Model Reaction Research Articles

Catalytic reduction of p-nitrophenol and Eosin Yellow by lemongrass tea-stabilized copper nanoparticles

ABSTRACT Green synthesis of nanoparticles for catalytic applications remains of continued interest, especially for reactions that would occur on an industrial scale or that may be of environmental significance. Here, ultrasmall 2.1-nm copper nanoparticles were synthesized under ambient conditions using a copper sulfate pentahydrate precursor and lemongrass extract as a reducing and capping agent. Their potential to act as catalysts was tested using model reactions: the sodium borohydride reduction reactions of p-nitrophenol and Eosin Yellow. Kinetics measurements were obtained with visible time-course spectroscopy and showed that copper nanoparticles effectively catalyzed both reactions. Temperature dependence followed Arrhenius behavior, indicating the catalyst surface was accessible to reactants. Activation energies of 59.2 and 38.5 kJ/mol were obtained for the reduction reactions of p-nitrophenol and Eosin Yellow, respectively. Large frequency factors for both reactions were found, implying large numbers of catalytic sites and/or facilitation of reaction by capping agents. This copper nanoparticle catalyst prepared via green synthesis demonstrates reproducible reduction behavior for two model reactions and observed rate constants that compare favorably with other copper nanoparticle catalysts, particularly in terms of rate constants normalized for available surface area and including catalysts produced via traditional synthetic methods.

Back-decay of the muonic molecular ion (αμt)012+ resonantly formed in (tμ)1s+4HeH+ collision

Abstract Resonant formation of the muonic molecular ion ( α μ t ) 01 2 + in the collision of the muonic tritium atom with the helium hydride ion, ( t μ ) 1 s + 4 HeH + → [ ( α μ t ) 01 2 + , p , e e ] + , is proposed. The ( α μ t ) 01 2 + ion is formed in the rotational-vibrational state (0,1) as one of the two nuclei of the final complex. Back-decay process [ ( α μ t ) 01 2 + , p , e e ] K n + → ( t μ ) 1 s + 4 HeH K ′ n ′ + , where K and n ( K ′ and n ′ ) is the rotational and vibrational quantum number, respectively, is considered in detail and the corresponding decay widths for all possible rotational-vibrational ( K , n ) → ( K ′ , n ′ ) transitions are calculated. Numerous inelastic decay channels of ( α μ t ) 01 2 + are also presented and discussed. The possible fast resonant formation of the ( α μ t ) 01 2 + ion may provide an interesting tool for experimental studies of t ( α , γ ) 7 Li nuclear fusion, which is one of the most important reactions in Big-Bang nucleosynthesis models. Studying this reaction may prove important for solving the lithium problem.

Promoting Charge-Carriers Dynamics by Relaxed Lattice Strain in A-site-doped Halide Perovskite for Photocatalytic H2 Evolution.

Because of the unique and superior optoelectronic properties, metal halide perovskites (MHPs) have attracted great interests in photocatalysis. Element doping strategy is adopted to modify perovskite materials to improve their photocatalytic performance. However, the contribution of bare doping-site onto photocatalytic efficiency, and the correlation between doping locations and activity have not yet to be demonstrated. Thispromoted us to explore the potential of A-site-doped MHPs for photocatalysis. Herein, we dope potassium (K+) into CsPbBr3 and first reveal that the occupied locations of K+ in CsPbBr3 is lattice incorporation rather than surface segregation, which would change from A-site substitution to interstitial site in lattice with the increase of K+ concentrations. Taking H2 evolution as a model reaction, photocatalytic activity of CsPbBr3 after K+ doping could be significantly improved ~11-fold with A-site substitution, which is superior to that of interstitial site doping. Moreover, other alkali metals including Li, Na, and Rb doping give the same results. The structure of photocatalysts during reaction confirmed the contribution of A-site doping onto enhanced photocatalytic activity. Mechanistic insights show it is a result of the relaxed residual lattice strain induced promoted charge-carriers dynamics and formed upward shifting of band after K+ A-site doping.

