Catalyst For Oxidation Of Alcohols Research Articles

Facile synthesis of CoSi alloy catalysts with rich vacancies for base- and solvent-free aerobic oxidation of aromatic alcohols

The rational design and green synthesis of low-cost, robust, and efficient catalysts for the selective oxidation of various alcohols are highly challenging. Herein, we report a fast and solvent-free arc-melting (AM) method to controllably synthesize a semimetallic CoSi alloy catalyst (denoted as AM-CoSi) that is efficient in the base- and solvent-free oxidation of six types of aromatic alcohols. X-ray absorption fine structure analysis, electron paramagnetic resonance spectroscopy, and aberration-corrected high angle annular dark field scanning transmission electron microscopy confirmed the successful synthesis of AM-CoSi with abundant Si vacancies (Siv). The as-prepared CoSi alloy catalysts exhibit an order of magnitude greater activity in the oxidation of a model reactant, benzyl alcohol (BAL) to benzyl benzoate (BBE), compared with their mono-counterparts, and provide 70% yield of BBE, the highest yield reported to date. Experimental results and density functional theory calculations suggest that the CoSi alloy structure improves the BAL conversion and that Si vacancy is the main contributor to the generation of BBE, based on which a potential reaction pathway is rationally proposed. Furthermore, the CoSi alloy maintains high stability and also exhibits high activity in the selective oxidation of various alcohols with different functional groups. This work demonstrates for the first time that semimetallic CoSi alloys can be robust catalysts for the green oxidation of various alcohols and proviedes a vast opportunity for the rational design and application of other semimetal alloy catalysts.

Studies on Catalytic and in Vitro Cytotoxicity Effects of ZnO Nanorods Containing Ag and Their Structural, Morphological, and Antimicrobial Properties

Zinc oxide (ZnO) and Ag-doped ZnO nanoparticles were synthesized using a soft chemical route, and their properties were characterized using various techniques, including X-ray diffraction (XRD), high-resolution scanning electron microscope (HRSEM), energy dispersive X-ray diffraction spectroscopy (EDS), and high-resolution transmission electron microscope (HRTEM). The ZnO (Ag[Formula: see text]Zn[Formula: see text]O (where [Formula: see text], 0.02 and 0.03) exhibited a hexagonal Wurtzite structure, and Ag doping resulted in the formation of nanorods with decreased grain size. The synthesized materials were found to have antimicrobial properties against human pathogenic bacteria and fungi. MTT assays showed that Ag-doped ZnO had higher cytotoxicity against human embryonic kidney cancer cell lines (HEK 293) compared to pure ZnO. The samples also demonstrated active activity towards the catalyst for the selective oxidation of alcohols. Finally, a statistical model was developed for antibacterial studies using ANOVA, which was consistent with the experimental findings. These results demonstrate the potential of Ag-doped ZnO nanoparticles for use in biomedical and catalytic applications.

Nanocrystal Facet Effects of Ceria in Pd/CeO2 Catalysts for Oxidation of Benzyl Alcohols

Key words ceria - palladium nanoparticles - oxidation - benzyl alcohols - benzaldehydes

Ruthenium(III) Chloride as an Efficient Catalyst for the Selective Oxidation of Fatty Alcohols to Aldehydes

AbstractThe oxidation of a series of fatty alcohols to yield the corresponding aldehydes is performed using RuCl3 ⋅ (H2O)x as a homogeneous catalyst and inexpensive trimethylamine N‐oxide (TMAO) as the oxygen source. The reaction conditions were optimized for both high conversion and high selectivity.

