Catalytic Oxidation Of Alcohols Research Articles

The Adaptative Modulation of the Phosphinito–Phosphinous Acid Ligand: Computational Illustration Through Palladium-Catalyzed Alcohol Oxidation

The phosphinito–phosphinous acid ligand (PAP) is a singular bidentate-like self-assembled ligand exhibiting dissymmetric but interchangeable electronic properties. This unusual structure has been used for the generation of active palladium hydride through alcohol oxidation. In this paper, we report the first theoretical highlight of the adaptative modulation ability of this ligand within a direct H-abstraction path for Pd and Pt catalyzed alcohol oxidation. A reaction forces study revealed rearrangements in the ligand self-assembling system triggered by a simple proton shift to promote the metal hydride generation via concerted six-center mechanism. We unveil here the peculiar behavior of the phosphinito–phosphinous acid ligand in this catalysis.

Cerium-Organic Framework UiO-66(Ce) as a Support for Nanoparticulate Gold for Use in Oxidation Catalysis.

An optimised synthesis of the metal-organic framework (MOF) UiO-66(Ce) is reported using a modulator-free route, yielding ~5 g of material with high crystallinity and 22% ligand defect. Two methods developed for loading gold nanoparticles onto the MOF. The first uses a double-solvent method to introduce HAuCl4 onto UiO-66(Ce), followed by reduction under 5% H2 in N2, while the second is a novel one-pot method where HAuCl4 is added to the synthesis mixture, forming Au nanoparticles within the pores of the UiO-66(Ce) during crystallisation. Analysis using powder X-ray diffraction (PXRD), nitrogen adsorption isotherms, transmission electron microscopy and small-angle X-ray scattering (SAXS) reveals that the two-step double-solvent method yields gold crystallites on the external surface of the MOF particles that are visible by PXRD. In contrast, the one-pot method forms smaller gold crystallites, with a distribution of sizes centred on ~4 nm diameter as seen by SAXS, with evidence from PXRD for the smallest particles being present within the MOF structure. The Au-loaded UiO-66(Ce) materials are evaluated for the catalytic oxidation of vanillyl alcohol to vanillin at 60 °C. Our findings indicate that incorporating Au nanoparticles via the one-pot synthesis method, enhances redox activity, achieving 43% conversion and 90% selectivity towards vanillin.

Investigation into the role of MoS2 in the composite of Cu-Cu2O/MoS2 in catalytic aerobic oxidation of benzylic alcohols

Cuprous oxide (Cu2O), as a common transition metal semiconductor material, has found extensive applications and research in the field of catalysis due to its unique physicochemical properties. To improve its catalytic performance, introducing carriers to form composite materials with Cu2O has proven to be a promising strategy for enhancing its stability, activity, and selectivity. In this study, we introduced MoS2 to form a composite material with Cu-Cu2O, investigating the impact of MoS2 on the activity of Cu-Cu2O in selective alcohol oxidation. The results demonstrate a significant improvement in the catalytic activity of Cu-Cu2O upon the introduction of MoS2. Further investigations substantiate the close correlation between the enhanced activity of Cu-Cu2O and the interaction with thin layered MoS2 flakes. The quantity of the thin layered MoS2 is small but its impact on the catalytic activity is significant. It induces changes in the band and electronic structures of Cu-Cu2O, and the changes facilitate the activation of O2 and electron transfer in the oxidation, and thus promote the catalysis.

Sub-nanometric ruthenium clusters prepared by solid-state dispersion for catalytic selective aerobic oxidation of aromatic alcohols

The selective aerobic oxidation of alcohols to corresponding aldehydes is one of the most important challenges in the green chemical industry. In this work, Ru/Al2O3-SSD catalyst with highly dispersed metallic ruthenium clusters (average particle size of 0.97 nm) was prepared by solid-state dispersion (SSD) for efficient selective aerobic oxidation of aromatic alcohols to aldehydes. Compared with the counterpart catalyst Ru/Al2O3-IM prepared by wet impregnation (IM), this catalyst has smaller metal particles (0.97 nm vs. 3.4 nm), resulting in a special electronic structure, and exhibits much higher TOF (234 h−1 vs. 98 h−1) in the aerobic oxidation reaction of benzyl alcohol at 80 °C. The catalyst also shows excellent catalytic activity in the preparation of vanillin by selective aerobic oxidation of vanillyl alcohol at 100 °C, delivering a vanillin yield of 99%. The solid-state dispersion strategy provides an efficient and facile way for the fabrication of high-performance sub-nanometric metal catalysts.

