High TOF Research Articles

Methyl Salicylate Functionalized Magnetic Chitosan Immobilized Palladium Nanoparticles: An Efficient Catalyst for the Suzuki and Heck Coupling Reactions in Water

AbstractA heterogeneous catalyst was fabricated by immobilization of chitosan (CS) on magnetic Fe3O4 following the deposition of palladium nanoparticles on its modified surface. The prepared catalyst was characterized using Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), X‐ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive X‐ray spectroscopy (EDX). The catalyst was investigated for the Suzuki‐Miyaura and Heck‐Mizoroki cross‐coupling reactions and afforded arylated products with high turnover number TON (980) and turnover frequency TOF (980 h−1). The optimized catalytic system was found practical and green as catalyst loading was low (0.10 mol%), water used as solvent and the catalyst was separated with external magnet. A wide variety of aryl halides including electro withdrawing and releasing groups were investigated and found excellent to good yield of Suzuki and Heck cross‐coupled products. Furthermore, the catalyst was recovered and reused up to seven times for Suzuki coupling reactions with 97% efficiency.

Fischer-Tropsch synthesis over carbon-encapsulated cobalt and iron nanoparticles embedded in 3D-framework of carbon nanotubes

Development of alternative ways to produce clean fuels is a significant and strategically important challenge. One of the most effective approaches is the Fischer-Tropsch synthesis (FTS), which is realized over Co- or Fe-based catalysts. In this work spark plasma sintering was applied for the synthesis of bulk core-shell Co and Fe CNT-supported FTS catalysts. The effect of the sintering temperature on the structure, evolution, and catalytic performance of the samples was studied by combination of physicochemical methods. Catalysts showed high activities and TOFs without pre-reduction: 11.6 molCOgCo−1 s−1 and 0.1 s−1 for Co and 20.3 molCOgFe−1 s−1 and ~0.9 s−1 for Fe samples. The unusual dependence of C5+ selectivity on the Co particle size along with the presence of the amorphous carbide and amorphous carbon layers under graphitic shell in Fe catalysts point to the diffusion of reagents and products through shell defects and the catalytic reaction on the particle core surface.

Application of Ag/TFPG-DMB COF in carbamates synthesis via CO2 fixation reaction and one-pot reductive N-formylation of nitroarenes under sunlight

We have designed mesoporous AgNPs decorated COF (Ag/TFPG-DMB COF) nanomaterial which has been formed by an easy ex-situ synthetic method. The synthesized material is characterized by FTIR, PXRD, UV–vis, N2 adsorption–desorption studies, TEM, FESEM and XPS. The material showed the generation of identical mesopore at 3.9 nm. It is observed that the material can perform as both thermally and photochemically active catalyst for carbamate synthesis and one-pot reduction and N-formylation of nitroarenes respectively. The catalytic activity of the Ag/ TFPG-DMB COF nanomaterial is checked for green synthesis of carbamates from different amines and alcohols under 1 atmospheric pressure of CO2 with excellent yield (upto 95 %) as well as with high TOF value (182 h−1) and high selectivity. Additionally, the Ag/ TFPG-DMB COF nanomaterial is also applied as a potentially active photocatalyst for one-pot nitroarene reduction along with N-formylation reaction under sunlight irradiation in green reaction conditions with exceptionally high yield of formylated products upto 99 % as well as with high TOF value (762 h −1). The catalyst efficiently reduced and formylated para-nitrophenol, a potential water pollutant, which elaborates its scope as an efficient catalyst for water purification also. The catalyst recyclability is also checked for five reaction cycles for both the reactions and the Ag/TFPG-DMB COF material showed outstanding recycling ability without any noticeable leaching of active metal or catalyst degradation.

