Highly efficient and reusable Cu-MCM-41 catalyst for the Baeyer–Villiger oxidation of cyclohexanone

A series of Cu-MCM-41 with different Cu contents were successfully synthesized by the direct hydrothermal (DHT) method and evaluated in the Baeyer–Villiger oxidation of cyclohexanone, using only 2 molar equiv of benzaldehyde as sacrificial agents. High conversion (99.0%) of cyclohexanone and ε-caprolactone selectivity (100%) were detected over Cu-MCM-41 (23) within 3 h. Various physical–chemical characterizations, including BET, XRD, UV–vis and H₂-TPR, revealed that isolated Cu^2 + species in the MCM-41 framework were responsible for the catalytic activities. This catalyst could be reused for three times without discernible loss in its activity and selectivity.     

Fabrication of Ag/WO3 nanobars for Baeyer–Villiger oxidation using hydrogen peroxide

We report the preparation of Ag/WO₃ nanobars, mediated by cationic surfactant CTAB through hydrothermal route. XRD revealed the formation of metallic Ag supported on monoclinic WO₃ phase and TEM diagram showed the formation of bar-like structure, where supported Ag nanoparticles are in the range between 2 and 7 nm. The catalyst exhibited high activity for selective oxidation of cyclohexanone to caprolactone with H₂O₂. A cyclohexanone conversion of 97% with 99% caprolactone selectivity was achieved over this catalyst at 80 °C temperature. Moreover, the catalyst did not show any significant activity loss even after 5 reuses and proved its efficiency in the oxidation of other cycloalkanones also.     

Effective Baeyer–Villiger oxidation of ketones over germanosilicates

Germanosilicates with various topologies (UTL, BEC, UWY, IWR) serve as efficient heterogeneous catalysts for the Baeyer–Villiger oxidation of ketones. The tetrahedrally coordinated Ge ions in germanosilicates exhibited Lewis acidity, and acted as the active sites for converting ketones to corresponding lactones effectively.     

Baeyer–Villiger oxidation of cyclohexanone catalyzed by cordierite honeycomb washcoated with Mg–Sn–W composite oxides

In this work, a series of Mg–Sn–W oxide powder catalysts with different tungsten oxide contents(0, 15 wt% and 30 wt%) were prepared and washcoated on cordierite honeycomb monoliths to produce monolithic catalysts,which were tested for the Baeyer–Villiger oxidation of cyclohexanone. The obtained monolithic catalysts,which combined the advantages of both homogeneous and heterogeneous catalysts, showed high catalytic efficiency and overcame the problems of product separation that occurred in the homogeneous catalytic process.SEM and EDX tests showed that the catalytic coating, with a thickness of approximately 20 μm, was compact and homogeneous, and an enlarged BET surface area was indicated by N_2 adsorption–desorption compared with the bare cordierite honeycomb. The chemical properties on the catalytic surface of the powder and monolithic catalysts were characterized by XPS, which indicated the tin and tungsten on the catalysts exhibited their full oxide states and presented mainly as stannate and tungstate, as confirmed by XRD and FTIR characterizations.Moreover, the catalytic activity test indicated that the tungsten content of the catalysts played an important role in catalytic efficiency and that monolithic catalysts were produced without obvious catalytic activity loss compared with the corresponding powders.(M)W30, which exhibited excellent mechanical stability and maintained high activity after recycling three times, was the optimal catalyst, showing a high selectivity that exceeded 86%and a conversion above 64%. Therefore, the structured Mg–Sn–W oxide catalysts have great potential for application in practical production.     