Catalytic oxidation of alcohols catalyzed by gold-coated iron oxide magnetic nanoparticles in water

Catalytic oxidation of alcohols catalyzed by gold-coated iron oxide magnetic nanoparticles in water

A broad-spectrum oxidation capability Ru-CeO2 catalyst for efficient synergistic selective oxidation of benzyl alcohol

Selective oxidation of alcohols to aldehydes by molecular oxygen is one of the most important transformations in multiphase catalysis. In this paper, a catalyst with selective oxidation ability was designed and synthesized for the selective catalytic oxidation of benzyl alcohol. N-doped carbon materials were prepared by high-temperature calcination using hydrothermal reaction products of citric acid and melamine as a carbon source, and a bimetallic catalyst supported by Ru-CeO2 was constructed using the mixture as the carrier for the selective oxidation of benzyl alcohol to benzaldehyde. The results showed that the introduction of CeO2 could effectively improve the oxidizing ability and catalytic activity of the catalyst. The Ru-Ce0.05/NC170–600 catalyst was able to convert 85.5 % benzyl alcohol into benzaldehyde at 140 °C, 6 h, and 2 MPa, and the selectivity for benzaldehyde was 100 %. It was demonstrated by DFT that it was theoretically feasible to generate benzaldehyde by extracting hydrogen atoms from benzyl alcohol molecules. Further, the selective oxidation experiments on other alcohols showed that the catalyst has high activity for the oxidation of various alcohols to generate the corresponding carbonyl products, and it is a catalyst with broad-spectrum selective oxidation ability. In this study, a green synthesis route of benzaldehyde was proposed to solve the problems in the traditional process. Meanwhile, it provides a new idea for the synthesis of carbonyl products by selective oxidation of alcohols.

Enhanced electrocatalytic biomass oxidation at low voltage by Ni2+-O-Pd interfaces

Challenges in direct catalytic oxidation of biomass-derived aldehyde and alcohol into acid with high activity and selectivity hinder the widespread biomass application. Herein, we demonstrate that a Pd/Ni(OH)2 catalyst with abundant Ni2+-O-Pd interfaces allows electrooxidation of 5-hydroxymethylfurfural to 2, 5-furandicarboxylic acid with a selectivity near 100 % and 2, 5-furandicarboxylic acid yield of 97.3% at 0.6 volts (versus a reversible hydrogen electrode) in 1 M KOH electrolyte under ambient conditions. The rate-determining step of the intermediate oxidation of 5-hydroxymethyl-2-furancarboxylic acid is promoted by the increased OH species and low C–H activation energy barrier at Ni2+-O-Pd interfaces. Further, the Ni2+-O-Pd interfaces prevent the agglomeration of Pd nanoparticles during the reaction, greatly improving the stability of the catalyst. In this work, Pd/Ni(OH)2 catalyst can achieve 100% 5-hydroxymethylfurfural conversion and >90% 2, 5-furandicarboxylic acid selectivity in a flow-cell and work stably over 200 h under a fixed cell voltage of 0.85 V.

Non-hydroxyl radical dominated catalytic oxidation of lignin-derived vanillyl alcohol by H2O2 upon ionic liquids for vanillin production

Oxidative conversion of lignin-derived vanillyl alcohol (VA) into value-added vanillin (VN) represents an important move towards sustainable valorization of lignin resource. However, the oxidation upon hydrogen peroxide often suffers from side reactions like over-oxidation, limiting the reaction efficiency. The key step to enhance VN yield from VA oxidized by H2O2 lies in the generation of selectively active oxidizing species as an alternative to hydroxyl radicals. To this end, we demonstrate a homogeneous oxidation of VA for VN acquisition using H2O2 in ionic liquid (IL) triethylammonium acetate [Et3NH][CH3COO] catalyzed by cobalt (II). The generation of hydroxyl radical was proved to be inhibited by [Et3NH][CH3COO], and the oxidative high valent metal–oxygen complexes Co(IV) = O with higher selectivity might be involved to promote the conversion efficiency upon the coordination of IL anion with cobalt ion. Compared to the oxidation proceed in non-IL system, the IL system contributed to higher reaction efficiency. 11.85 % VN yield was achieved for 81.65 % conversion rate of VA at 60 ℃ for 2 h in atmosphere with the addition of 0.04 mmol of Co2+ in [Et3NH][CH3COO].

