Heterogeneous Reactions Research Articles

Unraveling the adsorption-limited hydrogen oxidation reaction at palladium surface via in situ electron microscopy

Palladium (Pd) catalysts have been extensively studied for the direct synthesis of H2O through the hydrogen oxidation reaction at ambient conditions. This heterogeneous catalytic reaction not only holds considerable practical significance but also serves as a classical model for investigating fundamental mechanisms, including adsorption and reactions between adsorbates. Nonetheless, the governing mechanisms and kinetics of its intermediate reaction stages under varying gas conditions remain elusive. This is attributed to the intricate interplay between adsorption, atomic diffusion, and concurrent phase transformation of catalyst. Herein, the Pd-catalyzed, water-forming hydrogen oxidation is studied in situ, to investigate intermediate reaction stages via gas cell transmission electron microscopy. The dynamic behaviors of water generation, associated with reversible palladium hydride formation, are captured in real time with a nanoscale spatial resolution. Our findings suggest that the hydrogen oxidation rate catalyzed by Pd is significantly affected by the sequence in which gases are introduced. Through direct evidence of electron diffraction and density functional theory calculation, we demonstrate that the hydrogen oxidation rate is limited by precursors' adsorption. These nanoscale insights help identify the optimal reaction conditions for Pd-catalyzed hydrogen oxidation, which has substantial implications for water production technologies. The developed understanding also advocates a broader exploration of analogous mechanisms in other metal-catalyzed reactions.

Morphology and elemental composition of individual solid dust particles: From different sources to the atmosphere

This study investigates the morphology and elemental composition of individual solid dust particles from various sources (e.g., thermal power plant, domestic coal combustion, building construction dust, wind-blown dust, Asian dust storm, and road related dust) to the atmosphere under high and low relative humidity (RH) conditions in a coastal city of north China by using high-resolution electron microscopes. The results showed that distinct variations between dust particles from thermal power plant and domestic coal combustion, despite both using coal as fuel. Specifically, 88.6% (by number) of thermal power plant particles were spherical, whereas only 2 out of 347 particles from domestic coal combustion exhibited a spherical shape. Furthermore, domestic coal combustion particles showed a higher proportion of Ca-rich particles compared to those from thermal power plant. The wind-blown dust and Asian dust storm particles were mainly “Si + Al” subtype (52.0% v.s. 75.3%) and Si-dominant subtype (16.4% v.s. 11.7%) particles, which were mainly from crustal sources. However, wind-blown dust contained a higher fraction of Ca-rich (11.6%) and Fe-rich (5.3%) particles than Asian dust. The building construction dust particles primarily consisted of irregular Ca-dominant (39.4%) and “Ca + Si” subtype (29.8%) particles. Road related dust were also mainly Si-rich particles (52.9%), likely from re-suspended soil, along with a notable presence of spherical (8.0%) and Fe-rich particles (19.3%), possibly linked to vehicle emissions and brake wear. Additionally, relative number percentage of Na-rich particles and the average weigh ratios of Na in the atmospheric particles were higher than those from all above-mentioned source samples, suggesting that sea-salt related particles might be an important source of the atmospheric dust at the coastal city. The results indicated that Ca-rich particles were significantly modified by S and NaCl particles might lose Cl through heterogeneous reactions under higher RH.

Structure-activity relationship, adsorption, and fenton-like catalytic oxidation capacity of iron-oxide nano-confined materials