Promoting Charge‐Carriers Dynamics by Relaxed Lattice Strain in A‐site‐doped Halide Perovskite for Photocatalytic H2 Evolution

Because of the unique and superior optoelectronic properties, metal halide perovskites (MHPs) have attracted great interests in photocatalysis. Element doping strategy is adopted to modify perovskite materials to improve their photocatalytic performance. However, the contribution of bare doping‐site onto photocatalytic efficiency, and the correlation between doping locations and activity have not yet to be demonstrated. This promoted us to explore the potential of A‐site‐doped MHPs for photocatalysis. Herein, we dope potassium (K+) into CsPbBr3 and first reveal that the occupied locations of K+ in CsPbBr3 is lattice incorporation rather than surface segregation, which would change from A‐site substitution to interstitial site in lattice with the increase of K+ concentrations. Taking H2 evolution as a model reaction, photocatalytic activity of CsPbBr3 after K+ doping could be significantly improved ~11‐fold with A‐site substitution, which is superior to that of interstitial site doping. Moreover, other alkali metals including Li, Na, and Rb doping give the same results. The structure of photocatalysts during reaction confirmed the contribution of A‐site doping onto enhanced photocatalytic activity. Mechanistic insights show it is a result of the relaxed residual lattice strain induced promoted charge‐carriers dynamics and formed upward shifting of band after K+ A‐site doping.

2-D modeling of torrefaction of a large biomass particle: effect of L/D ratio, internal convection and shrinkage

ABSTRACT Torrefaction of a large biomass particle was investigated using a transient 2-D model, including primary and secondary reactions kinetics and heat transfer, internal convection, and shrinkage. The model predictions matched with the experimental results within +2%. Spatial and temporal distributions of temperature, residual mass fraction, velocity, and pressure inside the particle and the effect of reactor temperature, residence time, particle size, and shrinkage on the torrefaction behaviour were investigated. Evolution of moisture, volatiles and gases due to drying and torrefaction increase the pressure inside the particle, setting up a velocity field and internal convection. Average velocity and pressure reached a peak during the initial drying period due to moisture evolution, and a subsequent second peak due to the formation of volatiles and gases by torrefaction at a reactor temperature > 493 K. Internal convection influenced torrefaction significantly but the particle shrinkage did not impact it appreciably. The degree of overshoot of the particle center temperature above the reactor temperature increased with the reactor temperature and the particle diameter. Simulations suggest that a reactor temperature of 550 K and residence of about 30 min would be suitable for torrefaction of a particle with L = D = 25.4 mm.

Virus-like Particles-Based Vaccine to Combat Neurodegenerative Diseases.

Neurodegenerative diseases are regarded as gradual, incurable conditions with an insidious onset. Alzheimer's disease (AD) and Parkinson's disease (PD) are two of the most prevalent neurodegenerative diseases reported globally. Developing effective treatment strategies for neurodegenerative diseases has remained a primary objective and a huge challenge for researchers. The therapeutic medications that are now approved for the treatment of neurodegenerative diseases merely treat the symptoms; the underlying pathology is not addressed. Therefore, the emergence of novel disease-modifying therapeutic modalities such as immunotherapy has opened a new path in developing effective treatments for neurogenerative diseases. Compared to other types of subunit active vaccines, virus-like particles (VLPs) are considerably more immunogenic as they present dense and repetitive viral antigen epitopes on their surface, which can trigger both humoral and cell-mediated immune responses. They are also a much safer option than the traditional inactivated and live-attenuated vaccines since they are devoid of viral genomes and are, therefore, non-pathogenic and non-infectious. Researchers have turned their attention to VLPs as an active immunotherapy candidate for AD due to the lessons learned from the AN1792 trial. Studies have shown that they effectively induce anti-Aβ, anti-tau, and anti-α-Synuclein antibodies while avoiding T-cell-related immune reactions in animal models of AD and PD. This review compiles the findings of preclinical animal model studies and clinical investigations on VLP-based vaccines for neurogenerative diseases thus far. The technical limitations and potential difficulties associated with the future application of VLP-based vaccines in patients with neurodegenerative diseases have also been covered.

