Site Dilution Research Articles

Enhanced hydrogen production through methane dry reforming: Evaluating the effects of promoter-induced variations in reducibility, basicity, and crystallinity on Ni/ZSM-5 catalyst performance

The pursuit of sustainable hydrogen production through the conversion of methane (CH4) and carbon dioxide (CO2), two prevalent greenhouse gases, is advanced by utilizing cost-effective Ni-supported catalysts within the framework of methane dry reforming. Utilizing crystalline porous zeolite, specifically ZSM-5, enhances the dispersion of nickel (Ni) across the catalyst surface and within its pore channels, hence increasing catalytic efficiency. Herein, we investigate the impact of incorporating various promoters (Ce, Cs, Cu, Fe, Sr) into the 5Ni/ZSM-5 catalyst, systematically examining how these modifications influence the reducibility, basicity, and crystallinity of the catalyst’s active sites, thereby affecting its hydrogen yield potential.Our findings reveal that the inferior activity of Cu-promoted catalysts is due to the depletion of basic sites and larger NiO crystallite size (than rest-promoted catalysts). The introduction of Fe results in a highly dispersed Ni with a stable NiFe phase, but dilution of active sites results in low hydrogen yield. Conversely, Sr promotion enhances the basicity and accessibility of NiO active sites both on the surface and within the pore channels of the zeolite, leading to a notable hydrogen yield of 28 % at 700℃ after 300 min. Furthermore, the addition of 2 wt% ceria significantly optimizes Ni dispersion within the pore channels and surges the maximum population of basic sites (including the presence of very strong basic sites), achieving 35 % hydrogen yield at 700 °C and ∼ 70 % at 800℃. This investigation underscores the critical role of promoter-induced modifications in enhancing catalyst performance for hydrogen production, contributing to the development of more efficient and sustainable energy conversion technologies.

How do cicadas emerge together? Thermophysical aspects of their collective decision-making.

Periodical cicadas exhibit life cycles with durations of 13 or 17 years, and it is now accepted that large prime cycles arose to avoid synchrony with predators. Less well explored is how, in the face of intrinsic biological and environmental noise, insects within a brood emerge together in large successive swarms from underground during springtime warming. Here, we consider the decision-making process of underground cicadas experiencing random, spatially correlated thermal microclimates such as those in nature. Introducing short-range communication between insects leads to an Ising model of consensus building with a quenched, spatially correlated random magnetic field and annealed site dilution, which displays the kinds of collective swarms seen in nature. These results highlight the need for fieldwork to quantify the spatial fluctuations in thermal microclimates and their relationship to the spatiotemporal dynamics of swarm emergence.

14CO2 ACTIVITY IN AIR SAMPLES AND DILUTION FACTOR EVALUATION OF KAKRAPAR GUJARAT SITE, INDIA

ABSTRACT14CO2 activity in air samples collected at Kakrapar Gujarat Site, India, was measured, and site-specific dilution factor for 14CO2 has been evaluated. 14CO2 activity in air samples was monitored for 72 different sampling events at onsite stack of Nuclear Power Plant (NPP) and at ESL meteorology laboratory (at 1.6 km from NPP stack). 14CO2 activity in air at stack of NPP and at ESL meteorology laboratory was observed to 0.10–0.18 TBq (GWe.year)–1, with mean value 0.12 TBq (GWe.year)–1 and ≤0.04–0.13 Bq m–3, with mean value 0.08 Bq m–3 respectively. The results were correlated with meteorological parameters. Site specific dilution factor for 14CO2 in air was evaluated at 1.6 km and was found to be in the range of 4.6E-05 to 21E-05 s m–3. Inter angle (degree) between plume direction and fixed sampling location and rainfall (mm) are found to be the important influencing parameters for dilution factor of 14CO2 in air.