Ruthenium N‐Heterocyclic Carbene Complexes for Chemoselective Reduction of Imines and Reductive Amination of Aldehydes and Ketones

Chemoselective reduction of imines to secondary amines is catalyzed efficiently by tethered and untethered, half‐sandwich ruthenium N‐heterocyclic carbene (NHC) complexes at room temperature. The untethered Ru‐NHC complexes are more efficient as catalysts for the reduction of aldimines and ketimines than the tethered complexes. Using the best untethered complex as a catalyst, electronic and steric demands on the reaction was probed using a series of imines. Chemoselectivity of the catalyst towards imine reduction was tested by performing inter and intramolecular competitive reactions in a variety of ways. The catalyst exhibits a very high TON and TOF under anaerobic conditions.

Copper supported on N‐heterocyclic carbene‐functionalized porous organic polymer for efficient oxidative carbonylation of methanol

A new heterogeneous catalyst for the oxidative carbonylation of methanol to dimethyl carbonate based on copper coordinated in N‐heterocyclic carbene‐functionalized porous organic polymer (Cu@PQP‐NHC) was presented. The solid catalyst that featured relatively large surface area, hierarchical pore structure, and excellent swelling property, was prepared via a facile copolymerization reaction of tetra‐vinylphosphonium salt and bis‐vinylimidazolium salt, followed by successful immobilization of CuCl. Accordingly, the resulting Cu@PQP‐NHC showed excellent catalytic performance for the oxidative carbonylation of methanol. A 10 mmol/l of Cu usage was sufficient for 9.3% conversion of methanol with a high TOF number of 57 h−1. Importantly, the catalyst was easily recovered by simple centrifugation, and could be reused up to 10 consecutive recycles without obvious loss of its initial activity. Also, the solid catalyst showed negligible Cu leaching during the recycling, and 99% Cu species was still retained after reusing 10 times. The results in this study highlights the advantages of porous organic polymer supported NHC‐Cu catalyst as a highly active and stable heterogeneous catalyst, providing a promising route for the synthesis of dimethyl carbonate.

Engineering of catalytic sites of Pdx-Ce1-xO2-δ for dehydrogenation, oxygen insertion and reverse water gas shift reactions during methane combustion

Methane, a highly abundant greenhouse gas with a high global warming potential, is a relatively clean fuel due to its high H/C ratio. This study has taken a unique approach to discover key fundamentals during the solution combustion synthesis of Pd0.03Ce0.97O2-δ catalysts characterised using several physicochemical techniques for catalytic CH4 combustion. Oxygen vacancies were found to be key for the catalysts containing all PdOx substituted in the ceria lattice. On the other hand, catalysts containing both large surface supported PdO that is transformable to PdHx (in situ during the methane combustion reaction) and substituted PdOx were found to provide superior catalytic performance (complete CH4 conversion with 100% selectivity to CO2) with long life under dry and wet conditions. The discussed bifunctionality of the catalyst resulted in achieving a high TOF, high conversion and stability at elevated temperatures. Therefore, this study introduces a new strategy to improve the activity of combustion catalysts.

Surfactant-free self-assembly to the synthesis of MoO3 nanoparticles on mesoporous SiO2 to form MoO3/SiO2 nanosphere networks with excellent oxidative desulfurization catalytic performance

Recently, oxidative desulfurization (ODS) is favoured by researchers because it is based on mild conditions and does not consume hydrogen. However, the preparation process of catalyst for ODS was not green or costly, which limits its further industrial applications. In this study, a facile route has been explored to grow the mesoporous MoO3/SiO2 nanosphere networks (MoO3/SiO2 NN) using low-cost air without surfactants. Herein, the air not only served as the template to self-assemble and form the nanosphere network structure but acted as a mesopore-directing agent to make mesopores on the MoO3/SiO2 nanosphere. Moreover, the recovered waste mother liquor was also successfully applied to prepare nanomaterials. Gratifyingly, the nanocomposites of MoO3/SiO2 NN displayed remarkable pore structure, large specific surface area (201 m2 g−1) and excellent amphipathy (CA = 24.7° and 13.6° of water and n-octane, respectively) making it a promising catalyst for two-phase ODS reaction with H2O2 as an oxidant. Meanwhile, the high TOF value (56.6 h−1) and outstanding durability were obtained under optimum conditions (Yield > 99 % at 70 °C and O/S = 8:1 for 1 h, 20 mg catalyst) and the products were detected by GC–MS and 1H NMR. Therefore, an environmentally benign self-assembly procedure can facilely prepare more types of mesoporous catalysts for large-scale industrial application.

