Catalysts For Oxidation Research Articles

Isomeric organic ligands directing octamolybdates-linked Copper(II) functionalized complexes as active catalysts in electrochemistry and desulfurization

Two remarkable octamolybdates-based copper-organic complexes, namely, [Cu7(L)4(H2O)7(β-H2Mo8O26)]·7H2O (POM 1) and [Cu6(HX)4(β-Mo8O26)(H2O)6]·3H2O (POM 2) (H3L = 2-(pyridine-4-yl)-1H-imidazole-4,5-dicarboxylic acid; H3X = 2-(pyridine-3-yl)-1H-imidazole-4,5-dicarboxylic acid), were successfully assembled using two isomeric organic ligands under hydrothermal conditions. The two-dimensional metal-organic layers of POMs 1 and 2 were converted into three-dimensional frameworks by hexadentate β-H2Mo8O262− and tetradentate β-Mo8O264− clusters, respectively. The electrocatalytic properties of POM 1 were investigated, revealing its ability to catalyze the reduction of BrO3−, NO2− and H2O2 and the oxidation of ascorbic acid. Notably, POMs 1 and 2 demonstrated exceptional stability in organic solvents and exhibited excellent catalytic performance in oxidative desulfurization. When employed as catalysts for thioanisole oxidation, the conversion rates reached 94.5% after 150 min for POMs 1 and 99.9% after 120 min for POMs 2. In addition, their catalytic performances in model oil remained largely unchanged after five recycling cycles.

Metal Incorporated Zeolites as Heterogeneous Catalysts in the Selective Partial Oxidation of Methane to Methanol: A Review

Metal Incorporated Zeolites as Heterogeneous Catalysts in the Selective Partial Oxidation of Methane to Methanol: A Review

Preparation and evaluation of the LaCu1-xNixO3 (x = 0, 0.1, 0.3, 0.5 and 0.7) perovskite catalysts for total oxidation of methane

Preparation and evaluation of the LaCu1-xNixO3 (x = 0, 0.1, 0.3, 0.5 and 0.7) perovskite catalysts for total oxidation of methane

Physicochemical influence of graphite agent for fabrication of MoVTeNbO catalyst for direct oxidation of propene to acrylic acid

Physicochemical influence of graphite agent for fabrication of MoVTeNbO catalyst for direct oxidation of propene to acrylic acid

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.

Efficient Removal of Methylene Blue Using an Organic–Inorganic Hybrid Polyoxometalate as a Dual-Action Catalyst for Oxidation and Reduction

Efficient Removal of Methylene Blue Using an Organic–Inorganic Hybrid Polyoxometalate as a Dual-Action Catalyst for Oxidation and Reduction

Phenanthroline-functionalized MCM-41-immobilized copper(I) chloride complex: A highly active and recyclable catalyst for aerobic oxidation of alcohols

A new 1,10-phenanthroline-functionalized MCM-41-immobilized copper(I) complex [MCM-41-Phen-CuCl] was prepared from 1-(1,10-phenanthrolin-5-yl)-3-(3-(triethoxysilyl)propyl)urea via immobilization on MCM-41, followed by reacting with copper(I) chloride. It was found that this heterogenized copper(I) complex is a highly efficient catalyst for the oxidation of a wide variety of alcohols into aldehydes and ketones using molecular oxygen as the stoichiometric oxidant and 5 mol% of di-tert-butyl hydrazine-1,2-dicarboxylate (DBAD-H2) as additive, and can be recycled more than eight cycles with almost consistent activity.

Co3O4-modified 3DOM LaFe0.6Mg0.4O3 perovskite as robust catalysts for soot oxidation

In this study, 3DOM LaFe0.6Mg0.4O3 perovskite was prepared using a colloidal crystal template technique and subsequently decorated with Co3O4 for soot combustion. The results indicated that the LaFe0.6Mg0.4O3 perovskite with three-dimensional ordered macropores structure could facilitate the dispersion of Co3O4, boost the number of active sites for soot combustion, and significantly enhance the contact efficiency between the catalyst and soot. The interaction between Co3O4 and perovskite created additional oxygen vacancies and enhanced the redox ability of the catalysts. Meanwhile, the presence of Co3O4 facilitated the adsorption and activation of O2, which could accelerate the oxidation of soot particles. Notably, the 2.5 %Co/LaFe0.6Mg0.4O3 catalyst exhibited the highest performance, achieving a T50 of 407 °C for soot combustion in the presence of 500 ppm NO and 5 % O2. The catalyst also demonstrated excellent stability and water resistance, making it a promising candidate for practical applications.