Simultaneously catalytic oxidation of benzyl alcohol to benzaldehyde and selectively phase separation via a sandwich-like polymeric PVDF membrane

It is of significance to improve the interfacial catalytic performance of noble metal nanocatalysts in heterogeneous reactions and to achieve real-time oil-water phase separation to reduce the separation and purification process. In the current work, a sandwich-like polymeric membrane was prepared, with a core layer of poly(vinylidene fluoride) (PVDF)/poly(methacrylic acid) (PMAA) microspheres/Pd nanoparticles as the reaction center, and a hydrophilic semi-interpenetrating polymer network (semi-IPN) as well as a hydrophobic PVDF as shells for the benzaldehyde green preparation. The process proceeded by using the sandwich-like membrane to catalyze the interface reaction between the organic phase of benzyl alcohol and the aqueous phase of H2O2 and the effect factors such as reaction temperature, feed flow rate, the initial benzyl alcohol concentration and catalyst dosage were investigated to get the optimal oxidation conversion and selectivity. Results indicated that the interface reaction went well, without the aggregation and leaching of Pd nanoparticles from membrane support. Furthermore, the product benzaldehyde could be selectively transported to the organic phase. The sandwich-like catalytic composite membrane integrates the catalysis with phase separation, providing a new strategy for the preparation of the chloride-free benzaldehyde. What's more, the sandwich-like catalytic membrane acts as an ideal option for a large-scale catalysis application with integrated advantages of high activity, convenient operation and omitted separation of catalysts and products from heterogeneous catalytic interfacial reaction system.

Efficient Visible‐Light‐Driven Aromatic Alcohol Oxidation Using PI‐TiO2 Composite Photocatalyst

AbstractSynthesizing fine chemicals and valuable pharmaceutical intermediates through selective catalytic oxidation of alcohols is indispensable and crucial. However, the conventional methods of alcohol oxidation have inevitable drawbacks, including harsh reaction conditions and environmental pollution. Thus, it is imperative to develop efficient catalytic oxidation systems for alcohols. Herein, we successfully synthesized a 15 wt %PI‐TiO2 composite by a one‐step solid‐state heating polymerization technique. This catalyst exhibits excellent responsiveness to visible light and demonstrates remarkable catalytic activity. Furthermore, TEMPO was introduced as a cocatalyst to construct a PI‐TiO2/TEMPO/O2 system for the catalytic oxidation of alcohols. In comparison to the individual effects of PI or TiO2, this system showcases improved catalytic activity and broader substrate applicability. As a result, the conversion efficiency of benzyl alcohol increases by 3.44 times and 2.26 times, respectively. This research not only introduces a novel approach for preparing visible light‐active PI‐TiO2 catalysts but also indicates the significance of establishing an efficient electron transfer process in alcohol catalytic oxidation.

Facile preparation and catalytic property of a sandwich composite membrane

Membrane as a support for metal nanocatalysts, can greatly enhance the catalytic activity of metal nanoparticles and promote the efficient production and separation of products. In this study, a novel sandwich-structured composite membrane was designed and facilely fabricated by using palladium nanocatalysts as the core catalytic layer and two different structured PVDF layers as the outer layers. The composite membrane was used as a reaction interface as well as a separation barrier between reactants and products, efficiently realizing the catalytic oxidation of benzyl alcohol and convenient separation of the product benzaldehyde. The membrane was characterized in detailed and the effects of the membrane structure and various reaction conditions on the catalytic oxidation were systematically investigated. The results indicated that the reaction could be conveniently carried out under very mild experimental conditions, obtaining the product benzaldehyde at as high selectivity as 93.17 %. The successful implementation of the sandwich membrane for the production of chlorine-free benzaldehyde provides a new method for the interface reaction.

Catalytic oxidation of lignin model non-phenolic monomer Veratryl alcohol over iron containing mesoporous SBA-1

Catalytic oxidation of lignin model non-phenolic monomer Veratryl alcohol over iron containing mesoporous SBA-1

Catalytic oxidation of alcohols to aldehydes and ketones with ferric nitrate nonahydrate/trifluoroacetic acid via mechanochemical reaction

Benzylic alcohols and secondary aliphatic alcohols were readily converted into aldehydes and ketones with ferric nitrate nonahydrate/trifluoroacetic acid under ball milling. This method takes advantages of fast, effective, the use of cheap and readily available reagents and broad functional group compatibility.