Evolution of the inverse magnetocaloric effect for random-field to spin-glass crossover in SmCaCoMnO6−SmMnO3 nanocomposite

We observe an enhancement of inverse magnetocaloric effect (MCE) in $\mathrm{Sm}\mathrm{Ca}\mathrm{Co}\mathrm{Mn}{\mathrm{O}}_{6}$ (94%) and $\mathrm{Sm}\mathrm{Mn}{\mathrm{O}}_{3}$ (6%) nanocomposite due to uniform external field-induced random field (RF) to spin glass (SG) crossover. RF is generally observed in diluted antiferromagnet and dilute dipole-coupled Ising ferromagnet systems. Under the application of magnetic-field ($H$), such systems may show a crossover from RF to SG at low temperatures ($T$). Here, we report a similar type of crossover but in ferrimagnetic $\mathrm{Sm}\mathrm{Ca}\mathrm{Co}\mathrm{Mn}{\mathrm{O}}_{6}$ and antiferromagnetic $\mathrm{Sm}\mathrm{Mn}{\mathrm{O}}_{3}$ nanocomposite. A model of site dilution of the ferrimagnetic phase by the embedded antiferromagnetic regions is proposed. In this composite system, the RF appears at $T<35$ K, which shows a crossover to SG at $T<15$ K under the applied field. The enhanced inverse MCE (with an entropy change, $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}\ensuremath{\sim}\ensuremath{-}0.95$ J ${\mathrm{Kg}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ for a change in $H\ensuremath{\sim}70$ kOe at $T\ensuremath{\sim}7.5$ K) due to the SG state is the consequence of field-induced RF-SG crossover giving highly $H$-dependent $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}$ in the SG regime, a requisite for large MCE.

Aluminum and Zinc Co-substituted Cobalt Ferrite: Structural, Magnetic, and Magnetostrictive Properties

We report on the influence of Al and Zn co-substitution on the structural, magnetic, and magnetostrictive properties of cobalt ferrite (Co1–xZnxFe2–xAlxO4, 0 ≤ x ≤ 0.15; CZFAO) materials, which were made using a glycine-nitrate autocombustion process. The cubic spinel structure is present in both the as-synthesized and the sintered CZFAO samples, where it was evident that the crystallite size and lattice parameter reduced with increasing x due to the incorporation of smaller Al3+ ions in place of larger Fe3+ ions in spinel ferrite. Co-substitution induced changes in the metal–oxygen bond lengths, causing both the tetrahedral and octahedral infrared and Raman spectroscopic bands to shift toward higher wavenumbers. The electron microscopy analyses indicate that the Al–Zn substitution induces grain growth, leading to a dense, interconnected grain morphology. Mossbauer analyses indicate that the Al3+ occupies the octahedral site, whereas Zn2+ is substituted at the tetrahedral site. Due to equal magnetic dilution of both tetrahedral and octahedral sites caused by the presence of Zn and Al at the appropriate sites, the saturation magnetization MS of CZFAO is the same as that of pure CFO. All other magnetic parameters (coercivity HC, magnetocrystalline anisotropy constant K1, and Curie temperature TC) decrease with increasing x, where the decline observed is mostly due to superexchange interaction (A-O-B) reduction caused by the substituents’ non-magnetic character. CZFAO materials exhibit higher magnetostriction strain λ and strain sensitivity dλ/dH at relatively low magnetic fields; among all the samples, x = 0.15 demonstrates a maximum strain sensitivity of −2.53 × 10–9 m/A at 23 kA/m magnetic field. The composition-tuned CZFAO materials with desirable properties are suitable for application in torque sensors.

Effects of site dilution on Compensation in Ising Spin-1/2 trilayered triangular Ferrimagnets with non-equivalent planes

Using Monte Carlo simulations with the Metropolis algorithm, the magnetic and thermodynamic behaviours of a spin-1/2, trilayered ferrimagnetic system on triangular monolayers with quenched nonmagnetic impurities are studied. Two different theoretical atoms, A and B, make up the ABA and AAB types of distinct configurations. Like atoms (A-A and B-B) interact ferromagnetically, while unlike atoms (A-B) interact antiferromagnetically. Only the A-layers are randomly site-diluted with dilution percentages ranging from 5% to 45%. Such diluted magnetic thin systems exhibit magnetic compensation which depends sensitively on the concentration of impurities. The phase diagram in the Hamiltonian parameter space related to the occurrence of magnetic compensation phenomenon and the effect of site dilution is discussed in detail. Special attention is given to the mathematical dependencies of compensation temperature on the concentration of nonmagnetic impurities. Depending upon the concentration of nonmagnetic impurities, the compensation and critical points shift with the equilibrium magnetic behaviours changing between distinct ferrimagnetic behaviours. For each combination of the coupling strengths, with values of the impurity concentration above a threshold, compensation appears where previously was absent. Suggested mathematical formulae show how threshold impurity concentration relies on Hamiltonian parameters.

