Efficient Oxidation Catalysts Research Articles

Polyoxometalates ionic liquids based magnetic nanocomposites as an efficient heterogeneous catalysts for oxidation of thiobenzoic acid and dibenzothiophene by employing RP-HPLC-UV

Polyoxometalates ionic liquids based magnetic nanocomposites as an efficient heterogeneous catalysts for oxidation of thiobenzoic acid and dibenzothiophene by employing RP-HPLC-UV

Generation of Triplet States by Host‐Stabilized Through‐Space Conjugation for the Construction of Efficient Supramolecular Photocatalysts

AbstractPromoting the generation of triplet states is essential for developing efficient photocatalytic systems. This research presents a novel approach of host‐stabilized through‐space conjugation via the combination of covalent and non‐covalent methods. The designed building block, 4,4′‐(1,4(1,4)‐dibenzene cyclohexaphane‐1,4‐diyl)bis(1‐phenylpyridinium) chloride, features inherently stable through‐space conjugation. When this block forms a 1 : 1 host–guest complex with cucurbit[8]uril, the through‐space conjugation is further stabilized within the confined cavity. Both the generation and lifetime of triplet state are significantly increased, resulting from the host‐stabilized through‐space conjugation. Additionally, the ultrahigh binding constant of 6.58×1014 M−1 ensures the persistence of host‐stabilization effect. As a result, the host–guest complex acts as a highly efficient catalyst in the photocatalytic oxidation of thioether and aromatic alcohol. In the photodegradation of lignin, a complex natural product, the host–guest complex also exhibits high efficiency, demonstrating its robustness. This line of research is anticipated to enrich the toolbox of supramolecular photochemistry and provide a strategy for fabricating efficient supramolecular photocatalysts.

TEMPO‐Catalyzed Continuous‐Flow Aerobic Oxidations of Alcohols on Silica

Abstract2,2,6,6′‐Tetramethylpiperidine‐N‐oxyl (TEMPO) is a highly efficient oxidation catalyst, valued for its environmentally benign nature, particularly in comparison to transition‐metal catalysts. Despite their merits, TEMPO‐based catalysts are not notably cost‐effective. Immobilization of TEMPO onto supports offers a promising strategy to overcome this limitation. In this work, we present the synthesis and application of immobilized TEMPO catalysts 2–5, prepared via a straightforward condensation reaction, for the aerobic oxidation of alcohols. These catalysts demonstrate remarkable activity for alcohol oxidations under continuous‐flow conditions, employing nitric acid as the co‐catalyst. Notably, catalyst 2 immobilized by COOH silica gel exhibits outstanding performance for the oxidation of benzyl alcohol by oxygen gas, achieving a turnover frequency (TOF) of 15 h−1 and a turnover number (TON) exceeding 300. Catalyst 2 further demonstrates broad substrate scope, effectively oxidizing primary, secondary, and benzylic alcohols. Post‐reaction analysis of spent catalyst 2 reveals that deactivation primarily stems from nitrosation of the N−O bond. Interestingly, the amide moiety remains intact despite the harsh acidic reaction conditions.

Influence of different morphologies on the catalytic activity of Pt-Pd nanostructures for methanol oxidation

Developing efficient and durable catalysts for methanol oxidation in acidic media remains a significant challenge in electrochemical energy conversion. This study addresses this issue by synthesizing Pt-Pd bimetallic electrocatalysts with different morphologies, including nanowires, core-shell nanoparticles, and core-shell nanowires, and evaluating their catalytic activities. The electrocatalysts were prepared via chemical reduction of metal precursors using formic acid as a reducing agent. X-ray diffraction analysis revealed distortions in the lattice parameters of the nanostructured bimetallic catalysts, and STEM/EDX analysis confirmed the formation of the different morphologies on the carbon support. Electrochemical assessments showed that the bimetallic catalysts exhibited superior catalytic activities to nanostructured Pt/C catalysts. The Pd@Pt/C core-shell nanowires displayed the highest catalytic efficiency, with the lowest methanol oxidation onset potential (468 mV) and the highest mass and specific activities. Electrochemical impedance measurements revealed the lowest charge transfer resistance value for the Pd@Pt/C core-shell nanowires. Chronoamperometric tests further indicated that the Pd@Pt/C core-shell nanowires catalyst exhibited superior tolerance to inactivation by reaction intermediates, achieving mass and specific activities approximately twice as high as those of the Pt/C catalyst. The enhanced catalytic performance of the Pd@Pt/C core-shell nanowires was attributed to the synergistic effects of the two morphologies that alter the electronic and geometric structures of the Pt within the catalyst.

