆ oxidation. This study elucidated the influence of noble metal doping on the catalytic activity of catalysts at the molecular level, providing theoretical guidance for the design of a new generation of green and efficient catalysts. Full article

According to Bader’s quantum theory of atoms in molecules (QTAIM), the simultaneous presence of a bond path and the corresponding bond critical point between any two atoms is both a necessary and sufficient condition for the atoms to be bonded to one another. In principle, this means that this pair of atoms should make a stabilizing contribution to the molecular system. However, the multitude of so-called counterintuitive bond paths strongly suggests that this statement is not necessarily true. Particularly ‘troublesome’ are endohedral complexes, in which encapsulation-enforced proximity between the trapped guest (e.g., an atom) and the host’s cage system usually ‘produces’ many counterintuitive bond paths. In the author’s opinion, the best evidence to demonstrate the repulsive nature of the intra-cage guest⋯host interaction is the use of some trapping systems containing small escape channels and then showing that the initially trapped entity spontaneously escapes outside the host’s cage during geometry optimization of the initially built guest@host endohedral complex. For this purpose, a group of 24 Ng@[3${}_n$]cyclophane (3$\le n\le$6) endohedral complexes is used. As a result, arguments are presented showing that Bader’s topological bond path does not necessarily indicate a stabilizing interaction. Full article

In the present paper, we study the high-order above-threshold ionization of noble-gas atoms using a bi-elliptic orthogonal two-color (BEOTC) field. We give an overview of the SFA theory and calculate the differential ionization rate for various values of the laser field parameters. We show that the ionization rate strongly depends on the ellipticity and the relative phase between two field components. Using numerical optimization, we find the values of ellipticity and relative phase that maximize the ionization rate at energies close to the cutoff energy. To explain the obtained results, we present, to the best of our knowledge, for the first time the quantum-orbit analysis in the BEOTC field. We find and classify the saddle-point (SP) solutions and study their contributions to the total ionization rate. We analyze quantum orbits and corresponding velocities to explain the contribution of relevant SP solutions. Full article

The analysis and measurement of Wigner time delays can provide detailed information about the electronic environment within and around atomic and molecular systems, with one the key differences being the lack of a long-range potential after a halogen ion undergoes photoionization. In this work, we use relativistic random-phase approximation to calculate the average Wigner delay from the highest occupied subshells of the atomic pairings (2p, 2s in Fluorine, Neon), (3p, 3s in Chlorine, Argon), (4p, 4s, 3d, in Bromine, Krypton), and (5p, 5s, 4d in Iodine, Xenon). The qualitative behaviors of the Wigner delays between the isoelectronic pairings were found to be similar in nature, with the only large differences occurring at photoelectron energies less than $20 \mathrm{e}\mathrm{V}$ and around Cooper minima. Interestingly, the relative shift in Wigner time delays between negatively charged halogens and noble gases decreases as atomic mass increases. All atomic pairings show large differences at low energies, with noble gas atoms showing large positive Wigner delays, while negatively charged halogen ions show negative delays. The implications for photoionization studies in halide-containing molecules is also discussed. Full article

A hydrogen fuel cell is a highly promising alternative to fossil fuel sources owing to the emission of harmless byproducts. However, the operation of hydrogen fuel cells requires a constant supply of highly pure hydrogen gas. The scarcity of sustainable methods of producing such clean hydrogen hinders its global availability. In this work, a noble Au-atom-decorated glassy carbon electrode (Au/GCE) was prepared via a conventional electrodeposition technique and used to investigate the generation of hydrogen from acetic acid (AA) in a neutral electrolyte using 0.1 M KCl as the supporting electrolyte. Electrochemical impedance spectroscopy (EIS), open circuit potential measurement, cyclic voltammetry (CV), and rotating disk electrode voltammetry (RDE) were performed for the characterization and investigation of the catalytic properties. The constructed catalyst was able to produce hydrogen from acetic acid at a potential of approximately −0.2 V vs. RHE, which is much lower than a bare GCE surface. According to estimates, the Tafel slope and exchange current density are 178 mV dec⁻¹ and $7.90\times {10}^{-6}$ A cm⁻², respectively. Furthermore, it was revealed that the hydrogen evolution reaction from acetic acid has a turnover frequency (TOF) of approximately 0.11 s⁻¹. Full article

An atom confined in an optical dipole trap is a promising candidate for a qubit. Analyzing the temporal response of such trapped atoms enables us to estimate the speed at which quantum computers operate. The present work models an atom in an optical dipole trap formed using crossed laser beams and further examines the photoionization time delay from such confined atoms. We study noble gas atoms, such as Ne (Z = 10), Ar (Z = 18), Kr (Z = 36), and Xe (Z = 54). The atoms are considered to be confined in an optical dipole trap using X-ray Free Electron Lasers (XFEL). The present work shows that the photoionization time delay of the trapped atoms is different compared with that of the free atoms. This analysis alerts us that while talking about the speed of quantum computing, the temporal response of the atoms in the trapped environment must also be accounted for. Full article