A Comparative Review of Binder-Containing Extrusion and Alternative Shaping Techniques for Structuring of Zeolites into Different Geometrical Bodies

Zeolites are crystalline metallosilicates displaying unique physicochemical properties with widespread applications in catalysis, adsorption, and separation. They are generally obtained by a multi-step process that starts with primary mixture aging, followed by hydrothermal crystallization, washing, drying, and, finally, a calcination step. However, the zeolites obtained are in the powder form and because of generating a pressure drop in industrial fixed bed reactors, not applicable for industrial purposes. To overcome such drawbacks, zeolites are shaped into appropriate geometries and desired size (a few centimeters) using extrusion, where zeolite powders are mixed with binders (e.g., mineral clays or inorganic oxides). The presence of binders provides good mechanical strength against crushing in shaped zeolites, but binders may have adverse impacts on zeolite catalytic and sorption properties, such as active site dilution and pore blockage. The latter is more pronounced when the binder has a smaller particle size, which makes the zeolite internal active sites mainly inaccessible. In addition to the shaping requirements, a hierarchical structure with different levels of porosity (micro-, meso-, and macropores) and an interconnected network are essential to decrease the diffusion limitation inside the zeolite micropores as well as to increase the mass transfer because of the presence of larger auxiliary pores. Thus, the generation of hierarchical structure and its preservation during the shaping step is of great importance. The aim of this review is to provide a comprehensive survey and detailed overview on the binder-containing extrusion technique compared to alternative shaping technologies with improved mass transfer properties. An emphasis is allocated to those techniques that have been less discussed in detail in the literature.

Double dome structure of the Bose–Einstein condensation in diluted S = 3/2 quantum magnets

Bose–Einstein condensation (BEC) in quantum magnets, where bosonic spin excitations condense into ordered ground states, is a realization of BEC in a thermodynamic limit. Although previous magnetic BEC studies have focused on magnets with small spins of S ≤ 1, larger spin systems potentially possess richer physics because of the multiple excitations on a single site level. Here, we show the evolution of the magnetic phase diagram of S = 3/2 quantum magnet Ba2CoGe2O7 when the averaged interaction J is controlled by a dilution of magnetic sites. By partial substitution of Co with nonmagnetic Zn, the magnetic order dome transforms into a double dome structure, which can be explained by three kinds of magnetic BECs with distinct excitations. Furthermore, we show the importance of the randomness effects induced by the quenched disorder: we discuss the relevance of geometrical percolation and Bose/Mott glass physics near the BEC quantum critical point.

Effects of lattice dilution on the nonequilibrium phase transition in the stochastic susceptible-infectious-recovered model.

We investigate how site dilution, as would be introduced by immunization, affects the properties of the active-to-absorbing nonequilibrium phase transition in the paradigmatic susceptible-infectious-recovered (SIR) model on regular cubic lattices. According to the Harris criterion, the critical behavior of the SIR model, which is governed by the universal scaling exponents of the dynamic isotropic percolation (DyIP) universality class, should remain unaltered after introducing impurities. However, when the SIR reactions are simulated for immobile agents on two- and three-dimensional lattices subject to quenched disorder, we observe a wide crossover region characterized by varying effective exponents. Only after a sufficient increase of the lattice sizes does it become clear that the SIR system must transition from that crossover regime before the effective critical exponents asymptotically assume the expected DyIP values. We attribute the appearance of this exceedingly long crossover to a time lag in a complete recovery of small disconnected clusters of susceptible sites, which are apt to be generated when the system is prepared with Poisson-distributed quenched disorder. Finally, we demonstrate that this transient region becomes drastically diminished when we significantly increase the value of the recovery rate or enable diffusive agent mobility through short-range hopping.