Synergy between NiWO4 and chitosan for the development of catalysts for sulfide oxidation

In this work, catalysts based on composite films composed by chitosan with disordered NiWO4 (10, 20, and 40 % w/w) were synthesized for their application in the oxidation of sulfides to sulfones. The catalysts were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), optical profilometry, and contact angle measurements. Optimization of the catalytic conditions was performed using thioanisole as the standard molecule, resulting in optimal conditions of 50°C, 1 h, 10 mg catalyst loading, 8 equivalents of H2O2 as oxidant, and acetonitrile as solvent. The results obtained were superior to those with crystalline NiWO4 (highly ordered), highlighting the crystallinity of the system as a key factor in the development of new catalysts. The catalyst exhibited high stability over successive catalytic cycles, and scaling up to 50 times was achieved. Additionally, the reaction scope showed good conversion for a variety of different sulfides, indicating the robustness of the catalyst. Analysis of the catalytic mechanism through scavenger tests and spectroscopic probes revealed that reactive oxygen species (ROS) are responsible for the oxidation of sulfides to sulfones. Furthermore, it was observed that the synergy between NiWO4 and chitosan is crucial for the effective generation of ROS in this reaction.

Unveiling the mechanistic synergy in Mn-doped NiO catalysts with atomic-burry structure: Enhanced CO oxidation via Ni-OH and Mn bifunctionality

The development of non-noble metal catalysts for low-temperature CO oxidation is a pivotal subject in various disciplines. In this study, an optimized Mn-doped NiO catalyst (Mn-NiO-0.5), prepared via aerosol pyrolysis with an equal molar ratio of Ni to Mn, demonstrates remarkable performance. It achieves an 82 % CO conversion at -20 °C and a 100 % conversion between 10 °C and 800 °C. The catalyst’s turnover frequency (TOF) for CO oxidation significantly surpasses that of previously reported noble-metal-based catalysts, underscoring its superior efficiency. Dynamic analyses suggest that the enhanced catalytic activity is a result of the unique atom burr structure, which presents an extensive surface area replete with abundant active sites. This structural feature is instrumental in maximizing the catalyst’s interaction with CO molecules. Experimental findings, corroborated by density functional theory (DFT) calculations, elucidate the mechanism of CO oxidation on the Mn-NiO-0.5 catalyst. The process is facilitated by the synergistic action of bimetallic sites, where the Ni–OH site acts as the primary adsorption point for CO. Subsequently, the CO is oxidized to bicarbonate through the interaction with the oxygen (O or O2) at adjacent Mn sites. This pioneering study introduces a paradigm-shifting insight: the effectiveness of non-noble metal oxide catalysts can now compete with, and in some cases, outperform their noble metal counterparts. This breakthrough is set to transform the industry, presenting a compelling alternative to conventional noble metal catalysts and propelling the evolution of state-of-the-art environmental conservation technologies.

Strong interaction between promoter and metal in Pd-Ba/TiO2 catalysts for formaldehyde oxidation

As our previous works found, alkali metals have a common promotion effect on supported noble metals catalysts for formaldehyde (HCHO) oxidation. As second-group elements, alkaline earth metals (AEMs) are neighbors to the first-group elements and share some properties in common. However, detailed investigations into the specific mechanisms underlying AEMs’ effects on HCHO oxidation remain limited. In this study, we found that Ba addition showed a similar promotion effect on HCHO oxidation for Pd/TiO2. Ba species stabilized Pd groups, improved the dispersion, and even caused a large number of monatomic-like Pd sites to appear, which may be attributed to the electronic interaction between promoter and metal (EIPM) between Ba and Pd. Besides, AEM loading had the important effect of increasing the electron density of metallic Pd nanoparticles, which further improved the ability for O2 activation and so enhanced the mobility of chemisorbed oxygen on the catalyst surface. For Pd/TiO2, the HCHO oxidation path is mainly HCHO→HCOOH→HCOO→H2O+CO2. By contrast, for Pd-Ba/TiO2, with more surface-active species, the formate intermediate was more likely to be directly oxidized into H2O and CO2, which is a more effective reaction pathway. The details of the EIPM between Pd and Ba were investigated by GPAW (DFT calculation module) in ASE (Atomic Simulation Environment). The AEM Ba acted as an electron donor and could interact with Pd d orbital electrons through BaO sp orbital electrons. Ba species were highly dispersed on the carrier due to the Ba-Ti interaction. Ba species dispersed over large areas stabilized the Pd particles and donated electrons to Pd. Therefore, adding an AEM is an efficacious strategy to improve the performance of the catalytic oxidation of HCHO.

