Catalytic Implications Research Articles

Enhancing stability of cationic palladium complexes with hemilabile 2-benzyl oxazoline ligands: Structural insights and catalytic implications

This article describes the synthesis and characterization of Pd cationic complexes incorporating mono(2-benzyl oxazoline) ligands. Our study focuses on exploring the impact of electrostatic interactions of aromatic π-electrons of the benzyl group, aimed at enhancing the structural rigidity of cationic Pd complexes. Introduction of an aromatic moiety, which weakly coordinates with the Pd cation, led to a two-fold increase in the stability of the Pd cationic complex compared to complexes lacking any coordinating substituents. This research represents the initial instance of a cationic Pd complex with 2-benzyl oxazolines, highlighting the importance of weak electrostatic interactions in elucidating the three-dimensional structure of a metal complex.

Unravelling High Water Vapor-Induced Inhibitory Effects on Pt/Co3O4 Catalysts toward Benzene Oxidation.

Water vapor inevitably exists in the environment, which causes adverse impacts on many crucial chemical reactions. However, high water vapor of up to 10 vol %─relevant to a broad spectrum of industrial practices-for catalytic implications has been less investigated or neglected. As such, we explored an industry-relevant, humidity-highly sensitive benzene oxidation only in the presence of 10 vol % water vapor using the well-established Pt/Co3O4 catalysts, to bring such an important yet ignored topic to the forefront. Results revealed that Pt/Co3O4 catalysts possessing higher contents of Pt nanoparticles exhibited marked tolerance to water vapor interference. Under an incomplete benzene conversion condition, the input of 10 vol % water vapor indeed impaired the catalytic performance of Pt/Co3O4 catalyst significantly, which, in fact, was caused by the unfavorable formation of carboxylate species covering the catalyst's surface engendering irrecoverable activity loss, instead of the well-accepted water competitive adsorption. While such activity loss can be restored by elevating the reaction to a higher temperature. This study helps us to understand the compromised catalytic activity caused by high humidity, urging the systematic evaluation of well-established catalyst systems in high water vapor-contained conditions and pressing the development of water-tolerant catalysts for real-life application consideration.

Secondary Structure in Enzyme-Inspired Polymer Catalysts Impacts Water Oxidation Efficiency.

Protein structure plays an essential role on their stability, functionality, and catalytic activity. In this work, the interplay between the β-sheet structure and its catalytic implications to the design of enzyme-inspired materials is investigated. Here, inspiration is drawn from the active sites and β-sheet rich structure of the highly efficient multicopper oxidase (MCO) to engineer a bio-inspired electrocatalyst for water oxidation utilizing the abundant metal, copper. Copper ions are coordinated to poly-histidine (polyCuHis), as they are in MCO active sites. The resultant polyCuHis material effectively promotes water oxidation with low overpotentials (0.15V) in alkaline systems. This activity is due to the 3D structure of the poly-histidine backbone. By increasing the prevalence of β-sheet structure and decreasing the random coil nature of the polyCuHis secondary structures, this study is able to modulates the electrocatalytic activity of this material is modulated, shifting it toward water oxidation. These results highlight the crucial role of the local environment at catalytic sites for efficient, energy-relevant transformations. Moreover, this work highlights the importance of conformational structure in the design of scaffolds for high-performance electrocatalysts.

Grignard reagents as deprotonation agents for oxazoline-amido-phenolate ligands: structural and catalytic implications with the role of halogen ions.

In this study, various halogen-substituted Grignard reagents were assessed as deprotonating agents for the oxazoline-amido-phenolate ligand, leading to the formation of magnesium complexes. The newly synthesized complexes with halogen substituents displayed three distinct coordinative modes, all extensively characterized through crystallographic methods. The introduction of halogen substituents induced changes in the Lewis acid properties of the complexes, thereby impacting their structural attributes and catalytic behavior during the initiation and propagation of ring polymerization of cyclic esters.