Combustion of toluene over cobalt-modified MFI zeolite dispersed on monolith produced using 3D printing technique

A facile method of fabrication of ceramic monoliths assisted by 3D printing was developed for preparation of Co3O4-based catalysts of total oxidation of volatile organic compounds. The proposed approach was based on the production of a resin template, which was subsequently used at a casting step for the construction of corundum monolith. The walls of this material were additionally coated with a MFI zeolite layer providing the possibility of modification with a Co3O4 precursor using ion-exchange and impregnation techniques. The parent and Co3O4-modified monoliths with varying active phase content were characterized by SEM/EDS, XRD, XRF, XPS, UV–vis-DR and H2-TPR. Their catalytic performance in the toluene combustion was also tested. It was shown that the formation of Co3O4 spinel particles highly dispersed on the zeolite-coated monolith resulted in excellent catalytic activity measured by very high TOF values. Furthermore, stability tests confirmed that the obtained monolith catalysts can work for prolonged reaction time without noticeable changes in the toluene conversion and selectivity to CO2.

Two anionic Ni(II) porphyrinic metal−organic frameworks: Syntheses, flexibility and roles in visible-light photocatalytic CO2 reduction to CO in the Ru(bpy)3Cl2/TEA/CH3CN system

A 3D, anionic novel porphyrinic metal-organic framework (PMOF) 1 having [NH2(CH3)2]+ as counterions and Li+ -exchanged version of 1 (Li+-1) were synthesized. A very interesting feature of 1 and Li+-1 is their frameworks can change shape without breaking bonds, causing substantial changes of their PXRD patterns depending on what and how much is in the channels. Li+-1 has much larger surface area (Langmuir: 640 ​m2/g), compared with the 339 ​m2/g of PMOF 1. The CO2 adsorption capacities of 1 and Li+-1 are 38 (7.5 ​wt%) and 45 ​mL/g (8.9 ​wt%), respectively at 1 ​atm and 298 ​K, and 165–167 ​mL/g (33%) at 9.9 ​atm. They are direct-bandgap semiconductors with bandgaps of 1.56 (for 1) and 1.62 (for Li+-1) eV. The conduction and valence band-edge positions were determined in non-aqueous solutions as −0.29 and 1.27 (1), −0.32 and 1.30 ​V (Li+-1) versus NHE. PMOF 1 or Li+-1/Ru(bpy)3Cl2/TEA/CH3CN (bpy ​= ​2,2-bipyridine, TEA ​= ​triethylamine) system photocatalytically reduce CO2 to CO under visible light. PMOFs act as cocatalysts, and the photocatalysts were found to be the triplet excited state of Ru(bpy)32+ (Ru(II)∗) and its photodecomposition products. The TOFs contributed from PMOFs after 2 ​h were 0.091 and 0.097 h−1 (224 and 241 ​μmol ​g−1 ​h−1), respectively for 1 and Li+-1, respectively. In addition, the Ru(bpy)3Cl2/TEA/CH3CN system were found to have an unprecedented high TOF of 0.31 h−1 (412 ​μmol ​g−1 ​h−1) when small amounts of H2O (200 ​μL ​H2O in 40 ​mL CH3CN and 10 ​mL TEA) was added.

Undoped SnO2 as a Support for Ni Species to Boost Oxygen Generation through Alkaline Water Electrolysis.

