Catalytic Active Centers Research Articles

Identifying the active photocatalytic H2-production sites on TiO2-supported Pt nanoparticles by the in-situ infrared spectrum of CO

Identifying the active catalytic centers on catalyst surface is significant for exploring the catalytic reaction mechanism and further guiding the synthesis of high-performance catalysts. However, it remains a challange in developing the site-specific technology for the identification of the active catalytic centers. Herein, in-situ infrared spectroscopy of adsorbed CO, photocatalytic hydrogen evolution reaction (HER) test and theoretical simulation were used to distinguish and quantify the different surface sites and their H2-production catalytic activity on TiO2-supported Pt nanoparticles (PtNPs). Two different types of surface Pt sites, tip Pt (Pttip) and edge/terrace Ptedge/terrace, on TiO2-supported Pt nanoparticles (PtNPs) were identified. The photocatalytic H2-production activity of TiO2-supported PtNPs shows a linear functional relationship with the number of Pttip sites. However, the number of Ptedge/terrace sites produced little effect on the activity of TiO2-supported PtNPs. First-principle simulations confirmed that H2-evolution at the Pttip sites owns a lower energy barrier than that at Ptedge/terrace. This findings would be helpful for the fabrication of high-performance Pt catalysts.

Synthesis and Application of a Powerful Heterogeneous Photo-Fenton Catalyst Based on rGO/g-C3N4/Fe3O4/tiO2 Nano-Composite for the Removal of Sewage Contaminants

The reduced GO/g-CN/Fe3O4 nano-composite was prepared by the co-precipitation of pre-hydrolyses ferric and ferrous salts in the presence of GO/g-CN hybrid. Structural and morphological characterization of the synthesized rGO/g-CN/Fe3O4/TiO2 nano-composite were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. Their photo-Fenton catalytic performance under UV–visible light irradiation was evaluated by UV–vis spectrophotometry and electrochemical methods. The influence of heterogeneous catalyst composition on the MB degradation efficiency was examined and optimized. The highest MB degradation efficiency of ternary rGO/g-CN/Fe3O4 was 53% under UV light. Addition of nano TiO2 to the nano-composite effectively improved its photo-Fenton degradation efficiency (up to 97% within 20 min). As excellent conductive carrier, rGO connected g-CN to TiO2 and effectively separated photo-created electrons and holes. Uniform dispersion of g-CN on the rGO surface caused full harvest of incident light and more efficient interaction with pollutants. The significant improvement of photo-Fenton catalytic effect of rGO/g-CN/Fe3O4/TiO2 is attributed to the synergetic interaction and availability of the active catalytic centers that effectively facilitated the Fe3+/Fe2+ recycling. Experimental results confirmed the promising dual purpose application, photo-Fenton and adsorption properties of rGO/g-CN/Fe3O4/TiO2 nano-composite in wastewater treatment.

Prudent electrochemical pretreatment to promote the OER by catalytically inert "Iron incorporated metallic Ni nanowires" synthesized via the "non-classical" growth mechanism.

This study provides new insight towards the non-classical “amorphous to crystalline” growth mechanism for metal nanowire synthesis and reports an electrochemical strategy to activate inactive materials into efficient electrocatalysts for the OER. Despite considerable research on transition metal oxides/hydroxides, especially NiFe based hydroxides as OER electrocatalysts, poor conductivity of these materials plagues their catalytic efficiency. In contrast, lack of catalytic centers hinders the OER performance of conductive metals. Herein, we devised a suitable precondition strategy to transform only the surface of conductive metallic Ni nanowires into active catalytic centers. The resulting material with intimate contact between the electrically conductive core and electrocatalytically active surface showed promising “specific” and “geometric” electrocatalytic activity towards the alkaline OER at different pH. Upon iron incorporation, the Fe centers incorporated at the surface as well as in the bulk of the nanowires were found to further boost the OER activity of these materials. A one-pot strategy was adopted to produce iron free/incorporated Ni nanowires covered with nano-spikes. Growth analysis revealed a unique “non-classical amorphous-to-crystalline transformation” to be responsible for the formation of metallic nanowires.