Heterogeneous synthesis of benzo[f]indole-4,9-diones derivatives using sulfonic resin and photocatalytic study

This research introduces a heterogeneous approach utilizing a resin-bound sulfonic acid catalyst (Dowex®-H) to synthesize benzo[f]indole-4,9-dione derivatives using β-enaminones systems and 2-bromonaphtoquinone. This method facilitates synthesizing a diverse range of compounds with varying substitution patterns, achieving yields of 88 %. The catalyst can be reused for up to five cycles without requiring reactivation. These compounds absorption spectra also show absorption (λmax) around 250–260 nm with a significant transition around 400 nm. Their photocatalytic potential was assessed by the model reaction of benzylamine photooxidation, achieving a yield of over 99 % within 36 h.

Organic Two-Photon-Absorbing Photosensitizers Can Overcome Competing Light Absorption in Organic Photocatalysis.

Conventional organic photocatalysis typically relies on ultraviolet and short-wavelength visible photons as the energy source. However, this approach often suffers from competing light absorption by reactants, products, intermediates, and co-catalysts, leading to reduced quantum efficiency and side reactions. To address this issue, we developed novel organic two-photon-absorbing (TPA) photosensitizers capable of functioning under deep red and near-infrared light irradiation. Three model reactions including cyclization, Sonogashira Csp2-Csp cross-coupling, and Csp2-N cross-coupling reactions were selected to compare the performance of the new photosensitizers under both blue (427 nm) and deep red (660 nm) light irradiation. The obtained results unambiguously prove that for reactions involving blue light-absorbing reactants, products, and/or co-catalysts, deep red light source resulted in better performance than blue light when utilizing our TPA photosensitizers. This work highlights the potential of our metal-free TPA photosensitizers as a sustainable and effective solution to mitigate the competing light absorption issue in photocatalysis, not only expanding the scope of organic photocatalysts but also reducing reliance on expensive Ru/Ir/Os-based photosensitizers.

The Swiss Army Knife of Electrodes: Pillar[6]arene-Modified Electrodes for Molecular Electrocatalysis Over a Wide pH Range.

Molecularly-modified electrode materials that maintain stability over a broad pH range are rare. Typically, each electrochemical transformation necessitates a specifically tuned system to achieve strong binding and high activity of the catalyst. Here, we report the functionalisation of mesoporous indium tin oxide (mITO) electrodes with the macrocyclic host molecule pillar[6]arene (PA[6]). These electrodes are stable within the pH range of 2.4-10.8 and can be equipped with electrochemically active ruthenium complexes through host-guest interactions to perform various oxidation reactions. Benzyl alcohol oxidation serves as a model reaction in acidic media, while ammonia oxidation is conducted to assess the systems performance under basic conditions. PA[6]-modified electrodes demonstrate catalytic activity for both reactions when complexed to different guest molecules and can be reused by reabsorption of the catalyst after its degradation. Furthermore, the system can be employed to perform subsequent reactions in electrolyte with varying pH, enabling the same electrode to be utilised in multiple different electrocatalytic reactions.

Development of the esterase PestE for amide bond synthesis under aqueous conditions: Enzyme cascades for converting waste PET into tamibarotene.

A growing number of hydrolase enzymes show promiscuous acyltransferase activity, even under aqueous conditions. Here we report, for the first time, the ability of Pyrobaculum calidifontis VA1 esterase (PestE) to catalyse the formation of a wide range of amides in buffer, where the acyl donor forms a significant structural component in the amide product. The reactions occur under mild conditions and can achieve conversions up to 97% in 6 h for formation of N-benzylfuranamide as the model reaction. We demonstrate PestE's potential in enzyme cascades to make amides from waste PET plastic and the conversion of the terephthalic acid product to tamibarotene, a drug with activity against acute leukemia. Rational mutagenesis led to identification of PestE variants F33L_F289A and F33L. F33L_F289A increased conversion of N-benzylfuranamide by 1.2-fold, and F33L gave a 4-fold increase in conversion to tamibarotene.