Partially Thiolated Au25 Cluster Anchored on Carbon Support via Noncovalent Ligand–Support Interactions: Active and Robust Catalyst for Aerobic Oxidation of Alcohols

Partially thiolated atomically precise Au cluster catalysts were developed by controlled calcination of presynthesized thiolate-protected Au clusters on a porous carbon support. X-ray absorption fine structure analysis, powder X-ray diffraction, and aberration-corrected high-angle annular dark field scanning transmission electron microscopy revealed that calcination of 1 wt % of Au25(SR)18 (RS = 2-phenylethanethiolate, 1-dodecanethiolate) on carbon at 450 °C for 8–12 h produced partially thiolated Au25 clusters Au25(SR)/C without sintering. The Au25(SR)/C catalyst exhibited comparable catalytic activity to that of the thiolate-free Au25 cluster Au25/C for benzyl alcohol oxidation, whereas Au25(SR)/C showed higher durability than Au25/C. These results suggested that the residual RS ligands were distributed at the interface between the clusters and the support and suppressed the diffusion of the clusters by multiple van der Waals interactions. Large kinetic isotope effects indicated that the hydride abstraction from the α-carbon of the alkoxide was the rate-determining step. The O2 pressure dependence on rate constants was comparable to that reported for negatively charged Au clusters stabilized by poly(N-vinyl-2-pyrrolidone). This comparison suggests that electron-rich Au atoms left behind by desorbed RS served as active sites, which was supported by density functional theory calculations on model clusters. The partially thiolated Au25 cluster catalysts oxidized various p-substituted benzyl alcohols and benzylic secondary alcohols, with turn-over numbers exceeding 1 × 104. This work demonstrates that partially ligated, atomically precise metal clusters anchored by noncovalent ligand–support interaction are promising model catalysts with both high activity and durability.

Identification of the Optimal Framework for Nitroxyl Radical/Hydroxylamine in Copper-Cocatalyzed Aerobic Alcohol Oxidation

8-Azabicyclo[3.2.1]octan-8-ol (ABOOL) and 7-azabicyclo[2.2.1]heptan-7-ol (ABHOL) are the main homologues of hydroxylamine 2-azaadamantan-2-ol (AZADOL) and 9-azabicyclo[3.3.1]nonan-9-ol. Both homologues feature a small bicyclic backbone and are known to be stable; however, to date, they have not been used as catalysts for alcohol oxidation. Herein, we report that these hydroxylamines can efficiently catalyze the oxidation of various secondary alcohols to their corresponding ketones using molecular oxygen in ambient air as the terminal oxidant and copper cocatalysts at room temperature. Furthermore, we show that ABOOL and ABHOL can be easily synthesized from commercially available materials.

Mechanism-Guided Design of Robust Palladium Catalysts for Selective Aerobic Oxidation of Polyols

The palladium complex [(L1)Pd(μ-OAc)]2[OTf]2 (L1 = neocuproine) is a selective catalyst for the aerobic oxidation of vicinal polyols to α-hydroxyketones, but competitive oxidation of the ligand methyl groups limits the turnover number and necessitates high Pd loadings. Replacement of the neocuproine ligand with 2,2'-biquinoline ligands was investigated as a strategy to improve catalyst performance and explore the relationship between ligand structure and reactivity. Evaluation of [(L2)Pd(μ-OAc)]2[OTf]2 (L2 = 2,2'-biquinoline) as a catalyst for aerobic alcohol oxidation revealed a threefold enhancement in turnover number relative to the neocuproine congener, but a much slower rate. Mechanistic studies indicated that the slow rates observed with L2 were a consequence of precipitation of an insoluble trinuclear palladium species─(L2Pd)3(μ-O)22+─formed during catalysis and characterized by high-resolution electrospray ionization mass spectrometry. Density functional theory was used to predict that a sterically modified biquinoline ligand, L3 = 7,7'-di-tert-butyl-2,2'-biquinoline, would disfavor the formation of the trinuclear (LPd)3(μ-O)22+ species. This design strategy was validated as catalytic aerobic oxidation with [(L3)Pd(μ-OAc)]2[OTf]2 is both robust and rapid, marrying the kinetics of the parent L1-supported system with the high aerobic turnover numbers of the L2-supported system. Changes in ligand structure were also found to modulate regioselectivity in the oxidation of complex glycoside substrates, providing new insights into structure-selectivity relationships with this class of catalysts.