Antiferromagnetism beyond the classical percolation threshold in the diluted half-filled one-band Hubbard model in three dimensions

We investigate the impact of site dilution by setting the on-site repulsion strength ($U$) to zero at a fraction of sites in the half-filled Hubbard model on a simple cubic lattice. We employ a semi-classical Monte-Carlo approach first to recover the zero dilution (undiluted $x=1$) properties, including $U$ dependence of insulator to metal crossover temperature scale $T^*$ and long-range staggered antiferromagnetic ordering temperature ($T_N$). For the non-perturbative regime of $U \sim$ bandwidth, we find a rapid suppression of $T^*$ with reducing $x$ from 1 to 0.7. However, $T_N$ remains unchanged in this dilution range, showing a weakening of the insulating state but not of the magnetic order. At $x \leq 0.7$, $T^*$ and $T_N$ coincide and are suppressed together with further increase in site-dilution. Finally, the system loses the magnetic order and the insulating state for $x=0.15$, significantly below the classical percolation threshold $x_p^{sc} (\sim 0.31$). We show that the induced moments on $U=0$ sites drive the magnetic order below the classical percolation limit by studying local moment systematics and finite-size analysis of magnetic order. At the end, we show that either increasing $U$ to large values or raising temperature beyond a $U$ dependent critical value, suppresses the induced local moments of the $U=0$ sites and recovers the classical percolation threshold.

Disorder, Low-Energy Excitations, and Topology in the Kitaev Spin Liquid.

The Kitaev model is a fascinating example of an exactly solvable model displaying a spin-liquid ground state in two dimensions. However, deviations from the original Kitaev model are expected to appear in real materials. In this Letter, we investigate the fate of Kitaev's spin liquid in the presence of disorder-bond defects or vacancies-for an extended version of the model. Considering static flux backgrounds, we observe a power-law divergence in the low-energy limit of the density of states with a nonuniversal exponent. We link this power-law distribution of energy scales to weakly coupled droplets inside the bulk, in an uncanny similarity to the Griffiths phase often present in the vicinity of disordered quantum phase transitions. If time-reversal symmetry is broken, we find that power-law singularities are tied to the destruction of the topological phase of the Kitaev model in the presence of bond disorder alone. However, there is a transition from this topologically trivial phase with power-law singularities to a topologically nontrivial one for weak to moderate site dilution. Therefore, diluted Kitaev materials are potential candidates to host Kitaev's chiral spin-liquid phase.

Cover Feature: Tailored Lipid Monolayers Doped with Gold Nanoclusters: Surface Studies and Electrochemistry of Hybrid‐film‐covered Electrodes (ChemElectroChem 9/2022)

The Cover Feature illustrates the biological–nonbiological hybrid monolayer composed of lipids and gold nanoclusters, Au25(SC4)180 prepared at the air - water interface and transferred onto ITO surface. The Langmuir–Blodgett technique allows to design the mixed monolayer composition and together with AFM and electrochemistry shows the changes of the lipid monolayer organization and properties upon increasing dilution of the AuNCs sites in the lipid matrix. More information can be found in the Research Article by A. Wieckowska, E. Jablonowska, M. Dzwonek, M. Jaskolowski and R. Bilewicz.

Adverse Vaccination Reactions in Animals and Man

It was only possible because of vaccination that we were able to create a safe environment for us and animals/ pets. If it was not for rabies vaccination, we never would have kept dogs and cats as our companion animals as we do now, and we never would have been able to protect our domestic animals from diseases that not only reduce the productivity but may even be deadly. But the vaccines comes with their own adverse effects such as hypersensitivity reactions which occur due to some component of the infectious agent or one of its products; due to stabilizers like gelatin; due to adjuvants like aluminium hydroxide; due to preservatives like thiomersal; due to antibiotics like neomycin; and due to a biological culture medium like chicken embryo cells. Other adverse effects include autoimmune disorders like immune mediated hemolytic anemia, thrombocytopenia and neoplastic diseases like fibrosarcomas. Lack of efficacy, interference with diagnostic testing and other occasional suspected product-related issues have also been reported as adverse vaccination reactions. An absence of adverse reaction indicates that the immune system has not been stimulated but due to variability in the vaccines immune system, environmental conditions and the nature of the vaccine, sometimes there may be excessive stimulation of immune system thus causing serious reactions. The common reasons for occurrence of vaccine reactions are contamination of vaccines with extraneous chemical agents, failure to inactivate the vaccine organism in a killed vaccine, adverse vaccine reactions due to vaccine-induced immune suppression, adverse vaccine reactions due to excessive induction of cytokine release. Also other adverse reactions are due to human errors like administration at the wrong site or improper dilution of the vaccines, or improper storage or transportation of vaccines and thus can be minimized. Also some vaccine reactions occur due to simultaneous administration of different vaccines so is preventable. Due to a marked degree of underreporting and a bias toward more severe adverse reactions, proper data for the vaccine reactions is not available from field conditions, also due to limited number of animals used during vaccine trials, there is no accurate data even in controlled settings as to how much adverse reactions can be expected while administering a vaccine. To solve this problem post marketing surveillance for all the vaccines should be done which should involve four interrelated components, namely, data collection, analysis, interpretation, and timely dissemination. To tackle this problem of adverse vaccination reaction we can also go for double blind placebo trails as are done for drug testing in which comparison is done between vaccinated and unvaccinated group and not just one vaccinated group with other vaccinated group.