Nitrogen-Doped Porous Carbon Derived from Covalent Triazine Framework for Catalytic Oxidation of Benzyl Alcohol.

The catalytic oxidation of alcohols is an important transformation in the chemical industry. Carbon materials with a large surface area and N doping show great promise as metal-free catalysts for the reaction. In this study, a rich N-containing covalent triazine framework polymerized by cyanuric chloride and p-phenylenediamine was used to synthesize N-doped porous carbon with the assistance of a pore-forming agent-NaCl. First, the mass ratio of the polymer/NaCl was optimized to 1:9. Then, the influence of the pyrolysis temperatures (700-1000 °C) on the materials was studied in detail. It was found that the carbon materials were gradually exfoliated by molten salt at high temperatures. XRD and Raman characterizations showed them with a certain graphitization. The optimal doped carbon CNN-1-9-900 achieved the highest surface area of 199.03 m2g-1 with the largest pore volume of 0.29 cm3g-1. Furthermore, it had a high N content of 9.9 at% with the highest relative proportion of pyridinic/graphitic N. Due to the synergistic effect between the surface area and pyridinic/graphitic N, CNN-1-9-900 showed the best performance for benzyl alcohol oxidation with TBHP at moderate conditions, and the process also worked for its derivatives.

A new perspective for palladium(II)-catalyzed alcohol oxidation in aerobic means

The development of alternative and environmentally safe routes for the oxidation of primary and secondary alcohols has attracted the attention of several researchers due to the importance of these oxidized products in industries. Thereby, the oxidation of β-citronellol, geraniol, nerol, borneol, isoborneol, cinnamic alcohol, and benzyl alcohol is described herein. These reactions occurred in an aerobic environment, with or without system pressurization. Acetonitrile was the solvent used. The process was catalyzed by the bimetallic complex formed with palladium(II) acetate and copper(II) acetate, using p-benzoquinone as a cocatalyst in some reaction conditions. The applied system obtained 62.5 points on the eco-scale, with yields above 61%. Alcohol oxidation products are of great importance in industrial applications. Thus, this work presents a cleaner, more sustainable alternative to alcohol oxidations.

Selective direct oxidation of 1-butanol into acetal using hydrogen peroxide and Cs5MPW11(H2O)O39 (M=Fe, Co, Cu) catalysts.

Direct catalytic oxidation of alcohols to acetals in one step process is very attractive, because the two steps process leads firstly to aldehydes, which are unstable species serving as reactive intermediates to generate several by-products reducing process efficiency and selectivity. In this work, a new selective catalytic acetalization of 1-butanol into 1-1-dibutoxybutane acetal using H2O2 in one step process is investigated using Keggin-type polyoxometalates catalysts. The materials developed consisted of new lacunary phophotungstate salts Cs5MPW11(H2O)O39 (M=Fe, Co and Cu) which were prepared by inorganic solution condensation method and characterized using XRD, IR, SEM and EDX analysis to verify their structure, surface morphology and chemical composition. Cs5CuPW11(H2O)O39 catalyst allowed the highest performance for the oxidation of 1-butanol at 60 °C using H2O2 excess with a yield approaching 92 % and a turnover number of 784. Such activity is related to a bifunctional behavior of the catalyst as superacid and redox operating system and the synergistic effect created between the [PW11O39]7- Keggin framework, Cs+ and Cu2+.

Operando film-electrochemical EPR spectroscopy tracks radical intermediates in surface-immobilized catalysts

The development of surface-immobilized molecular redox catalysts is an emerging research field with promising applications in sustainable chemistry. In electrocatalysis, paramagnetic species are often key intermediates in the mechanistic cycle but are inherently difficult to detect and follow by conventional in situ techniques. We report a new method, operando film-electrochemical electron paramagnetic resonance spectroscopy (FE-EPR), which enables mechanistic studies of surface-immobilized electrocatalysts. This technique enables radicals formed during redox reactions to be followed in real time under flow conditions, at room temperature and in aqueous solution. Detailed insight into surface-immobilized catalysts, as exemplified here through alcohol oxidation catalysis by a surface-immobilized nitroxide, is possible by detecting active-site paramagnetic species sensitively and quantitatively operando, thereby enabling resolution of the reaction kinetics. Our finding that the surface electron-transfer rate, which is of the same order of magnitude as the rate of catalysis (accessible from operando FE-EPR), limits catalytic efficiency has implications for the future design of better surface-immobilized catalysts.

