High TOF Research Articles

Enhanced Catalytic Activity of Binuclear Oxidovanadium(IV) Bisbenzimidazole Linked Porphyrin Dimer for the Generation of Biologically Active 3,4-Dihydropyrimidinones and Their Corresponding Thiones.

Binuclear vanadyl(IV) porphyrin (V2BP), where two vanadium(IV) porphyrin macrocycles are linked through benzimidazole units at the β-positions, has been prepared and characterized with various techniques, such as UV-vis, Fourier transform-infrared, electron paramagnetic resonance, cyclic voltammetry, density functional transform calculations, and mass spectrometry. V2BP exhibits a red shift (Δλmax = 10 nm) in the Soret band as compared with unsubstituted parent vanadyl(IV) meso-tetraphenylporphyrin (VP). The synthesized binuclear vanadyl(IV) porphyrin (V2BP) has further been studied as a catalyst to explore a single-pot multicomponent Biginelli reaction producing biologically active 3,4-dihydropyrimidin-2-(1H)-one (DHPM)-based biomolecules and the corresponding thiones under solvent-free conditions and its catalytic activity has been compared with vanadyl(IV) meso-tetraphenylporphyrin (VP). Several reaction conditions, such as the amount of catalyst, time, solvent, and temperature, have been optimized to obtain the maximum yield of DHPMs or thiones. The synthesized β-functionalized V2BP porphyrin dimer manifests much higher conversion (84-95% yield) of DHPMs or the corresponding thiones under the optimized reaction conditions with high TON (4454-5037) and TOF (1113-1259 h-1) values for the one-pot multicomponent Biginelli reaction as compared to the literature. The catalyst exhibited excellent recyclability up to 10 cycles.

Development of a High Granular TOF Neutron Detector for the BM@N Experiment

Development of a High Granular TOF Neutron Detector for the BM@N Experiment

Unveiling the integrated function of metallo‐/ionic‐covalent organic polymers for boosting atmospheric CO2 conversion

Unveiling the integrated function of metallo‐/ionic‐covalent organic polymers for boosting atmospheric <scp>CO₂</scp> conversion

Boosting electrocatalytic hydrogen generation from water splitting with heterostructured MoS2/NiFe2O4 composite in alkaline media

Design and synthesis of earth-abundant and robust bifunctional electrocatalysts have been greatly sought for commercialization of the technology for clean and renewable energy and replacement of the energy equipment based on fossil fuels. In this work, a facile hydrothermal approach is used to synthesize MoS2/NiFe2O4-based nanocomposite as a novel electrocatalyst for alkaline water splitting. Surface analysis was conducted using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Benefiting from the synergy of lamellar MoS2 and crystalline NiFe2O4, the obtained MoS2/NiFe2O4 composite shows excellent hydrogen evolution reaction (η10 = 190 mV, η50 = 279 mV) and oxygen evolution reaction (OER) (η50 = 350 mV, η100 = 360 mV) activity with high TOF (0.01 s−1@190 mV for HER and 0.24 s−1 @360 mV for OER) and displays good electrochemical stability. Explicitly, the electrocatalyst requires a cell voltage of 1.69 V to drive overall water splitting at a current density of 10 mA cm−2. Density functional theory (DFT) results demonstrated that the MoS2/NiFe2O4 composite electrocatalyst has smaller hydrogen adsorption free energy (|ΔGH*|) than pristine MoS2 and NiFe2O4, which demonstrates the effective adsorption and cleavage of water on the catalyst surface. This work thus presents an approach for the synthesis and rational design of metal oxide/metal sulfide hybrids as an electrocatalyst with high performance for overall water splitting.

Study on oxygen evolution reaction efficiency demonstrated by Ce-E (E = S, Se and te) electrocatalyst

The strategy of generating sustainable energy with hydrogen fuel is highly significant and promising. Hydrogen fuel being non-toxic proves beneficial for the environment and can be produced in a variety of ways, as industrial water splitting into oxygen and hydrogen is a crucial future plan. This study aims to investigate cerium-based chalcogens (CeS, CeSe, and CeTe), as a catalyst to broaden the family of highly effective OER electrocatalysts based on transition metal chalcogenides. CeTe on NF was found to exhibit lowest onset potential with an overpotential of 333 mV at 10 mAcm−2 and a 51 mVdec−1 Tafel value among CeE (E = S, Se) chalcogenides with comparable stoichiometry. Using different analyses, it was determined that CeTe had a large surface area of 83.7 m2g-1, a cubic structure, and a highly crystalline nanoflakes morphology. High electrochemical surface area of 562 cm2, small resistance as Rs of 1.12 Ω, and Rct 729 mΩ, along with high TOF value of 0.174 s−1, 0.059 s−1, 0.009 s−1 for CeTe as compared to CeSe and CeS have supported by CV results. In particular, CeTe showed exceptional catalytic efficiency and was highly active and durable in oxygen evolution reactions.