Engineering Oxygen Vacancies of Co-Mn-Ni-Fe-Al High-Entropy Spinel Oxides by Adjusting Co Content for Enhanced Catalytic Combustion of Propane.

Transition metal-based oxides with similar oxidation activities for catalytic hydrocarbon combustion have attracted much attention. In this study, a new class of metal high-entropy oxides (CoxMnNiFeAl)3O4 (x = 1, 2, 3, 4, 5) with a porous structure was fabricated through a simple and inexpensive NaCl template-assisted sol-gel approach, which was employed for the catalytic oxidation of propane. The results indicated that the content of cobalt has a great impact on its activity, and the (Co4MnNiFeAl)3O4 catalyst exhibited the best catalytic activity. At the high space velocity of 60 000 mL·g-1·h-1, the optimized one with high-temperature treatment can still achieve 90% propane conversion at 309 °C, which is 68 and 178 °C lower than those of the (CoMnNiFeAl)3O4 catalyst and pure cobalt oxide, respectively. Meanwhile, it has the lowest apparent activation energy (46.6 KJ·mol-1) and the fastest reaction rate (26.976 × 10-6 mol·gcat-1·s-1 at 290 °C). The improved performance of the (Co4MnNiFeAl)3O4 catalyst could be attributed to the enhancement of low-temperature reducibility, the increased number of reactive surface oxygen species, and the cocktail effect of the high-entropy oxides. This work provides new insights into the preparation of efficient light alkane degradation catalysts and a realistic approach for the large-scale application of high-entropy oxides in the field of oxidation catalysts.

Impact of Cu content on the activity of TiO2-based catalysts for toluene oxidation

Toluene is one of the most toxic contaminants in industrial waste gases, it can enter the body through the respiratory system and skin. Long-term exposure to it can lead to skin inflammation and neurasthenia, and even cause lesions in organs. Over the years, catalytic oxidation technology has been extensively employed to the remove of toluene, and oxides, especially copper oxide, is considered to be an effective catalyst technology and has been extensively studied. In this work, we introduced CuO as an active species to investigate the impact of Cu content in TiO2@CuO (TC-x, x=1, 2, 3, and 5) catalyst on the activity, reusability, and stability of toluene oxidation. The result demonstrated that the addition of Cu species, facilitating the generation of active oxygen obviously reduced the complete oxidation temperature of toluene. Among them, TC-3 catalyst exhibited the highest activity (T50 = 234 ℃, T90 = 289 ℃, and T100 = 310 ℃, with Ctoluene=1000 ppm, WHSV=20,000 mL/ (g h)), great reusability, and stability for toluene degradation. According to the in-situ DRIFTS, the ultimate degradation products of toluene were CO2 and H2O, which were clean and free of secondary pollution.

Fe2O3/γ-Al2O3 and NiO/γ-Al2O3 catalysts for the selective catalytic oxidation of ammonia