Coupled Lattice‐Expanded Ni and MoO2 Array for Efficient Alkaline Hydrogen Evolution

AbstractTransition metal oxides have attracted much attention due to their good electrical conductivity, high chemical stability, and easy electronic structure modulation. However, it is still a great challenge to solve the problems of sluggish reaction kinetics and high overpotential in the alkaline hydrogen evolution reaction (HER) due to their poor intrinsic activity. Herein, a lattice‐expanded Ni‐decorated MoO2 array (Ni‐MoO2‐700) catalyst is prepared for the alkaline HER. Unlike most of the reported literature, the decoration of metal heteroatoms may lead to lattice expansion of the carrier catalyst. In contrast, lattice expansion of Ni is also achieved by adjusting the annealing temperature in this work. The Ni‐induced lattice‐expanding effect can not only modulate the electronic structure of the catalyst but also accelerate electron transfer during the reaction, thus increasing its intrinsic activity for the HER. As a result, Ni‐MoO2‐700 exhibits significantly enhanced catalytic activity with an overpotential of 74.9 mV at 10 mA cm−2 in 1.0 m KOH, which is far superior to that of most of the reported advanced Ni‐ and Mo‐based materials. This work provides deep intrinsic insight and a great opportunity to design efficient transition metal oxide catalysts for the alkaline HER.

Construction of Multiphase Concave Tetrahedral PdInMo Nanocatalyst for Enhanced Alcohol Oxidation

AbstractHeterogeneous palladium‐based catalysts show excellent catalytic properties for electrocatalytic oxidation of alcohols, but the construction of such heterogeneous catalysts is a challenge. Here, a multiphase tetrahedral PdInMo nanocatalyst is prepared by a one‐pot reaction method. And the multiphase tetrahedral PdInMo nanocatalyst consists of a face‐centered cubic structure and an intermetallic structure. Due to the oxygen affinity of indium and molybdenum atoms, the interface defects of internal multiphase structure, and intermetallic structure, the multiphase concave tetrahedral PdInMo nanocatalyst shows enhanced catalytic efficiency in the electrocatalytic oxidation reaction of methanol and ethanol. Compared with commercial Pd/C catalysts, PdIn0.117Mo0.037 nanocatalyst has the best mass activity and specific activity. In electrocatalysis of methanol oxidation, the mass activity (2205.57 mA mgPd−1) and specific activity (6.67 mA cm−2) are 4.81 and 3.40 times than that of a commercial Pd/C nanocatalyst (458.5 mA mgPd−1, 1.96 mA cm−2), respectively. In the electrocatalysis of ethanol oxidation, the mass activity (2668.49 mA mgPd−1) and specific activity (8.11 mA cm−2) are 4.06 and 3.14 times than that of the commercial Pd/C nanocatalyst (655.83 mA mgPd−1, 2.58 mA cm−2), respectively. This study provides a reference for the design of highly efficient palladium catalysts for alcohol oxidation.

Cauliflower-like Pd/MoC||Mo2C/C heterostructure as an efficient trifunctional catalyst for formic acid oxidation, hydrogen evolution, and oxygen reduction reactions