Microwave-Assisted Transfer Hydrogenation of Carbonyl and ­Nitro Compounds Using Bimetallic Ru(II) Cymene Complexes

AbstractWe report an investigation of the microwave-assisted catalytic transfer hydrogenation (TH) of carbonyl and nitro compounds by employing Ru(II) complexes: bimetallic [(p-cymene)2(RuCl)2L1]2X (X = BF4 (Cat2); X = PF6 (Cat3)) and mononuclear [(p-cymene)(RuCl)L2]BF4 (Cat4) (where L1 = N,N′-(3,3′,5,5′-tetraisopropyl-[1,1′-biphenyl]-4,4′-diyl)bis(1-(pyridin-2-yl)methanimine) and L2 = N-(2,6-diisopropylphenyl)-1-(pyridin-2-yl)methanimine). At a low catalyst loading of 0.01 mol% (Cat2/Cat3), a broad range of substrates, comprising aromatic as well as aliphatic ketones and aldehydes, undergo the TH reaction in a short reaction time of just 10 minutes. Additionally, chemoselective hydrogenation of nitroaromatic compounds is achieved under microwave irradiation in the presence of Cat2 within 5 minutes. Control experiments demonstrate that microwave heating conditions outperform conventional heating in terms of improved catalytic activity and reaction efficiency. The bimetallic catalyst Cat2 is used at a very low loading of 0.001 mol% to achieve high TONs and TOFs of 7.7 × 104 and 2.3 × 105 h–1, respectively, for the TH reaction. Spectrometry experiments involving trapping of intermediates are used to propose a mechanism for the TH of the carbonyl compounds.

Efficient electrocatalytic alkyne Semi-Hydrogenation and deuteration using Pd/PANI catalysts supported on nickel foam

In this study, we synthesized Pd/PANI catalysts anchored on nickel foam (NF) via a single-step CV electrodeposition process. The resulting Pd0.3/PANI-NF materials exhibited outstanding selectivity and activity for electrocatalytic alkyne semi-hydrogenation and deuteration under ambient conditions. Characterization of Pd/PANI and control experiment revealed that the combination of PANI and Pd had a synergistic effect on the catalytic performance of Pd/PANI-NF for alkyne semi-hydrogenation. Optimized conditions in H-cells allowed efficient conversion of various terminal and internal alkynes into their corresponding alkenes with remarkable yields up to 92 % and a Faradaic efficiency of 88 %, even at low Pd loading (0.4 mol%). The Pd0.3/PANI-NF showed sustained catalytic activity for gram-scale alkene synthesis through five usage cycles under continuous flow conditions, marked by a high TOF (up to 230 h−1) and combined TONs of 2151, establishing its practical viability for electrocatalytic hydrogenation.

Enhancing the Green Synthesis of Glycerol Carbonate: Carboxylation of Glycerol with CO2 Catalyzed by Metal Nanoparticles Encapsulated in Cerium Metal-Organic Frameworks.

The reaction of glycerol with CO2 to produce glycerol carbonate was performed successfully in the presence of gold nanoparticles (AuNPs) supported by a metal-organic framework (MOF) constructed from mixed carboxylate (terephthalic acid and 1,3,5-benzenetricarboxylic acid). The most efficient were two AuNPs@MOF catalysts prepared from pre-synthesized MOF impregnated with Au3+ salt and subsequently reduced to AuNPs using H2 (catalyst 4%Au(H2)@MOF1) or reduced with NaBH4 (catalyst 4%Au@PEI-MOF1). Compared to existing catalysts, AuNPs@MOFs require simple preparation and operate under mild and sustainable conditions, i.e., a much lower temperature and the lowest CO2 overpressure ever reported, with MgCO3 having been found to be the optimal dehydrating agent. Although the yield of the process is still not competitive with previously developed systems, the most promising advantage is the highest TOF (78 h-1) ever reported for this reaction. The optimal parameters observed for AuNPs were also tested on AgNPs and CuNPs with promising results, suggesting their great potential for industrial application. The catalysts were characterized by XRD, TEM, SEM-EDS, ICP-MS, XPS, and porosity measurements, confirming that AuNPs are present in low concentration, uniformly distributed, and confined to the cavities of the MOF.

