Phenomenon Of Catalysis Research Articles

On the EFT of dyon-monopole catalysis

Monopole-fermion (and dyon-fermion) interactions provide a famous example where scattering from a compact object gives a cross section much larger than the object’s geometrical size. This underlies the phenomenon of monopole catalysis of baryon-number violation because the reaction rate is much larger in the presence of a monopole than in its absence. It is sometimes claimed to violate the otherwise generic requirement that short distance physics decouples from long-distance observables — a property that underpins the general utility of effective field theory (EFT) methods. Decoupling in this context is most simply expressed using point-particle effective field theories (PPEFTs) designed to capture systematically how small but massive objects influence their surroundings when probed only on length scales large compared to their size. These have been tested in precision calculations of how nuclear properties affect atomic energy levels for both ordinary and pionic atoms. We adapt the PPEFT formalism to describe low-energy S-wave dyon-fermion scattering with a view to understanding whether large catalysis cross sections violate decoupling (and show why they do not). We also explore the related but separate issue of the long-distance complications associated with polarizing the fermion vacuum exterior to a dyon and show in some circumstances how PPEFT methods can simplify calculations of low-energy fermion-dyon scattering in their presence. We propose an effective Hamiltonian governing how dyon excitations respond to fermion scattering in terms of a time-dependent vacuum angle and outline open questions remaining in its microscopic derivation.

Unraveling the role of EPOC during the enhancement of RWGS reaction in a Pt/YSZ/Au single chamber reactor

The hydrogenation of CO2 remains one of the most intriguing and effective strategies for addressing the continuous increase of CO2 emissions in the atmosphere. At the same time, it serves as an effective pathway for the formation of value-added products. This work explores the Electrochemical Promotion of Catalysis (EPOC) phenomenon on the CO2 hydrogenation reaction, utilizing a single chamber reactor with a Pt/YSZ/Au electrochemical cell. Experiments were conducted under ambient pressure conditions, within a temperature range of 200–400 °C, for a reactant flow rate of 100 cm3/min under reducing (PCO2: PH2 = 1:7) and oxidizing (PCO2: PH2 = 2:1) conditions. The effect of reactant ratio, reactor temperature, and applied current/potentials on the reaction rate were thoroughly investigated. The only observed product was carbon monoxide through the Reverse Water Gas Shift Reaction (RWGS). Under purely catalytic operation of the cell (open circuit), reducing conditions were found to be more favorable for the RWGS reaction as compared to oxidizing ones. The imposition of negative potential values under reducing environment resulted in a 2.3-fold increase in the RWGS reaction rate (rCO = 21 × 10−9 mol/s) as compared to open circuit values (rCO = 9 × 10−9 mol/s). On the other hand, application of positive potentials had no profound effect on the catalytic rate, which was attributed to competing electrochemical and surface processes taking place on the catalyst electrode. The kinetic results are discussed in conjunction with the physicochemical and the morphological characteristics of the catalytic film.

Reduction of pseudocritical temperatures of chiral restoration and deconfinement phase transitions in a magnetized PNJL model

We investigate the chiral restoration and deconfinement phase transitions under an external magnetic field in the frame of a Pauli-Villars regularized Polyakov loop extended Nambu-Jona-Lasinio model. A running Polyakov loop scale parameter T0(eB) is introduced to mimic the reaction of the gluon sector to the presence of magnetic fields. It is found that a decreasing T0(eB) with magnetic fields can realize the inverse magnetic catalysis phenomena of chiral condensates of u and d quarks, increase of Polyakov loop, and the reduction of pseudocritical temperatures of chiral restoration and deconfinement phase transitions. Published by the American Physical Society 2024

Kinetics insights into size effects of carbon nanotubes’ growth and their supported platinum catalysts for 4,6-dinitroresorcinol hydrogenation