The use of Pd-based catalytic materials as electrocatalysts for formic acid oxidation reaction (FAO), hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) has been well-established for some time. The incorporation of a second phase can markedly enhance the electronic properties of the composites. The combination of different compounds with superior electronic properties is crucial for the design and preparation of catalysts with optimal catalytic activity and stability. In this study, a novel cauliflower-like Pd/MoC||Mo2C/C composite with heterostructure is synthesised, which exhibits excellent catalytic activity and long-term stability against FAO, HER, and ORR. The high-temperature treatment results in the formation of small-sized Mo₂C and MoC nanoparticles on the carbonaceous substrate, thereby exposing a greater number of Mo and Mo-C active sites. The formation of heterostructures between Mo₂C and MoC optimises the electronic structure of the composite, thereby facilitating enhanced reaction processes. In terms of FAO, the mass activity of Pd/MoC||Mo2C/C is 1.87A mgPd-1, which is 2.75 times higher than that of Pd/C (0.68A mgPd-1). As for the HER, a much lower overpotential of 28mV is required to achieve a current density of 10mAcm-2 compared to Pd/C (40mV). Fortunately, Pd/MoC||Mo2C/C also shows excellent ORR activity with a half-wave potential of 0.798V and the maximum current density of approximately 5.73mAcm-2 in alkaline electrolyte. These findings may contribute to the development of other noble metal-based materials loaded on intermetallic compounds with stable and effective electrocatalytic performance.

Enhancing Activity and Stability of Pd-on-TiO2 Single-Atom Catalyst for Low-Temperature CO Oxidation through in Situ Local Environment Tailoring.

The development of efficient Pd single-atom catalysts for CO oxidation, crucial for environmental protection and fundamental studies, has been hindered by their limited reactivity and thermal stability. Here, we report a thermally stable TiO2-supported Pd single-atom catalyst that exhibits enhanced intrinsic CO oxidation activity by tunning the local coordination of Pd atoms via H2 treatment. Our comprehensive characterization reveals that H2-treated Pd single atoms have reduced nearest Pd-O coordination and form short-distanced Pd-Ti coordination, effectively stabilizing Pd as isolated atoms even at high temperatures. During CO oxidation, partial replacement of the Pd-Ti coordination by O or CO occurs. This unique Pd local environment facilitates CO adsorption and promotes the activity of the surrounding oxygen species, leading to superior catalytic performance. Remarkably, the turnover frequency of the H2-treated Pd single-atom catalyst at 120 °C surpasses that of the O2-treated Pd single-atom catalyst and the most effective Pd/Pt single-atom catalysts by an order of magnitude. These findings open up new possibilities for the design of high-performance single-atom catalysts for crucial industrial and environmental applications.

Atomically Permeated MoP‐WOx Core‐Shell Catalysts for Efficient and Selective Oxidation of Thiophenic Sulfides in Fuels via Direct Electron Transfer Mechanism

AbstractHeterogeneous interfaces designed rationally in catalysts can induce geometrical, compositional, and electronic effects that can be applied to modulate catalytically active sites and consequently accelerate reaction kinetics. Here, a core‐shell heterostructure catalyst consisting of crystalline molybdenum phosphide (MoP) cores and amorphous tungsten oxide (WOx) shells on porous carbon nanosheets (PCN) is developed for oxidative desulfurization (ODS) of fuels. The strongly coupled core‐shell heterogeneous interface triggers a distinctive atomic permeation effect that induces substantial electron transfer from MoP to WOx and subsequent generation of electron‐rich W sites, consequently optimizing the adsorption of intermediates and substrates. The resulting catalyst (WOx@MoP/PCN) demonstrates a turnover frequency as high as 768.1 h−1 for ODS at 60 °C, exceeding that of almost all the state‐of‐the‐art ODS catalysts by 1–2 orders of magnitude. Moreover, a novel surface oxidation pathway based on direct electron transfer is identified in the WOx@MoP/PCN‐H2O2 system, which bypasses the formation of reactive oxygen species, consequently endowing the system with a moderate redox potential. Thus, WOx@MoP/PCN exhibits unprecedented selectivity, achieving 100% removal of thiophenic sulfides from real diesel with minimal consumption of oxidant.

Fe3O4 magnetic nanoparticles (MNPs) as an efficient catalyst for allylic oxidation of chromenes to coumarins with TBHP

Synthesis of coumarins via allylic oxidation of 2H-chromenes using the Fe3O4 magnetic nanoparticles (MNPs) in combination with tert‑butyl hydroperoxide (TBHP) as an oxidant is reported. This strategy is straightforward and performed at mild and economical reaction conditions. The process environmentally benign, versatile, and efficiently converting various chromenes into coumarins, which are compounds of interest in the pharmaceutical industry due to their wide range of biological activities.