Cation migration in siliceous CHA probed with DFT simulation and its catalytic implication

The migration or diffusion of cations in siliceous CHA with an approximate Si/Al ratio of 11 has been investigated to explore the impact of their location on catalytic performance, using DFT simulation. The migration of protons within the CHA cage and the resulting total energy were calculated to determine the activation energy for this migration. As the distance between the Al site and the nearby framework oxygen decreased, the activation energy for site-to-site migration decreased as well. Eventually, the proton was stabilized near the Al site, where the activation energy for reverse migration reached its maximum at 1.60 eV. The migration of Na cations and Cu cations was also examined. The activation energy for Na cations was only 0.49 eV, which can be attributed to multiple coordination and explains the facile migration. On the other hand, Cu+2 migration had an activation energy of 1.56 eV, while Cu+1 migration had an activation energy of 1.06 eV. Consequently, under the given reaction conditions, the facile migration of the catalytic component Cu+1 can be expected. Thus, CHA containing Na cations exhibits improved low-temperature activity in NH3 SCR, despite the potential for thermal degradation at high temperatures.

Experimental Evidence for Alloying Effects in Au–Pt-Catalyzed Low-Temperature CH4Activation with NO

The activation of methane with nitric oxide at low temperatures (300–400 °C) and atmospheric pressure was studied on Au–Pt nanoparticles with different Au/Pt ratios supported on alumina. The reaction forms HCN, a valuable chemical intermediate, via concurrent or successive C–H bond cleavage, NO dissociation, and C–N coupling reactions. The catalysts with different Au/Pt ratios had similar particle morphology and bulk properties, as evidenced by scanning transmission electron microscopy imaging and X-ray absorption near-edge structure spectroscopy, respectively. However, they exhibited different electronic and geometric surface properties, according to in situ diffuse reflectance infrared Fourier transform spectra of preadsorbed CO, a likely consequence of Au surface enrichment. These differences had catalytic implications, where the relative proportion of electron-deficient Pt sites on the surface of the catalysts was found to track with activity, expressed as turnover frequency for the total CH4 conversion and HCN formation. Based on the activity trend, kinetic comparison of reaction orders, temperature-programmed desorption experiments, and comparisons to the literature, it is proposed that the CH4–NO catalysis occurred mainly on contiguous Pt sites, that the higher C–H activation activity of electron-deficient Pt species may be related to weaker adsorption of CH4, and that the higher NO dissociation activity of metallic Pt species may have contributed to the complete oxidation of CH4 to CO2. Nonetheless, contact time and in situ spectroscopic studies at isothermal conditions revealed only subtle differences in the reaction scheme by surface modifications, indicating that Au affected the reactivity indirectly.

Structural features, thermal stability and catalytic implication of Fe–Ni nanoparticles

We have carried out Monte Carlo and molecular dynamics simulations on FexNi1-x nanoparticles (NPs), and systematically studied their structural features and thermal stability. The required potential adopted the angular-dependent potential, which was newly obtained by us. It is found that when x ​< ​0.375, the surface of FexNi1-x NPs is completely occupied by Ni atoms. When x ​> ​0.375, the surface Fe concentration gradually increases with the increase of x. Inside the NPs, Fe atoms occupy the subsurface preferentially, and the Fe atom layer and Ni atom layer are arranged alternately. With the increase of x, the melting temperature of FexNi1-x nanoparticle first ascends, then descends near x ​= ​0.375, and then rises again near x ​= ​0.875. In addition, the catalytic performance of FexNi1-x NPs in methane dry reforming was discussed. Considering the catalytic activity, carbon deposition resistance and sintering resistance, Fe0.375Ni0.625 NPs are the best choice.

