High Concentration Of Active Sites Research Articles

Cu3P Nanoarrays Derived from 7,7,8,8-Tetracyanoquinodimethane for High-Rate Electrocatalytic Oxygen Reactions of Lithium-Oxygen Batteries

Efficient electrocatalysis at the cathode is crucial for addressing the challenges faced by lithium-oxygen batteries (LOBs), including limited stability and low-rate capability. To develop an efficient cathode for aprotic LOBs, self-supported copper phosphide nanoarrays on carbon cloth are prepared at different heating rates via a phosphidation process using CuTCNQ nanoarrays. Different ramping rates have effects on particle size and intrinsic interaction, which in turn affect their catalytic properties. When phosphidation is carried out at a slow rate, it results in the formation of smaller, evenly distributed Cu3P particles on the nanoarrays (SG-Cu3P NAs/CC) compared to fast rate phosphidation (FG-Cu3P NAs/CC). As a result, SG-Cu3P NAs/CC exhibits lower resistance and a higher concentration of active sites than FG-Cu3P NAs/CC. The SG-Cu3P NAs/CC demonstrates LOBs with a low overpotential of 1.51 V at a high current rate of 1 mA cm−2 and a long cycle life of 115 cycles at 0.1 mA cm-2. The in situ Raman spectroscopy supports that Li2O2 is uniformly formed and decomposed on the SG-Cu3P NAs/CC surface. This study provides a compelling approach for the precise fabrication and analysis of binder-free, self-supported copper phosphides as highly efficient and stable materials for bifunctional oxygen electrocatalysis.

A Cleaner Approach for Controllable Synthesis of Au/TiO2 Nanocomposite as an Efficient Catalyst for 4‐Nitrophenol Reduction

AbstractSupported metal catalysts have attracted considerable attention because of their remarkably high catalytic activity and thermal stability. In this work, we report a facile and eco‐friendly method to synthesize porous Au/TiO2 nanocomposites with tunable size and different loading of Au nanoparticles. Porous TiO2 particles with average size of 20 nm were obtained using deep eutectic solvent‐assisted solvothermal method, in which Au NPs were immobilized by citrate reduction process. By adjusting the molar ratio of citrate and gold precursor, the size and loading of Au particles could be effectively controlled. The optimized nanocomposite with maximum Au loading and smallest particle size of 9 nm manifested the best catalytic activity in the 4‐nitrophenol reduction and excellent reusability. The superior catalytic performance can be ascribed to the strong interfacial interaction between small Au NPs and porous TiO2 support together with the high concentration of active sites at the interface.

High-Performance Bimetallic Mo/Ni-N-C Electrocatalyst for Efficient Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is a crucial process in a variety of energy-related technologies, including water splitting and electrochemical conversion. Despite significant progress in the development of OER catalysts, there is still a need for more efficient and cost-effective materials. M-N-C (metal-nitrogen-carbon) materials appear as efficient, low-cost, and sustainable alternatives for the oxygen evolution reaction (OER).In this work, we have synthesized bimetallic Mo/Ni-C catalysts using shungite carbon codoped with nitrogen, molybdenum, and nickel precursors and characterized their physical and chemical properties using a variety of techniques, including X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Due to their highly porous structure along with the high concentration of active sites these catalysts exhibit excellent activity and stability for the OER, with low overpotentials.Overall, our work highlights the potential of bimetallic Mo/Ni-N-C catalysts as efficient and cost-effective alternatives to noble-metal-based catalysts for the OER with significant implications in renewable energy technologies.