In situ-generated mononuclear half-sandwich [(η6‐p‐cymene)RuCl(amide)] complexes as efficient catalysts in the selective oxidation of benzyl alcohol to benzaldehyde

The application of in situ-generated mononuclear Ru(II)-organometallic complexes (1–7) i.e., [(η6-p-cymene)RuCl(L)], produced by the interaction of Ru dimer [(p-cymene)RuCl2]2 with some polyfunctional amide ligands(L) as highly efficient catalystsin the oxidation of various benzyl alcohols (B-OLs) by tert-butyl hydroperoxide (TBHP) oxidant to produce selectively the benzaldehydes (B-ALs) in high yields in CH3CN is described. The in situ-generated catalysts were found to be highly active than the [(p-cymene)RuCl2]2 precursor (dimer) in the oxidation of B-OL to B-AL. The influence of various reaction parameters such as type of catalyst, reaction temperature, oxidant and solvent during the B-OL oxidation was systematically monitored to optimize the catalytic conditions. In order to confirm the formation of predicted in situ-generated mononuclear Ru(II) complex catalysts during the oxidation of B-OL, one of the Ru(II) complex (1) was synthesized and characterized by Elemental analysis (EA), Infrared (IR), Proton-NMR and Mass spectral techniques and its mono nuclear structure is proposed. Further, it was observed that the activity of in-situ generated and pre-synthesized Ru(II) catalyst was almost same in the oxidation of B-OL to B-AL.

Construction of Cobalt-Containing Polyoxovanadate-Based Inorganic-Organic Hybrids as Heterogeneous Catalysts for the Selective Oxidation of Sulfides.

In order to develop efficient catalysts for the selective oxidation of sulfides, in this work, two polyoxovanadate-based inorganic-organic hybrids, [Co(H2O)3(3-bpfb)0.5(V2O6)]·(3-bpfb)0.5 (1) and [Co(H2O)2(4-bpfb)0.5(V2O6)] (2) [3-bpfb = N, N'-bis(3-pyridylformamide)-1, 4-benzenediamine, 4-bpfb = N, N'-bis(4-pyridylformamide)-1, 4-benzenediamine], were isolated under hydrothermal conditions. The structures of 1 and 2 embodied two kinds of different cobalt-containing polyoxovanadate-based inorganic chains. Compound 1 contained a one-dimensional inorganic zigzag chain created by the aggregation of {V2O6} clusters with each other, on which Co (II) ions were fixed. But it was an inorganic dimeric chain constructed from two linear {V2O6} cluster-based chains gathered by Co (II) ions in 2. The 3-bpfb and 4-bpfb ligands, as the bidentate linkers, coordinated with two Co (II) ions from adjacent chains to organize them into two-dimensional layers. The hydrogen bonds made important contributions to the formation of supramolecular structures of the two compounds. The two compounds served as heterogeneous catalysts and exhibited efficient activity for the selective oxidation of sulfide to sulfoxide and could be reused at least six times without loss of catalytic activity and stability.

Unveiling the Role of Boron on Nickel‐Based Catalyst for Efficient Urea Oxidation Assisted Hydrogen Production

AbstractUrea oxidation reaction (UOR) is an ideal alternative to oxygen evolution reaction (OER) for efficient hydrogen production but is immensely plagued by slow kinetics. Herein, a multilayer hole amorphous boron‐nickel catalyst (a‐NiBx) is fabricated through a simple chemical plating method, which displays intriguing catalytic activity toward UOR, demanding a low working potential of 1.4 V to reach 100 mA cm−2. The high performance is credited to the formation of metaborate (BO2−), which can promote the formation of high‐oxidation‐state NiOOH active phase and optimize the adsorption of urea molecules. This can be confirmed by the operando spectroscopy characteristics and density functional theory calculations. Consequently, the assembled electrolyzer utilizing NiBx as bifunctional catalysts exhibited splendid catalytic activity, requiring an evidently lower voltage of 1.66 V to reach a current density of 100 mA cm−2 and 1.57 V when using Pt/C as a cathode catalyst. Moreover, the assembled electrolyzer secured a robust stability of over 200 h, as well as a four times higher hydrogen production rate than traditional water electrolysis.