The synthesis of highly nonplanar oxidovanadium(IV) porphyrins as robust catalysts for oxidative bromination of phenols in aqueous medium

Two new complexes, oxidovanadium(IV) 2,3,5,10,12,13,15,20-octaphenyl-7,8,17,18-tetrabromoporphyrin V(IV)O(OPP)Br4 (2), and oxidovanadium(IV) 2,3,5,10,12,13,15,20-octaphenyl-7,8,17,18-tetrachloroporphyrin V(IV)O(OPP)Cl4 (3) starting from oxidovanadium(IV) 2,3,5,10,12,13,15,20-octaphenylporphyrin V(IV)O(OPP) (1) have been prepared in good yields and characterized by various spectroscopic techniques. The single-crystal and DFT-optimized structures of these porphyrins showed a highly nonplanar saddle-shape conformation of the porphyrin macrocycle. In the cyclic voltammograms, the first ring oxidation potential and the first ring reduction potential of V(IV)O(OPP)Br4 (2) and V(IV)O(OPP)Cl4 (3) showed anodic shift as compared to V(IV)O(OPP) (1), indicating the electron-deficient nature of both the porphyrins. The oxidation state of vanadium in the synthesized complexes as +4 was confirmed by EPR spectroscopy, and these porphyrins exhibited axially compressed [Formula: see text] configuration. These porphyrins were utilized as catalysts for the oxidative bromination of thymol and other phenol derivatives with excellent conversion ([Formula: see text] 99.9%), good selectivity, and high TOF value (86869 h[Formula: see text].

Trans‐Dioxidomolybdenum(VI) Porphyrins and their Catalytic Activity Mimicking Oxidative Bromination

AbstractSynthesis of trans‐dioxidomolybdenum(VI)‐meso‐tetraphenylporphyrin (trans‐[MoVIO2(TPP)], 1) and trans‐dioxidomolybdenum(VI)‐meso‐tetra(p‐chlorophenyl)porphyrin (trans‐[MoVIO2(TCPP)], 2) by reacting the corresponding free‐base porphyrins with Mo(CO)6 in 1,2,4‐trichlorobenzene at 190 °C has been reported. These are the second examples in the literature where molybdenum‐porphyrins have trans‐[MoVIO2] group, identified by single crystal X‐ray study. Both complexes have been utilized as functional model of haloperoxidases for the oxidative bromination of various phenol derivatives using KBr, H2O2 and HClO4 as green brominating reagents in aqueous medium. These complexes displayed very high TOF values (up to 16.2 s−1 for catalyst 2) representing excellent catalytic activity. To the best of our knowledge, this is the first report presenting trans‐dioxidomolybdenum(VI) based porphyrin as haloperoxidases mimicking oxidative bromination of various phenol derivatives.

FeCoCuMnRuB Nanobox with Dual Driving of High-Entropy and Electron-Trap Effects as the Efficient Electrocatalyst for Water Oxidation.

High-entropy borides hold potential as electrocatalysts for water oxidation. However, the synthesis of the tailored nanostructures remains a challenge due to the thermodynamic immiscibility of polymetallic components. Herein, a FeCoCuMnRuB nanobox decorated with a nanosheet array was synthesized for the first time by a "coordination-etch-reduction" method. The FeCoCuMnRuB nanobox has various structural characteristics to express the catalytic performance; meanwhile, it combines the high-entropy effect of multiple components with the electron trap effect induced by electron-deficient B, synergistically regulating its electronic structure. As a result, FeCoCuMnRuB nanobox exhibits enhanced OER activity with a low overpotential (η10 = 233 mV), high TOF value (0.0539 s-1), small Tafel slope (61 mV/dec), and a satisfactory stability for 200 h, outperforming the high-entropy alloy and low-entropy borides. This work develops a high entropy and electron-deficient B-driven strategy for motivating the catalytic performance of water oxidation, which broadens the structural diversity and category of high-entropy materials.

