Clean Oxidation Research Articles

Efficient day-night photocatalysis performance of 2D/2D Ti3C2/Porous g-C3N4 nanolayers composite and its application in the degradation of organic pollutants

It is hindered by the limited light time that the development of photocatalysis technology, which is a clean and energy-saving advanced oxidation process. In this work, a 2D/2D Ti3C2/porous g-C3N4 nanolayers composited van der Waals (VDW) heterostructure photocatalyst (Ti3C2/PCN) was prepared by a straightforward vacuum filtration method after an ultrasonic stripping process. In this Ti3C2/PCN composite photocatalyst, PCN nanolayers play the role of absorbing visible light, while Ti3C2 nanolayers form VDW heterojunction with PCN nanolayers, which is beneficial to migration of photo-generated electrons from PCN to Ti3C2. The band structure match of Ti3C2/PCN and the build-in electric field from the VDW heterojunction both favor the effective separation and migration of photo-induced charge carriers that is why the Ti3C2/PCN composite shows good day-photocatalytic capability with 98% phenol removal efficiency. Besides, as a good electronic storage material, the Ti3C2 can store excess photo-generated electrons under light irradiation and release them when exposed to electron acceptors in the dark condition. Therefore, the night-photocatalysis can work out even without sunlight, in which 32% phenol was decomposed. In addition, the universality of Ti3C2/PCN day-night photocatalytic system is proved by the degradation of various organic pollutants. The design of this day-night photocatalyst can facilitate the application of photocatalytic reaction to actual environmental scenes, since it reduces the limitation imposed by the presence or absence of sunlight.

Gold(I) and Gold(III) Complexes of Expanded-Ring N-Heterocyclic Carbenes: Structure, Reactivity, and Catalytic Applications

The oxidative addition of bromine to homo- and heterobis(carbene) gold(I) complexes 1–6 containing expanded-ring N-heterocyclic carbene (erNHC) ligands was explored to prepare the first examples of gold(III) erNHC complexes. The use of stoichiometric amounts of bromine consistently gave clean gold-centered oxidations leading to the isolation of monocarbene and mixed carbene complexes of the type [AuBr3(erNHC)] (7–9) and trans-[AuBr2(iPr2-bimy)(erNHC)]BF4 (13–15), respectively. The use of excess bromine additionally led to ligand brominations in the monocarbene series affording [AuBr3(erNHCBr2)] complexes (10–12), while in the case of the heterobis(carbene) series, tribromide complexes of the type trans-[AuBr2(iPr2-bimy)(erNHC)]Br3 (16–18) were obtained instead. Comparison of the catalytic activities of all complexes in the hydroamination of alkynes revealed the superior performance of mono-erNHC complexes in all cases.

2020 Roadmap on gas-involved photo- and electro- catalysis

Green reactions not only provide us chemical products without any pollution, but also offer us the viable technology to realize difficult tasks in normal conditions. Photo-, photoelectro-, and electrocatalytic reactions are indeed powerful tools to help us to embrace bright future. Especially, some gas-involved reactions are extremely useful to change our life environments from energy systems to liquid fuels and cost-effective products, such as H2 evolution (H2 production), O2 evolution/reduction, CO2 reduction, N2 reduction (or N2 fixation) reactions. We can provide fuel cells clean H2 for electric vehicles from H2 evolution reaction (HER), at the same time, we also need highly efficient O2 reduction reaction (ORR) in fuel cells for improving the reaction kinetics. Moreover, we can get the clean oxidant O2 from water through O2 evolution reaction (OER), and carry out some reactions without posing any pollution to reaction systems. Furthermore, we can translate the greenhouse gas CO2 into useful liquid fuels through CO2 reduction reaction (CRR). Last but not the least, we can get ammonia from N2 reduction reaction (NRR), which can decrease energy input compared to the traditional Hubble process. These reactions, such as HER, ORR, OER, CRR, and NRR could be realized through solar-, photoelectro- and electro-assisted ways. For them, the catalysts used play crucial roles in determining the efficiency and kinds of products, so we should consider the efficiency of catalysts. However, the cost, synthetic methods of catalysts should also be considered. Nowadays, significant progress has been achieved, however, many challenges still exist, reaction systems, catalysts underlying mechanisms, and so on. As extremely active fields, we should pay attention to them. Under the background, it has motivated us to contribute with a roadmap on ‘Gas-Involved Photo- and Electro-Catalysis’.