Boron nitride nanotube confining selected platinum group metal (PGM=Pd and Pt) single atoms catalysts for efficient CO oxidation: Theoretical insight into confinement effect

Despite platinum group metal have been widely used in catalytic converters, high cost and reaction temperature hindered their application. Inspired by the single-atom catalysts and confinement effect, selected PGM confined on the boron nitride nanotube with vacancy defects for CO oxidation have been systematically investigated. For PGM–BNNT catalysts, CO oxidation would proceed competitively in Eley–Rideal and Langmuir–Hinshelwood pathways. With N vacancy, Pd/Pt-BNNT(6,6) needs 0.33 and 0.28 eV to overcome the reaction barriers through the LH mechanism. The internal of BNNT will provide a more favorable nano-confinement environment than exterior surface, with the more activated adsorbed gases andelectron transfer.

Asymmetric oxygen vacancies of self-supporting Co3O4/CuOx on Cu foam boosts propane total oxidation

As a low-cost and environmentally friendly transition metal oxides material, the Co3O4 has good catalytic activity for volatile organic compounds (VOCs) oxidation. However, the active components of powder cobalt-based catalysts may present uneven distribution and aggregation, thus affecting the catalytic efficiency. Herein, the Co/Cu-CF monolithic catalyst with asymmetric oxygen vacancies was developed through in-situ growth of Cu(OH)2 nanoarrays on Cu foam, which exhibits excellent performance for propane oxidation (T90 at 215 ℃). It is impressive that the catalyst shows satisfactory stability in terms of long-term, cyclic and water resistance. The results indicate that the existence of nanoarrays can provide a rich load surface and better disperse the active components, which effectively facilitates the interface interaction between cobalt and copper, inducing the generation of asymmetric oxygen vacancies. And, the activity of catalyst was significantly improved owing to the double activation effect of asymmetric oxygen vacancy on molecular oxygen and lattice oxygen. Therefore, this research offers a novel approach for designing efficient nanoarray monolithic catalysts for VOCs oxidation and other environmental applications.

Keggin-type polyoxometalates/Amberlite nanocomposites as efficient catalysts for the aqueous oxidation of sulfides: Crucial roles of mono-iron and mono-manganese substituents

The condensation of Keggin-type polyoxometalates including H3PW12O40, H3PMo12O40, and their Mn(III) and Fe(III) derivatives with nano-structured Amberlite, nanoAmbN(Me)3Cl led to the formation of electrostatically immobilized polyoxometalates on the anion exchange polymer with a size less than ca. 70 nm. The nanocomposites were characterized by FT-IR, XRD, solid state diffuse-reflectance and solution UV–vis spectroscopy, TGA, BET and FESEM-EDX-Mapping and used for the oxidation of sulfides with periodate under aqueous and non-aqueous conditions. In spite of the small difference between the catalytic activity of H3PMo12O40 and H3PW12O40, the corresponding mono-iron and manganese substituted derivatives showed significantly different catalytic activities. Furthermore, nanoAmbN(Me)3@PW11MnO39 showed a high selectivity towards sulfone (72 %), compared to the highly chemoselective formation of sulfoxide in the presence of nanoAmbN(Me)3@PW11FeO39. NanoAmbN(Me)3@PW11FeO39 as the best catalyst of the series was recovered and reused at least six times for the oxidation of methyl phenyl sulfide. The increased catalytic activity of the iron-containing polyoxometalates than that of the corresponding manganese compounds was attributed to the Jahn-Teller distortion around the manganese(III) center.

Regulating active oxygen species and acidity of Ca doped LaMnO3 perovskite catalysts toward efficient n-butylamine oxidation