Monte Carlo Simulation of a Mixed Spin‐1/2 and Spin‐3/2 Ising Ferrimagnetic System with Site Dilution

A study of the magnetic behavior of a mixed Ising system on a square lattice, where spins are located on alternating sites with spins , is presented. The change in the magnetic behavior of the system when empty sites are introduced in one of the sublattices or in both is analyzed. This system can be thought of as a site‐diluted ferrimagnet or as a system with nonmagnetic impurities. The Hamiltonian of the model contains an exchange interaction between nearest neighbors S–σ, next‐nearest‐neighbors , and a crystal field. The dependence of the total magnetization, the sublattice magnetizations, and the specific heat, with dilution is calculated. It is found that the behavior of the critical and compensation temperatures is strongly affected by dilution and where it is located. There is critical dilution, above which the compensation temperature disappears.

Ferromagnetic insulating behavior at low temperature induced by Sn doping in the ceramic SrRuO3

AbstractEffects of Sn doping at Ru site on the structural, magnetic, and transport behavior of polycrystalline SrRu1−xSnxO3 (x ≤ 0.1) have been investigated here. Substitution of Sn4+ for Ru4+ remains the same crystal symmetry with that of Sn‐free SrRuO3, while induces the Ru(Sn)O6 octahedral distortions. Samples with the low doping concentration (x ≤ 0.08) show a metallic behavior at high temperature, while a metal to insulator transition occurs at low temperature. On the other hand, an insulator behavior is detected for sample with x = 0.1, which follows Arrhenius‐type process in the temperature range of 80–140 K and Mott's variable range hopping model in the temperature range of 140–300 K. Further, we find that Sn4+ has a significant effect on the magnetic behavior of Sn doping in SrRuO3 where ferromagnetic transition temperature and magnetic moment decrease rapidly due to octahedral distortion and site dilution.

Directional clogging and phase separation for disk flow through periodic and diluted obstacle arrays.

We model collective disk flow though a square array of obstacles as the flow direction is changed relative to the symmetry directions of the array. At lower disk densities there is no clogging for any driving direction, but as the disk density increases, the average disk velocity decreases and develops a drive angle dependence. For certain driving angles, the flow is reduced or drops to zero when the system forms a heterogeneous clogged state consisting of high density clogged regions coexisting with empty regions. The clogged states are fragile and can be unclogged by changing the driving angle. For large obstacle sizes, we find a uniform clogged state that is distinct from the collective clogging regime. Within the clogged phases, depinning transitions can occur as a function of increasing driving force, with intermittent motion appearing just above the depinning threshold. The clogging is robust against the random removal or dilution of the obstacle sites, and the disks are able to form system-spanning clogged clusters even under increasing dilution. If the dilution becomes too large, however, the clogging behavior is lost.

A magnetic site dilution approach to achieve bifunctional fluorescent thermometers and single-ion magnets.

In complex [Na-Dy(μ2-L)4]n(HL = 8-hydroxyquinoline) (1), the DyL4 units were linked by the NaI ions to form one-dimensional chains. The chain exhibited slow magnetic relaxation behavior at low temperature, accompanied by obvious quantum tunneling of magnetization (QTM). Very weak fluorescence was detected in 1 due to the mismatch of the state energy between DyIII and the L ligand. Through the magnetic dilution of diamagnetic YIII ions, complex [NaDy0.02Y0.98(μ2-L)4]n (2) was obtained; in 2 the QTM of DyIII was suppressed and the single ion magnet (SIM) behavior was enhanced. More interestingly, the fluorescence emission of 8-hydroxyquinoline was lightened by the YIII ions in 2, whose intensity is linearly correlated with the temperature variation. The examples of dual functional fluorescent thermometers and SIM materials are attained simply by ion dilution, achieving the effect of killing two birds with one stone.