Synthesis of (E,E)-Dienones and (E,E)-Dienals via Palladium-Catalyzed γ,δ-Dehydrogenation of Enones and Enals.

SummaryA new strategy for the synthesis of conjugated (E,E)-dienones and (E,E)-dienals via a palladium-catalyzed aerobic γ,δ-dehydrogenation of enones and enals has been developed. The method can be employed in the direct and efficient synthesis of various (E,E)-dienones and (E,E)-dienals, including non-substituted α-, β-, and γ- and/or δ-substituted (E,E)-dienones and (E,E)-dienals. The protocol is featured by the ready accessibility and elaboration of the starting materials, good functional group compatibility, and mild reaction conditions. Furthermore, the reaction is of complete E,E-stereoselectivity and uses molecular oxygen as the sole clean oxidant.

Catalyst-Free Selective Oxidation of Diverse Olefins to Carbonyls in High Yield Enabled by Light under Mild Conditions.

The selective oxidation of olefins, in particular, aromatic olefins to carbonyls, is of significance in organic synthesis. In general, stoichiometric toxic oxidants or a high-cost catalyst is required. Herein we report a novel and practical light-enabled protocol for the synthesis of carbonlys in high yield through a catalyst-free oxidation of olefins using H2O2 as a clean oxidant. A broad scope of carbonyls can be synthesized in high yield, and no catalyst or toxic oxidant is required.

A Facile Synthesis of ZrOx-MnCO3/Graphene Oxide (GRO) Nanocomposites for the Oxidation of Alcohols using Molecular Oxygen under Base Free Conditions

Graphene and its nanocomposites are showing excellent potential in improving the catalytic performances of different materials. However, the synthetic protocol and its form, such as graphene oxide (GRO) or highly reduced graphene oxide (HRG), influence the catalytic efficiencies. Here, we present, a facile synthesis of graphene oxide (GRO) and ZrOx-MnCO3-based nanocomposites [(1%)ZrOx–MnCO3/(x%)GRO] and their outcome as an oxidation catalyst for alcohol oxidation under mild conditions using O2 as a clean oxidant. The ZrOx–MnCO3/GRO catalyst prepared by incorporating GRO to pre-calcined ZrOx-MnCO3 using ball milling showed remarkable enhancement in the catalytic activities as compared to pristine ZrOx–MnCO3, ZrOx–MnCO3 supported on HRG or ZrOx–MnCO3/GRO prepared by in-situ growth of ZrOx–MnCO3 onto GRO followed by calcination. The catalyst with composition (1%)ZrOx–MnCO3/(1%)GRO exhibited superior specific activity (57.1 mmol/g·h) with complete conversion and >99% selectivity of the product within a short period of time (7 min) and at a relatively lower temperature (100 °C). The catalyst could be recycled at least five times with a negligible decrease in efficiency and selectivity. The catalytic study was extended to different aromatic as well as aliphatic alcohols under optimized conditions, which confirmed the efficiency and selectivity of the catalyst.

Visible-Light-Induced Oxidation/[3 + 2] Cycloaddition/Oxidative Aromatization to Construct Benzo[a]carbazoles from 1,2,3,4-Tetrahydronaphthalene and Arylhydrazine Hydrochlorides.

An efficient synthesis of benzo[a]carbazoles via visible-light-induced tandem oxidation/[3 + 2] cycloaddition/oxidative aromatization reactions was reported. The benzylic C(sp3)-H of tetrahydronaphthalene was activated through visible-light photoredox catalyst with oxygen as the clean oxidant under mild reaction conditions. This protocol proceeds efficiently with broad substrate scope, and the mechanism study was performed.

