Selective Liquid Phase Oxidation Research Articles

Soft-templating synthesis of mesoporous MnSiOx composites as catalytic supports for Pd nanoparticles towards solvent-free oxidation of benzyl alcohol under atmospheric pressure O2

Solvent-free and liquid-phase selective oxidation of aromatic alcohols using O2 as an oxidant is a green strategy for the synthesis of aromatic aldehydes and other carbonyl compounds. Wherein, the design and preparation of heterogeneous catalysts with high activity and selectivity is a hot topic in this process. Herein, a series of manganese oxide-silica (MnSiOx) composites were synthesized using cetyltrimethylammonium bromide as a soft template. During the preparation process, the amounts of tetraethyl orthosilicate and ammonia and the calcination temperature significantly affected the textural properties and Mn cation distributions of MnSiOx. The MnSiOx composites were then employed as catalysts for Pd nanoparticles. In the solvent-free and atmospheric conditions, Pd/MnSiOx materials showed high catalytic conversions of benzyl alcohol (BZA), and the catalytic activity thereof is related to the fractions of Pd0 and Mn3+. As the reaction time and temperature are 4 h and 90 °C, the conversion of BZA (feeding dosage: 4 mL) and the selectivity of benzaldehyde are 64.8 % and 94.9 %, respectively. The catalyst can be reused at least five times without any significant loss of activity. Furthermore, the correlation between physiochemical properties and catalytic activity of Pd/MnSiOx was analyzed.

A new Janus mesh membrane with ultrafast directional water transportation and improved fog collection

Fog collection materials have been intensively investigated and can potentially be used to alleviate freshwater shortages. However, developing highly efficient fog collection materials remains challenging. Requisite improvements in fog collection technology are the ultrafast transportation of captured water and the effective regeneration of fresh regions on the surfaces of fog collection materials. Herein, a novel Janus mesh membrane (JMM) with an alternating hydrophobic–superhydrophilic-patterned hydrophobic surface and asymmetric wettability interface is prepared by a selective liquid-phase surface oxidation strategy. The unique structure and high-contrast wettability of the JMM enable ultrafast directional transportation of tiny water droplets (< 0.1 μL), thereby achieving an excellent water collection efficiency of 15.28 g h−1 cm−2, which is much higher than those of conventional Janus membranes. The JMM functioned as a versatile fog collector and maintained continuous fog collection regardless of the fog flow direction. This study offers a novel approach for preparing innovative fog collection materials and establishes a foundation for developing advanced fog collection systems suitable for diverse applications.

Preparation of cobalt catalyst supported on perovskite-type oxide and application in liquid-phase selective oxidation reaction

Abstract Cobalt catalyst supported on the perovskite-type oxide sodium tantalate, NaTaO3 (NTO) was prepared by using the hydrothermal method and used in liquid-phase p-xylene oxidation, which led to p-methyl benzyl alcohol, p-tolualdehyde, and p-toluic acid. Investigation showed that the formation of alcohol and aldehyde was a competitive reaction. Further oxidation of the alcohol did not occur. On the other hand, the oxidation of p-tolualdehyde led to the formation of acid. Co-NTO catalyst showed higher selectivity toward the route of p-tolualdehyde than the p-methylbenzyl alcohol compared with the bulk Co3O4.

Streamlined synthesis of iron and cobalt loaded MCM-48: High-performance heterogeneous catalysts for selective liquid-phase oxidation of toluene to benzaldehyde

Hydrothermal synthesis of MCM-48 molecular sieves featuring the incorporation of both iron and cobalt with Si/M ratios of 20, 40 and 80 (where M represents either iron or cobalt) was performed using tetraethyl orthosilicate as the silica source and cetyltrimethylammonium bromide as a template. To gain a comprehensive understanding of the synthesized materials, these were thoroughly characterized using various techniques, including XRD, XPS, UV–Vis (DRS), FT-IR, N2 adsorption-desorption analysis, SEM with EDX, TEM, TGA and NH3-TPD analysis. XRD analysis revealed the presence of well-ordered MCM-48 structure in the metal-incorporated materials, while XPS and UV–Vis DRS confirmed the successful partial incorporation of metal ions precisely in their desired tetrahedral coordination within the framework. To assess their catalytic performance, we studied the activity and selectivity of these catalysts in liquid phase oxidation of toluene using tert-butyl hydroperoxide as the oxidant. Under optimized conditions, employing a 6% (w/w) Fe-MCM-48 (40) catalyst and maintaining a toluene to oxidant molar ratio of 1:3 at 353 K in a solvent-free environment for 8 h, the oxidation reaction resulted in the formation of benzaldehyde (88.1%) as the major product and benzyl alcohol (11.9%) as the minor product.