The multifunctional mesoporous Sn–Cu–Ti catalysts for the B–V oxidation of cyclohexanone by molecular oxygen

The multifunctional three-component mesoporous Sn–Cu–Ti samples were successfully prepared by a facile one-pot AcHE method and characterized by XRD, N₂ sorption, ICP, FT-IR, UV–vis, SEM and TEM techniques, and their catalytic performances were carried out in the B–V oxidation of cyclohexanone by molecular oxygen. The results show that both tin and copper species can homogeneously incorporated in the crystalline framework of mesoporous anatase TiO₂, where tin species as the active sites would increase the Lewis acidity and the oxidation of benzaldehyde as pro-oxygenic agent would be promoted by the introduction of little copper species resulting in the improving catalytic performance. The prepared 15Sn–3Cu–Ti catalyst shows higher yield of ε-caprolactone than other catalysts and exhibits excellent catalytic stability even after repeated reaction for five times without any further treatment. The outstanding catalytic performance for Sn–Cu–Ti catalysts could offer a valuable reference for the industrial development of B–V oxidation of cyclohexanone.     

A new hybrid porphyrin-heteropolyacid material: Synthesis,characterization and investigation as catalyst in Baeyer–Villiger oxidation. Synergistic effect

A new tetraphenylporphyrin-tungstophosphoric acid hybrid was synthesized and physico-chemically characterized by different techniques. This hybrid, its molybdenum analogue, tungstophosphoric and molybdophosphoric acids as well as their Mn, Fe and Co salts were applied in Baeyer–Villiger oxidation of cyclohexanone to caprolactone with molecular oxygen. Due to the synergistic effect porphyrin-heteropolyacid hybrids exhibit similar catalytic activity as appropriate heteropoly salts and much higher activity than parent heteropolyacids.     

Baeyer–Villiger oxidation of cyclic ketones with aqueous hydrogen peroxide catalyzed by transition metal oxides

The Baeyer–Villiger oxidation of cyclic ketones to the corresponding lactones using aqueous hydrogen peroxide as an oxidant over transition metal oxides was investigated. MoO₃ and WO₃ were found to exhibit higher catalytic activity than TiO₂, Fe₂O₃, Co₃O₄, ZnO and ZrO₂. The high catalytic activity was attributed to the interaction of MoO₃/H₂O₂ and WO₃/H₂O₂. Additionally, the reaction mechanism on MoO₃ and WO₃ was proposed.     

Mesoporous Pt–Ni catalyst and their electro catalytic activity towards methanol oxidation

Mesoporous Pt/Ni architecture has been prepared by template assisted electrochemical deposition of Pt–Ni over anodized aluminum oxide template followed by controlled de-alloying with nitric acid. Surface characteristics of the ordered bimetallic mesoporous Pt/Ni structure were systematically characterized through XRD, SEM, AFM and XPS analyses. It is designated by XPS analysis that presence of Ni significantly modifies surface characteristics and electronic states of Pt accompanied with a downshift in the d-band character of Pt. Mesoporous morphology is highly beneficial to offer readily accessible Pt catalytic sites for methanol oxidation reaction. The prepared bimetallic Pt/Ni was used as electro catalyst for DMFC. Comparison of electrocatalytic activity of bimetallic mesoporous Pt/Ni with bimetallic smooth Pt/Ni was interrogated using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy analyses. Distinctly enhanced electrocatalytic activity with improved CO tolerance associated with bimetallic mesoporous Pt/Ni electrode towards methanol oxidation stems from a synergy existing between mesoporous structure with bi-metallic composition.     

Highly active and stable synergistic Ir–IrO2 electro-catalyst for oxygen evolution reaction

The design of efficient and stable electrocatalysts is still crucial to realize oxygen evolution reaction (OER) in acid and corrosive environment. Inspired by the metal/metal oxides catalysts, we hydrothermally synthesized Ir–IrO₂ composites duly confirmed by X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive spectrometer (EDS), X-ray absorption data, and transmission electron microscope results. A low onset over-potential of merely 234?mV and a Tafel slope of 53?mV?dec^?1 were obtained for the prepared catalyst Ir–IrO₂_0.5AF. In addition, Ir–IrO₂_0.5AF catalyst retained high activity for long time under constant potential polarization. The enhanced performance is attributed to the introduction of lower valence Ir as hydrogen acceptor: hydrogen transfers from –OOH intermediate in OER to adjacent H acceptor site, forming intermediate with relatively lower Gibbs free energy, and resulting in higher activity. The present study emphasizes on important role of the lower valence composition in launching H acceptors and providing wide opportunities toward rational designing of efficient and stable electro-catalysts.     