Carbonate dimorphism, and the reinterpretation of rates of lattice and excess oxygen-driven catalytic cycles

Catalytic implications of local deviations from nominal oxide stoichiometry remain critical to consider yet challenging to elucidate in the context of bulk oxide-mediated light alkane oxidation reactions, in part due to a lack of a priori knowledge of surface active oxygen site counts. Carbonate dimorphism, i.e., differences in carbonate speciation resulting from CO2 adsorption onto unsupported nickel oxide surfaces, can be exploited toward quantifying the surface density of lattice and excess oxygens, and to further deconvolute their respective contributions toward specific steps within the ethane oxidation reaction network. Density functional theory, volumetric gas sorption, in situ titration, in situ spectroscopy, and transient kinetic data interpreted in light of quantitative estimates of surface excess oxygen density confirm the involvement of excess oxygen in partial oxidative turnovers producing ethene from ethane and O2. These collective studies cast a more nuanced interpretation of site requirements pertaining to nickel oxide-mediated alkane oxidation. Our findings reveal that excess oxygen atoms can be titrated under reaction conditions, and that these sites are (on average) more selective to ethene than lattice oxygens. Tools and methodologies employed herein connect seemingly disparate elements of bulk oxide catalysis research – the need for quantitative estimates of oxide surface non-stoichiometry on the one hand, and the propensity of unsupported oxides toward carbonate formation on the other – and provide a template for the possible broader application of quantitative analyses of probe-molecule binding characteristics toward elucidation of active site density and speciation in catalytic partial oxidation reaction systems of commercial relevance.

Nickel Nanoparticles for Liquid Phase Toluene Oxidation – Phenomenon, Opportunities and Challenges

AbstractEffective oxidative transformation of toluene into valuable products was achieved under solvent‐free reaction conditions with as‐prepared nickel nanoparticles as heterogeneous catalysts in liquid phase. The crystalline structure and size of the as‐prepared nanoparticles were confirmed by X‐ray diffractometry (XRD) and dynamic light scattering (DLS). The catalytic implications of the different crystalline forms (face‐centred cubic: fcc; hexagonal close‐packed: hcp) of these nanocatalysts were investigated. The product selectivity of toluene oxidation was found to vary depending on the crystalline forms of the catalyst. Fcc nanocatalysts showed remarkable chemoselectivity (83 mol %) for the product benzyl alcohol and were readily reusable. In contrast, the hcp Ni phase showed reasonable reusability but lower chemoselectivity (29 mol %) compared to its fcc counterpart. Moreover, the simple organic solvents used had a remarkable effect on the crystal structure and phase purity of the Ni nanocrystals, which also affected the catalytic process.

A Homoleptic Alkynyl‐Protected Au(I)9‐Ag(I)9 Cluster: Structure Analysis, Optical Properties, and Catalytic Implications

AbstractWe report the structure analysis, optical property, and catalytic implications of homoleptic alkynyl‐protected Au(I)‐Ag(I) nanocluster, namely Au9Ag9(C≡CArF)18 (abbreviated as Au9 Ag9 hereafter). Single crystal X‐ray diffraction analysis disclosed that, the core of Au9Ag9 cluster features intriguing ichthyomorphic assembled structure driven by metallophilic interactions and Au‐acetylide linkages. The Au9Ag9 nanocluster is fluorescent in both solution and solid state, and it has much higher quantum yield in solid state. In the electrochemical hydrogen evolution reaction (HER) test, Au9Ag9 nanocluster exhibits a favorable overpotential of 274 mV at 10 mA cm−2 with a Tafel slope of 99 mV dec−1, which markedly surpass than the [Au(C≡C‐ArF)]f and [Ag(C≡C‐ArF)]f control samples. Furthermore, Au9Ag9 nanocluster shows much higher activity than the other two to catalyze the reduction of 4‐nitrophenol.

A Computational Investigation of Histone‐Deacetylase‐6’s role in Osteoclast Dislodgement from Bone