Liquid-Phase Selective Oxidation of Methane to Methane Oxygenates

Methane is an abundant and relatively clean fossil fuel resource; therefore, its utilization as a chemical feedstock has a major impact on the chemical industry. However, its inert nature makes direct conversion into value-added products difficult under mild conditions. Compared to the gas-phase selective oxidation of methane, there have been several recent advances in the liquid-phase conversion of methane. This review categorizes the reports on the liquid-phase selective oxidation of methane according to the solvent and oxidant used. The advantages and disadvantages of each approach are discussed. High yields of methyl bisulfate as a methanol precursor can be achieved using SO3 in sulfuric acid; however, more attention should be paid to the separation process and overall economic analysis. However, the aqueous-phase selective oxidation of methane with in situ generated H2O2 is quite promising from an environmental point of view, provided that an economical reducing agent can be used. Based on the current state-of-the-art on this topic, directions for future research are proposed.

Liquid phase selective oxidation of veratryl alcohol to veratraldehyde using pure and Mg-doped copper chromite catalysts.

Mg-doped copper chromite (CuCr2O4) nanocomposites were synthesised through conventional technique. The pure and doped CuCr2-xMgx O4 (x = 0.00-0.1, 0.2 and 0.3%) nanocomposites were characterized in terms of their morphology, crystal structure, surface area and catalytic performance. The chemical composition of CuCr2-xMgx O4 was confirmed via FT-IR. The formation of pure and doped catalysts was validated by XRD results. TEM/SEM confirmed the formation of CuCr2-xMgxO4 nanoparticles. Mg-doped samples possess a high specific surface area compared to pure CuCr2O4. Thus, the effects of temperature, solvent, time, oxidant and the amount of catalyst on the oxidation of veratryl alcohol were reported. Furthermore, detailed mechanisms of the catalytic oxidation of veratryl alcohol as well as the reusability and stability of the nanomaterial were investigated. The resulting composites were shown to be effective heterogeneous catalysts for the oxidation of veratryl alcohol.

Heterogeneous H2O2-based selective oxidations over zirconium tungstate α-ZrW2O8.

Catalytic properties of a crystalline zirconium tungstate, ZrW2O8, the material known mainly for its isotropic negative coefficient of thermal expansion, have been assessed for the liquid-phase selective oxidation of a range of organic substrates comprising CC, OH, S and other functional groups using aqueous hydrogen peroxide as the green oxidant. Samples of ZrW2O8 were prepared by hydrothermal synthesis and characterised by N2 adsorption, PXRD, SEM, EDX, FTIR and Raman spectroscopic techniques. Studies by IR spectroscopy of adsorbed probe molecules (CO and CDCl3) revealed the presence of Brønsted acidic and basic sites on the surface of ZrW2O8. It was demonstrated that ZrW2O8 is able to activate H2O2 under mild conditions and accomplish the epoxidation of CC bonds in alkenes and unsaturated ketones, oxidation of thioethers to sulfoxides and sulfones, along with the oxidation of alcoholic functions to produce ketones and aldehydes. The oxidation of tetramethylethylene and α-terpinene over ZrW2O8 revealed the formation of peroxidation products, 2,3-dimethyl-3-butene-2-hydroperoxide and endoperoxide ascaridole, respectively, indicating the involvement of singlet oxygen in the oxidation process. The ZrW2O8 catalyst preserves its structure and morphology under the turnover conditions and does not suffer from metal leaching. It can be easily recovered, regenerated by calcination, and reused without the loss of activity and selectivity.