In this study, the synergistic behavior of Ni species and bimodal mesoporous undoped SnO2 is investigated in oxygen evolution reactions (OERs) under alkaline conditions without any other modification of the compositional phases or using noble metals. An efficient and environmentally friendly hydrothermal method to prepare bimodal mesoporous undoped SnO2 with a very high surface area (>130 m2 g-1) and a general deposition-precipitation method for the synthesis of well-dispersed Ni species on undoped SnO2 are reported. The powders were characterized by adsorption-desorption isotherms, TG-DTA, XRD, SEM, TEM, Raman, TPR-H2, and XPS. The best NiSn composite generates, under certain experimental conditions, a very high TOF value of 1.14 s-1 and a mass activity higher than 370 A g-1, which are remarkable results considering the low amount of Ni deposited on the electrode (3.78 ng). Moreover, in 1 M NaOH electrolyte, this material produces more than 24 mA cm-2 at an overpotential value of approximately +0.33 V, with only 5 wt % Ni species. This performance stems from the dual role of undoped SnO2, on the one hand, as a support for active and well-dispersed Ni species and on the other hand as an active player through the oxygen vacancies generated upon Ni deposition.

Unusual Photoactive Water Oxidation Activity of Pt/PtOx Cocatalyst Decorated Crystalline α‐Fe2O3 Nanostructures: Exposed Facets Dependent Reactivity

AbstractA key challenge remains the preparation of an active and robust water oxidation photocatalyst with abundant earth materials. As a useful to improve photocatalytic efficiency, the development of α‐Fe2O3 nanocrystals with different exposed facets and interfaces has attracted enormous attention. But literature survey shows that α‐Fe2O3 nanomaterials were mainly used in photoelectrochemical cell for water splitting as anode materials. In this work, highly efficient Pt/PtOx cocatalyst decorated α‐Fe2O3 shaped‐photocatalysts were derived as photocatalyst for white light‐induced O2 generation from water without any electric potential. The maximum apparent quantum efficiency of photooxidation reaction was reached 55.33 % by Pt/PtOx decorated bitruncated‐dodecahedron shaped α‐Fe2O3 and around 30.5, 2.3, 1.28 times better than the Pt/PtOx decorated nanocuboid, nanorod and bitruncated‐octahedron shape respectively. The Pt/PtOx decorated bitruncated‐dodecahedron shaped α‐Fe2O3 display an unusual photooxidation activity with a high TOF (1.96×10−2 s−1) due to presence of destabilized and unsaturated Fe centre containing high energy {104} and {100} facets. The present findings clearly demonstrate that the selective O2 evolution from water can possible without any sacrificial agent.

Tuning electronic correlations of ultra-small IrO2 nanoparticles with La and Pt for enhanced oxygen evolution performance and long-durable stability in acidic media

The rational design of electrocatalysts with active and long-durable characters applying in acidic proton exchange membrane electrolyzers is a spotlight for the sustainable energy storage. With the aim of tuning electronic structure of electrocatalysts and altering potential limiting step of the oxygen evolution reaction (OER), the ultra-small Pt, La co-doped IrO2 nanoparticles with average size of 2 nm highly dispersed on N-doped carbon (NC) was designed. Impressively, the representative Pt0.1La0.1-IrO2@NC exhibited the record performance toward OER in 0.5 M H2SO4 with a low overpotential of 205 mV (10 mA·cm−2), an extremely excellent stability of 135 h, and a fairly high TOF value of 5.71 s−1 at η =280 mV. Theoretical calculations revealed that the co-doping of Pt, La into the lattice of IrO2 could rationally tune d band centers and lower the energy barrier for the potential-determining step (from *O to *OOH) toward OER.

Two Schiff-base complexes of copper and zirconium oxide supported on mesoporous MCM-41 as an organic–inorganic hybrid catalysts in the chemo and homoselective oxidation of sulfides and synthesis of tetrazoles

A simple and efficient procedure was reported for the synthesis of tetrazole derivatives, the chemo and homoselective oxidation of sulfides to sulfoxides in the presence of two Schiff-base complexes of zirconium oxide and copper anchored on MCM-41 as mesoporous and organometallic catalysts under green conditions. All the products were obtained in excellent yields with high TOF values indicating the high activity of the synthesized catalysts. These catalysts were characterized by XRD, TGA, SEM, EDS, FT-IR, TEM, WDX, BET and AAS techniques and can be recycled for several times without significant loss in catalytic activity. The recovered catalysts were characterized by SEM, FT-IR and AAS analysis which shown an excellent agreement with fresh catalysts.