Additive-free selective oxidation of aromatic alcohols with molecular oxygen catalyzed by a mixed-valence polyoxovanadate-based metal-organic framework.

Selective oxidation of alcohols to aldehydes is an industrially significant chemical transformation. Herein, we report a mixed-valence polyoxovanadate-based metal-organic framework (MOF), (H2bix)5{[Cd(bix)2][VIV8VV7O36Cl]2}·3H2O (V-Cd-MOF), for catalyzing the additive-free oxidation of a series of aromatic alcohols with high selectivity and in nearly quantitative yield to the corresponding aldehydes with O2 as the oxidant. Experimental results, corroborated with density functional theory calculations, indicate that it is the synergistic operation of the dual active sites of the VIV-O-VV building units in the polyoxovanadate cluster that is responsible for the excellent catalytic performance observed: on the one hand, the exposed and readily accessible reduced VIV site is believed to activate O2, resulting in a reactive oxygen species for the subsequent activation and breaking of the substrate's Cα-H bond. On the other hand, the VV site coordinates with the alcoholic O atom to facilitate the cleavage of the O-H bond. The catalyst can be recycled by centrifugation and re-used at least five times with uncompromised performance. To our knowledge, V-Cd-MOF represents the first example of a polyoxometalate-based MOF catalyst for additive-free selective oxidation of alcohol to aldehyde with O2 as an oxidant.

An Fe·MOF–Mo·POM hybrid material: a novel and efficient catalyst for selective benzyl alcohol oxidation to benzaldehyde

Designing and synthesis of an efficient catalyst for the selective oxidation of benzyl alcohol (BzOH) to benzaldehyde (BzCHO) is a significant method in green chemistry and catalysis.

Ultrasonic irradiation-assisted MnFe2O4 nanoparticles catalyzed solvent-free selective oxidation of benzyl alcohol to benzaldehyde at room temperature.

Magnetic nanoparticles (NPs) play a vital role in heterogeneous catalysis because of their easy separation, and effective recyclability. Herein, we report the synthesis of MnFe2O4 NPs for use as catalysts in the selective oxidation of benzyl alcohol to benzaldehyde under mild conditions. The MnFe2O4 NPs have been synthesized by precipitation method followed by hydrothermal ageing at 180 °C for 4.0 h. We have investigated the effect of chitosan and carboxymethyl cellulose on the size or morphology of the formed MnFe2O4 NPs. The X-ray diffraction study confirms the formation of pure and crystalline MnFe2O4 with varying average crystallite sizes ranging from 18 to 28 nm based on the type of additive used. The electron microscopy study reveals that the additive plays a significant role in controlling the morphology of the formed MnFe2O4 NPs. These MnFe2O4 NPs exhibit superparamagnetic behaviour at room temperature and can effectively catalyze the solvent-free selective oxidation of benzyl alcohol to benzaldehyde in the presence of tert-butyl hydroperoxide at room temperature under ultrasonic irradiation. The developed protocol can be extended to various substituted benzyl alcohols having both the electron withdrawing and electron donating groups to afford moderate to excellent yield of the products. The catalyst is magnetically retrievable, highly stable, and can be reused up to the sixth run without significant loss of catalytic activity.

Unsymmetric bi-functional Mn-salen complex bearing TEMPO and Mn-complex for the synthesis of magnetic Mn/TEMPO-doped Fe3O4 NPs: a simple catalyst (magnetic oxidant) for selective oxidation of alcohols

Unsymmetric bi-functional Mn-salen complex bearing TEMPO and Mn-complex for the synthesis of magnetic Mn/TEMPO-doped Fe3O4 NPs: a simple catalyst (magnetic oxidant) for selective oxidation of alcohols

4-Amino-TEMPO-Immobilized Polymer Monolith: Preparations, and Recycling Performance of Catalyst for Alcohol Oxidation.