Polyoxovanadate derived VN@C composite catalysts by different synthesis routes as Pt-free counter electrode for dye-sensitized solar cells

Vanadium-based nitrides have been applied as Pt-free counter electrodes (CEs) electro-catalysts for dye-sensitized solar cells (DSSCs) due to inexpensive cost and easy doping and modification. Herein, polyoxovanadate (NH4)2V6O16 assisted by melamine to prepare VN@C composites by five different synthesis routes, including solvothermal, sol–gel, hydrothermal, ball milling, and chemical mixing method. And then, five VN@C composites were assembled as CEs in the encapsulated DSSCs, and yielded power conversion efficiencies of 4.47, 5.04, 5.35, 5.49 and 6.11% for regenerate traditional I3−/I− shuttles by the photocurrent-photovoltage (J-V) test, respectively. The catalytic performances of VN@C composites CEs were assessed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Tafel polarization experiments, and the significant effects of different synthetic routes were confirmed. The results revealed that VN@C composite CEs prepared by chemical mixing method had higher catalytic performance in DSSCs, which is due to the improvement of conductivity and the high concentration of active sites.

An efficient and durable bifunctional electrocatalyst based on PdO and Co2FeO4 for HER and OER

The adoption of effective, minimal, and versatile electrocatalysts for water splitting to generate hydrogen fuels is of critical importance. The bulk of newly described materials have considerable onset potential, but their electrocatalytic activity is limited by weak electrical conductivity and a limited range of catalytic sites. The combination of a few precious metals added with transition metal-based compounds is a novel and captivating approach. Herein, cobalt ferrite oxide (Co2FeO4) @ palladium oxide (PdO) nanostructures have been prepared through the combined use of hydrothermal and ultraviolet (UV) irradiation techniques. For hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) kinetics, the modified composition offers a high concentration of active sites, improved electrical conductivity, and stability. The Co, Fe, and Pd ions at the composite system's interface may affect the adsorption energy of reaction intermediates synergistically, enabling the process to continue with less potential. The electrocatalyst Co2FeO4@PdO demonstrates an excellent bifunctional approach to electrochemical water splitting (EWS) for HER and OER in alkaline medium. As-prepared electrocatalyst shows an overpotential value of 269 and 259 mV for HER and OER at 10 and 20 mA/cm2 current densities respectively. The low charge transfer resistance values such as 72.2 and 62.4 Ω and durability for 48 h has been observed toward HER and OER, support this material as an efficient and durable electrocatalyst for energy conversion systems.

Effectively enhanced oxygen reduction activity and stability of triple-conducting composite cathodes by strongly interacting interfaces for protonic ceramic fuel cells

Here, a novel triple-conducting composite cathode for protonic ceramic fuel cells, with superior oxygen reduction reaction (ORR) activity and stability, is developed by replacing cerium with zirconium in BaCo0.7(Ce0.8Y0.2)0.3O3−δ (BCCY) to construct strongly interacting interfaces. The one-step synthesized BaCo0.7(Zr0.8Y0.2)0.3O3−δ (BCZY) is composed of multiple phases with different functionalities, reaching a polarization resistance of 0.25 Ω cm2 at 600 °C while maintaining excellent performance stably for 206 h. The excellent ORR activity is attributed to the high concentration of active sites and the strong hydration capability at strongly interacting interfaces of Co-rich and Zr-rich phases which is introduced by the interdiffusion of Co and Zr. The low thermal expansion coefficient is also achieved through this interface, contributing to the excellent stability of BCZY. This study highlights the role of strongly interacting interfaces in enhancing the ORR activity and stability of materials and provides a new strategy for developing triple-conducting composite cathodes.

Zn-ethylenediaminetetraacetic acid complex derived N-doped porous carbon for high-performance supercapacitor

The development of N-doped porous carbon is an effective strategy to improve supercapacitor performance such as energy density and rate capability. The synthesis of N-doped porous carbon with high surface area by a simple method remains a challenge since it usually requires an additional chemical activation. In this work, we developed Zn-ethylenediaminetetraacetic acid (EDTA) coordination complexes, and then synthesized N-doped porous carbon with high surface area through pyrolysis of Zn-EDTA complexes based on the high nitrogen content of EDTA and the activation ability of Zn species. The morphology and surface area of the obtained porous carbon significantly depend on the morphology of the Zn-EDTA complexes, which can be easily controlled by adjusting the amount of Zn salt. The porous carbon exhibited a specific capacitance of 251.9 F g−1 at 1 A g−1 and 194.4 F g−1 at 20 A g−1 in a two-electrode system. Furthermore, the assembled supercapacitor device displayed an energy density of 8.7 Wh kg−1 at a power density of 248.7 W kg−1 at 1 A g−1 and good cycling performance with capacitance retention of 100 % over 10,000 cycles at the current density of 10 A g−1. The excellent supercapacitive performance should be mainly ascribed to the large surface area and abundant micro-, meso-, and macropores, which offer large electrode/electrolyte interfaces and fast ion diffusion. In addition, the high-level and uniformly distributed N atoms endow the porous carbon with both a high concentration of active sites and good wettability.