In this study, iron-oxide was loaded into polystyrene macroporous microspheres containing sulfonate groups to prepare an environmental purification material with adsorption and Fenton-like oxidizing abilities. Iron-oxide is prone to inactivation due to reunion in the process of preparation and application, and this modification aimed to mitigate this problem. Subsequently, based on the microscopic characterization results and the effect on the treatment of methylene blue (MB) simulated wastewater, the structure-activity relationship of two key (OH− concentrations in precipitation solution and iron ion compositions in the impregnation solution) factors with the adsorption and catalytic oxidation ability of the iron-oxide nano-confined materials were explored. The results indicated that the samples both exhibited adsorption and catalytic oxidation capabilities. The removal efficiency of MB simulated wastewater can reached 95.3% after adsorption for 9 h, reaching 99.98% after catalytic oxidation for 6 h. In addition, the removal efficiency of the MB simulated wastewater exceeded 95% after 6 cycles. The concentration of OH− in precipitation solution could affect the volume of iron crystals on the carrier which affected the pore size of the sample and the adsorption capacity. It also influenced whether iron ions could be stably loaded inside the carrier, determining the conducting homogeneous or heterogeneous Fenton-like reactions and the stability of the samples. The composition of iron ions in the impregnating solution regulated the volume of the crystals and adsorption sites, which influenced the adsorption ability of the samples. In addition, the presence of Fe2+ could promote the progress of Fenton-like reactions. The identification results of the ROSs showed that •OH was the main free radical. The quenching experiment results showed that the contribution rate of •OH toward MB degradation reached 99.81%. In addition, the possible degradation pathways of MB were analyzed.

Study of the kinetics and mechanisms of rare earth elements leaching from end-of-life NdFeB magnets through Hydro-Nd process

With the growing demand for REEs in numerous high-tech and energy transition-related applications, recycling these elements from secondary sources, mainly from end-of-life permanent magnets, has become crucial for responsible sourcing of raw materials from a circular economy. To date, numerous processes have been developed and optimized to allow this recovery to be sustainable from both an economic and environmental point of view. In this context, hydrometallurgy is one of the most promising avenues. Through an innovative hydrometallurgical process (Hydro-Nd), this research investigated the kinetics and mechanisms involved in leaching REEs from end-of-life permanent magnets. This process involves the use of citric acid in the leaching phase. Through systematic experimentation and analysis, the article elucidates key factors influencing leaching kinetics, providing insight into critical mechanisms of the process. In particular, ANOVA was used to study the influence of important factors (temperature, particle size, and agitation) on the recovery yields of the elements of interest. The shrinking core model studied the leaching mechanisms to identify a possible rate-determining step. Thanks to the results obtained, the Arrhenius parameters were estimated for the different heterogeneous reactions involved in the process, and the trend of the time constants versus the average diameter of the solid particles was identified. Also, the results showed that 100 % of Nd, Fe, Dy, B, and Pr from small PM particles (0–40 µm) in 4 h and more than 90 % of the mentioned metals from large particles (1000–1700 µm) within 5 h of leaching time were dissolved by citric acid solution. This research not only contributes to the development of an even more sustainable rare earth recovery process thanks to the optimization of several factors but also clarifies fundamental aspects of leaching kinetics and mechanisms, paving the way for future advances in the recovery of REEs from different sources.

A CAPRAM Modeling Study on the Role of Heterogeneous Reactions on Dust in Tropospheric Chemistry

A CAPRAM Modeling Study on the Role of Heterogeneous Reactions on Dust in Tropospheric Chemistry

Spontaneous Molecular Bromine Production in Sea-Salt Aerosols.

Bromine chemistry is responsible for the catalytic ozone destruction in the atmosphere. The heterogeneous reactions of sea-salt aerosols are the main abiotic sources of reactive bromine in the atmosphere. Here, we present a novel mechanism for the activation of bromide ions (Br-) by O2 and H2O in the absence of additional oxidants. The laboratory and theoretical calculation results demonstrated that under dark conditions, Br-, O2 and H3O+ could spontaneously generate Br and HO2 radicals through a proton-electron transfer process at the air-water interface and in the liquid phase. Our results also showed that light and acidity could significantly promote the activation of Br- and the production of Br2. The estimated gaseous Br2 production rate was up to 1.55×1010 molecules cm-2 ⋅ s-1 under light and acidic conditions; these results showed a significant contribution to the atmospheric reactive bromine budget. The reactive oxygen species (ROS) generated during Br- activation could promote the multiphase oxidation of SO2 to produce sulfuric acid, while the increase in acidity had a positive feedback effect on Br- activation. Our findings highlight the crucial role of the proton-electron transfer process in Br2 production; here, H3O+ facilitates the activation of Br- by O2, serves as a significant source of atmospheric reactive bromine and exerts a profound impact on the atmospheric oxidation capacity.