Efficient and Facile Synthesis of High-Quality Au Nanotwins

Gold nanoparticles with regular morphology and excellent monodispersion were prepared in oleylamine (OLA) via solvothermal method using HAuCl4 as the gold source and OLA-Ag ligand as the reducing agent. The size range of gold nanoparticles was limited to within 10–15 nm by regulating the reaction time and reaction temperature. On this basis, gold nanoparticles with a nanotwin structure were prepared successfully by reasonably setting the temperature and time of the gradient. These characteristics lay a good foundation for studies on monatomic catalysts and offer a feasible way to establish the dependent relationship between nanotwin structure and catalytic activity center.

Coupled transport of electrons and protons in a bacterial cytochrome c oxidase-DFT calculated properties compared to structures and spectroscopies.

After a general introduction to the features and mechanisms of cytochrome c oxidases (CcOs) in mitochondria and aerobic bacteria, we present DFT calculated physical and spectroscopic properties for the catalytic reaction cycle compared with experimental observations in bacterial ba3 type CcO, also with comparisons/contrasts to aa3 type CcOs. The Dinuclear Complex (DNC) is the active catalytic reaction center, containing a heme a3 Fe center and a near lying Cu center (called CuB) where by successive reduction and protonation, molecular O2 is transformed to two H2O molecules, and protons are pumped from an inner region across the membrane to an outer region by transit through the CcO integral membrane protein. Structures, energies and vibrational frequencies for Fe-O and O-O modes are calculated by DFT over the catalytic cycle. The calculated DFT frequencies in the DNC of CcO are compared with measured frequencies from Resonance Raman spectroscopy to clarify the composition, geometry, and electronic structures of different intermediates through the reaction cycle, and to trace reaction pathways. X-ray structures of the resting oxidized state are analyzed with reference to the known experimental reaction chemistry and using DFT calculated structures in fitting observed electron density maps. Our calculations lead to a new proposed reaction pathway for coupling the PR → F → OH (ferryl-oxo → ferric-hydroxo) pathway to proton pumping by a water shift mechanism. Through this arc of the catalytic cycle, major shifts in pKa's of the special tyrosine and a histidine near the upper water pool activate proton transfer. Additional mechanisms for proton pumping are explored, and the role of the CuB+ (cuprous state) in controlling access to the dinuclear reaction site is proposed.

Glucose Isomerizes to Fructose Catalyzed by the Eco‐Friendly and Biodegradable Ionic Liquids

AbstractIn this study, a new and cost‐effective strategy is proposed for the selective isomerization of glucose to fructose in the aqueous solutions involving eco‐friendly and biodegradable ionic liquids, which consist of a choline cation and natural amino acid anions. The results show that these ionic liquid aqueous solutions demonstrate impressive performances on the glucose isomerization. At the reaction conditions of 70 °C for 30 min and 1.0 MPa N2, a 37.6% fructose yield is obtained with a 77.2% selectivity in the presence of choline proline. It is noteworthy that both of these fructose yield and selectivity are higher than those of many current base‐catalyzed techniques. This high performance should be ascribed to the intensive enhancement of choline cation on the catalytic active centre of proline anion which consequentially facilitates the isomerization of glucose. Furthermore, this robust catalyst of [Ch]Pro is recyclable, where a satisfied catalytic activity is shown even after five consecutive runs, indicating its great potential in both biomass valorization and food industry.