Structural and electronic engineering of zirconium-induced bimetallic phosphides supported by nitrogen-doped carbon fibers for highly efficient oxygen evolution reaction

The exploitation of non noble metal oxygen evolution reaction (OER) electrocatalysts with tuneable electronic structures and chemical compositions is an effective way to improve water splitting, which is of great significance to the development of clean energy. Here, we report a zirconium-induced transition metal phosphide supported by nitrogen-doped carbon fiber (P–CoFeZr/NCBC) as an efficient electrocatalyst for the OER. The electrocatalyst is produced in situ on the surface of nitrogen-doped carbon fibers to form an open structure, achieving a high concentration of active sites. Additionally, the electronic structure is modified through the introduction of zirconium to increase the intrinsic activity of the electrocatalyst. These phenomena greatly enhance the oxygen evolution activity of the electrocatalyst. In alkaline media, P–CoFeZr/NCBC exhibits excellent catalytic activity and fast kinetics, with overpotentials and Tafel slopes of 300 mV and 51 mV/dec at 10 mA/cm2, and displays excellent long-term stability for more than 24 h at 50 mA/cm2.

A Facile Synthesis of Noble-Metal-Free Catalyst Based on Nitrogen Doped Graphene Oxide for Oxygen Reduction Reaction.

A simple method for the mechanochemical synthesis of an effective metal-free electrocatalyst for the oxygen reduction reaction was demonstrated. A nitrogen-doped carbon material was obtained by grinding a mixture of graphene oxide and melamine in a planetary ball mill. The resulting material was characterized by XPS, EPR, and Raman and IR spectroscopy. The nitrogen concentration on the N-bmGO surface was 5.5 at.%. The nitrogen-enriched graphene material (NbmGO has half-wave potential of −0.175/−0.09 V and was shown to possess high activity as an electrocatalyst for oxygen reduction reaction. The electrocatalytic activity of NbmGO can be associated with a high concentration of active sites for the adsorption of oxygen molecules on its surface. The high current retention (93% for 12 h) after continuous polarization demonstrates the excellent long-term stability of NbmGO.

Steric Hindrance- and Work Function-Promoted High Performance for Electrochemical CO Methanation on Antisite Defects of MoS2 and WS2.

CO methanation from electrochemical CO reduction reaction (CORR) is significant for sustainable environment and energy, but electrocatalysts with excellent selectivity and activity are still lacking. Selectivity is sensitive to the structure of active sites, and activity can be tailored by work function. Moreover, intrinsic active sites usually possess relatively high concentration compared to artificial ones. Here, antisite defects MoS2 and WS2 , intrinsic atomic defects of MoS2 and WS2 with a transition metal atom substituting a S2 column, were investigated for CORR by density functional theory calculations. The steric hindrance from the special bowl structure of MoS2 and WS2 ensured good selectivity towards CO methanation. Coordination environment variation of the active sites, the under-coordinated Mo or W atoms, effectively lowered the work function, making MoS2 and WS2 highly active for CO methanation with the required potential of -0.47 and -0.49 V vs. reversible hydrogen electrode, respectively. Moreover, high concentration of active sites and minimal structural deformation during the catalytic process of MoS2 and WS2 enhanced their attraction for future commercial application.

A sandwich model of Cr(VI) adsorption and detoxification by Fenton modified chitosan.