Amphiphilic Janus dendrimer-stabilized Au, Ag and Pd nanoparticles for the reduction of 4-nitrophenol and Suzuki-Miyaura cross-coupling reactions

Dendrimers with symmetrical 3D structures can be designed with various interior or exterior functional groups, which has been regarded as good stabilizers for various metal nanoparticles in catalysis. Nevertheless, Janus dendrimers with asymmetric structures are hardly researched to load metal nanoparticle catalysts. Here, an amphiphilic Janus dendrimer is used to stabilize metal (Au, Ag and Pd) nanoparticles, whose catalytic activities are also investigated. Au, Ag and Pd nanoparticles have the average diameters of 2.6 ± 2.0 nm, 5.8 ± 3.0 nm and 2.0 ± 1.0 nm, respectively, and show clear lattice fringes. Au and Pd nanoparticles are observed to have significantly higher catalytic performance than that of Ag nanoparticles in the 4-nitrophenol reduction, and Pd nanoparticles possess the highest catalytic activity (TOF: 2250 h−1). In addition, Pd nanoparticles are also highly active in the Suzuki-Miyaura reactions with low catalyst loading (50 ppm) and high TOF (2475 h−1) and show good applicability to tolerate various substituents.

Ir(tri-N-heterocyclic carbene)-catalyzed upgrading of glycerol: C-C bond formation for the synthesis of α-hydroxy acids.

Ir(triNHC) complexes catalyzed glycerol and alcohol dehydrogenative coupling, yielding diverse α-hydroxy acids. Unlike conventional conditions, Ir(triNHC) facilitated additional C-C bond formation after lactic acid production from glycerol, exhibiting high TOFs. This protocol successfully converted 1,2-propanediol and sorbitol into α-hydroxy acids, highlighting biomass-derived sources' potential as valuable platform chemicals.

Covalent organic frameworks with interlayer fixed Pt atoms for efficient electrocatalytic hydrogen evolution

TTB-COF with different crystallinities loaded with Pt atoms were synthesized for HER. The Pt@TTB-COF with higher crystallinity exhibited excellent performance with low overpotential of 5 mV at 10 mA cm−2 and high TOF value of 5.43 H2 S−1 at 50 mV.

Designing highly-efficient oxygen evolution reaction FeCoNiCrMnOx electrocatalyst via coexisted crystalline and amorphous Phases: Experiment and theory

The design of phase structure was an effective method to improve the catalytic performance of catalysts. In this work, a new electrocatalyst of FeCoNiCrMn based high entropy oxide (HEO) with coexisted crystalline and amorphous phases was designed and analyzed by experimental and theoretical methods. The raising crystallization of specimen could effectively increase the d electron density and d band center of Ni2+ active ion, which contributed to increase the chemical activity of active ion and adjust the catalytic activity of HEO specimen. The designed HEO specimen with coexisted crystalline and amorphous phases exhibited the fairly low experimental oxygen evolution reaction overpotential of 219 mV at the current density of 10 mA cm−2 and 271 mV at the current density 100 mA cm−2 with the small Tafel slope of 42 mV dec-1, fast charge transfer rate, high intrinsic activity TOF of 0.078 s−1 at experimental overpotential of 350 mV and stable electrocatalytic activity, which were better than single crystalline or amorphous phase. This design strategy would be adopted to provide an effective enhancement scheme for HEO systems.

Markovnikov-Selective Cobalt-Catalyzed Wacker-Type Oxidation of Styrenes into Ketones under Ambient Conditions Enabled by Hydrogen Bonding.

The replacement of palladium catalysts for Wacker-type oxidation of olefins into ketones by first-row transition metals is a relevant approach for searching more sustainable protocols. Besides highly sophisticated iron catalysts, all the other first-row transition metal complexes have only led to poor activities and selectivities. Herein, we show that the cobalt-tetraphenylporphyrin complex is a competent catalyst for the aerobic oxidation of styrenes into ketones with silanes as the hydrogen sources. Remarkably, under room temperature and air atmosphere, the reactions were exceedingly fast (up to 10 minutes) with a low catalyst loading (1 mol %) while keeping an excellent chemo- and Markovnikov-selectivity (up to 99 % of ketone). Unprecedently high TOF (864 h-1 ) and TON (5,800) were reached for the oxidation of aromatic olefins under these benign conditions. Mechanistic studies suggest a reaction mechanism similar to the Mukaiyama-type hydration of olefins with a change in the last fundamental step, which controls the chemoselectivity, thanks to a unique hydrogen bonding network between the ethanol solvent and the cobalt peroxo intermediate.