A density functional theory analysis on syngas adsorption on NiO (100) surface

Oxygen carrier (OC) design can effectively improve the performance of chemical looping combustion (CLC) and realize fossil fuel combustion at low energy-cost CO2 capture. This study describes the adsorption principles of syngas (i.e. CO and H2) on a clean nickel oxide (100) surface under single and multiple nearest neighbor effects. The results show that the adsorption stability of CO and H2 is mostly weakened by the first neighbor compared to the rest. With the same species as nearest neighbors (uniform adsorption), syngas adsorption stability is reduced when the number of neighbors increases. Similarly, when compared to uniform adsorption, the adsorption stability of CO and H2 is slightly stronger with neighboring sites occupied with different species (hybrid adsorption). In addition, a lower degree of symmetry tends to strengthen CO and H2 adsorption. Results from this analysis show that the adsorption stability of CO and H2 with neighbors are highly related to steric, hybrid and symmetry effects. An electronic property analysis was performed to further support the key role of hybrid neighboring effects in the adsorption process of syngas on the nickel oxide (100) surface.

Sulfonic Acid Functionalized MIL‐101(Cr) Metal‐Organic Framework for Catalytic Production of Acetals

AbstractA simple and green process for acetalization of benzaldehyde derivatives in the presence of a new solid acid nanocatalyst is reported. For this purpose, MIL‐101(Cr) was synthesized in the absence of HF and then sulfonic acid functionalized MOF was prepared under mild conditions without using hazardous chemicals. First, the MIL‐101(Cr) was functionalized with cysteamine as a non‐toxic material to afford MIL‐101(Cr)‐SH. Then, reaction of the MIL‐101(Cr)‐SH with hydrogen peroxide as a clean oxidant followed by acidification with diluted sulfuric acid produced MIL‐101(Cr)‐SO3H solid acid nanocatalyst. Characterization of the prepared nanocatalyst was carried out with various physicochemical methods. The results of elemental analysis and FT‐IR spectroscopy confirmed the stepwise functionalization of MIL‐101(Cr) with sulfonic acid groups. Nitrogen adsorption‐desorption analysis indicated the reduction of surface area after functionalization of pristine MIL‐101(Cr). X‐ray diffraction (XRD) analysis showed that the MIL‐101(Cr) kept its crystal structure during the modification steps. Finally, the activity of prepared catalyst was evaluated in the clean acetalization of benzaldehyde derivatives with ethylene glycol which exhibited excellent efficiencies and produced water as the only byproduct. The nanocatalyst was consecutively recovered and applied 5‐times without notable loss of its activity.

Palladium-based catalysts for methane oxidation by co-flow diffusion flame synthesis

Pd supported on mixed ceria-titania oxide catalysts are synthesized with a co-flow diffusion flame, and the catalytic activities for CH4 oxidation are evaluated in a lab-scale fixed bed. The as-prepared catalysts exhibit high catalytic activities and good Pd cluster distribution. Among them, Pd supported on pure CeO2 is found to show the best performance. The results show that it has fairly low T10, and complete oxidation occurs as low as 400 °C. It is deduced that three factors facilitate the reaction between the adsorbed CH4 and O2, namely, solid-solution-like PdxCe1-xO2 structures, highly active sites provided by atomic-level assembly during the flame synthesis, and the presence of lattice oxygen. Additionally, the deactivation of the catalyst may be caused by the decreasing of lattice oxygen, the reduction of PdO and the instability of PdxCe1-xO2. These results may aid in the development of better catalytic nanomaterials for clean methane oxidation.

Formate Oxidase (FOx) from Aspergillus oryzae: One Catalyst Enables Diverse H2 O2 -Dependent Biocatalytic Oxidation Reactions.

An increasing number of biocatalytic oxidation reactions rely on H2O2 as a clean oxidant. The poor robustness of most enzymes towards H2O2, however, necessitates more efficient systems for in situ H2O2 generation. In analogy to the well‐known formate dehydrogenase to promote NADH‐dependent reactions, we here propose employing formate oxidase (FOx) to promote H2O2‐dependent enzymatic oxidation reactions. Even under non‐optimised conditions, high turnover numbers for coupled FOx/peroxygenase catalysis were achieved.

A Study of Catalytic Oxidation of a Library of C₂ to C₄ Alcohols in the Presence of Nanogold.