Single atom manganese catalyst boosting selective oxidation of alcohols with activated peroxymonosulfate

Selective oxidations are important reactions in organic synthesis for fine chemical industry and conventional methods are expensive and produce a lot of toxic wastes. Herein, we demonstrate a facile and environmentally benign technique for liquid phase selective oxidation based on graphene-supported Mn single-atom-catalyst (SAMn-G) for efficient peroxymonosulfate (PMS) activation. The active Mn component in the developed SAMn-G catalyst reached single-atomic dispersion on graphene substrate via the coordination of individual Mn atoms with the doped N from the graphene framework. SAMn-G activated PMS via a nonradical-dominated pathway, which could convert aromatic alcohols into aldehydes or ketones at a mild temperature. The SAMn-G catalyst exhibited superior conversion and aldehyde selectivity in alcohol oxidation in comparison with their counterpart catalysts possessing either homogeneous Mn ions or oxide particles. The high activation efficiency of SAMn-G is due to the synergistic effect between Mn atoms and graphene substrate, as well as the dominated reaction pathway from nonradical oxidation, which is more selective than these free radicals to oxidize the alcohols. Concerted experimental evidence indicates that the non-radical oxidation process was highly possible to follow the electron transfer mechanism by PMS/organic adsorption on the surface of the catalyst. This study provides a fundamental understanding of PMS activation mediated by single atom catalyst for organic synthesis and the achieved insights can also help the catalyst design for other liquid phase selective oxidation processes.

Comprehensive Study on Kinetic Modeling of Liquid-Phase Selective Oxidation Using Au-Supported Catalysts for Efficient Production of Value-Added Chemicals from Glycerol

Comprehensive Study on Kinetic Modeling of Liquid-Phase Selective Oxidation Using Au-Supported Catalysts for Efficient Production of Value-Added Chemicals from Glycerol

Liquid phase selective oxidation of cyclohexane using gamma alumina doped manganese catalysts and ozone: an insight into reaction mechanism

Abstract In this study, we investigate the oxidation of cyclohexane using various percentages of Mn/γ-Al2O3 catalysts. The catalysts were characterized with various spectroscopic and microscopic techniques. The XRD showed the presence of γ-Al2O3 and MnO only. However, the XPS showed that AlO, AlOH, Mn2O3 and MnO2 also exist. The TEM results of pristine γ-Al2O3 showed characteristics of a spherically shaped material, whereas Mn/γ-Al2O3 catalysts displayed rod shaped particles. The EPR results showed that hydroxide radicals are the main reactive species responsible for the significant oxidation of cyclohexane and the catalysts play a profound role in the generation of hydroxide radicals. The oxidation of cyclohexane was performed for 1 h and the reaction products were analysed using GC-MS and FT-IR in 30 min intervals. The 2.5% Mn/γ-Al2O3 was the most reactive catalyst with a percentage conversion of 33% after 1 h oxidation. The cyclohexanol and the cyclohexanone were the only reaction products obtained. This study exhibited that Mn/γ-Al2O3 catalysts when used in conjunction with ozone are potential replacement for industrially used homogeneous manganese catalysts.

Selective liquid-phase oxidation of toluene over heterogeneous Mn@ZIF-8 derived catalyst with molecular oxygen in the solvent-free conditions

In this work, liquid-phase catalytic oxidation of toluene was carried out under solvent-free conditions, and highly selective synthesis of benzaldehyde (BAL) and benzyl alcohol (BOL) and benzoic acid (BAC) in the presence of Mn@ZIF-8 calcined material as catalyst with oxygen molecules. As a heterogeneous catalyst, the zeolitic imidazolate framework Mn@ZIF-8 derived material exhibited reasonable substrate-product selectivity (70.3% of selectivity to BAL and BOL, 95.1 % of selectivity to BAL, BOL and BAC) and conversion (6.5%) under optimum reaction conditions. The catalysts were characterized by BET-specific surface area determination, XRD, XPS, FT-IR, TG-DTG and SEM-EDS-Mapping. The results demonstrated that the catalytic capacity of the catalysts was enhanced by the good dispersion of amorphous Mn species in ZIF-8 derivatives and high specific surface area. The possible reaction pathway for the catalytic oxidation of toluene was also suggested. Maybe this method employing Mn@ZIF-8 as efficient catalyst affords a new and environmentally friendly route for the synthesis of BOL and BAL from the selective oxidation of toluene.

H2O2-Based Selective Oxidations Catalyzed by Supported Polyoxometalates: Recent Advances

Polyoxometalates (POMs) are transition metal oxygen anionic clusters that are oxidatively and thermally robust due to their inorganic, metal oxide-like nature. The versatility of their structures and compositions ensures tunable acid and redox properties, solubility, and functionality. The potential of POMs as homogeneous catalysts and building blocks for the construction of heterogeneous selective oxidations catalysts is being intensively investigated. POM catalysts immobilized on solid supports have the clear advantages of easy separation and reuse and, thus, better meet the requests of sustainable chemistry, provided that they are leaching-resistant under the reaction conditions. Here, we give a brief overview of recent advances in the field of liquid-phase selective oxidation of organic compounds using supported POMs and the green oxidant–hydrogen peroxide, with a focus on the critical issues of the catalyst stability and reusability. The scope and limitations of various approaches to POM immobilization are discussed.