The Fenton reaction has the advantages of short reaction time, low cost, no toxicity, and straightforward application and control. The Fenton reaction generates highly reactive HO•, which has been applied effectively. However, the effect of the generated Fe3+ has not been investigated widely. In this study, the Fenton reaction was used to improve the Cr(VI) adsorption and detoxification capacities of chitosan. After the Fenton modification, chitosan efficiently adsorbed Cr(VI) and transformed it into the less toxic Cr(III) in a wide pH range as a result of layer formation, which was described by a sandwich model. The adsorption of Cr(VI) onto the Fenton modified chitosan was in good agreement with the Freundlich adsorption model, and the adsorption capacity exceeded 120mg/g. During the Fenton reaction, H2 O2 and HO• with high oxidative activity broke the hydrogen bonds in the chitosan structure, resulting in the release of free amine groups for Fe3+ to form metal-binding biopolymers. The distance between the chitosan polymers increased, and additional adsorption sites were created. HCrO4 - entered the gap between the chitosan polymer and was adsorbed on the newly created adsorption sites. The sandwich adsorption model indicated that the Fenton modified chitosan provided a high concentration of active sites for Cr(VI) capture and detoxification. PRACTITIONER POINTS: Fenton reaction was used to improve the adsorption ability of chitosan. The formed Fe3+ in Fenton reaction was utilized. HO· broke the hydrogen bonds and Fe3+ ions chelated with chitosan in modification. Cr(VI) could be adsorbed and reduced efficiently by Fenton modified chitosan. The Fenton modified chitosan provided a high concentration of active sites for Cr(VI) capture and detoxification.

Dual-Enhanced Doping in ReSe2 for Efficiently Photoenhanced Hydrogen Evolution Reaction.

Rhenium dichalcogenides (ReX2, X = S or Se) are catalysts that have great promise for the photoenhanced hydrogen evolution reaction (PE‐HER) because of their unique physiochemical properties. However, the catalytic performance is still restricted by their low concentration of electrocatalytic activity sites and poor injection of hot electrons. Herein, dual‐enhancement in ReSe2 nanosheets (NSs) with high concentration of active sites and efficient use of hot electrons is simultaneously achieved with moderate Mo doping. Contributions from exposed catalytically active sites, improved electrical conductivity, and enhanced solar spectral response are systematically investigated. Superior PE‐HER catalytical performance is obtained in Re0.94Mo0.06Se2, which has more catalytically active sites and optimized band structure than other Re1− xMoxSe2 samples. Here, it is demonstrated that only doping can reduce the overpotential (η10) from 239 to 174 mV at −10 mA cm−2 (Δ1η10 = 65 mV). Then, η10 is further improved to 137 mV under simulated AM 1.5 sun illumination (Δ2η10 = 37 mV). The total improvement (Δη10) toward PE‐HER is 102 mV (Δ1η10 + Δ2η10 = 102 mV) in optimal Re0.94Mo0.06Se2. This work presents a new perspective for researching high‐efficiency photoenhanced HER ReSe2‐based electrocatalysts and other layered transition metal dichalcogenides.

Chemo-catalytic Esterification and Transesterification over Organic Polymer-Based Catalysts for Biodiesel Synthesis

The major sources of fuels in today's world predominantly come from traditional fossil resources such as coal, petroleum and natural gas, which are limited and nonrenewable. Meanwhile, their consumption releases large undesirable greenhouse gas and noxious gases. Therefore, the development of renewable and sustainable feedstocks to replace traditional fossil resources has attracted great interest. Biodiesel, mainly produced through esterification and transesterification reaction from renewable oil resources using acids and bases as catalysts, is deemed as a green and renewable biofuel that shows enormous potential to replace fossil diesel. Compared to homogeneous catalytic systems, the development of efficient and stable heterogeneous catalysts is vital to synthesizing biodiesel in an efficient and green manner. Among the developed solid catalysts, organic polymer- based catalytic materials are an extremely important topic, wherein distinct advantages of higher concentration of active sites and better stability of active groups are associated with each other. In this review, effective catalytic valorization of sustainable feedstocks into biodiesel via transesterification and esterification reactions mediated by functionalized organic polymer-based catalysts is discussed. Special emphasis has been given to the synthetic routes to the versatile organic polymers-based catalytic materials, and some other interesting catalytic roles derived from physicochemical property, like adjustable hydrophilicity and hydrophobicity along with swelling property in transesterification and esterification, are also illustrated.