Microwave-Assisted Oxidation of N2 into NOx over a La-Ce-Mn-O Perovskite Yielding Plasmas in a Quartz Flow Reactor at Atmospheric Pressure

N2 oxidation to NOx is a challenging reaction, and alternative routes to the industrial Ostwald process are of interest. A perovskite under flowing O2-N2 mixtures at atmospheric pressure in a quartz tube reactor was irradiated by microwaves (MW), leading to the formation of hot spots and plasmas within the catalyst bed. NOx concentrations up to 2.5 vol.% in one pass were obtained at 600 W. Using a lower MW power of 100 W led to a pulsed mode yielding lower NOx concentrations and no noticeable damage to the quartz reactor. The formation of plasma was strongly dependent on the perovskite bed packing. The perovskite acted primarily as a susceptor and likely also as a catalyst, although the proportion of heterogeneous and homogenous reactions could not be determined in the present study. The simple reactor layout allowing operation at atmospheric pressure is promising for the development of practical MW-assisted N2 fixation technologies.

Sequential-Flow Synthesis of Donepezil: A Green and Sustainable Strategy Featuring Heterogeneous Catalysis and Hydrogenation.

An atom-economical sequential-flow synthesis of donepezil, a widely prescribed drug for Alzheimer's disease, was accomplished using inexpensive, commercially available precursors. This achievement was made possible by reconfiguring the synthetic route to include only heterogeneous catalytic addition and condensation reactions, with a particular emphasis on skeletal transformation and bond formation through hydrogenation processes. Notably, water was the sole byproduct in this synthesis. A crucial aspect of this work was the development of appropriate continuous-flow processes to achieve a one-flow synthesis. This was accomplished by implementing in-line treatments of the main reaction stream to eliminate inhibitory factors that could affect catalyst performance in the hydrogenation steps.

Insight into the Hamilton and Crosser model for ternary hybrid nanofluid flow over a Riga wedge with heterogeneous catalytic reaction

Insight into the Hamilton and Crosser model for ternary hybrid nanofluid flow over a Riga wedge with heterogeneous catalytic reaction

New insights into the quantiffcation of Fe(IV) using methyl phenyl sulfoxide (PMSO) as probe in the iron-based heterogeneous catalyst activated persulfate process

Ferryl ions (Fe(IV)) are often thought to play an important role in iron-based advanced oxidation processes (AOPs), and their presence is typically inferred through the unique pathway of methyl phenyl sulfoxide (PMSO) conversion to methyl phenyl sulfone (PMSO2). Here, we first employed probe method by degrading the mixed system containing PMSO, benzoic acid (BA), nitrobenzene (NB) to analyze the steady-state concentration of Fe (IV) in the iron-based heterogeneous persulfate reaction system. In addition, studies were conducted on the direct oxidation of PMSO by different oxidants under different pH conditions, and the results showed that peroxymonosulfate (PMS), sodium hypochlorite (NaClO) and sodium periodate (PI) can directly oxidize PMSO and convert it into PMSO2. Furthermore, the influence of different types of iron salts and biomass on the prepared iron-biochar (Fe-BC) for the activation of persulfate on degradation of PMSO and the formation of PMSO2 was also investigated. This study may provide new insights into the use of PMSO as a probe for the analysis of Fe(IV) in heterogeneous reaction systems.

XCT images-based modeling for elucidating electrochemical inert phase-dependent multiscale electrode kinetic behaviors