Phosphine-free pincer-ruthenium catalyzed biofuel production: high rates, yields and turnovers of solventless alcohol alkylation

High TONs and TOFs are observed for the β-alkylation of alcohols using phosphine-free pincer-ruthenium catalysts at a very low base loading. Kinetic studies and DFT calculations were complementary and provide a clear understanding on the mechanism.

Pseudo-atomic-scale metals well-dispersed on nano-carbons as ultra-low metal loading oxygen-evolving electrocatalysts.

Solving challenges for the scaling-up, high metal loadings and low turnover frequency (TOF, defined as mol O2 per mol metal per second), of FeNi catalysts in water electrolysis, we report the first discovery of pH tunable tannic acid single molecular layer formed on nano-sized carbons (NCs), which promotes the gram-production of pseudo-atomic-scale FeNi oxyhydroxide nanoclusters well-dispersed on NCs. It results in ultra-low metal loading (0.42 μg cm−2) and remarkably large TOF of 14.03 s−1 for the oxygen evolution reaction, which is three orders of magnitude higher than that of state-of-the-art FeNi catalysts. A “volcano”-shaped activity trend in specific activity and TOF was found to depend on the Fe content in FeNi oxyhydroxide. The micro-morphologies from the atomic-level exposure of active sites and surface spectra analyses confirm the model of synergism between Ni and Fe centers.

Reducing-agent-free facile preparation of Rh-nanoparticles uniformly anchored on onion-like fullerene for catalytic applications.

Herein we report a very simple ‘mix and heat’ synthesis of a very fine Rh-nanoparticle loaded carbon fullerene-C60 nanocatalyst (Rh(0)NPs/Fullerene-C60) for the very first time. The preparation method used no reducing agent and capping agent to control the morphology of the nanocatalyst. Transmission electron microscopy (TEM) results confirmed the uniform decoration of small Rh-nanoparticles on the surface of fullerene-C60. The Rh-content in Rh(0)NPs/Fullerene-C60 was found to be 2.89 wt%. The crystalline properties of Rh(0)NPs/Fullerene-C60 were studied by X-ray diffraction (XRD). The metallic state of Rh-nanoparticles in Rh(0)NPs/Fullerene-C60 was confirmed by X-ray photoemission spectroscopy (XPS). Raman results depicted good interaction between Rh-nanoparticles and fullerene-C60. To our delight, the present Rh(0)NPs/Fullerene-C60 showed excellent catalytic activity in the reduction of 4-nitrophenol with NaBH4 in water. Very high kapp, k′ and TOF values of 82.14 × 10−3 min−1, 4107 × 10−3 min−1 and 138 min−1, respectively, were calculated for the Rh(0)NPs/Fullerene-C60 catalyzed reduction of 4-nitrophenol. To the best of our knowledge, this is the most efficient fullerene-based nanocatalyst for the rapid reduction of 4-nitrophenol reported to date. Moreover, the catalytic activity of Rh(0)NPs/Fullerene-C60 was also tested towards Suzuki cross-coupling reactions. Reusability of the Rh(0)NPs/Fullerene-C60 was also tested.

A highly active Rh1/CeO2 single-atom catalyst for low-temperature CO oxidation.

Rh1/CeO2 single-atom catalyst is highly active for CO oxidation and has the potential to serve as a multifunctional catalyst to save the usage of other noble metals in three-way catalysts. The high activity is achieved on single-atom active sites via the Mars-van Krevelen mechanism, thus avoiding CO poisoning at low temperatures.