Activated charcoal and reduced graphene sheets composite structure for highly electro-catalytically active counter electrode material and water treatment

In quest of finding a sustainable solution for metal-free counter electrode materials, reduced graphene oxide (rGO) is emerged as the best alternative due to its intrinsic high electrocatalytic activity. However, owing to its two-dimensional sheets like structure, there is re-stacking of rGO sheets, which reduces exposed surface area and hinders in electrolyte diffusion. To avoid these issues, activated charcoal (AC) is explored as an active spacer material between rGO sheets, for the first time. By loading an optimum concentration of AC in rGO, a high porosity, high conductivity, and high concentration of active sites were gathered in the single composite structure. Such synchronized features of the proposed composite were utilized for Pt-free counter electrode application in dye-sensitized solar cell (DSSc). The composite structure showed high electrocatalytic activity, with a low charge transfer resistance of 0.7 Ω, which is far lower than Pt and rGO (8.5 Ω and 7.5 Ω). The DSSc fabricated with optimized composite showed power conversion efficiency of 8.6%, compared to Pt-based DSSc with 7.9% efficiency. Additionally, the potential of the electrode was also tested for the electro-photocatalytic (99%) degradation of methylene blue dye from water, in 60 min. The proposed highly efficient nanocomposite structure possesses the highest efficiency as compared to other previously studied rGO based counter-electrodes.

Enhanced peroxidase-like activity of Fe@PCN-224 nanoparticles and their applications for detection of H2O2and glucose

Inspired by natural hemin structure, the fabrication of metal organic framework (MOF) nanomaterials constructed by metal ions and iron porphyrin for peroxidase mimicking has attracted extensive attention recently due to their high concentration of active sites and great channeling for substrate diffusion. Herein, by using benzoic acid as capping agent, we fabricated uniform PCN-224 nanoparticles (NPs), which were composed of Zr6 cluster and tetrakis(4-carboxyphenyl)porphyrin (H2TCPP). Then Fe(Ⅲ) ions were incorporated into the center of H2TCPP producing iron porphyrin unit similar to hemin serving as catalytic active site. The procedure of iron incorporation didn't change the size and morphology of PCN-224 NPs. The newly formed Fe@PCN-224 NPs possessed peroxidase-like activity with much lower Km values and higher Kcat values than most of peroxidase-like nanozymes as well as natural horseradish peroxidase (HRP), indicating their enhanced catalytic activity. Taking advantage of the excellent peroxidase-like activity of Fe@PCN-224 NPs, we successfully developed a colorimetric method for simple and sensitive detection of hydrogen peroxide and glucose in combination with glucose oxidase.

Spherical-like Pd/SiO2 catalysts for n-butylamine efficient combustion: Effect of support property and preparation method

Abstract Two types spherical-like SiO2 with different specific surface area (SSA) and porosity were synthesized and used as support for Pd catalysts, which were prepared by various protocols (in situ synthesis (IS, Pd/S-1IS, and Pd/S-2IS), wet impregnation (WI, Pd/S-1WI, and Pd/S-2WI), and grafting (GA, Pd/S-1GA, and Pd/S-2GA)) and adopted in n-butylamine combustion. Results suggest that Pd dispersion is positive correlation with support SSA and GA method is the most favorable approach to obtain highly dispersed Pd active sites. Pd/S-1IS, Pd/S-1WI, and Pd/S-1GA catalysts with small SSA show inferior activity and higher NOx yield than those of Pd/S-2IS, Pd/S-2WI, and Pd/S-2GA with large SSA, irrelevant with the preparation methods. Amongst, Pd/S-2GA possesses the smallest Pd average diameter (ca. 1.72 nm) and highest activity with 90% of n-butylamine destructed at 234 °C; however, the yield of NOx over Pd/S-2GA is much higher than the other catalysts (except Pd/S-1GA) as the GA approach provides high concentration of active sites and the preparation procedure sacrifices the SSA and porosity of supports to some extent. In situ DRIFTS results reveal that the developed porosity of catalyst promotes nitrogen-containing by-products (NHx) transfer and diffusion and avoids their further oxidizing to NOx. The activity of samples prepared by the WI process is lower than that prepared by the IS or GA method due to limited active sites. Comparatively, the Pd/S-2IS prepared by the IS method has relative high activity (T90 of 240 °C) and low NOx yield (0.99% at T90) in n-butylamine oxidation among all materials, exhibiting an attractive prospective in nitrogen-containing VOC environment-friendly elimination.