Development of the esterase PestE for amide bond synthesis under aqueous conditions: Enzyme cascades for converting waste PET into tamibarotene.

A growing number of hydrolase enzymes show promiscuous acyltransferase activity, even under aqueous conditions. Here we report, for the first time, the ability of Pyrobaculum calidifontis VA1 esterase (PestE) to catalyse the formation of a wide range of amides in buffer, where the acyl donor forms a significant structural component in the amide product. The reactions occur under mild conditions and can achieve conversions up to 97% in 6 h for formation of N‐benzylfuranamide as the model reaction. We demonstrate PestE’s potential in enzyme cascades to make amides from waste PET plastic and the conversion of the terephthalic acid product to tamibarotene, a drug with activity against acute leukemia. Rational mutagenesis led to identification of PestE variants F33L_F289A and F33L. F33L_F289A increased conversion of N‐benzylfuranamide by 1.2‐fold, and F33L gave a 4‐fold increase in conversion to tamibarotene.

The Swiss Army Knife of Electrodes: Pillar[6]arene‐Modified Electrodes for Molecular Electrocatalysis Over a Wide pH Range

AbstractMolecularly‐modified electrode materials that maintain stability over a broad pH range are rare. Typically, each electrochemical transformation necessitates a specifically tuned system to achieve strong binding and high activity of the catalyst. Here, we report the functionalisation of mesoporous indium tin oxide (mITO) electrodes with the macrocyclic host molecule pillar[6]arene (PA[6]). These electrodes are stable within the pH range of 2.4–10.8 and can be equipped with electrochemically active ruthenium complexes through host–guest interactions to perform various oxidation reactions. Benzyl alcohol oxidation serves as a model reaction in acidic media, while ammonia oxidation is conducted to assess the systems performance under basic conditions. PA[6]‐modified electrodes demonstrate catalytic activity for both reactions when complexed to different guest molecules and can be reused by reabsorption of the catalyst after its degradation. Furthermore, the system can be employed to perform subsequent reactions in electrolyte with varying pH, enabling the same electrode to be utilised in multiple different electrocatalytic reactions.

High-Temperature Behavior of Pd/MgO Catalysts Prepared via Various Sol–Gel Approaches

A series of Pd/MgO catalysts based on nanocrystalline MgO were prepared via different sol–gel approaches. In the first two cases, palladium was introduced during the gel preparation, followed by drying it in supercritical or ambient conditions. In the third case, aerogel-prepared MgO was impregnated with an ethanol solution of Pd(NO3)2. The prepared catalysts differ in particle size and oxidation state of palladium. The catalytic performance and thermal stability of the samples were examined in a model reaction of CO oxidation at prompt thermal aging conditions. The as-prepared and aged materials were characterized by low-temperature nitrogen adsorption, UV-vis spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and ethane hydrogenolysis testing reaction. The highest initial activity (T50 = 103 °C) was demonstrated by the impregnated sample, containing Pd0 particles of 3 nm in size. The lowest T50 value (215 °C) after aging at 1000 °C was demonstrated by the impregnated Pd/MgO-WI sample. The high-temperature behavior of the catalysts was found to be affected by the initial oxidation state and dispersion of Pd. Two deactivation mechanisms, such as the agglomeration of Pd particles and migration of small Pd species into the bulk of the MgO support with the formation of Pd-MgO solid solutions, were discussed.

Freestanding Penta-Twinned Pd-Ag Nanosheets.

2D metal nanosheets have attracted significant attention as efficient catalysts for various important chemical reactions. However, the development of metal nanosheets with controlled compositions and morphologies has been slow due to the challenges associated with synthesizing thermodynamically unfavorable 2D structures. Herein, we report a synthesis route of freestanding Pd-Ag penta-twinned nanosheets (Pd-Ag ptNSs) with distinct 5-fold twin boundaries. Through the coreduction of Ag and Pd precursors on presynthesized Pd ptNSs, Ag could be homogeneously alloyed with Pd, leading to the formation of well-defined Pd-Ag ptNSs. The promotional effects of the bimetallic composition, 2D structure, and twin boundaries on catalysis were studied by using Pd-Ag ptNS-catalyzed H2 production from formic acid decomposition as a model reaction. Notably, the catalytic activity of the Pd-Ag ptNSs drastically outperformed those of monometallic, bimetallic, and 3D counterparts, such as Pd ptNSs, Pd-Ag nanosheets without a TB, and Pd-Ag octahedral nanocrystals, demonstrating the promising potential of the integration of twin boundaries and multiple compositions in the development of high-performance 2D nanocatalysts.