Continuous flow reactors with immobilized catalysts are in great demand in various industries, to achieve easy separation, regeneration, and recycling of catalysts from products. Oxidation of alcohols with 4-amino-TEMPO-immobilized monolith catalyst was investigated in batch and continuous flow systems. The polymer monoliths were prepared by polymerization-induced phase separation using styrene derivatives, and 4-amino-TEMPO was immobilized on the polymer monolith with a flow reaction. The prepared 4-amino-TEMPO-immobilized monoliths showed high permeability, due to their high porosity. In batch oxidation, the reaction rate of 4-amino-TEMPO-immobilized monolith varied with stirring. In flow oxidation, the eluent permeated without clogging, and efficient flow oxidation was possible with residence times of 2-8 min. In the recycling test of the flow oxidation reaction, the catalyst could be used at least six times without catalyst deactivation.

Selective oxidation of benzyl alcohols by silica‐supported heterogeneous catalyst containing dioxidotungsten(VI) core

A dioxidotungsten(VI) complex, [WO2L(CH3OH)]·0.5(CH3OH) (1), was prepared by the reaction of WCl6 and tridentate ONO‐donor Schiff base ligand (H2L) that was obtained from the reaction of 2‐hydroxy‐1‐naphthaldehyde with 4‐aminobenzoic hydrazide. Both H2L and 1 were characterized by various analyses including nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT‐IR) and UV–Vis spectroscopy, and elemental analysis. Single crystal X‐ray analysis was used to determine the crystal structure of the complex, which revealed that there is a free ‐NH2 group in its structure. Therefore, the heterogeneous catalyst was obtained by supporting of 1 on propionyl chloride‐functionalized silica gel. The synthesized supported catalyst (Si‐W) was characterized by diffuse reflectance spectroscopy (DRS), thermogravimetric analysis (TGA), FT‐IR, scanning electron microscope (SEM), X‐ray photoelectron spectroscopy (XPS), energy‐dispersive spectroscopy (EDS), and X‐ray powder diffraction (XRD) analyses. The heterogeneous catalyst (Si‐W) was utilized in the oxidation of benzyl alcohol derivatives with H2O2 under reflux condition at air atmosphere. The effects of the concentration of oxidant, temperature, and the nature of solvent on catalytic performance of the resulting compound were investigated and the results indicated that they have considerable effect on the activity and selectivity of Si‐W. The heterogeneous catalyst was recovered several times and reused for oxidation reaction. The results of various analyses including FT‐IR spectroscopy, SEM, TGA, EDS, and XRD indicated that there are no considerable differences between recovered catalyst and the fresh one. The results show that the synthesized silica supported dioxidotungsten(VI) complex is active and stable catalyst for oxidation of benzylic alcohols and its selectivity depends on the reaction condition.

Modular Synthesis of New Pyrroloquinoline Quinone Derivatives

AbstractPyrroloquinoline quinone (PQQ) is an important cofactor of methanol dehydrogenases and glycose dehydrogenases. In addition, isolated PQQ is used as a central component in sensors and biomimetic complexes. The synthesis of PQQ derivatives is of interest for developing new alcohol oxidation catalysts and redox sensors. This work describes a modular synthesis for derivatives of PQQ bearing methyl and ketone groups instead of carboxylic acid moieties. These modifications reduce the possible coordination sites of PQQ for metal ions outside the protein environment.