The classical stoichiometric oxidation of alcohols is an important tool in contemporary organic chemistry. However, it still requires huge modifications in order to comply with the principles of green chemistry. The use of toxic chemicals, hazardous organic solvents, and the large amounts of toxic wastes that result from the reactions are a few examples of the problems that must be solved. Nanogold alone or conjugated with palladium were supported on different carriers (SiO2, C) and investigated in order to evaluate their catalytic potential for environmentally friendly alcohol oxidation under solvent-free and base-free conditions in the presence H2O2 as a clean oxidant. We tested different levels of Au loading (0.1–1.2% wt.) and different active catalytic site forms (monometallic Au or bimetallic Au–Pd sites). This provided new insights on how the structure of the Au-dispersions affected their catalytic performance. Importantly, the examination of the catalytic performance of the resulting catalysts was oriented toward a broad scope of alcohols, including those that are the most resistant to oxidation—the primary aliphatic alcohols. Surprisingly, the studies proved that Au/SiO2 at a level of Au loading as low as 0.1% wt. appeared to be efficient and prospective catalytic system for the green oxidation of alcohol. Most importantly, the results revealed that 0.1% Au/SiO2 might be the catalyst of choice with a wide scope of utility in the green oxidation of various structurally different alcohols as well as the non-activated aliphatic ones.

Selective Aerobic Oxidation of 4-Ethylnitrobenzene to 4-Nitroacetophenone Promoted by Metalloporphyrins

A solvent-free and environment-friendly process for the oxidation of 4-ethylnitrobenzene to 4-nitroacetophenone promoted by metalloporphyrins was developed in a pressure reactor using O2 as a clean oxidant. The activities and reaction selectivities of the metalloporphyrins could be significantly affected by their central metal ions as well as the nature and position of the substituted groups, which were systematically investigated by employing more than 60 metalloporphyrins. Generally, the Fe(III)- and Mn(II)-porphyrins exhibited high activities. Moreover, metalloporphyrins with electron-withdrawing substituents on the para-positions of the phenyl rings showed activities in the order T(p-Br)PPM T(m-Cl)PPM > T(p-Cl)PPM and T(o-OMe)PPM < T(m-OMe)PPM < T(p-OMe)PPM were observed. Furthermore, selectivities over 90.0% and a TON of 5370 could be achieved for the desired ketone. Especially, the T(p-Cl)PPMn demonstrated a ...

The partial reduction of clean and doped α-Fe2O3(0001) from first principles

Fe surfaces have a wide range of applications due to the ability of Fe to be present in a number of different oxidation states, which can be further influenced by the presence of dopants that change the energetic and electronic surface properties. Thus, having an understanding of the elementary reduction processes of clean Fe oxide surfaces, and how dopants affect the energetics and electronics of such processes, is crucial to the science-guided design and optimization of said surfaces. In this work, we use density functional theory (DFT) to investigate the partial reduction of α-Fe2O3(0001) in the absence and presence of Pd and Pt dopants. In order to account for the strong on-site Coulombic interactions present in transition metal oxides, we used both the DFT + U method and 2006 Heyd-Scuseria-Ernzerhof functional and compare the results obtained from the different methods. We find that oxygen vacancies created in the clean α-Fe2O3(0001) surface prefer to diffuse into a subsurface layer, with the charge left behind from the first surface oxygen vacancy distributing between all of the near surface Fe atoms. The addition of Pd or Pt to the α-Fe2O3(0001) surface significantly decreases the energy required to create the first surface oxygen vacancy, suggesting the dopants intrinsically promote the reduction of α-Fe2O3(0001). Additionally, the presence of the dopants caused the charge left behind by the creation of the first surface oxygen vacancy to be localized on the dopant itself as well as the highest Fe atom. Overall, this work provides insight into the elementary energetic and electronic properties of the fully oxidized and partially reduced α-Fe2O3(0001) surface in the absence and presence of Pd and Pt dopants, which has potential implications for the design and optimization of doped Fe oxide surfaces.

Rh/O2-Catalyzed C8 Olefination of Quinoline N-Oxides with Activated and Unactivated Olefins.

The rhodium/O2 system-catalyzed distal C(sp2)-H olefination of quinoline N-oxides is developed. Molecular oxygen has been explored as an economic and clean oxidant, an alternative to inorganic oxidants. A wide substrate scope with respect to quinoline N-oxides and olefins (activated acrylates and styrenes; unactivated aliphatic olefins) demonstrates the robustness of the developed catalytic method. Interestingly, 2-substituted quinoline N-oxides also afforded good yields of the corresponding C8-olefinated products. Kinetic isotope studies and deuterium-labeling experiments have been performed to understand the preliminary mechanistic pathway. The applicability of the developed method is demonstrated by utilizing natural product-derived substrates and by converting the C8-olefinated quinoline N-oxides into various other useful molecules.