A high resolution multi-turn TOF mass analyzer

An ion optical design of a high resolution multi-turn time-of-flight mass analyzer (MT-TOF MA) is presented. The analyzer has rotationally symmetric main electrodes with additional mirror symmetry about a mid-plane orthogonal to the axis of symmetry. Rotational symmetry allows a higher density of turns in the azimuthal (drift) direction compared to MT-TOF MAs that are linearly extended in the drift direction. Mirror symmetry about a mid-plane helps to achieve a high spatial isochronicity of the ions’ motion. The analyzer comprises a pair of polar-toroidal sectors S1 and S3, a pair of polar (trans-axial) lenses, and a pair of conical lenses for longitudinal and lateral focusing. A toroidal sector S2 located at the mid-plane of the analyzer has a set of embedded drift focusing segments providing focusing and spatial isochronicity in the drift direction. The ions’ drift in the azimuthal direction can be reversed by using dedicated reversing deflectors. This gives the possibility of several operational modes with different numbers of turns and passes in the drift direction. According to numerical simulations, the mass resolving power of the analyzer ranges from [Formula: see text]40 k (fwhm) at small (typically below ten) numbers of turns to [Formula: see text]450 k (fwhm) at 96 turns.

Synthesis and characterization of molybdenum (VI) complex immobilized on polymeric Schiff base‐coated magnetic nanoparticles as an efficient and retrievable nanocatalyst in olefin epoxidation reactions

In this study, a new polymeric functionalized magnetic nanocatalyst containing a molybdenum Schiff base complex was prepared using a few consecutive steps. Poly (methylacrylate)‐coated magnetic nanoparticles were synthesized via radical polymerization of methyl acrylate onto modified magnetic nanoparticles followed by the amidation of the methyl ester groups with hydrazine. Polymeric functionalization efficiently provides the advantage that more catalytic units can be grafted on the surface of magnetic nanoparticles. The functionalization process was continued with salicylaldehyde which introduced Schiff base groups on to the surface of the polymeric support. In the final step, the desired catalytic system was prepared via complexation of the Schiff base groups with MoO2(acac)2. The resulting nanoparticles were characterized by infrared spectroscopy, powder X‐ray diffraction, scanning and transmission electron microscopy, elemental analysis, inductively coupled plasma optical emission spectrometry, vibrating sample magnetometry and thermogravimetric analysis. This heterogenized catalytic system was also found to be highly active, sustainable and recyclable nanocatalyst in alkene epoxidation. Eventually, the attractive features of the synthesized catalyst such as simple work‐up, good stability, magnetic separation, high TOF and high surface area; make it appropriate for oxidation reactions.

Propane Dehydrogenation over Pt Clusters Localized at the Sn Single-Site in Zeolite Framework

Catalytic dehydrogenation of propane over a Pt-based catalyst to propylene has received considerable interests in recent years because this route is able to provide an economical and efficient way to fill the gap between supply and demand in propylene market. The low dispersion of a Pt particle at the support surface and sintering of Pt nanoparticles under the harsh reaction condition are the main challenges in the practical application of this catalyst. Herein, highly efficient Pt/Sn-Beta catalysts are developed for propane dehydrogenation, which exhibits high activity, selectivity, and stability in this reaction. Full characterizations with XRD, STEM, XPS, CO-IR, H2-TPR, and Py-IR techniques on these catalysts reveal that the Pt clusters are localized at the Sn single-site in the zeolitic framework, which allows the generated Pt clusters to be homogeneously dispersed at the surface zeolite. The high performance of Pt/Sn-Beta catalysts under a high reaction temperature is mainly due to a strong interaction between the Pt cluster and Sn-zeolite. An initial propane conversion of 50%, high propylene selectivity of above 99%, low deactivation rate of 0.006 h–1, high TOF of 114 s–1, and good regenerability have been achieved in the Pt-Sn2.00/Sn-Beta catalyst for propane dehydrogenation at 570 °C.