Catalyst For Oxidation Of Alcohols Research Articles

One-pot synthesis of 3D surface-wrinkled PdAu nanospheres for robust alcohols electrocatalysis

Three dimensional (3D) noble-metal nanomaterials with special surface structures have been regarded as high-performance catalysts for alcohol oxidation on account of their superior thermal stability, electrical conductivity and large specific surface area. Although extensive efforts have been devoted to the preparation of 3D Pd-based catalysts with superior activity and stability, designing a simple, effective and eco-friendly method remains a challenge. Herein, we developed a facile one-step coreduction strategy to synthesize a series of 3D surface-wrinkled PdAu nanospheres (NSs) with tunable Pd/Au atomic ratios and found a universal method to prepare surface-wrinkled PdM (M = Au, Pt, Cu and Pb) NSs. Benefiting from the function of the surfactant cetyltrimethylammonium chloride (CTAC), the synthesized PdAu NSs with different composition possess abundant surface wrinkles, which is beneficial for exposing more electroactive centers. Attributed to the unique geometric morphology and optimized atomic ratio, the PdAu-2 NSs exhibited an optimal mass activity (MA) of 8103 mA mg−1 and 5113 mA mg−1 for the ethylene glycol oxidation reaction (EGOR) and ethanol oxidation reaction (EOR), which was 6.1 and 4.1 times that of commercial Pd/C, respectively. Moreover, the PdAu-2 NSs exhibited superb stability after long-term current–time (i-t) and cyclic voltammetry (CV) tests of the EGOR and EOR. This work not only provides new avenues to engineer PdAu NSs with enhanced electrocatalytic performance but also offers guidance for extending to more 3D PdM (M = other metals) NSs with novel morphology applied to fuel cell fields.

Metal-Support Interaction in Gold Zeolitic Octahedral Metal Oxide and the Catalytic Activity for Low-Temperature Alcohol Oxidation.

Au nanoparticles are efficient catalysts for selective oxidations. The interaction between Au nanoparticles and supports is critical for achieving high catalytic activity. Herein, Au nanoparticles are supported on a zeolitic octahedral metal oxide based on Mo and V. The charge of Au is controlled by the surface oxygen vacancies of the supports, and the redox property of the zeolitic vanadomolybdate is highly dependent on Au loading. The Au-supported zeolitic vanadomolybdate is used as a heterogeneous catalyst for alcohol oxidation under mild conditions with molecular oxygen as an oxidant. The supported Au catalyst can be recovered and reused without the loss of activity.

Mononuclear Cu-complex embedded ordered nano-porous silica based hybrid catalyst for oxidation of benzyl alcohol

A novel mixed ligand copper (׀׀) complex having 2,9-dimethyl-1,10-phenanthroline and nitrate has been successfully synthesized and characterized by single crystal XRD. Following synthesis, this complex was anchored on acid functionalized nano-porous materials such as MCM-41-SO3H and SBA-15-SO3H, and these hybrid materials were characterized using a variety of techniques such as FT-IR, PXRD, BET, SEM, TG, and so on. These modified mesoporous materials (MCM-41-SO3HCu and SBA-15-SO3HCu) were subjected to solvent-free selective benzyl alcohol oxidation with TBHP (Tert-Butyl Hydroperoxide) as an oxidant. Various reaction parameters were investigated to optimize the reaction conditions. MCM-41-SO3HCu was discovered to be an excellent catalyst in terms of benzyl alcohol conversion and benzaldehyde selectivity.

Ti doped CeO2 nanosheets supported Pd catalyst for alcohol oxidation: Catalysis of interfacial sites

AbstractThe oxidation of alcohols is a significant chemical reaction, and the efficient oxidation of alcohols over heterogeneous catalysts using oxygen as oxidant has attracted much attention in recent years. Among them, Pd/CeO2 exhibits excellent alcohol oxidation performance. However, the structure-activity relationship between the catalyst's structure and its catalytic performance for alcohol oxidation is still not clearly understood. This study involved the preparation of CeO2 nanosheets with different concentrations of surface oxygen vacancies (Ov) and their subsequent loading with Pd to explore their catalytic performance for alcohol oxidation. The findings obtained through XPS, Raman, and XAS indicated a positive correlation between the surface Ov concentration of CeO2 as well as the ratio of Pd2+ fraction. The alcohol oxidation results and structure-performance relationship studies showed that there was a good linear relationship between the Pd2+ ratio as well as the surface Ce3+ concentration and the TOF of benzyl alcohol oxidation reaction, respectively. And the interfacial site (Pd–O–Ce) formed by Pd and CeO2 was the main catalytic site for this type of alcohol oxidation catalysts. This study contributes to the understanding of the catalytic role of interfacial sites in metal and oxide support for the development of better alcohol oxidation catalysts.

Nanoflower core-shell Cu@Pd catalysts for glycol oxidation reaction with an enhanced performance

Direct alcohol fuel cells' performance is significantly affected by the phase and composition of the catalyst, thereby the development of high-performance alcohol oxidation catalysts is essential. In this study, PVA preparation was used for the first time to create PdCu core-shell nanoflowers with a high electrochemically active surface area and a potent synergistic effect. Notably, the presence of PVA causes Pd and Cu nanoparticles with different reduction rates to form a core-shell structure, and the Pd nanoparticles continue to migrate regularly under the action of PVA, forming a flower-like morphology with a high degree of branching. Cu@Pd22.3 catalyst exhibited 13 times higher catalytic performance (4353.04 mA mgPd−1) than Pd/C (334.09 mA mgPd−1) in ethylene glycol oxidation reaction. The Cu@Pd22.3 catalyst also exhibits higher stability than commercial Pd/C in stability tests lasting up to 20,000 s. This core-shell combination and highly branched structural design result in more active sites for fast ion adsorption/desorption,offering an original method to improving the activity and endurance of polyol oxidation.

Iron-palladium supported graphene as an efficient bimetallic catalyst for the selective oxidation of benzyl alcohol to benzaldehyde

The catalytic oxidation of benzyl alcohol (OBA) is one of the significant methods to produce benzaldehyde, an essential reagent in the chemical and pharmaceutical industries. However, developing an active and efficient catalyst for OBA is a tremendous challenge in commercialization. This research describes a simple, eco-friendly method for producing Fe, Pd, and Fe: Pd bimetallic nanoparticles fabricated by sol immobilization over graphene to conduct OBA. The resulting composite nano-alloys were then characterized using X-ray diffraction (XRD), Fourier transforms infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM). The oxidation state and elemental composition of as-fabricated nanoparticles were analyzed using XPS. The point of zero charges (pHPZC) was analyzed and the PZC value indicated that the proposed adsorbent material tends to have a positive charge. The OBA reaction efficiency (87%) of bimetallic nanocatalysts stabilized in graphene support was increased through surface modification of the ratio of both metals. The experimental error was based on three parallel tests and the carbon balance (99.6%) was analyzed during the experiments A proposed reaction mechanism of OBA validated the β-hydride step's elimination by molecular oxygen converting the metal hydride into a water molecule, forming a peroxide intermediate to form water and oxygen molecules. The Fe on the nanocatalyst’s surface is preferentially responsible for the adsorption of the substrate molecule, resulting in the formation of metal-alkoxide. Since it lacks electrons, Fe is more likely to be oxidized, allowing it to perform better than monometallic catalysts in terms of catalytic activity. The present study has great potential to be applied on an industrial scale and studied for industrialists, researchers, and academicians.

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.