Unraveling the Oxygen Vacancy-Performance Relationship in Perovskite Oxides at Atomic Precision via Precise Synthesis.

Understanding the fundamental effect of the oxygen vacancy atomic structure in perovskite oxides on catalytic properties remains challenging due to diverse facets, surface sites, defects, etc. in traditional powder catalysts and the inherent structural complexity. Through quantitative synthesis of tetrahedral (LaCoO2.5-T), pyramidal (LaCoO2.5-P), and octahedral (LaCoO3) epitaxial thin films as model catalysts, we demonstrate the reactivity orders of active-site geometrical configurations in oxygen-deficient perovskites during the CO oxidation model reaction: CoO4 tetrahedron > CoO6 octahedron > CoO5 pyramid. Ambient-pressure Co L-edge and O K-edge XAS spectra clarify the dynamic evolutions of active-site electronic structures during realistic catalytic processes and highlight the important roles of defect geometrical structures. In addition, in situ XAS and resonant inelastic X-ray scattering spectra and density functional theory calculations directly reveal the nature of high reactivity for CoO4 sites and that the derived shallow-acceptor defect levels in the band structure facilitate the adsorption and activation of reactive gases, resulting in more than 23-fold enhancement for catalytic reaction rates than CoO5 sites.

Multifunctional TiO2(R)/Fe2O3 Photocatalytic Composites Obtained from Ilmenite Ore

AbstractThe commercialization of the photocatalysis technology requires that the synthesis of the photocatalytic material is easy to scale up. Thus, the synthesis from earth‐abundant minerals represents one plausible solution to obtain materials by a scalable process with a lower environmental impact. So far, the most promising photocatalyst for this application is titanium dioxide (TiO2), which can be obtained from ilmenite ore; however, its synthesis usually implies toxic solvents and complicated reaction conditions. Thus, here is proposed an optimized method to extract higher amounts of TiO2 by a multivariable Plackett‐Burman design of experiments considering the mass of the ore precursor, the addition of phosphoric acid (H3PO4), the digestion temperature, the amount of base to adjust the pH, and the final thermal treatment. From this design, it was possible to minimize the heat treatment and the amount of base used to favor higher TiO2 (rutile) content with the presence of additional phases of iron oxides (Fe2O3) that act as co‐catalyst to enhance the photocatalytic activity. The photocatalytic activity of the TiO2/Fe2O3 composites obtained was investigated in four model reactions to obtain solar fuels (H2 evolution and CO2 reduction) and to remove endocrine water pollutants (bisphenol A and dyeing water), using visible and natural solar irradiation, respectively.

A Rootless Duckweed-Inspired Flexible Artificial Leaf from Plasmonic Photocatalysts.

The naturally existing leaves are ubiquitous two-dimensional flexible solar-to-chemical conversion systems that can run continuously in a sustainable manner. However, the current artificial photocatalytic systems are unable to achieve this due to the grand challenge in integrating existing photocatalysts in a flexible layout with high conversion efficiency and the ability to function independently. Here, we report on a rootless duckweed-inspired artificial leaf based on a lightweight, flexible, Janus plasmonic nanosheet-integrated sponge. The Janus plasmonic catalytically active nanosheet was made from self-assembled gold nanocube nanoassemblies grown on the porous sponges, which were further coated with an ultrathin palladium layer on one side via a ligand symmetry-breaking method. This sponge-based photocatalytic system is lightweight yet able to float on a water surface and conducts the gas-liquid reaction without auxiliary pumping and mixing devices. In a model reaction of 4-nitrophenol reduction, this floating leaf could achieve 2.5-fold and 65-fold higher efficiency than the corresponding dispersion and precipitation systems, respectively. The film theory is used to explain the sponge-based lightweight solar-to-chemical conversion system in a detailed kinetic and thermodynamic analysis, including the reaction rate constant, activation energy, enthalpy, entropy, Gibbs energy, and equilibrium constant.