The electrochemically inert phase (EIP) within the electrode is formed by the combination of carbon black and binder, characterized by a highly heterogeneous spatial distribution and structural morphology. This heterogeneity impairs electrode performance under varying discharge rates and temperatures. In this study, X-ray computed tomography is employed to image the original electrode. The resulting grayscale images are digitally processed to reveal the two-dimensional (2D) and three-dimensional (3D) features of the EIP morphology, thereby providing a design window to understand the influence of EIP morphology. The physical structure characterization indicates that, compared to bulk-like EIP (B-EIP), film-like EIP (F-EIP) tends to cover the active surface of the active material (AM), exacerbating the heterogeneity of the lithiation reactions within the electrode. The reduction in the AM active surface area correlates the state of lithiation (SOL) of particles with their active specific surface area (αa). At low temperatures, the temperature sensitivity of electrodes intensifies the risk of αa loss, promoting heterogeneous reaction transfer between particles. The Biot number (Bi) is used to evaluate the competing mechanisms between interfacial reactions and bulk diffusion within particles. In electrodes with a high EIP content, the reaction rate at the particle/electrolyte interface is accelerated, causing particle performance to be dominated by interfacial reactions. Finally, the electrochemistry and heat generation from the particle-level to the electrode-level in thicker electrodes are examined. It demonstrates that ion diffusion in the pore controls interfacial reactions and heat transport behavior. Aggregated high-flux reactions and localized hot spots exacerbate the heterogeneous degradation and side reactions within the electrode.

Development of Organocatalytic Darzens Reactions Exploiting the Cyclopropenimine Superbase.

A truly organocatalytic approach to the Darzens reaction affording α,β-epoxy carbonyl compounds in good yields was developed taking advantage of the high basic strength and low nucleophilicity of cyclopropenimine superbases. The catalytic active free base can easily be generated in situ from its hydrochloride salt and maintained in the active deprotonated form by performing the reactions in a heterogeneous reaction system in the presence of excess potassium carbonate as a sacrificial base.

Pyridine-2-olato bridged dirhodium(III) acyl organometallics: Synthesis, spectroscopic, structural and theoretical studies

The heterogeneous phase reaction of [Rh(MeLsb)(PPh3)2Cl2] (1) with the sodium salt of three different pyridine-2-olato ligands [Na(R‒Opy), R = H, Me, NO2] in dichloromethane–acetone–water medium afforded the complexes of type [Rh(Lal)(PPh3)(R-Opy)]2 (2(R)) in excellent yield. These are the first examples of dirhodium(III) acyl complexes with the bridging pyridine-2-olato ligand. The penta coordinated dirhodium(III) acyl complexes are formed by the cleavage of the RhCl and RhPPh3 bonds of the precursor complex 1. The two R-Opy ligands bridge the two rhodium centers through their OOpy donor centers. The conversion of 1→2(R) is attended with the concomitant hydrolysis of the aldiminium function in 1. The spectral (UV–vis, IR, NMR) data of the complexes are reported. The identity of 2(Me) has been established by single crystal X–ray structure determination which revealed distorted trigonal bipyramidal RhCNO2P coordination sphere. The Rh, C, N and Ophenolato atoms define the equatorial plane whereas Rh, OOpy and P atoms define the axial plane. The electronic structures and absorption spectra of the complexes are also scrutinized by the density functional theory (DFT) and time–dependent DFT calculations.

Enhancing the Fenton catalytic activity of Fe-MOFs by incorporation of carbon nanotubes: The crucial role of C-O-Fe coordination structure

Fe-based metal–organic frameworks (MOFs) have garnered significant attention as catalysts for heterogeneous Fenton reactions, while the limited efficiency of the Fe(III)/Fe(II) redox cycle hinders their widespread use in wastewater treatment. Herein, we successfully incorporated carbon nanotubes (CNTs) into MIL-101(Fe) to modulate the coordination environment of Fe for achieving better catalytic activity. The MIL-101(Fe)/CNTs/H2O2 system shows outstanding performance in degrading various pollutants, with the catalytic activity of the MIL-101(Fe)/CNTs composites (98.8%) significantly surpassing that of MIL-101(Fe) alone (26.4%) or CNTs alone (3.5%). Multiple experimental findings suggest that this synergistic effect is primarily attributed to the C-O-Fe bridge bonds resulting from the interaction of surface carboxyl groups on CNTs with Fe in MIL-101(Fe). This unique coordination structure accelerates the redox cycle of Fe(III)/Fe(II), thereby promoting the generation of hydroxyl radicals (HO•). Furthermore, the MIL-101(Fe)/CNTs composites demonstrate excellent reusability and stability, maintaining effectiveness over a wide pH range from 3.0 to 6.5. This study provides new insights into regulating the microstructure of Fe-based MOFs to enhance their Fenton catalytic activity.