It is of great significance to design catalysts with high activity, N2 selectivity and stability for nitrogen-containing volatile organic compound (NVOC) catalytic purification. Meanwhile, the role of oxygen species in NVOC catalytic oxidation is still ambiguous. Herein, the oxygen species of La-Mn perovskite catalysts were engineered by doping Ca in La site to elucidate their role in catalytic n-butylamine oxidation. Results demonstrate that La0.9Ca0.1MnO3 exhibits the highest activity owing to its abundant adsorbed oxygen species and high surface area, achieving 100 % n-butylamine conversion (500 ppm; GHSV=60,000 mL g−1h−1) at 200 °C with N2 selectivity of ca. 95 %. More adsorbed oxygen species generated due to Ca doping accelerates the oxidation rate and C-C cleavage of alcohol and acetate intermediates, resulting in higher CO2 yield. Meanwhile, Ca-doping also modifies the acidity of catalysts, which affects the adsorption/desorption process of alkaline substances and yield of nitrogen-containing products. In addition, La0.9Ca0.1MnO3 shows superior stability, high water and SO2 resistance, and acceptable activity for other common NVOCs, demonstrating a promising catalyst for NVOC oxidation even under harsh operation conditions. Furthermore, the toxic effect of pollutant or products during n-butylamine catalytic oxidation on the growth of Chlorella Vulgaris was investigated and results suggest that catalytic oxidation is an environmentally friendly method for NVOC purification. This work sheds light on the relationships among oxygen species, catalyst acidity, and n-butylamine catalytic oxidation, which expand the understanding of rational design of efficient catalyst for NVOC oxidation.

Hydrothermal synthesis of La0.5Sr0.5MnO3 nanostructures for enhanced CO oxidation

This study focuses on the synthesis and characterization of La0.5Sr0.5MnO3 (LSMO) perovskite nanostructures via the hydrothermal method and their catalytic performance evaluation in CO oxidation. Structural analysis using techniques like XRD, FE-SEM, FTIR, and Raman spectroscopy analysis verified the development of LSMO nanostructures exhibiting a rhombohedral phase configuration. The catalytic activity of the annealed LSMO nanostructures was assessed, demonstrating significant CO conversion efficiency attributed to structural modifications enhancing catalytic performance. These findings highlight the potential of LSMO perovskite nanostructures as efficient catalysts for CO oxidation.

Mn/CeO2 contains enriched surface lewis acid sites and pore structures accelerated catalytic oxidation of propane at low temperature

The development of highly efficient non-precious metal catalysts for the low-temperature catalytic oxidation of volatile organic compounds (VOCs) is a critical imperative in VOCs control. In this study, a series of highly active CeMnOx catalysts with Mn-doped CeO2 were investigated. The catalysts (WHSV=30,000 mL g−1 h−1) exhibited the highest catalytic propane oxidation activity (T90 = 230 °C) and excellent stability over 600 h, When the Mn:Ce ratio was 2.5. The introduction of Mn doping resulted in modifications to the pore structure of CeO2, leading to an increase in specific surface area and enhanced gas transfer kinetics. Additionally, it induced surface electronic defects and elevated the concentration of acidic sites, thereby facilitating the adsorption and activation of propane. Consequently, these improvements contributed to an enhanced catalytic performance of the catalyst. The in-situ DRIFTS infrared spectra revealed that Mn doping reduced the activation energy of the reaction and facilitated the conversion of acetone groups as well as decomposition of carboxylic acid groups.

Constructing homo/hetero-nuclear carbon and oxygen atoms co-doped graphitic carbon nitride assisted by ionic liquid for photothermal synergistic catalytic oxidation of cyclohexane

The adoption of photothermal synergistic catalysis for cyclohexane oxidation can balance the advantages of high conversion of thermal catalysis and high selectivity of photocatalytic technology to achieve better catalytic performance. Here, we prepared functional carbon nitride (BCA-CN) by self-assembly strategy of ionic liquid [Bmim]CA (1-Butyl-3-methylimidazole citrate) with melamine and cyanuric acid utilizing abundant elements and anionic/cationic hydrogen bonding interactions. The introduction of [Bmim]CA embeds C-C (carbon and carbon band) and C-O-C (ether bond) structures into graphitic carbon nitride (g-C3N4) framework, significantly improving light absorption capacity and migration of photo generated charge carriers. Compared to g-C3N4, both BCA-CN increases cyclohexane conversion and KA oil (the mixture of cyclohexanol and cyclohexanone) selectivity by 1.3 times under photothermal catalysis. The surface reactions are facilitated by changing adsorption sites of cyclohexane to increase adsorption energy and obtaining more hydroxyl radicals and superoxide radicals. Furthermore, the enhanced selectivity is attributed to the difficulty in generating cyclohexanone radicals. This work offers the reference scheme for the development of efficient photothermal catalysts in the selective oxidation of cyclohexane.