Ammonia, a significant atmospheric pollutant, requires effective emission control due to its inherent toxicity and the generation of secondary pollutants like particulate matter. This control can be achieved through various methods, including catalytic processes. Therefore, our study focuses on evaluating the potential of catalysts based on iron oxide and nickel oxide supported on γ–Al2O3 for the selective catalytic oxidation of NH3 to N2 (NH3-SCO). The γ–Al2O3 was obtained by thermal decomposition of aluminum hydroxide, and 5 or 10 wt% of Fe or Ni was added through wetness incipient impregnation. XRD diffractograms confirmed the formation of the γ–Al2O3 phase. XRD, H2-TPR, and UV–vis DRS data showed the presence of Fe2O3, NiO, and NiAl2O4 in the catalysts. Introducing metal oxides onto the support led to a drop in the specific area, pore size, pore volume, and NH3 desorption, which was higher for the catalysts containing Fe. The catalysts were active in NH3-SCO, and the insertion of Fe or Ni was essential because it promoted a significant increase in the NH3 conversion (∼75 % Fe and ∼55 % Ni), compared to pure support (∼8 %), mainly from 400 °C. However, doubling the metal content has not resulted in a considerable increase in NH3 conversion. The N2 selectivity was higher for the catalysts containing Ni (∼85 %) from 400 °C compared to catalysts containing Fe (∼76 %). Such behavior was due to the larger surface area of the Ni-containing catalysts. Despite that, the 5Fe/γ–Al2O3 catalyst emerged as the most effective option for NH3-SCO applications, combining higher NH3 conversion and good N2 selectivity.

Enhancing acidity of Ru/Ce/ZrO2 bifunctional catalysts for promoting N2 selectivity in selective catalytic oxidation of NH3

To solve the problem of low N2 selectivity of Ru/Ce/ZrO2 (R/C/Z) catalysts in NH3 selective catalytic oxidation (NH3-SCO) reaction, herein ZrO2 supports were treated with sulfuric acid and its effects on NH3-SCO performance were investigated systematically. The results showed that Ru/Ce/ZrO2-10S (R/C/Z-10S) catalyst, in which the mass ratio of sulfuric acid to ZrO2 was 10 %, exhibited N2 selectivity of 95.7 % at 350 °C, that was significantly higher than R/C/Z catalyst (57.8 %). NH3-TPD tests indicated that sulfate treatment of ZrO2 supports in R/C/Z catalysts led to more abundant acidic sites on catalyst surface, which was in favor of enhancing NH3 adsorption capacity remarkably. But when mass ratio of sulfuric acid to ZrO2 increased up to 20 %, an aggregation of metal oxides on the surface of R/C/Z-20S catalyst could be observed clearly, which might impose an adverse impact on NH3-SCO performance. In-situ DRIFTS results revealed that, compared to R/C/Z catalyst, there were much more Brönsted acid sites on the surface of R/C/Z-10S catalyst, and the corresponding NH3 species on acidic sites could be consumed quickly in intermediate reactions. More importantly, amide (-NH2) species rather than imide (-NH) and nitrosyl (-HNO) species, were the majority on the surface of R/C/Z-10S catalyst, implying that there might be a suppressing effect on further dehydrogenation of -NH2 species into -NH species owning to sulfate treatment of ZrO2 supports in R/C/Z catalysts. Therefore, internal selective catalytic reduction (i-SCR) mechanism rather than -NH mechanism played a vital role in NH3-SCO reaction over R/C/Z-10S catalyst.

High-Performance Low-Iridium Catalyst for Water Oxidation: Breaking Long-Ranged Order of IrO2 by Neodymium Doping.

Exploring efficacious low-Irelectrocatalysts for oxygen evolution reaction (OER) is crucial for large-scale application of proton exchange membrane water electrolysis (PEMWE). Herein, an efficient non-precious lanthanide-metal-doped IrO2 electrocatalyst is presented for OER catalysis by doping large-ionic-radius Nd into IrO2 crystal. The doped Nd breaks the long-ranged order structure by triggering the strain effect and thus inducing an atomic rearrangement of Nd─IrO2 involving the forming of Nd─O─Ir bonds along with an increased amount of oxygen vacancies (Ov), giving rise of a long-ranged disorder but a short-ranged order structure. The formed Nd─O─Ir bonds tailor the electronic structure of Ir, leading to a lowered d-band center that weakens intermediates absorption on Ir sites. Moreover, doping Nd triggers Nd─IrO2 to catalyze OER mainly through lattice oxygen mechanism (LOM) by activating lattice oxygen owing to abundant Ov. The optimal catalyst only requires a relatively low overpotential of 263 mV@10mA cm-2 with a high mass activity of 216.98 A gIr -1 (at 1.53V) (eightfold of commercial IrO2), and also shows a superior durability at 50mA cm-2 (20h) than commercial IrO2 (3h) due to the oxidation-suppressing effect induced by Nd doping. This work offers insights into designing high-performance low-Ir electrocatalysts for PEMWE application.