Size effects are a well-documented phenomenon in heterogeneous catalysis, typically attributed to alterations in geometric and electronic properties. In this study, we investigate the influence of catalyst size in the preparation of carbon nanotube (CNT) and the hydrogenation of 4,6-dinitroresorcinol (DNR) using Fe2O3 and Pt catalysts, respectively. Various Fe2O3/Al2O3 catalysts were synthesized for CNT growth through catalytic chemical vapor deposition. Our findings reveal a significant influence of Fe2O3 nanoparticle size on the structure and yield of CNT. Specifically, CNT produced with Fe2O3/Al2O3 containing 28% (mass) Fe loading exhibits abundant surface defects, an increased area for metal-particle immobilization, and a high carbon yield. This makes it a promising candidate for DNR hydrogenation. Utilizing this catalyst support, we further investigate the size effects of Pt nanoparticles on DNR hydrogenation. Larger Pt catalysts demonstrate a preference for 4,6-diaminoresorcinol generation at (1 0 0) sites, whereas smaller Pt catalysts are more susceptible to electronic properties. The kinetics insights obtained from this study have the potential to pave the way for the development of more efficient catalysts for both CNT synthesis and DNR hydrogenation.

Exploring the Interfacial Hydrogen Transfer between Pt and the Siliceous Framework and Its Promotional Effect on the Isotope Catalytic Exchange.

Interfacial hydrogen transfer between metal particles and catalyst supports is a ubiquitous phenomenon in heterogeneous catalysis, and this occurrence on reducible supports has been established, yet controversies remain about how hydrogen transfer can take place on nonreducible supports, such as silica. Herein, highly dispersed Pt clusters supported on a series of porous silica materials with zeolitic or/and amorphous frameworks were prepared to interrogate the nature of hydrogen transfer and its promotional effect on H2-HDO isotope catalytic exchange. The formation of zeolitic frameworks upon these porous silica supports by hydrothermal crystallization greatly promotes the interfacial hydrogen bidirectional migration between metal clusters and supports. Benefiting from this transfer effect, the isotope exchange rate is enhanced by 10 times compared to that on the amorphous counterpart (e.g., Pt/SBA-15). In situ spectroscopic and theoretical studies suggest that the defective silanols formed within the zeolite framework serve as the reactive sites to bind HDO or H2O by hydrogen bonds. Under the electrostatic attraction interaction, the D of hydrogen-bonded HDO scrambles to the Pt site and the dissociated H on Pt simultaneously spills back to the electronegative oxygen atom of adsorbed water to attain H-D isotope exchange with an energy barrier of 0.43 eV. The reverse spillover D on Pt combines with the other H on Pt to form HD in the effluent. We anticipate that these findings are able to improve our understanding of hydrogen transfer between metal and silica supports and favor the catalyst design for the hydrogen-involving reaction.

An NJL model analysis of a magnetised nonextensive QCD medium

We investigate the effect of a background magnetic field when applied to a nonextensive QCD medium in a 2+1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2+1$$\\end{document} flavour Nambu— Jona-Lasinio model. The effect of a constant as well as an eB-dependent coupling is considered. For the constant coupling, the well-known magnetic catalysis effect is observed with reduced strength in both the condensates and the transition temperatures compared to the standard extensive medium. In the case of a field-dependent coupling, we observe a competition between the nonextensive parameter, q and eB. With sufficiently high q-values, the phenomenon of inverse magnetic catalysis —, a well-known trait in effective models featuring eB-dependent coupling, appears to be eliminated within the range of magnetic fields examined in our present study.

Demagnetizing Ferromagnetic Catalysts to the Sabatier Optimal of Haber-Bosch Process.

Achieving the Sabatier optimal of a chemical reaction has been the central topic in heterogeneous catalysis for a century. However, this ultimate goal was greatly hindered in previous catalyst design strategies since the active sites indeed changed. Fortunately, the magneto-catalytic effect (MCE) provides a promising solution to this long-standing challenge. Recent research suggests that the performance of ferromagnetic catalysts is capable to be promoted without changing its chemical structure. Herein, we use time-dependent density functional perturbation theory (TDDFPT) calculations to elucidate that a partially demagnetized (DM) ferromagnet could be a Sabatier optimal catalyst. Using ammonia synthesis as the model reaction, we determined the activity of Cobalt at each DM state by including the magnetic thermal excitations via magnon analysis, making the 55% DM Co to the genuine Sabatier optimal. As an essential but underexcavated phenomenon in heterogeneous catalysis, the MCE will open a new avenue to design high-performance catalysts.