Predictors of ICU Surrogates' States of Concurrent Prolonged Grief, Post-Traumatic Stress, and Depression Symptoms.

Scarce research explores factors of concurrent psychologic distress (prolonged grief disorder [PGD], post-traumatic stress disorder [PTSD], and depression). This study models surrogates' longitudinal, heterogenous grief-related reactions and multidimensional risk factors drawing from the integrative framework of predictors for bereavement outcomes (intrapersonal, interpersonal, bereavement-related, and death-circumstance factors), emphasizing clinical modifiability. Prospective cohort study. Medical ICUs of two Taiwanese medical centers. Two hundred eighty-eight family surrogates. None. Factors associated with four previously identified PGD-PTSD-depressive-symptom states (resilient, subthreshold depression-dominant, PGD-dominant, and PGD-PTSD-depression concurrent) were examined by multinomial logistic regression modeling (resilient state as reference). Intrapersonal: Prior use of mood medications correlated with the subthreshold depression-dominant state. Financial hardship and emergency department visits correlated with the PGD-PTSD-depression concurrent state. Higher anxiety symptoms correlated with the three more profound psychologic-distress states (adjusted odds ratio [95% CI] = 1.781 [1.562-2.031] to 2.768 [2.288-3.347]). Interpersonal: Better perceived social support was associated with the subthreshold depression-dominant state. Bereavement-related: Spousal loss correlated with the PGD-dominant state. Death circumstances: Provision of palliative care (8.750 [1.603-47.768]) was associated with the PGD-PTSD-depression concurrent state. Surrogate-perceived quality of patient dying and death as poor-to-uncertain (4.063 [1.531-10.784]) correlated with the subthreshold depression-dominant state, poor-to-uncertain (12.833 [1.231-133.775]), and worst (12.820 [1.806-91.013]) correlated with the PGD-PTSD-depression concurrent state. Modifiable social-worker involvement (0.004 [0.001-0.097]) and a do-not-resuscitate order issued before death (0.177 [0.032-0.978]) were negatively associated with the PGD-PTSD-depression concurrent and the subthreshold depression-dominant state, respectively. Apparent unmodifiable buffering factors included surrogates' higher educational attainment, married status, and longer time since loss. Surrogates' concurrent bereavement distress was positively associated with clinically modifiable factors: poor quality dying and death, higher surrogate anxiety, and palliative care-commonly provided late in the terminal-illness trajectory worldwide. Social-worker involvement and a do-not-resuscitate order appeared to mitigate risk.

A crystallinity control strategy for controllable Heterogeneous-Homogeneous reaction and catalytic performance in wet-mechanochemical synthesized FeS2 Fenton system

In heterogeneous Fenton system, the Heterogeneous-Homogeneous reaction type induced by surface-bonded or dissolved catalytic center plays a vital role in determining Fenton performance. However, how to directionally control the reaction type with facile method still remains challenging. Herein, a novel crystallinity control strategy based on wet-mechanochemical synthesis combined with heat-treatment was applied to synthesize FeS2 nanoparticles with different crystallinity. The different crystalline FeS2 based Fenton system exhibited superior sulfamethoxazole removal performance at wide pH range (5.6–11) with •OH as dominating reactive oxygen species. The relative degradation contribution of homogeneous and heterogeneous Fenton reaction was semi-quantitatively evaluated, and the relationship between crystallinity indexes of FeS2 and degradation kinetic constants was established. It’s found that FeS2 crystallinity was directly correlated with its degradation efficiency, which first increased and then declined with crystallinity increasing. Crystallinity control strategy effectively determined dominating reaction type (homogeneous or heterogeneous) and further regulated catalytic performance in FeS2 Fenton system based on the interaction of specific surface area and Fe2+ dissolution ability. This work provides a novel crystallinity control strategy to build a correlative bridge among crystallinity, dominating reaction type and catalytic performance in FeS2 Fenton system.