Investigation of thermo-mechanical behavior, proton transfer and methanol permeation of polymer electrolyte membrane in low sulfonated state modified with thermally stable surface functionalized graphene oxide nanosheets

Sulfonated polyether ether ketone is currently under investigation to replace the expensive Nafion® as polymer electrolyte membrane. Sulfonic acid group is hydrophilic in nature and plays a key role in proton transfer in polymer electrolyte membranes. The higher the degree of sulfonation the higher proton conductivity in sPEEK based polymer exchange membrane is achieved; however, high degree of sulfonation causes severe dimensional instability due to higher water uptake which in turn affects membrane fuel retention capabilities as well as thermo-mechanical strength. Graphene oxide nanosheets were functionalized with aryl dizonium salt of p-Aminobenzene sulfonic acid for modification of sPEEK in low sulfonated state (DS = 53%) to improve its proton conductivity and suppress fuel crossover. The functionalization was carried out to compensate for the possible dilution of proton exchangeable sites by fillers. The resulting membranes were characterized in terms of morphology, thermo-mechanical behavior, methanol permeability, water uptake, and proton conductivities. The results proved that sulfonated GO not only improved thermo-mechanical behavior of the membrane but also dramatically increased proton conductivity (47 mS cm−1) than pristine sPEEK (25 mS cm−1). The composite membranes showed highly reduced methanol crossover compared with pristine sPEEK. The electrochemical selectivity increased from 9.5 × 104 Scm−3s (pristine sPEEK) to 26.9 × 104 Scm−3s.

Majority-vote model with limited visibility: An investigation into filter bubbles

The dynamics of opinion formation in a society is a complex phenomenon where many variables play essential roles. Recently, the influence of algorithms to filter which content is fed to social networks users has come under scrutiny. Supposedly, the algorithms promote marketing strategies, but can also facilitate the formation of filters bubbles in which a user is most likely exposed to opinions that conform to their own. In the two-state majority-vote model, an individual adopts an opinion contrary to the majority of its neighbors with probability q, defined as the noise parameter. Here, we introduce a visibility parameter V in the dynamics of the majority-vote model, which equals the probability of an individual ignoring the opinion of each one of its neighbors. For V=0.5 each individual will, on average, ignore the opinion of half of its neighboring nodes. We employ Monte Carlo simulations to calculate the critical noise parameter as a function of the visibility qc(V) and obtain the phase diagram of the model. We find that the critical noise is an increasing function of the visibility parameter, such that a lower value of V favors dissensus. Via finite-size scaling analysis we obtain the critical exponents of the model, which are visibility-independent, and show that the model belongs to the Ising universality class. We compare our results to the case of a network submitted to a static site dilution and find that the limited visibility model is a more subtle way of inducing opinion polarization in a social network.

Thermodynamic and transport properties in disordered Kitaev models

Effects of bond randomness and site dilution are systematically investigated for the Kitaev model describing a quantum spin liquid with fractional excitations of itinerant Majorana fermions and localized fluxes. We find that, in the high-temperature region where the itinerant Majorana fermions release their entropy, both types of disorders suppress the longitudinal thermal conductivity while keeping the specific heat almost unchanged. This suggests that both disorders reduce the mean-free path of the Majorana fermions. On the other hand, in the low-temperature region, the other specific heat peak associated with the entropy release from the localized fluxes is suppressed for both cases, but it is broadened and shifted to the lower-temperature side by the bond randomness, while the position and the width are almost unchanged against the site dilution. Contrasting behavior is also found in the thermal Hall effect under a magnetic field; the half quantization of the thermal Hall conductivity is fragile against the site dilution, while it remains for the bond randomness despite the reduced onset temperature. We discuss the contrasting behavior from the stability of the topological nature by calculating flux condensation and Majorana excitation gap.