Human Bone constantly undergoes reconstruction via the actions of osteoclasts, which degrade old bone using powerful enzymes such as Tartrate‐Resistant Acid Phosphatase. When osteoclasts adhere to the bone surface, they form sealing zones that maintain cellular attachment, thereby allowing for continuous digestion. After the process has been completed, osteoclasts dislodge before migrating to a new location. This study focuses on the molecular mechanisms underlying the physiology of osteoclast disengagement via the action of histone deacetylase 6 (HDAC6), a large protein involved in alpha‐tubulin de‐acetylation, podosome degradation, and enhanced cellular motility. Unlike other HDAC proteins, HDAC6 contains a second catalytic domain with deacetylase activity. Ras Homolog Family member A (RhoA) and Diaphanous‐related formin‐2 (mDia2) form a dimer (RhoA‐mDia2) that allosterically activates HDAC6. Upon stimulation by RhoA‐mDia2, HDAC6 targets alpha‐tubulin, and by removing the acetyl‐moiety on Lys‐40, it enhances its susceptibility to ubiquitination. As microtubule integrity diminishes, the adherence of the osteoclast is weakened. While the details of the molecular mechanism of HDAC6 deacetylation have been elucidated, the molecular mechanism of its allosteric activation remains unexplored. This study focuses on RhoA‐mDia2 stimulation of HDAC6, and the determination of which catalytic domain might be the major player in the process. Using computational tools, we have investigated the differential response of the first deacetylase domain (DD1) and the second deacetylase domain (DD2) to RhoA‐mDia2 stimulation. Using the known structures of RhoA, mDia2, HDAC6, and Alpha‐Tubulin, we performed protein‐protein docking to explore the structure‐function relationship of the protein players participating in the deacetylation process. Here, we present our investigations regarding the structural details and catalytic implications of the allosteric stimulation of HDAC6 by the RhoA‐mDia2 dimer based on our docking results. We detail a functional comparison between the first and second deacetylase domains of HDAC6 and show that HDAC6 DD1 predominates the binding interface with alpha‐tubulin before RhoA‐mDia2 allosteric activation, and the pattern reverses once RhoA‐mDia2 binds HDAC6. We also explored the pathways of HDAC6 inhibition by Cdc42 and Rac1, both of which promote podosome stability. Lastly, we compared DD1 and DD2 of HDAC6 with the HDAC10 deacetylase domain, the closest homologue that disfavors acetyl lysine hydrolysis. A comprehensive sequence analysis combined with analysis of binding interfaces, and in silico mutagenesis experiments all indicate greater similarity between HDAC10’s deacetylase domain and HDAC6 DD1 than with HDAC6 DD2. We therefore speculate that DD1 may not be conducive to alpha‐tubulin lysine‐40 deacetylation in a similar manner as HDAC10. Combining all our findings, we can reasonably conclude that HDAC6 DD2 likely preferentially attracts alpha‐tubulin, whereas DD1 plays a regulatory function. This work is pivotal not only for understanding bone physiology, but the research could also provide valuable information for developing treatments of chronic pathologies such as osteoporosis.

“Doing More with Less”: Ni(II)@ORMOSIL, a Novel Sol-Gel Pre-Catalyst for the Reduction of Nitrobenzene

Reduction of nitrobenzene with NaBH4 using zero-valent iron nanoparticles (ZVI-NPs) and NiCl2∙6H2O incorporated in organically modified hybrid silica matrices as ZVI@ORMOSIL and Ni(II)@ORMOSIL catalysts is proposed as a remediation strategy. Ni(II)@ORMOSIL is prepared by ion-exchanging H+ of the ORMOSIL matrix with NiII. Ni(II)@ORMOSIL is a pre-catalyst that undergoes reduction by NaBH4 by an in-situ reaction and promotes nitrobenzene reduction by the unconsumed NaBH4, leading to sparing use of the catalyst. Ni(II)@ORMOSIL undergoes color change from green to black in this process, returning to a green hue after washing and drying. Nitrobenzene reductions were examined in aqueous acetonitrile solvent mixtures, and the reduction cascade produced the reaction end-products with catalytic implications. Plausible mechanisms of ZVI@ORMOSIL and Ni(II)@ORMOSIL catalyzed reductions of nitrobenzene are discussed. This work is the first to report M(II)@ORMOSIL pre-catalysts for in-situ reduction of nitrobenzene, and expands the scope of the ORMOSIL series of catalysts for the reduction of polluting compounds. This approach enables the development of catalysts that use very low concentrations of transition metal cations.