Synthesis of Encapsulant by Clean Oxidation Under Halide-Free Conditions

Synthesis of Encapsulant by Clean Oxidation Under Halide-Free Conditions

Minireview: Selective production of hydrogen peroxide as a clean oxidant over structurally tailored carbon nitride photocatalysts

Hydrogen peroxide (H2O2) is a clean oxidant, and its demand has continuously risen in various industries for pulp/paper bleaching, chemical synthesis, wastewater treatment, etc. H2O2 is commercially produced by the anthraquinone method, which has some drawbacks, including (i) toxic solvent, (ii) explosive hydrogen gas as a precursor, and (iii) a high energy input; therefore, a new technology based on cost-effective and green processes is required. Photocatalytic production of H2O2 can be considered the most environmentally benign and economically feasible process because it requires only dissolved oxygen, water, and sunlight. Among various photocatalysts, polymeric carbon nitride (C3N4) is a promising candidate for H2O2 production by virtue of its (i) simple synthesis by a thermal polymerization, (ii) structure consisting of earth-abundant carbon and nitrogen, (iii) effective bandgap size for visible light absorption, and (iv) suitable position of conduction band for reduction of oxygen dissolved in water. In this minireview, the mechanism of H2O2 formation over C3N4 has been discussed, and the strategies to optimize the photocatalytic activity have been summarized regarding structural and surface modification techniques. This overview of diverse methodologies to selectively control electron transfer to dissolved oxygen should be in demand not only for developing new-generation C3N4-based materials, but also for commercialization of solar-light-driven photocatalytic H2O2 production system.

Synthesis of Cyanide‐Functionalized Imidazo[1,5‐a]quinolines via Copper‐Mediated Aerobic Three‐Component Cyclizations

AbstractA three‐component cyclization of 2‐methylquinolines, trimethylsilyl cyanide, and alkylamines or α‐amino acids mediated by CuSO4 was developed. By employing oxygen as the clean oxidant, cyanated imidazo[1,5‐a]quinolines were constructed with high efficiency for the first time. The loading of CuSO4 could be lowered to 20 mol% with a slightly diminished yield. The synthetic utility of this method is further highlighted by the gram‐scale synthesis and tolerance of sensitive functional group.magnified image

Synthesis of Enones and Enals via Dehydrogenation of Saturated Ketones and Aldehydes

AbstractA general, efficient and economic palladium‐catalyzed dehydrogenation to form enones or enals has been developed. The approach possesses extremely broad substrate scope including various linear or cyclic saturated ketones and aldehydes. The protocol is ligand‐free, and molecular oxygen is used as the sole clean oxidant in the reaction. Due to mild reaction conditions, good functional group compatibility, and versatile utilities of enones and enals, the method can be applied in the late‐stage synthesis of natural products, pharmaceuticals and fine chemicals.magnified image

Oxidative Cleavage of Fatty Acid Derivatives for Monomer Synthesis

Oxidative cleavage of fatty acids and fatty acid derivatives is a practical way to obtain bifunctional molecules that can be used in polycondensation reactions. Diacids, hydroxyacids, and amino acids can then be used to produce polyesters or polyamides and also a large range of other products, such as lubricants and plasticizers. Ozonolysis has long been the sole industrial process for oxidative cleavage, but recently, routes using hydrogen peroxide as a clean oxidant have regained interest. Hydrogen peroxide is easier to use, but the kinetics of the catalyzed reactions are still slow. Although several catalytic systems have been described in the literature, tungsten-based catalysts are still the preferred choices. Different catalysts can trigger different mechanisms, such as a radical mechanism instead of a catalytic reaction. In addition, some side products and co-products often disregarded in the literature, such as shorted cleavage products, indicate the presence of side reactions that affect the quality of the final products. The oxidative cleavages in continuous and batch processes have significant differences, which are discussed with an illustration of our understanding of the process used by Matrica S.p.A.