Quantifying the surface properties of enzymatically-made porous starches by using a surface energy analyzer

The behavior of starch during processing and its performance in products is influenced by the surface energetics/structure of the constituent particles. This work investigates the effect of enzymatically-produced porous maize starch particles on their energetic surface properties using inverse gas chromatography-based surface energy analysis (SEA). Three modified maize starch samples treated with amylase (AM), glucoamylase (AMG) and cyclodextrin-glycosyltransferase (CGT), were used for the study. The dispersive surface energy varied from 36.71 (native) to 43.34 mJ/m2 (AMG < CGT < AM). Enzyme catalysis resulted in porous starches with a more acidic (AMG) and a more basic (AM) surfaces. CGT exhibited similar acid-base balance as native starch but with higher concentration of active sites on the surface. This is the first study on the surface energy of enzymatically-treated porous starch materials using SEA, revealing significant information regarding the surface interactions that can affect performance of food and pharmaceutical products.

Nanowire-Templated Three-Dimensional out-of-Plane Fuzzy Graphene As Thin Film Supercapacitor

Supercapacitors have gained popularity as future energy storage solutions due to their simple architecture, long cycling life, pulse power supply, and high dynamic charge propagation.1 They are generally categorized as Electrical Double Layer Capacitors (EDLCs) or pseudo-capacitors.2 EDLCs store energy as electrostatic charge on the electrodes’ surfaces; their efficiency is thus limited by the electrochemically active surface area available to the electrolyte.3 Whereas, pseudo-capacitors utilize fast and reversible faradaic processes due to electro-active species localized on the electrode surface to enhance current density.1, 4 Concentration of electro-active charged species and electro-chemical efficiency governs the efficiency of these supercapacitors. Recently, carbon-based materials (such as CNTs, graphene foams, graphene aerogels) have received research interest as promising candidates for supercapacitors due to their high electrochemical surface area, high electrical conductivity and accessible surface active sites for modification with electro-active species.5 Graphene has emerged as an ideal EDLC electrode material due to its superior electrical properties and high theoretical surface area.6 Current graphene electrodes are either pinned to a two-dimensional (2D) surface (such as graphene foams) or are tethered to a 2D substrate (such as carbon nanowalls). Graphene based hybrid-nanomaterials that leverage graphene’s outstanding surface-to-volume ratio coupled with pseudo-capacitive species for high efficiency supercapacitors have not been demonstrated to date. Here we demonstrate that direct synthesis of three-dimensional (3D) out-of-plane fuzzy graphene (3DFG) on Si nanowire (SiNW) mesh template (NT-3DFG) provides an ideal surface for functionalization with electro-active species to develop EDLC and pseudo-capacitive supercapacitors. We report fine control over 3DFG flake size and edge density by varying the partial pressure of CH4 precursor, plasma enhanced chemical vapor deposition (PECVD) synthesis process time, and PECVD synthesis temperature (Figure 1.A and B).7 Through electron microscopy (SEM and TEM) and Raman spectroscopy a distinct increase in single-to-few layer out-of-plane graphene edges is observed. High density of graphene edges presents high concentration of active sites for surface functionalization through surface doping, such as that through treatment with HNO3. Post treatment, the electrical conductivity of NT-3DFG is observed to be as high as 2400 S m-1. Leveraging on graphene’s outstanding surface-to-volume ratio, we have developed a material capable of attaining electrochemically active surface area of ca. 1017 m2 g-1. The introduction of electro-active species on this high surface area material renders specific capacitance as high as 87 ± 8 F g-1 (Figure 1.C). This value is further enhanced by decorating the template with metal oxide nanoparticles. The reported novel graphene based hybrid-nanomaterial shows great potential to be utilized in next-generation energy storage solutions. Figure 1. Characterization of NT-3DFG. (A) SEM image of NT-3DFG synthesized with increasing partial pressure of CH4 and increasing PECVD process time. (B) Effect of increasing PECVD process temperature on NT-3DFG synthesized under 25 mTorr partial pressure of CH4 for 10 min. (C) Cyclic voltammetry characterization of NT-3DFG before and after HNO3 treatment. (I) Representative cyclic voltammograms presenting double layer capacitance of NT-3DFG. Blue, yellow and red denote Au working electrode, NT-3DFG synthesized under 25 mTorr partial pressure of CH4 for 30 min and NT-3DFG synthesized under 25 mTorr partial pressure of CH4 for 90 min, respectively. Dashed lines represent respective samples after 2-hour HNO3 treatment. (II) Current density as a function of scan rate. Blue, yellow and red denote Au working electrode, NT-3DFG synthesized under 25 mTorr partial pressure of CH4 for 30 min and NT-3DFG synthesized under 25 mTorr partial pressure of CH4 for 90 min, respectively. Closed and open square represent samples before and after 2-hour HNO3 treatment, respectively.