Spectroscopic and molecular docking studies of the interaction between meloxicam and pepsin

In order to study the interaction mechanism between meloxicam and pepsin, the interaction between meloxicam and pepsin was studied by fluorescence spectroscopy, UV-visible absorption spectroscopy, circular dichroism spectroscopy and molecular docking under physiological conditions (pH = 2.20). The results of spectral experiments showed that meloxicam quenched the intrinsic fluorescence of pepsin by static quenching, formed a stable complex at 1:1, and changed the conformation of pepsin. The thermodynamic results showed that the main force type of meloxicam and pepsin system was hydrophobic interaction. Molecular docking showed that there was a hydrogen bond in addition to hydrophobic interaction, and the best binding site between meloxicam and pepsin was near the catalytic active center of pepsin. The results showed that the combination of the meloxicam and pepsin changed the microenvironment of amino acid residues at the catalytic active center of pepsin. Under the experimental conditions, the protein binding rate of meloxicam to pepsin W(B) was 2.97–48.3%, indicating that the binding of meloxicam to pepsin had an effect on the number of free pepsin. The drug binding rate of the system W(Q) was 2.97–1.39%, indicating that the binding effect of meloxicam and pepsin on the number of free drug molecules was weak, so the binding effect would not have a significant effect on the efficacy of meloxicam.

Intensification of Catalytic Processes through the Pellet Structuring: Steady-State Properties of a Bifunctional Catalyst Pellet Applied to Generic Chemical Reactions and the Direct Synthesis of DME

Structuring of different types of catalytic active centers at a single-pellet level appears to be a promising and powerful tool for integration and intensification of multistep solid-catalyzed chemical reactions. However, the enhancement in the product yield and selectivity strongly depends on the proper choice of the distribution of different catalysts within the pellet. To demonstrate potential benefits from properly designed catalyst pellet, numerical studies were conducted with the aid of the mathematical model of a single spherical bifunctional catalyst pellet. The analysis was performed both for a system of two generic chemical reactions and for a real process, i.e., direct synthesis of dimethyl ether (DME) from synthesis gas via methanol. Evaluation of the pellet performance was done for three arrangements of the catalytic active sites within the pellet, i.e., a uniform distribution of two types of catalytic active centers in the entire volume of the pellet, and two core–shell structures. It was demonstrated that, especially for the larger pellets typical for fixed-bed applications, the product yield might be significantly improved by selecting proper catalyst arrangements within the pellet.

Preparation and Application of Ordered Mesoporous Metal Oxide Catalytic Materials

The ordered mesoporous metal oxides as catalytic carrier or active center have been reported by many literatures. The large specific surface area and ordered mesoporous structure had caused great concern in the field of catalysis. In the catalytic reaction, the ordered mesoporous materials had great mechanical properties and the active centers had strong interaction between each other. There were obviously advantages of these ordered mesoporous materials than bulk materials or routine nano-materials in the catalytic conversion of volatile organic compound, CO, NOx and other polluting gases. At present, researchers prepared a variety of ordered mesoporous metal oxides by different synthetic methods. Based on the analysis and summary of the literature, this paper briefly reviewed the preparation methods and application of ordered mesoporous metal oxide catalysts and the prospect of future development is worth expecting.

Exploring the Influence of Halogen Coordination Effect of Stable Bimetallic MOFs on Oxygen Evolution Reaction.

The energy crisis and environmental pollution have forced scientists to explore alternative energy conversion and storage devices. The anodic reactions of these devices are all oxygen evolution reactions (OER), so the development of efficient OER electrocatalysts is of great significance. At the same time, understanding the reaction mechanism of OER is conducive to the rational design of efficient OER electrocatalysts. In general, catalytic active centers play a direct role in OER performance. In this paper, a series of stable bimetallic metal-organic frameworks (MOFs, named as Fe3 -Con -X2 , n=2, 3 and X=F, Cl, Br) with similar structure were synthesized by changing the halogen coordinated with the cobalt metal active center, aiming to investigate the influence of halogen substitution effect on OER performance. It was found that the OER activity of Fe3 -Co3 -F2 is much better than Fe3 -Co2 -Cl2 and Fe3 -Co2 -Br2 , indicating that the regulation of the electronegativity change of the coordination halogen atom can regulate the coordination electron structure of the metal active center, thereby achieving effective regulation of OER performance.