Insight into the promotional effect of Ce doped in (FeCoNiCrMn)3O4 high entropy oxides for solvent-free aerobic oxidation of benzyl alcohol

It is desired but challenging to develop a non-noble metal catalyst for the selective oxidation of benzyl alcohol with O2 under solvent-free conditions. Herein, a series of Ce-doped high entropy oxides (Ce/HEOs) were prepared via co-precipitation and subsequent thermal treatment method. It was found that, the doping of Ce could remarkably promote the catalytic activity for selective oxidation of benzyl alcohol to benzaldehyde. The improved activity was ascribed to the good distribution of active Ce species, the increased oxygen vacancies, and the synergistic effect between CeO2 and high entropy oxides (HEOs). In addition, the surface oxygen of Ce/HEOs towards Ce displayed stronger reducibility compared to that of bare CeO2, endowing it stronger deprotonation ability towards benzyl alcohol during the reaction. The prepared catalyst exhibited satisfactory reusability and stability owing to the entropy-stabilized effect of HEOs and the interaction between CeO2 and HEOs, and negligible loss in catalytic activity was observed after seven runs. Besides, DFT calculations disclosed that, with the doping of Ce, the Ce/HEOs catalyst possessed stronger adsorption ability towards benzyl alcohol, and lower free energy was required for the rate-determining step during the whole oxidative reaction. This work gave some insights into the promotional effect of Ce doped into high entropy oxides for the solvent-free catalytic oxidation of benzyl alcohol.

Mesoporous silica-supported Ni–Co composite metal oxide as a heterogeneous catalyst for air oxidation of benzyl alcohols

A mesoporous silica-supported Ni–Co composite metal oxide has been synthesized and applied as an effective heterogeneous catalyst for the selective catalytic oxidation of benzyl alcohols. Various characterization methods were employed to confirm the successful synthesis of the catalysts and their nanostructure. The catalytic performances of these catalysts in the selective oxidation of substituted benzyl alcohols to aromatic aldehydes were systematically investigated using molecular oxygen from the air as the oxidant under atmospheric pressure. The NiCo@SBA-15 catalyst exhibited remarkable performance, achieving nearly 98 % conversion and almost complete selectivity at a temperature of 120 °C for 10 h, operating at 1 atm of air pressure. This catalytic performance can be attributed to the synergistic effect between Ni and Co ions, resulting in the generation of new surface-active sites in the catalyst. The catalyst also demonstrated favorable applicability and universality. Moreover, A plausible catalytic mechanism has been proposed involving the synergistic effect between bimetal species and oxygen vacancy.

Catalytic aerobic oxidation of lignin-based vanillyl alcohol over LaFeO3 perovskite towards vanillin production: Relationships between the activity and acid-base property as well as oxygen vacancy

Developing high-performance acid-base catalysis over perovskite for alcohol aerobic oxidation has received increasing attention, but the fundamental understanding of its surface acid-base property and performance relationship remains largely unknown. Accordingly, a series of LaFeO3 perovskites were fabricated via modified Pechini approach with the addition of different chelating agents to modulate their respective acid-base amount and oxygen vacancy concentration, which subsequently were employed in the aerobic oxidation of vanillyl alcohol (a lignin model), to generate vanillin for elucidating the relationships between the catalytic activity of LaFeO3 perovskite and its acid-base property as well as oxygen vacancy. The results demonstrated that existence of non-linear relationships between the vanillin yield and the acid-base amount as well as oxygen vacancy concentration of LaFeO3 catalyst. Moreover, neither acid-base sites nor oxygen vacancies were the solely factors affecting the activity of LaFeO3 perovskite towards vanillyl alcohol oxidation for vanillin production. Mechanism studies proclaimed that the reactive oxygen species derived from the adsorption of molecule oxygen on oxygen vacancies generated by anion defects combing with Lewis acid sites (Fe3+/Fe2+) to yield FeOx active pairs, which jointly dominated the pathway for vanillyl alcohol oxidation to produce vanillin. Overall, this work offers guidance for designing effective perovskite-based catalysts for lignin conversion to produce value-added chemicals by selectively modulating its acid-base property and oxygen vacancy.