Effect of the Potentiostatic and Potentiodynamic Dealloying on the Structure and Chemical Distribution of Ag Atoms in Au-Enriched Nanoparticles

Recently, nanoporous gold (np-Au) prepared by dealloying has emerged as an efficient and durable catalyst for electrochemical oxidation of small alcohols. [1] An additional increase of surface-to-volume ratio by nano-sizing of AuxAg1-x master alloy might improve the catalytic methanol oxidation reaction (MOR). Only few research groups have recently shown that the morphology, structure and elemental distribution of dealloyed nanoparticles (NPs) depend on the various parameters such as initial particle size and composition.[2-4] Starting from AuxAg1-x alloy NPs, it is, however, unclear how the different dealloyed Au-rich NP motifs such as core-shell, hollow or porous NPs and the Ag distribution influence the catalytic MOR performance.In this work, we have investigated the effects of potentiodynamic and potentiostatic dealloying methods on the structure and chemical distribution of the residual Ag atoms for dealloyed Au-rich NPs. First, two size types of Ag-rich AuxAg1-x alloy NPs were prepared by one pot colloidal route and wet impregnation route. Larger Au23Ag77 NPs (size of 77 ± 26 nm) form a homogeneous disordered alloy, while the Au14Ag86 NPs with a size of 12 ± 5 nm show a strong enrichment of Ag atoms at the particle surface, referred to as core-shell arrangement. Subsequently, the as-prepared NPs with two sizes (12 nm and 77 nm) were electrochemically dealloyed using a potentiodynamic (cyclic voltammetry, CV) or potentiostatic (chronoamperometry, CA) method in 0.1 M HClO4. We observed that the CV method leads to the formation of pores inside the initial 77 nm NPs. Very interestingly, high-resolution STEM-EDX shows the appearance of Ag-rich regions near to the pore network of these dealloyed NPs. Unlike, after the dealloying by CV method the initial 12 nm NPs are still dense and solid, forming a thin Au-rich particle shell. After the exposure to air, the internal Ag atoms tend to segregate to the particle surface. In the CA method, we pointed out that the applied anodic potential has a strong influence of the surface diffusion behavior of the remaining Au atoms. Below a critical potential of 1.3 V vs. RHE, the dealloying process is kinetically hindered by the passivation of Au surface atoms. This critical potential in the CA method is strongly different to the critical dissolution potential of Ag atoms for AgxAu1-x NPs obtained from the CV profile (around 1.05 V vs. RHE). However, when the applied potential is larger than the critical potential, e.g. 1.6 V vs. RHE, the difference in the obtained structure and composition of dealloyed 77 nm NPs is negligible between potentiodynamic and potentiostatic approaches. On the other hand, the potentiostatic dealloying at 1.6 V vs. RHE leads to higher surface content of residual Ag for dealloyed NPs with 12 nm compared to potentiodynamic. This increased enrichment of the residual Ag atoms near the particle surface is also supported by XPS.In summary, we correlate the structural parameters (initial particle size, composition/distribution) of dealloyed AgxAu1-x NPs with the electrochemical dealloying methods (potentiostatic vs. potentiodynamic). Tailoring the surface diffusion rate of the Au atoms and the Ag distribution helps to improve the catalytic performance for MOR.

Mesoporous hybrid organosilica for stabilizing Pd nanoparticles and aerobic alcohol oxidation through Pd hydride (Pd–H2) species

The hybrid periodic mesoporous organosilica (PMO) with APTES/DAR Schiff-based precursor 3-aminopropyltriethoxysilane (APTES) and 4,6-diacetylresorcinol (DAR) was synthesized in the presence of a structure-directing agent cetyltrimethylammonium bromide and tetraethoxysilane. Then, Pd (II) ions, as well as Pd nanoparticles, were incorporated inside the pore walls of the synthesized APTES/DAR-PMO. The PMO structure was characterized by HRTEM, FT-IR, TEM, FE-SEM, BET, SEM-EDX, low angle XRD, HADAF-mapping, TGA, and atomic absorption spectroscopy (AAS). Subsequently, the as-fabricated green heterogeneous nanocatalysts (Pd-NPs@APTES/DAR-PMO) was used as effective and sustainable catalysts for the aerobic oxidation of benzylic alcohols into their corresponding aldehydes in pure water A high Pd-NPs@APTES/DAR-PMO-catalyzed conversion level of the primary and secondary alcohols was demonstrated. Furthermore, the environmentally friendly catalyst showed outstanding stability, so that readily separated by centrifugation and reused for seven consecutive cyclic terms with good retention of high catalytic activities.