Electrochemistry of Ru(edta) complexes relevant to small molecule transformations: Catalytic implications and challenges

Electrochemistry of Ru(edta) complexes (edta4− = ethylenediaminetetraacetate) progressed over a period of several decades, with significant increase in understanding of the electro-catalytic processes involving the substrate coordinated to the metal center. While electrochemistry studies of many Ru(edta) complexes were published in several papers, no attempt has been made to provide a comprehensive and systematic overview of its electrochemical properties, evaluating its application to catalytic electrochemical transformation of small molecules. In this article, results of the electrochemical studies of both mononuclear and binuclear complexes of Ru(edta) are reviewed with regard to electron-transfer reaction mechanism and activity. Their potential to act as redox mediators or catalysts in electrochemical transformations of small molecules and enzymatic reactions, are highlighted. This review aims to contribute to the mechanistic understanding of Ru(edta) complexes in catalysis of such electrochemical transformations.

CuFeO2–Water Interface under Illumination: Structural, Electronic, and Catalytic Implications for the Hydrogen Evolution Reaction

CuFeO2 is a p-type semiconductor that has been recently identified as a promising photocathode material for photoelectrochemical water splitting. CuFeO2 can absorb solar light and promote the hydrogen evolution reaction (HER), even though the photocurrents achieved so far are still well below the theoretical upper limit. While several experimental and theoretical works have provided a detailed characterization of the bulk properties of this material, surfaces have been largely unexplored. In this work, we perform first-principles simulations based on DFT to investigate the structure, electronic properties, and thermodynamic stability of CuFeO2 surfaces both in vacuum and in an electrochemical environment. To estimate the alignment of the band edges on the electrochemical scale, we perform ab initio molecular dynamics in explicit water, unraveling the structure of the solid/liquid interface for various surface terminations. We consider the system both in the dark and under illumination, showing that light absorption can induce partial reduction of the surface, giving rise to states in the gap that can pin the Fermi level, in agreement with recent measurements. Using the free energy of adsorption of atomic hydrogen as a descriptor of the catalytic activity for the HER, we show that hydride species formed at oxygen vacancies can be highly active and could therefore be an intermediate of reaction.

Tailoring Lewis/Brønsted acid properties of MOF nodes via hydrothermal and solvothermal synthesis: simple approach with exceptional catalytic implications.

The Lewis/Brønsted catalytic properties of the Metal–Organic Framework (MOF) nodes can be tuned by simply controlling the solvent employed in the synthetic procedure. In this work, we demonstrate that Hf-MOF-808 can be prepared from a material with a higher amount of Brønsted acid sites, via modulated hydrothermal synthesis, to a material with a higher proportion of unsaturated Hf Lewis acid sites, via modulated solvothermal synthesis. The Lewis/Brønsted acid properties of the resultant metallic clusters have been studied by different characterization techniques, including XAS, FTIR and NMR spectroscopies, combined with a DFT study. The different nature of the Hf-MOF-808 materials allows their application as selective catalysts in different target reactions requiring Lewis, Brønsted or Lewis–Brønsted acid pairs.

Zeolite-driven Ag species during redox treatments and catalytic implications for SCO of NH3

The zeolite topology directs the formation of different silver species with catalytic implications for the NH3-SCO reaction.

Alkanediyl-α,ω–type gemini micelles–catalyzed study between ninhydrin and [Ni(II)-Trp]+ complex

In this work, a series of alkanediyl-α,ω–type gemini micelles symbolized as 16-s-16 (s = spacer) was synthesized. Synthesized products were characterized by 1H NMR technique. By conductivity method, cmc of these surfactants was determined by measuring specific electrical conductivity at different concentrations. Alkanediyl-α,ω–type gemini micelles–catalyzed interaction between [Ni(II)-Trp]+ complex and ninhydrin has been studied with the help of spectrophotometric studies. The catalytic implication of gemini micelles on rate constant (kψ) in ninhydrin and [Ni(II)-Trp]+ has been explored and discussed at 343 K and pH 5.0. Catalyzing behavior obtained by geminis confirmed that they influenced the study remarkably over their monomeric conventional counterpart. Results were also suggested that small amount of geminis at concentration below cmc was sufficient to induce the reaction more than aqueous. Though, 16-4-16 is detected to catalyze the work more among geminis and follows the order at each concentration as: 16-4-16 > 16-5-16 > 16-6-16. This catalytic implication produced by gemini micelles can efficiently be deduced using pseudophase model for micellar activity. In addition, by varying temperatures, several thermodynamic quantities were evaluated. A lower enthalpy value, ΔH#, with significant negative entropy value, ΔS#, is acquired in geminis than aqueous system.