Quarkonia dissociation at finite magnetic field in the presence of momentum anisotropy

In this study, we investigate the potential of heavy quarkonia within a magnetized hot QGP medium having finite momentum anisotropy. The phenomenon of inverse magnetic catalysis is introduced into the system, influencing the magnetic field-modified Debye mass and thereby altering the effective quark masses. Concurrently, the impact of momentum anisotropy in the medium is considered that influence the particle distribution in the medium. The thermal decay width and dissociation temperature of quarkonium states, specifically the 1S and 2S states of charmonium and bottomonium, are computed. Our results reveal that both momentum anisotropy and the inverse magnetic catalysis effects play a significant role in modifying the thermal decay width and dissociation temperature of these heavy quarkonia states.

Mass and spectral function of scalar and pseudoscalar mesons in a hot and chirally imbalanced medium using the two-flavor NJL model

We explore the properties of neutral mesons within the context of a chirally imbalanced medium, employing the two-flavor Nambu–Jona-Lasinio model. The temperature dependence of the constituent quark mass at finite values of the chiral chemical potential (CCP) demonstrates the well-established phenomena of chiral catalysis at lower temperatures and inverse chiral catalysis at higher temperatures. The polarization functions in both the scalar (σ) and pseudoscalar (π0) channels have been evaluated using the real-time formalism of thermal field theory. These have been used to determine the masses and spectral functions of σ and π mesons. Detailed investigation of the analytic structure of the imaginary part of the polarization function for σ and π mesons results in the emergence of nontrivial Landau-cut contributions due to the presence of chiral imbalance. The multiple solutions for the mass of the π meson for specific values of CCP have been analyzed on the basis of their residue at the pole. Furthermore, we have observed abrupt changes in the masses of both scalar and pseudoscalar mesons at finite CCP values, particularly at higher temperatures. A decreasing trend in the Mott transition temperature is seen with the increase in CCP. Published by the American Physical Society 2024

A Primer on 2D Descriptors in Selectivity Modeling for Asymmetric Catalysis.

Machine learning has permeated all fields of research, including chemistry, and is now an integral part of the design of novel compounds with desired properties. In the field of asymmetric catalysis, the preference still lies with models based on a physical understanding of the catalysis phenomenon and the electronic and steric properties of catalysts. However, such models require quantum chemical calculations and are thus limited by their computational cost. Here, we highlight the recent advances in modeling catalyst selectivity by using the 2D structures of catalysts and substrates. While these have a less explicit mechanistic connection to the modeled property, 2D descriptors, such as topological indices, molecular fingerprints, and fragments, offer the tremendous advantages of low cost and high speed of calculations. This makes them optimal for the in-silico screening of large amounts of data. We provide an overview of common quantitative structure-property relationship workflow, model building and validation techniques, applications of these methodologies in asymmetric catalysis design, and an outlook on improving the understanding of 2D-based models.

Magnetic catalysis in holographic model with two types of anisotropy for heavy quarks

In our previous paper (Aref’eva et al. in JHEP 07:161, 2021, arXiv:2011.07023 [hep-th]) we have constructed a twice anisotropic five-dimensional holographic model supported by Einstein-dilaton-three-Maxwell action that reproduced some essential features of the “heavy quarks” model. However, that model did not describe the magnetic catalysis (MC) phenomena expected from lattice results for the QGP made up from heavy quarks. In this paper we fill this gap and construct the model that improves the previous one. It keeps typical properties of the heavy quarks phase diagram, and meanwhile possesses the MC. The deformation of previous model includes the modification of the “heavy quarks” warp factor and the coupling function for the Maxwell field providing the non-trivial chemical potential.