Comprehensive mechanism and microkinetic model-driven rational screening of 4N-modulated single-atom catalysts for selective oxidation of benzene to phenol

Comprehensive mechanism and microkinetic model-driven rational screening of 4N-modulated single-atom catalysts for selective oxidation of benzene to phenol

Hierarchical Anion Exchange and Reverse Electron Transfer in Layered Double Hydroxides/Peroxymonosulfate System for Roxarsone Elimination.

Roxarsone (ROX) is the main form of arsenic pollution in the world, and developing effective methods for its elimination is beneficial to human health and the ecological environment. Herein, we report glutaraldehyde cross-linked chitosan-encapsulated CoCe-LDH (layered double hydroxides) as an outstanding catalyst for the advanced oxidation of ROX and the efficient adsorption of inorganic arsenic. 100% of ROX and more than 98.5% of As(III)/As(V) were eliminated, and over 99.3% of remaining inorganic arsenic was oxidized to low-toxicity As(V) in the peroxymonosulfate (PMS) activation system, and some specific properties of LDH are considered the main reasons. The hierarchical anion exchange has been confirmed to be beneficial for constructing a high-concentration PMS interlayer microenvironment. The unique reverse electron transfer process induced 100% selective production of singlet oxygen. This work not only develops an advanced ROX removal method but also provides a new understanding of the LDH-based advanced oxidation process.

Tailored Engineering of Layered Double Hydroxide Catalysts for Biomass Valorization: A Way Towards Waste to Wealth.

Layered double hydroxides (LDH) have significant attention in recent times due to their unique characteristic properties, including layered structure, variable compositions, tunable acidity and basicity, memory effect, and their ability to transform into various kinds of catalysts, which make them desirable for various types of catalytic applications, such as electrocatalysis, photocatalysis, and thermocatalysis. In addition, the upcycling of lignocellulose biomass and its derived compounds has emerged as a promising strategy for the synthesis of valuable products and fine chemicals. The current review focuses on recent advancements in LDH-based catalysts for biomass conversion reactions. Specifically, this review highlights the structural features and advantages of LDH and LDH-derived catalysts for biomass conversion reactions, followed by a detailed summary of the different synthesis methods and different strategies used to tailor their properties. Subsequently, LDH-based catalysts for hydrogenation, oxidation, coupling, and isomerization reactions of biomass-derived molecules are critically summarized in a very detailed manner. The review concludes with a discussion on future research directions in this field which anticipates that further exploration of LDH-based catalysts and integration of cutting-edge technologies into biomass conversion reactions hold promise for addressing future energy challenges, potentially leading to a carbon-neutral or carbon-positive future.

Bioinspired octanuclear copper cubane complex as an efficient molecular electrocatalyst for water oxidation

Water oxidation catalysts (WOCs) with excellent activity and stability are highly desired. Numerous efforts have been dedicated to develop WOCs mimicking the cubic structure and activity of Mn4CaO5 cluster in oxygen-evolving center (OEC) of photosynthesis system II (PSII). Herein, a octanuclear Cu cluster [Cu8(dpy{OH}O)8(OAc)4]4+ (1, dpy{OH}O− = the monoanion of the hydrated, gem-diol form of di-2-pyridyl ketone) that contains two Cu4O4 cubic fragments with bioinspired structure mimicking the Mn4CaO5 cluster of OEC of natural PSII is developed as efficient homogeneous catalyst for electrochemical water oxidation under near neutral condition for the first time. It exhibits outstanding water oxidation catalytic activity via accelerating oxygen evolution with onset overpotential of 730 mV and appreciable turnover frequency of 20.1 s−1. Collective experiments together confirmed the homogeneity and stability of cluster 1 under long-term water oxidation catalytic cycle. Kinetic study reveals the water nucleophilic attack (WNA) catalytic mechanism occurs on the coordination unsaturated Cu center of the cluster. This work provides the inspiration of the development of robust bioinspired catalyst for electrochemical water oxidation.