N‐Arylphenothiazines and N,N‐Diarylphenazines as Tailored Organophotoredox Catalysts for the Reductive Activation of Alkenes

AbstractA small library of N‐arylphenothiazines, N‐arylbenzo[b]phenothiazines and N,N‐diarylphenazines has been synthesized as strongly reducing organophotocatalysts without the need for sacrificial reagents or electrochemistry. Their opto‐electronic properties and their suitability as organophotoredox catalysts for the efficient activation of olefins was investigated using the addition of methanol to α‐methylstyrene as a model reaction. The findings were supported by DFT calculations. Three photocatalysts were identified that allowed quantitative yields with 10 mol % catalyst loading and 20 h irradiation by a 365 nm LED. The catalyst loading was gradually reduced to 0.5 mol % and the irradiation time was reduced to only 20 min. These experiments revealed that N,N‐diisobutyl‐4′‐(10H‐phenothiazin‐10‐yl)‐[1,1′‐biphenyl]‐4‐amine is the most efficient photocatalyst among the N‐arylphenothiazines. This chromophore combines high electron density introduced by the diisobutylamino phenyl group with high absorptivity at 365 nm caused by the phenylene bridge to the phenothiazine core. In an attempt to shift the excitation wavelength into the visible light range for selectivity and sustainability purposes (potential use of sunlight as a light source), N‐arylbenzo[b]phenothiazines N,N‐diarylphenazines were designed that exhibit a red‐shifted and broad absorbance shoulder into the visible range, but only N,N‐diarylphenazines allow photocatalysis and the one‐electron activation of alkenes by visible light (450 nm LED).

Multicomponent one pot synthesis of substituted pyridines with a highly active and recyclable hydrotalcite-lanthanum nanocatalyst

Herein, the synthesis of 2-amino-3,5-dicyano-6-sulfanyl pyridine derivatives has been studied due to wide applications of highly substituted pyridines. At first, Hydrotalcite (HT) with various loading amounts of lanthanum (HT-La) was synthesized. Then, their catalytic activities were investigated for the condensation reaction of benzaldehyde, malononitrile, and thiophenol under reflux condition as a model reaction. The prepared HT nanocatalyst with 10 mol% of La showed the best performance in this multicomponent reaction. In addition, the reusability of the nanocatalyst was studied and the results showed, that the prepared nanocatalyst could be reused several times with an only moderate decrease in activity. Subsequently, HT-La (10 mol%) efficiently catalyzed the one-pot condensation reaction for the synthesis of highly substituted pyridines under reflux conditions. The products were produced with excellent yields, short reaction times, and easy recyclability of the nanocatalyst.

N─N Bond Oxidative Addition‐Promoted Diaziridinone Activation: A Mechanistic Study

AbstractDensity functional theory (DFT) calculation has been used to reveal palladium‐catalyzed mode of diaziridinone ring activation. Our theoretical studies found that oxidative addition of di‐tert‐butyldiaziridinone to Pd(II) can give a high valent Pd(IV) intermediate, along with the cleavage of N─N bond in di‐tert‐butyldiaziridinone through a concerted three‐membered‐cyclic transition state. Subsequent transformations via reductive elimination and β‐N elimination give the desired indolo[3,2‐b]indole product. The competitive activation modes such as metathesis and migratory insertion can be excluded in our selected model reaction. The rate‐determining step of this reaction is the oxidative addition of di‐tert‐butyldiaziridinone step. Distortion‐interaction analysis was conducted to reveal that the oxidative addition mode of di‐tert‐butyldiaziridinone is superior to the metathesis mode due to the lower interaction energy.