QCD phase diagram in the presence of electric and magnetic fields

In this contribution, We revisit the effect of electric eE and magnetic field eB and on the critical temperature T χ,C c of the chiral symmetry breaking/restoration and confinement/deconfinement phase transition in the QCD Phase diagram. In this context, we use the symmetrypreserving vector-vector contact interaction model of quarks, in the Schwinger-Dyson equations framework and in the proper time regularization scheme. We also describe the phenomenon of inverse electric catalysis in the pure electric case, magnetic catalysis (and inverse magnetic catalysis) in the pure magnetic case and inverse electromagnetic catalysis in the presence of both electric and magnetic background fields.

Realistic geometric modeling of the dielectric constant and its effect on the discharge with a porous dielectric

Porous dielectric discharge (PDD) is a critical phenomenon in plasma catalysis, biomedical tissue surface functionalization, and all-solid-state battery design. The dielectric constant of porous dielectric (PD) significantly impacts discharge characteristics and breakdown mechanisms across different applications. However, the complex spatial structure of porous media presents challenges in diagnosing and simulating PDD, limiting our understanding of its mechanism. In this study, the real geometric model of PD obtained from x-ray computed tomography (X-Ray-μ CT) and a two-dimensional fluid model were used to simulate and analyze the effect of dielectric constant on PDD-plasma characteristics, especially the generation and disappearance of charged particles. The simulation results reveal the following: (1) At the breakdown moment, PDD is a density-unbalanced discharge where the electron density is two orders of magnitude higher than the ion density; (2) The breakdown discharge follows the most accessible channel instead of filling the entire gap, which is guided by the electron temperature gradient; and (3) It was first discovered that the breakdown voltage exhibits a saturated growth curve under the control of the dielectric constant. By combining these mechanisms, a comprehensive explanation has been provided for this phenomenon. This study offers a robust simulation and theoretical basis for understanding the breakdown characteristics of PDD.

Magnetic catalysis in the ( 2+1 )-dimensional Gross-Neveu model

We study the Gross-Neveu model in $2+1$ dimensions in an external magnetic field $B$. We first summarize known mean-field results, obtained in the limit of large flavor number $N_\mathrm{f}$, before presenting lattice results using the overlap discretization to study one reducible fermion flavor, $N_\mathrm{f}=1$. Our findings indicate that the magnetic catalysis phenomenon, i.e., an increase of the chiral condensate with the magnetic field, persists beyond the mean-field limit for temperatures below the chiral phase transition and that the critical temperature grows with increasing magnetic field. This is in contrast to the situation in QCD, where the broken phase shrinks with increasing $B$ while the condensate exhibits a non-monotonic $B$-dependence close to the chiral crossover, and we comment on this discrepancy. We do not find any trace of inhomogeneous phases induced by the magnetic field.

Strong Metal-Support Interaction (SMSI) in Au/TiO2 photocatalysts for environmental remediation applications: Effectiveness enhancement and side effects

Strong Metal−Support Interaction (SMSI) is a well-known phenomenon of heterogeneous catalysis that have not been extensively investigated in photocatalytic applications. Moreover, the reactions previously studied for photocatalysts under SMSI state are mainly restricted to energy related uses. The present work seeks to explore the effect of SMSI induced by soft wet-chemistry in a Au/TiO2 photocatalyst with specific focus on photocatalytic environmental remediation. With this aim, the developed photocatalyst has been evaluated considering liquid, gas and solid pollutants in order to represent the wide range of environmental photocatalysis applications. These photooxidation scenarios were methylene blue dissolved in water, gaseous NO, and soot directly deposited on the photocatalyst. The results revealed that the SMSI induction has a generally positive effect on photoactivity promoting the MB and soot removal by 53% and 60%, respectively. However, the SMSI did not provide any additional benefit in the NOx elimination compared to the non-SMSI Au/TiO2 photocatalyst, because the enveloping of AuNPs limits the gold-pollutant interaction.