Markovnikov‐Selective Cobalt‐Catalyzed Wacker‐Type Oxidation of Styrenes into Ketones under Ambient Conditions Enabled by Hydrogen Bonding

AbstractThe replacement of palladium catalysts for Wacker‐type oxidation of olefins into ketones by first‐row transition metals is a relevant approach for searching more sustainable protocols. Besides highly sophisticated iron catalysts, all the other first‐row transition metal complexes have only led to poor activities and selectivities. Herein, we show that the cobalt‐tetraphenylporphyrin complex is a competent catalyst for the aerobic oxidation of styrenes into ketones with silanes as the hydrogen sources. Remarkably, under room temperature and air atmosphere, the reactions were exceedingly fast (up to 10 minutes) with a low catalyst loading (1 mol %) while keeping an excellent chemo‐ and Markovnikov‐selectivity (up to 99 % of ketone). Unprecedently high TOF (864 h−1) and TON (5,800) were reached for the oxidation of aromatic olefins under these benign conditions. Mechanistic studies suggest a reaction mechanism similar to the Mukaiyama‐type hydration of olefins with a change in the last fundamental step, which controls the chemoselectivity, thanks to a unique hydrogen bonding network between the ethanol solvent and the cobalt peroxo intermediate.

A theoretical study into the performance of DACs loaded on MgO utilized in CO oxidation

Single-atom catalysts (SACs) have garnered significant attention due to their unique combination of advantages from both heterogeneous and homogeneous catalysts. However, SACs composed of just one metal cannot adequately meet the various catalytic requirements. Thus, this study focused on the addition of a second metal atom to M1/MgO systems (M = Au, Ag and Cu) to create dual-atom catalysts (DACs) supported on different di-vacancy types on MgO(100) surfaces. Homogeneous (Au2, Ag2, Cu2) and multiphase (Au1Ag2, Au1Cu2 and Ag1Cu2) were analyzed for their selectivity in CO oxidation by Langmuir-Hinshaw (LH) and Eley-Rideal (ER) mechanisms using density functional theory (DFT) method. The results indicated that the tri-molecules ER pathway had the highest selectivity, and the multiphase DACs had better CO catalytic oxidation activity compared to homogeneous DACs. Among all multiphase DACs in the tri-molecules ER pathway, alloy DACs of Au1Ag2/MgO(Fc-Fc) and Au1Cu2/MgO(Fc-Vc) had the lowest energy barrier for CO oxidation, and the addition of a second metal atom improved stability compared to SAC of Au1/MgO(Fc). DFT calculations combined with microkinetic simulations revealed that under reaction conditions, Au1Cu2/MgO(Fc-Vc) had a remarkably high TOF of CO2, making it a promising DAC for practical applications. This study provides valuable insights into the development of efficient and low-cost atomic-scale catalysts.

Biosynthesis of Copper Nanoparticles Using Aqueous Pisa Plant Leaf Extracts: Antimicrobial Activities and Catalytic Application for Xanthene Synthesis

AbstractA simple, efficient and environmentally benign approach has been investigated for synthesis of copper nanoparticles using Actinodaphnehookeri (Pisa) plant leaf extract as a reducing agent. The synthesized copper NPs showed antimicrobial activity against pathogenic Gram‐positive and Gram‐negative microbial infections, also showed the catalytic activity (15 mol%) for synthesis of xanthenes with high TONs and TOFs. It's interesting that this catalyst quantitatively recovered from the reaction medium and recycled up to five cycles, and there was no noticeable loss of catalytic performance.

Synthesis of defect-engineered molybdenum sulfides on reduced graphene oxide for enhanced hydrogen evolution reaction kinetics

Amorphous molybdenum sulfide (a-MoS3) is a promising non-precious electrocatalyst for hydrogen evolution reaction owing to the abundant defective active sites. Here in, we show a rapid microwave-assisted synthesis method to produce a-MoS3 catalysts on reduced graphene oxide (rGO) substrates. The a-MoS3 reported in this study comprise of two possible 1D chain-like structures, i.e., with molybdenum (IV) in Weber's model and molybdenum (V) in Hibble's model, unlike the polymeric cluster type a-MoS3 structures reported in literature. Thermal annealing of the microwave-prepared a-MoS3 produced a family of defect-engineered MoSx/rGO hybrids, from a-MoS3 to crystalline MoS2, which showed tunable HER activities. XPS analysis provided in-depth understanding of the compositional changes in MoSx/rGO with thermal annealing. The a-MoS3/rGO 250 (annealed at 250 °C) exhibited the highest HER catalytic activity among all the MoSx/rGO hybrids, with an overpotential of 208 mV at 10 mA/cm2, a low Tafel slope of 52 mV/decade, a high double layer capacitance of 3.7 mF/cm2 and a high TOF value of 0.43 H2/s per site at the HER overpotential of 208 mV. The excellent HER activity is attributed to both MoV and sulfur active sites. This study provides a controllable, scalable and rapid synthesis method to produce 1D chain-like a-MoS3 structures for HER electrocatalysis.