Immobilization of Polyoxometalates on Carbon Nanotubes: Tuning Catalyst Activity, Selectivity and Stability in H2O2-Based Oxidations

In recent years, carbon nanotubes (CNTs), including N-doped ones (N-CNTs), have received significant attention as supports for the construction of heterogeneous catalysts. In this work, we summarize our progress in the application of (N)-CNTs for immobilization of anionic metal-oxygen clusters or polyoxometalates (POMs) and use of (N)-CNTs-supported POM as catalysts for liquid-phase selective oxidation of organic compounds with the green oxidant–aqueous hydrogen peroxide. We discuss here the main factors, which favor adsorption of POMs on (N)-CNTs and ensure a quasi-molecular dispersion of POM on the surface and their strong attachment to the support. The effects of the POM nature, N-doping of CNTs, acid additives, and other factors on the POM immobilization process and catalytic activity/selectivity of the (N)-CNTs-immobilized POMs are analyzed. Particular attention is drawn to the critical issue of the catalyst stability and reusability. The scope and limitations of the POM/(N)-CNTs catalysts in H2O2-based selective oxidations are discussed.

Templated Synthesis of Mesoporous Co3O4 Nanostructures for the Liquid-Phase Aerobic Oxidation of Benzyl Alcohol to Benzaldehyde

Mesoporous Co3O4 nanostructures, templated from different mesoporous silicas, SBA-3, SBA-5, and SBA-16, were used as catalysts for the liquid-phase selective oxidation of benzyl alcohol using molecular oxygen as the oxidant. The nanostructured Co3O4-16, templated from SBA-16, showed the best activity for the reaction, with 97.5% benzyl alcohol conversion and 100% benzaldehyde selectivity obtained after 3 h of reaction at 100 °C. This could be attributed to its large number of oxygen vacancies and low surface Co3+/Co2+ ratio that were beneficial to O2 activation, together with its three-dimensional nanostructure that facilitated the adsorption of benzyl alcohol, compared to Co3O4-3 and Co3O4-15. The material could be reused without losing activity if the organics adsorbed on the surface of the used sample were removed by calcination at 300 °C for 1 h. A mechanism for the reaction was proposed, considering that the activation of molecular oxygen was the rate-determining step of the reaction.

Catalytic oxygen atom transfer promoted by tethered Mo(VI) dioxido complexes onto silica-coated magnetic nanoparticles

The preparation of three novel active and stable magnetic nanocatalysts for the selective liquid-phase oxidation of several olefins, has been reported. The heterogeneous systems are based on the coordination of cis-MoO2 moiety onto three different SCMNP@Si-(L1-L3) magnetically active supports, functionalized with silylated acylpyrazolonate ligands L1, L2 and L3. Nanocatalysts thoroughly characterized by ATR-IR spectroscopy, TGA and ICP-MS analyses, showed excellent catalytic performances in the oxidation of conjugated or unconjugated olefins either in organic or in aqueous solvents. The good magnetic properties of these catalytic systems allow their easy recyclability, from the reaction mixture, and reuse over five runs without significant decrease in the activity, either in organic or water solvent, demonstrating their versatility and robustness.

Hetero-mixed TiO2-SnO2 interfaced nano-oxide catalyst with enhanced activity for selective oxidation of furfural to maleic acid

Herein we report on the catalytic activity of hetero-mixed TiO2-SnO2 nano-oxide catalyst for the selective liquid-phase oxidation of furfural to maleic acid using H2O2 oxidant. The high surface area and strong interaction of the two oxides with modified electronic structure manifested enhanced effective oxygen vacancies, and redox activity performance of the TiO2-SnO2 catalyst for furfural oxidation reaction. The structure of the catalyst was investigated by the powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transition electron microscopy (HRTEM), electron paramagnetic resonance (EPR) and Brunauer-Emmett-Teller (BET) surface area analyser techniques. The interfaced TiO2-SnO2 oxide catalyst was more catalytically active than its single counterpart SnO2 and TiO2 oxides to give a furfural conversion of 96.2% at up to 63.8% yield of maleic acid. The catalytic performance shown by TiO2-SnO2 present encouraging prospects for an economical solid metal oxide catalyst to access biobased maleic acid from renewable biomass-derived furfural.