Elucidating the alkene hydrogenation reaction based on cotton textile reduced graphene oxide under the influence of external electric field: Illustration of new noble method

The hydrogenation reaction of alkene is one of the most used industrial chemical process for various materials of daily life and energy consumption. This is a heterogeneous reaction and traditionally carried out by metallic catalysis. However, these conventional catalytic hydrogenations of alkene suffer from various setbacks such as catalyst poisoning, less recyclability and are environmentally unfriendly. Therefore, in recent years, researchers have been trying to develop the alternatives to metal catalysis hydrogenation of alkene. Heterogeneous catalysis under the external electric field is considered the future of green catalysis. In this paper, we report a comprehensive investigation dealing with the theoretical basis for simulating the phenomenon of heterogeneous catalysis, on a molecular level, under an external electric field. The illustration of the prospect as well as the effects of the mostly used catalytic systems, reduced graphene oxide, under the influence of external electric fields is provided. Moreover, a noble method of alkene hydrogenation reaction based on cotton textile reduced graphene oxide (CT-RGO) under the influence of an external electric field is introduced. The corresponding theoretical investigation was carried out within the framework of the density functional theory (DFT) method using first-principles calculations. The study has been carried out by elucidating DFT calculations for three different proposed catalytic systems, namely without electricity, with electricity and with an external electric field of 2 milli-Atomic unit. The obtained results indicate that adsorption energy of H2 on the CT-RGO surface is significantly higher when the electric field is applied along the bond axis, suggesting thereby that hydrogenation of alkene can be induced with CT-RGO catalyst support under external electric fields. The obtained results shed light on the effect of the external electricity field on the graphene-hydrogen complex, the activation energy of graphene radicals to achieve the transition states as well as the adsorption of the hydrogen atoms over the graphene surface. Altogether, the theoretical results presented herein suggested that the proposed catalytic system holds promise for facilitating the alkene hydrogenation under external electric fields.

Approaching Molecular Definition on Oxide-Supported Single-Atom Catalysts.

ConspectusSingle-atom catalysts (SACs) offer unique advantages such as high (noble) metal utilization through maximum possible dispersion, large metal-support contact areas, and oxidation states usually unattainable in classic nanoparticle catalysis. In addition, SACs can serve as models for determining active sites, a simultaneously desired as well as elusive target in the field of heterogeneous catalysis. Due to the complexity of heterogeneous catalysts bearing a variety of different sites on metal particles and the respective support as well as at their interface, studies of intrinsic activities and selectivities remain largely inconclusive. While SACs could close this gap, many supported SACs remain intrinsically ill-defined due to complexities arising from the variety of different adsorption sites for atomically dispersed metals, hampering the establishment of meaningful structure-activity correlations. In addition to overcoming this limitation, well-defined SACs could even be utilized to shed light on fundamental phenomena in catalysis that remain ambiguous when studies are obscured by the complexity of heterogeneous catalysts.In this Account, we describe approaches to break down the complexity of supported single-atom catalysts through the careful choice of oxide supports with specific binding motives as well as the adsorption of well-defined ligands such as ionic liquids on single metal sites. An example of molecularly defined oxide supports is polyoxometalates (POMs), which are metal oxo clusters with precisely known composition and structure. POMs exhibit a limited number of sites to anchor atomically dispersed metals such as Pt, Pd, and Rh. Polyoxometalate-supported single-atom catalysts (POM-SACs) thus represent ideal systems for the in situ spectroscopic study of single atom sites during reactions as, in principle, all sites are identical and thus equally active in catalytic reactions. We have utilized this benefit in studies of the mechanism of CO and alcohol oxidation reactions as well as the hydro(deoxy)genation of various biomass-derived compounds. More so, the redox properties of polyoxometalates can be finely tuned by changing the composition of the support while keeping the geometry of the single-atom active site largely constant. We further developed soluble analogues of heterogeneous POM-SACs, opening the door to advanced liquid-phase nuclear magnetic resonance (NMR) and UV-vis techniques but, in particular, to electrospray ionization mass spectrometry (ESI-MS) which proves powerful in determining catalytic intermediates as well as their gas-phase reactivity. Employing this technique, we were able to resolve some of the long-standing questions about hydrogen spillover, demonstrating the broad utility of studies on defined model catalysts.