Quantitative screening of an extended oxidative coupling of methane catalyst library

A comprehensive microkinetic model, including catalyst descriptors, that accounts for the homogeneous as well as heterogeneously catalyzed reaction steps in Oxidative Coupling of Methane (OCM) was used in the assessment of large kinetic datasets acquired on five different catalytic materials. The applicability of the model was extended from alkali magnesia catalysts represented by Li/MgO and Sn-Li/MgO and alkaline earth lanthana catalysts represented by Sr/La2O3 to rare earth-promoted alkaline earth calcium oxide catalysts, represented by LaSr/CaO, and to a Na-Mn-W/SiO2 catalyst. The model succeeded in adequately simulating the performance of all five investigated catalysts in terms of reactant conversion and product selectivities in the entire range of experimental conditions. It was found that the activity of Sr/La2O3, in terms of methane conversion, is approximately 2, 5, 30 and 33 times higher than over the La-Sr/CaO, Sn-Li/MgO, Na-Mn-W/SiO2 and Li/MgO catalysts, respectively, under identical operating conditions. This was attributed mainly to the high stability of adsorbed hydroxyls, the high stability of adsorbed oxygen and the high concentration of active sites of Sr/La2O3. The selectivity towards C2 products was found to depend on the methyl radical sticking coefficient and the stability of the adsorbed oxygen and was the highest on the Na-W-Mn/SiO2 catalyst, that is 75% at about 1% methane conversion and 1023K, 190kPa and inlet molar CH4/O2 ratio of 4.

Enhancement of Catalytic Activity in Epoxide Hydration by Increasing the Concentration of Cobalt(III)/Salen in Porous Polymer Catalysts

AbstractThe rational design of catalytic materials from the reaction characteristics is expected to be a useful strategy to create highly efficient catalysts. Herein, according to a well‐established reaction pathway of epoxide hydration catalyzed a dual‐molecular system of Co3+/salen in which a high concentration of active sites is favorable to enhance the activity, we provide an alternative way to prepare a highly efficient heterogeneous catalyst with a high concentration of Co3+/salen from the polymerization of vinyl‐functionalized salen monomers followed by the loading of Co3+ species (Co3+/POL‐salen). Co3+/POL‐salen has a hierarchical porosity and an extraordinary hydrothermal stability. Importantly, catalytic tests in epoxide hydration demonstrate that Co3+/POL‐salen affords excellent high activities, which are even better than those of the homogeneous version. This phenomenon is related to the very high concentration of Co3+/salen in the catalyst. In addition, this catalyst can be recycled readily because of its excellent hydrothermal stability.