Heteroployacid on the composite of boehmite and polyionic liquid as a catalyst for alcohol oxidation and tandem alcohol oxidation Knoevenagel condensation reactions

Using boehmite as an available and low-cost natural compound, a bi-functional catalytic composite is prepared through vinyl-functionalization of boehmite, followed by polymerization with the as-prepared bis-vinylimidazolium bromide ionic liquid and supporting of phosphotungstic acid. The catalyst was characterized via ICP, XRD, TGA, FTIR, SEM/EDS and elemental mapping analysis and applied for promoting alcohol oxidation reaction and one-pot tandem alcohol oxidation/Knoevenagel condensation reaction in aqueous media under mild reaction condition. The results indicated high catalytic activity of the catalyst for both reactions. This protocol showed high generality and aliphatic, aromatic and heterocyclic alcohols could be applied as substrates to furnish the corresponding products in high to excellent yields. Furthermore, hot filtration test confirmed true heterogeneous nature of the catalysis. The catalyst could also be recovered readily and reused for at least five runs of the reaction with low loss of the activity and phosphotungstic acid leaching upon each run.

Dual Pd2+ and Pd0 sites on CeO2 for benzyl alcohol selective oxidation

Solvent-free aerobic oxidation of benzyl alcohol is a green approach for synthesizing fine chemicals. Pd-based catalysts are extensively investigated due to their excellent catalytic activity compared to other metal catalysts. Most researchers believe that metallic Pd species (Pd0) provide active centers. However, the critical role of active oxygen and the function of Pd2+ is neglected. Herein, supported Pd clusters on CeO2 (Pd/CeO2) with a stable high Pd2+/(Pd0 + Pd2+) ratio are prepared by atomic layer deposition (ALD). The turnover frequency (TOF) and activity on as-prepared Pd/CeO2 catalysts in solvent-free aerobic oxidation of benzyl alcohol reach 3.50 × 105 h−1 and 1.85 × 105 mol/(molPd·h), respectively, which are much superior to previously reported results. As the Pd loading increases, the TOFs exhibit a volcano relationship with the Pd2+/(Pd0 + Pd2+) ratio, pointing to a dual Pd0 and Pd2+ sites catalyzed mechanism. O2 kinetic isotopic effect and further evidence support a dual-site catalyzed oxygen-promoted β-hydride elimination mechanisms, in which benzyl alcohol is selectively adsorbed to Pd2+ sites and reacts with active oxygen species on nearby Pd0 sites during the reaction.

Porous Heteroatom‐Doped Carbons: Efficient Catalysts for Selective Oxidation of Alcohols by Activated Persulfate

AbstractAldehydes are essential chemicals for industrial feedstock. However, the traditional processes to produce these chemicals face many limitations, such as waste generation, low selectivity, or high cost. Herein, we report the synthesis and characterization of a group of porous heteroatom (P, B or N)‐doped carbons and their use as catalysts for the oxidation of primary alcohols by activating peroxydisulfate. Among the heteroatom‐doped carbons, porous N‐doped carbons pyrolyzed at 700 or 800 °C show the highest activity. Experimental studies were performed suggesting a considerable contribution of a non‐radical oxidation process. Furthermore, N‐doped carbons can act as a catalyst in the oxidation of a large substrate scope of substituted alcohols.

Highly recyclable palladium ion substituted TiO2 as the versatile ligand-free catalyst for the selective oxidation of alcohols and the reduction of nitroarenes

Highly recyclable palladium ion substituted TiO2 as the versatile ligand-free catalyst for the selective oxidation of alcohols and the reduction of nitroarenes