An investigation of the Nernst–Planck model of an electro-viscous fluid flow between squeezing plates with homogeneous–heterogeneous reactions

An investigation of the Nernst–Planck model of an electro-viscous fluid flow between squeezing plates with homogeneous–heterogeneous reactions

Metal‐Supported Heterogeneous Catalysts for the Synthesis of Nitrogen‐Containing Heterocycles: A Comprehensive Review

AbstractThe use of metals in the preparation of heterocycles has become increasingly popular due to several key advantages of metals as catalysts. These include recycling capability, eco‐friendliness, simplicity of catalyst preparation and separation, longer lifespan, abundance, and higher yields. As a result of their novel applications in organic, inorganic, medicinal, industrial, polymer chemistry, material sciences, nanotechnology, and biological processes, the utilization of nitrogen‐containing heterocycles has rapidly increased in recent years. Various nitrogen‐containing organic moieties are used in therapeutic processes to enhance effectiveness against several bacterial and viral diseases. This review covers the preparation of imidazoles, triazoles, tetrazoles, pyridine derivatives, azo compounds, pyrimidines, quinoxalines, and quinolines using metals as heterogeneous catalysts. It provides an overview of current methodologies for metal‐assisted heterogeneous catalytic reactions, including product yield, operating temperature, and solvents, among other factors. Heterogeneous catalyst‐mediated organic synthetic reactions offer several advantages, particularly in medicinal chemistry, pharmaceuticals, and industrial applications, by reducing time and energy consumption. This review emphasizes recent advancements in the fabrication of nitrogen heterocycles utilizing heterogeneous catalysts, taking into account various economic, eco‐friendly, and user‐friendly considerations. Additionally, it discusses the benefits, reaction conditions, and yields reported in the literature over the past six years.

Water-Driven Surface Lattice Oxygen Activation in MnO2 for Promoted Low-Temperature NH3-SCR.

Water is ubiquitous in various heterogeneous catalytic reactions, where it can be easily adsorbed, chemically dissociated, and diffused on catalyst surfaces, inevitably influencing the catalytic process. However, the specific role of water in these reactions remains unclear. In this study, we innovatively propose that H2O-driven surface lattice oxygen activation in γ-MnO2 significantly enhances low-temperature NH3-SCR. The proton from water dissociation activates the surface lattice oxygen in γ-MnO2, giving rise to a doubling of catalytic activity (achieving 90% NO conversion at 100 °C) and remarkable stability. Comprehensive in situ characterizations and calculations reveal that spontaneous proton diffusion to the surface lattice oxygen reduces the orbital overlap between the protonated oxygen atom and its neighboring Mn atom. Consequently, the Mn-O bond is weakened and the surface lattice oxygen is effectively activated to provide excess oxygen vacancies available for converting O2 into O2-. Therefore, the redox property of Mn-H is improved, leading to enhanced NH3 oxidation-dehydrogenation and NO oxidation processes, which are crucial for low-temperature NH3-SCR. This work provides a deeper understanding and fresh perspectives on the water promotion mechanism in low-temperature NOx elimination.

The Democracy I Like: Perceptions of Democracy and Opposition to Democratic Backsliding

Abstract When democracy is under attack, the hope is often that citizens will punish undemocratic incumbents. However, recent studies show that not all citizens punish governments for their undemocratic actions. In this article, we argue that citizens' understanding of and satisfaction with democracy are sources of heterogeneous reactions. In a survey experiment conducted in Germany and Poland, we show that the importance that citizens attach to specific institutions under threat, as well as their understanding of democracy, can explain much of the variance in citizens' responses to undemocratic actions. Citizens are willing to defend what they consider important for democracy – regardless of whether this reflects theoretical conceptions of democracy. Moreover, in times of democratic backsliding, Polish ‘critical citizens’, those who are dissatisfied with the way democracy works in Poland, are more likely to punish governments for undemocratic actions. Our findings help us understand how to increase citizens' resilience against democratic backsliding.