Surface-Modified Hollow Ternary NiCo2Px Catalysts for Efficient Electrochemical Water Splitting and Energy Storage.

Generally, a cost-effective electrocatalytic process that offers an efficient electrochemical energy conversion and storage necessitates a rational design and selection of structure as well as composition of active catalytic centers. Herein, we achieved an unprecedented surface morphology and shape tuning to obtain hollow NiCo2Px with a continuum of active sharp edges (spiked) on a hollow spherical surface by means of facile hydrothermal treatments. The highly exposed, branched spike-covered hollow structure of NiCo2Px shows remarkable performance enhancement for hydrogen evolution reaction and oxygen evolution reaction in a wide range of Ph solutions. This catalytic performance was utilized to assemble a water electrolyzer working in an alkaline environment. In particular, this electrolyzer only requires an output voltage of 1.62 V to deliver a current density of 10 mA cm-2 and shows almost no decrease in this value even after a continuous run for 50 h. The new surface-engineered NiCo2Px establishes to be highly active, cost-effective, and robust toward electrochemical energy conversion. Additionally, the charge storage capabilities of spike-covered hollow NiCo2Px structures is also investigated, and it shows a specific capacitance of 682 and 608 F g-1 at a current density of 1 A g-1 with excellent rate capacitance retention. Thus, the importance of surface engineering of nanocrystalline morphologies in design toward the development of a multifunctional electrocatalyst for efficient water splitting and charge storage applications is demonstrated.

In Situ Derived Electrocatalysts from Fe–Co Sulfides with Enhanced Activity toward Oxygen Evolution

Development of active but earth-abundant electrocatalysts for oxygen evolution remains a great challenge. In this work, we report a one-step organic amine-mediated method to synthesize Fe–Co sulfide composites. Electrochemical results show better oxygen evolution activity of the sulfides obtained with more sulfur dosage and Co–Fe molar ratio in the range of 1:2–2:1. The optimized Fe–Co sulfide presents a lower overpotential of 288 mV at 10 mA cm–2 in 1 M KOH. The electrocatalyst also shows a considerable long-term stability. During the electrocatalytic process, the involved cobalt species on the surface layer was lost, only leaving oxidized Fe species that would act as catalytic active centers. The excellent catalytic activity can be attributed to the porous structure of the in situ derived active phase, the high conductivity of inner layer metal sulfides, and the residues of sulfur species that may tune the electronic structure of metal sites.

Ruthenium Inlaying Porous Aromatic Framework for Hydrogen Generation From Ammonia Borane

Porous organic frameworks (POFs) are a new family of porous materials, which are characterized by high chemical and thermal stabilities, structural design-abilities, chemical functionalities, high porosities, etc. Designable skeletons of POFs lead to different application in many fields. Herein, we report a porous aromatic framework PAF-72 synthesized via ionothermal reaction. The inherently nitrogen contained skeleton of PAF-72 is beneficial for introducing catalytic active center Ruthenium, which is verified by ICP, TGA and TEM element mapping. Besides, Ru/PAF-72 shows excellent activity in hydrogen generation from hydrolysis of ammonia borane and good cyclic performance.

Interaction of hen egg white lysozyme with cefpiramide sodium: multi-spectroscopic and computational simulations

Under simulated physiological conditions (pH = 7.40), the interaction between cefpiramide sodium and hen egg white lysozyme was studied with multi-spectroscopy and molecular docking. The results showed that cefpiramide sodium quenched the fluorescence of hen egg white lysozyme by static quenching, and the number of binding site n was about 1. The binding distance (r) between cefpiramide sodium and hen egg white lysozyme was obtained based on the Förster nonradioactive resonance energy transfer and r was less than 7 nm, which indicated that there was a non-radiative energy transition in the system. The thermodynamic parameters were obtained from the van't Hoff equation, and the Gibbs free energy ΔG < 0, indicating that the reaction was spontaneous; ΔH < 0, ΔS > 0, indicating hydrophobic interaction played a major role in forming the cefpiramide sodium-hen egg white lysozyme complex. Synchronous spectra, circular dichroism spectra and UV-Vis spectra showed that cefpiramide sodium changed the conformation of hen egg white lysozyme. The molecular docking results showed that the binding position of cefpiramide sodium was close to the active center composed of Asp52 and Glu35 residues, suggesting that cefpiramide sodium could change the microenvironment of amino acid residues at the catalytic active center of hen egg white lysozyme.