Metal-Organic Frameworks in Oxidation Catalysis with Hydrogen Peroxide

In recent years, metal–organic frameworks (MOFs) have received increasing attention as selective oxidation catalysts and supports for their construction. In this short review paper, we survey recent findings concerning use of MOFs in heterogeneous liquid-phase selective oxidation catalysis with the green oxidant–aqueous hydrogen peroxide. MOFs having outstanding thermal and chemical stability, such as Cr(III)-based MIL-101, Ti(IV)-based MIL-125, Zr(IV)-based UiO-66(67), Zn(II)-based ZIF-8, and some others, will be in the main focus of this work. The effects of the metal nature and MOF structure on catalytic activity and oxidation selectivity are analyzed and the mechanisms of hydrogen peroxide activation are discussed. In some cases, we also make an attempt to analyze relationships between liquid-phase adsorption properties of MOFs and peculiarities of their catalytic performance. Attempts of using MOFs as supports for construction of single-site catalysts through their modification with heterometals will be also addressed in relation to the use of such catalysts for activation of H2O2. Special attention is given to the critical issues of catalyst stability and reusability. The scope and limitations of MOF catalysts in H2O2-based selective oxidation are discussed.

Extra-Large Pore Titanosilicate Synthesized via Reversible 3D–2D–3D Structural Transformation as Highly Active Catalyst for Cycloalkene Epoxidation

Titanosilicates with extra-large pores or cages are expected to effectively release the diffusion constraints suffered by the bulky substrates in the hydrogen peroxide-involved liquid-phase selective oxidation reactions. A reversible 3D–2D–3D structural transformation was developed to fabricate a highly active IWV-type titanosilicate (Ti-IWV) with a two-dimensional intersecting 12-membered ring (MR) channel system and extra-large 14-MR supercages. The IWV germanosilicate was readily disassembled into a layered 2D material (Hydro-IWV) in HNO3 aqueous solution, which was reconstructed to Ti-IWV with various Ti contents (Si/Ti ratio of 40–∞) through the (NH4)2TiF6-assisted isomorphous substitution of Ti and structure repair. The fluoride anions were critical to recover the interlayer double-four-ring (d4r) units, which were destroyed in the hydrolysis process. Ti-IWV was extremely active in the liquid-phase epoxidation reaction of cycloalkenes, especially showing a much higher conversion (99%) for cyclooctene than conventional titanosilicates. Rather than diffusion rate, the high capacity for the adsorption of bulky alkene molecules of extra-large 14-MR cages contributed to the outstanding activity of Ti-IWV.

Catalytic Oxidation of o-Chlorotoluene with Oxygen to o-Chlorobenzaldehyde in a Microchannel Reactor

Liquid-phase selective oxidation of o-chlorotoluene (OCT) to o-chlorobenzaldehyde (OCBD) with oxygen as the oxidant catalyzed by a cobalt acetate/manganese acetate/potassium bromide (Co(OAc)2/Mn(OA...

A Composite Fe–V/g-C3N4 for Liquid-Phase Selective Oxidation of Methanol with O2 Oxidant

A composite material Fe–V/g-C3N4 prepared by impregnation achieved an efficient performance for heterogeneously catalytic oxidation of methanol to dimethoxymethane (DMM) and poly(oxymethylene) dimethyl ethers (POM) by O2 oxidant in batch reactor, exhibiting 34.3% conversion and > 99.0% selectivity to DMM and POM. However, a pioneered strategy for tuneable synthesis of DMM and POM was realized by controlling the reaction time. The experimental results revealed that FeVO4 and V2O5 nanoparticle crystallizes served as the active sites and higher specific areas 29.3–51.9 m3/g for the catalysts were jointly responsible for the high activity. Besides, the catalyst could be easily recovered and effectively reused. A composite material Fe–V/g-C3N4 with higher specific area exhibited efficient performance for heterogeneously catalytic oxidation of methanol to dimethoxymethane (DMM) and polyoxymethylene dimethyl ether (POM) in batch reactor using O2 oxidant. Moreover, a pioneered strategy for tunable synthesis of DMM and POM was realized by controlling the reaction time. The catalyst was easily recovered and had excellent recycle lifetime and stability.