Role of Fluxionality and Metastable Isomers in the ORR Activity: A Case Study

Understanding the dynamic reconstruction of active sites and the fluxional behavior of subnanoclusters has become the heart of operando modeling techniques. An accurate description of catalysis phenomena extends toward incorporating the activity of thermally accessible ensembles of metastable isomers in addition to the global minima (GM). Considering the Pt13 cluster as a model catalyst for gas-phase oxygen reduction reaction (ORR), we have studied the role of metastable isomers and unravelled their distinct catalyst dynamics leading to high fluxionality. The different adsorption energetics and ORR activity featured by the metastable isomers reveal the importance of addressing the fluxional behavior of subnanoclusters. A detailed mechanistic ORR investigation provided isomers possessing an activity comparable to GM. Furthermore, a statistical ensemble representation demonstrates the substantial role of metastable isomers within 0.4 eV relative energy difference from GM, with negligible activity enhancement of isomers with high energy at 300 K. Ab initio thermodynamics-based stability analysis represents different energetics associated with the Pt13 clusters at high oxygen coverage. This study highlights the importance of exploring the role of metastable isomers in determining the cumulative catalytic activity of subnanometer clusters.

Magnetic field driven catalysis of multiferroic magnetoelectric nanocomposites

Magnetic field as a booster for catalytic reactions has been widely studied in the past few decades. Recently, multiferroic materials with intriguing magnetoelectric coupling effects have been emerging as a new type of catalyst, providing a unique opportunity for magnetically-driven catalytic reactions in a variety of fields, including clean energy, environmental and biomedical applications. In this review, we describe this entirely new catalysis phenomenon observed in multiferroic magnetoelectric composite materials, aiming at giving an in-depth understanding of magnetically-driven catalysis processes based on the direct magnetoelectric-catalytic effect. Moreover, the latest progress in catalytic applications of magnetoelectric nanocomposite nanomaterials is comprehensively summarized. Finally, the challenges and future perspectives for the design and application of high-efficient magneto-multiferroic catalysts are discussed.

Frustration and the Kinetic Repartitioning Mechanism of Substrate Inhibition in Enzyme Catalysis.

Substrate inhibition, whereby enzymatic activity decreases with excess substrate after reaching a maximum turnover rate, is among the most elusive phenomena in enzymatic catalysis. Here, based on a dynamic energy landscape model, we investigate the underlying mechanism by performing molecular simulations and frustration analysis for a model enzyme adenylate kinase (AdK), which catalyzes the phosphoryl transfer reaction ATP + AMP ⇋ ADP + ADP. Intriguingly, these reveal a kinetic repartitioning mechanism of substrate inhibition, whereby excess substrate AMP suppresses the population of an energetically frustrated, but kinetically activated, catalytic pathway going through a substrate (ATP)-product (ADP) cobound complex with steric incompatibility. Such a frustrated pathway plays a crucial role in facilitating the bottleneck product ADP release, and its suppression by excess substrate AMP leads to a slow down of product release and overall turnover. The simulation results directly demonstrate that substrate inhibition arises from the rate-limiting product-release step, instead of the steps for populating the catalytically competent complex as often suggested in previous works. Furthermore, there is a tight interplay between the enzyme conformational equilibrium and the extent of substrate inhibition. Mutations biasing to more closed conformations tend to enhance substrate inhibition. We also characterized the key features of single-molecule enzyme kinetics with substrate inhibition effect. We propose that the above molecular mechanism of substrate inhibition may be relevant to other multisubstrate enzymes in which product release is the bottleneck step.