Induction of Concerted Proton-Coupled Electron Transfer during Oxygen Evolution on Hematite Using Lanthanum Oxide as a Solid Proton Acceptor

The utilization of a support material has been an effective method for the management of proton transfer on catalytic active centers. Previous studies showed that the large overpotential of α-Fe2O3...

Non-PGM Electrocatalysts for Oxygen Reduction Reaction Inspired By Metalloenzyme Active Sites

Oxygen reduction reaction (ORR) is a key reaction in future energy generation devices such as polymer electrolyte fuel cells (PEFCs) and metal–air batteries. To drive the ORR in state-of-the-art PEFCs, platinum group metal (PGM) alloys have been used. Since platinum is rare and expensive, there is a need to develop highly active PGM-free ORR electrocatalysts for wide spread applications of PEFCs. In nature, catalytic active sites based on 3d transition metals are widely utilized as catalytic reaction centers in metalloenzymes: for example, laccases and cytochrome c oxidases are known to catalyze the ORR with almost no energy loss at the active sites of multinuclear metal complexes.[1,2] We present ORR electrocatalysts with multinuclear copper active sites incorporated in nitrogen-doped carbon nanosheets, which were inspired by the active site of laccases. Our copper-based electrocatalyst exhibited high ORR activity in alkaline aqueous solution. Physicochemical measurements including in situ X-ray absorption spectroscopy[3] revealed that multinuclear copper sites were embedded in nitrogen-doped carbon nanosheets and worked as the catalytic active center.[4] We also prepared a Fe–Cu-codoped carbon electrocatalyst inspired by the active site of cytochrome c oxidase.[5] Optimization of synthetic conditions and doping ratios of Fe to Cu into carbon resulted in the improvement of the ORR activity in acidic media. The electrocatalyst codoped with Fe and Cu showed higher ORR activity than those with Fe or Cu. Our bioinspired approaches will offer guidance for developing non-PGM ORR electrocatalysts with high activity.

Модификация активирующего раствора на основе меди(I) oрганическими растворителями и поверхностно-активными веществами в процессе химического меднения

In the processes of chemical and galvanic metallization of dielectric materials, in particular in the production of printed circuit boards, surface activation mainly uses compounds of precious metals and colloidal solutions characterized by limited stability during storage due to the coagulation process. To activate dielectric materials it is advisable to use true solutions based on monovalent copper compounds. For continuous metallization of the dielectric, it is necessary to obtain a sufficiently large number of catalytic active centers on the surface. This can be achieved in two ways: to create a high concentration of Cu(I) in the activation solution or to increase the thickness of the activating layer. The aim of this work is to modify the activating solution by introducing organic solvents and surfactants into its composition, contributing to an increase in the concentration of catalytically active centers on the dielectric surface. In order to better distribute the activating solution on the dielectric surface and in the holes, as well as to increase the sorption of copper(I) by the adhesive layer, the modifying effect of organic solvents on the activating composition was studied. As such solvents, dimethylformamide (DMFA) and dimethyl sulfoxide (DMSO) used in the preparation of the surface of the adhesive layer were studied. In the process of swelling, the solvent penetrates into the thickness of the adhesive layer. Due to this, the activator containing an organic solvent has the ability to be fixed on the surface not only due to the micro-roughness created in the etching process, but also able to penetrate deep into the swollen layer. It is established that the maximum thickness of the swollen layer for 10% solution is reached by the time of swelling 30-40 minutes, for 20% ‒ 20 minutes, for 50% ‒ more than 45 minutes. By the time of swelling, equal to 5 minutes, for 10, 20 and 50% solutions, the thickness of the swollen layer, respectively, is 1.00; 1.14; 1.55 microns. It is shown that the presence of organic solvents in the activator increases the adhesion of the metal coating by an average of 1.3 times. In order to better distribute the activator on the dielectric surface and in the holes, as well as to increase the adsorption of copper(I), it is advisable to introduce surfactants into the activator, which reduce the surface tension at the interface. Introduction to the composition of the surfactant activating solution affect the adhesion of the metal to the dielectric. It was found that the introduction of surfactant into the activating solution leads to an increase in the concentration of copper on the dielectric surface. Nonionic surfactant brand OP-10 in the activator provides a high concentration of catalytically active centers and get the highest adhesion of metal to the dielectric.