Risk Management: Rethinking Fashion Supply Chain Management for Multinational Corporations in Light of the COVID-19 Outbreak

Through an international business risk management lens, the widespread and catalytic implications of the 2020 COVID-19 pandemic on the supply chains (SCs) of fashion multinational corporations (MNC) are analyzed to contribute to existing research on supply chain management (SCM). While a movement towards agile, networked supply chain models had been in consideration for many firms prior to the outbreak, the pandemic highlights issues inherent in supply chains that employ concentrated production. We examined the current state of fashion supply chains, risks that have arisen historically and recently, and existing risk mitigation methods. We found that while lean supply chain management is primarily favored for its cost and waste reduction advantages, the structure is limited by the lack of supply chain transparency that results as well as the increasing demand volatility observed even before the COVID-19 outbreak. Although this problem might exist in the agile supply chain, agile supply chains combat this by focusing on enhancing communication and buyer-supplier relationships to improve information exchange. However, this structure also entails an associated increase in inventory and inventory costs. The COVID-19 pandemic has caused supply and demand disruptions which have resonating effects on supply chain activities and management, indicating a need to build flexibility to mitigate epidemic and demand risks. To address this, several strategies that firms can adopt to control for such risks are outlined and key areas for further research are identified which consider parties both upstream and downstream of the fashion supply chain.

Carrier Dynamics and Transfer across the CdS/MoS2 Interface upon Optical Excitation.

Carrier dynamics across the interface of heterostructures have important technological, photovoltaic, and catalytic implications. Using first-principles time-dependent density functional theory, we have systematically investigated the charge transfer of excited carriers from CdS to MoS2 and found that two interdependent mechanisms are responsible for the transfer, one slow and one fast. While the slower process may be attributed to typical electron-phonon coupling, the interfacial dipole resulting from this transfer enables a fast secondary process involving a level crossing of the excited carrier state in CdS with receiving states in MoS2. An analysis based on the interfacial binding energy reveals that the Cd-terminated (001) interface is by far the most energetically favorable, which in addition to its calculated fast resonant electron transfer suggests it is a good candidate to explain the experimentally observed charge transfer between CdS and MoS2.

Synthesis, Structure, Reactivity and Catalytic Implications of a Cationic, Acetylide-Bridged Trigold-JohnPhos Species.

The cationic complex [(JohnPhos-Au)3 (acetylide)][SbF6 ] (JohnPhos=(2-biphenyl)di-tert-butylphosphine, L1) has been characterised structurally and features an acetylide-trigold(I)-JohnPhos system; the trinuclear-acetylide unit, coordinated to the monodentate bulk phosphines, adopts an unprecedented μ,η1 ,η2 ,η1 coordination mode with an additional interaction between distal phenyl rings and gold centres. Other cationic σ,π-[(gold(I)L1)2 ] complexes have also been isolated. The reaction of trimethylsilylacetylene with various alcohols (iPrOH, nBuOH, n-HexOH) catalysed by cationic [AuI L1][SbF6 ] complexes in CH2 Cl2 at 50 °C led to the formation of acetaldehyde acetals with a high degree of chemo- and regioselectivity. The reaction mechanism was studied, and several organic and inorganic intermediates have been characterised. A comparative study with the analogous cationic [CuI L1][PF6 ] complex revealed different behaviour; the copper metal is lost from the coordination sphere leading to the formation of cationic vinylphosphonium and copper nanoparticles. Additionally, a new catalytic approach for the formation of this high-value cationic vinylphosphonium has been established.