Exploring the Interaction of Tartrazine and Lipase: A Multispectroscopic Analysis, Docking and Computational Simulation Methods

The interaction between food colorant tartrazine and lipase was studied by multi-spectroscopic and molecular docking simulation under simulated physiological conditions to evaluate the toxic of tartrazine at the protein level. The results showed that tartrazine could effectively quench the endogenous fluorescence of lipase. The thermodynamic parameters were obtained from the van't Hoff equation, and the Gibbs free energy ΔG&lt;0, indicating that the reaction was spontaneous; ΔH&lt;0, ΔS&gt;0, indicating hydrophobic interaction played a major role in forming the tartrazine-lipase complex. as shown by the synchronous fluorescence, UV-vis absorption and circular dichroism data, tartrazine could lead to the conformational and micro environmental changes of lipase, which may affect its physiological function. Molecular docking results showed that tartrazine was site in the active center of lipase, which altered the microenvironment of amino acid residues at the catalytic active center of lipase.&#x0D;

Biomimetic oxidase based on functionalized mesoporous SiO2 and metalloporphyrin for 5-hydroxymethylfurfural conversion

Abstract 2,5-Furandicarboxylic acid (FDCA) has the potential to replace terephthalic acid (TPA) as a building block in the preparation of bio-based and degradable polyester materials. However, the lack of efficient and stable catalysts limits the commercial viability of FDCA production. In this work, metalloporphyrins were immobilized on mesoporous SiO2 and used as a novel oxidase to convert 5-hydroxymethylfurfural (HMF) to FDCA. As the catalytic active center of P450 monooxygenases and horseradish peroxidase, supported palladium, manganese, ferri, and cobalt porphyrins via ionic-liquid-functionalized SiO2 (PdPOP-SiO2, MgPOP-SiO2, FePOP-SiO2 and CoPOP-SiO2) were able to simulate oxidase alone under mild conditions. 100% HMF (0.02 M) conversion and 94.94% FDCA yield were achieved using PdPOP-SiO2 as a biomimetic oxidase after a 12 h reaction at 373 K in water at atmospheric pressure. This type of mimetic oxidase is stable, inexpensive, and readily available, and the method developed in this work can potentially be used to oxidize HMF to FDCA in an industrial setting.

Catalytic performance of bulk and colloidal Co/Al layered double hydroxide with Au nanoparticles in aerobic olefin oxidation

A Co/Al layered double hydroxide material was synthesized in both bulk and exfoliated (colloidal) forms. Anion exchange with methionine allowed immobilization of Au nanoparticles previously prepared by a biomimetic method using an anti-oxidant tea aqueous extract to reduce the Au salt solution. The catalytic performance of bulk and exfoliated clays Au-hybrid materials was assessed in aerobic olefin epoxidation. Both catalysts were very active towards the epoxide products and with very interesting substrate conversion levels after 80 h reaction time. The Au-exfoliated material, where the nanosheets work as large ligands, yielded higher product stereoselectivity in the case of limonene epoxidation. This arises from a confined environment around the Au nanoparticles wrapped by the clay nanosheets modulating access to the catalytic active centres by reagents. Mechanistic assessment was also accomplished for styrene oxidation by DFT methods.