Ag–Cu–BTC prepared by postsynthetic exchange as effective catalyst for selective oxidation of toluene to benzaldehyde

A mixed-node MOF catalyst Ag–Cu–BTC was prepared by postsynthetic exchange (PSE) method. It is believed that PSE method can realize isomorphous replacement of Ag ion to framework Cu ion in Cu–BTC successfully. The catalytic performance of Ag–Cu–BTC was investigated via selective oxidation of toluene to benzaldehyde by molecular oxygen in the absence of solvent and initiator. This catalyst exhibits good catalytic performance: on the premise of keeping highly selective catalysis of Cu–BTC for toluene oxidizing to benzaldehyde, the introduction of Ag (Ag content is 2.76 wt.%) can promote toluene conversion from 6.5% to 12.7%.     

Highly active metal–acid bifunctional catalyst system for hydrogenolysis of glycerol under mild reaction conditions

Combination of active carbon supported Ru catalyst with a cation exchange resin (Amberlyst 15) exhibited much higher activity in glycerol hydrogenolysis under mild reaction conditions such as 393 K and 4 MPa H₂, than other metal–acid bifunctional catalyst systems using various zeolites, sulfated zirconia, H₂WO₄, and liquid H₂SO₄.     

Highly active and selective catalytic transfer hydrogenolysis of α-methylbenzyl alcohol catalyzed by supported Pd catalyst

A novel supported Pd catalyst was synthesized by using plant tannin grafted collagen fiber as the supporting matrix. The as-prepared Pd catalyst was subsequently used for the catalytic transfer hydrogenolysis of α-methylbenzyl alcohol. Due to the fibrous morphology of collagen fiber and the well dispersed Pd nanoparticles anchored by tannins, the as-prepared Pd catalyst showed superior activity for the catalytic transfer hydrogenolysis of α-methylbenzyl alcohol when compared with the Pd catalyst supported on inorganic oxides. Moreover, the as-prepared Pd catalyst can be reused at least 6 times without significant loss of activity and selectivity, suggesting a satisfied reusability.     

Preparation and characterization of CeOx@MnOx core–shell structure catalyst for catalytic oxidation of NO

The CeOx@MnOx catalyst with a core–shell structure was prepared and used for catalytic oxidation of NO. It was found that CeOx@MnOx catalyst showed higher intrinsic catalytic activity than CeMnOx catalyst prepared by citric acid method. Based on the characterization results of N₂ adsorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature-programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS), we may conclude that the excellent catalytic performance of CeOx@MnOx catalyst is related to its low crystallinity, good reducibility, and high concentrations of Mn^4 + and active oxygen species.     

Highly active recyclable SBA-15-EDTA-Pd catalyst for Mizoroki-Heck,Stille and Kumada C–C coupling reactions

Highly efficient SBA-15-EDTA-Pd(11) heterogeneous catalyst was synthesized by covalent anchoring Pd-EDTA complex over organo-modified surface of SBA-15. SBA-15-EDTA-Pd(11) catalyst was found to exhibit excellent catalytic activity in appreciable yield for Heck, Stille and Kumada cross-coupling reactions. Catalytic system exhibited excellent activity for completion of reaction, isolation, Pd loading (0.87 mmol%) and yields of products as compared to earlier reported heterogeneous supported Pd catalysts. Covalently anchored heterogeneous SBA-15-EDTA-Pd(11) catalyst can be recycled for more than five times without noticeable loss in activity and selectivity.     

Exploring the Substrate Specificity and Enantioselectivity of a Baeyer–Villiger Monooxygenase from Dietzia sp. D5: Oxidation of Sulfides and Aldehydes

Baeyer–Villiger monooxygenases (BVMOs) are valuable enzymes for specific oxyfunctionalization chemistry. They catalyze the oxidation of ketones to esters, but are also capable of oxidizing other chemical functions, namely aldehydes and heteroatoms such as sulfur, nitrogen, selenium and boron. The oxidation specificity and enantioselectivity of a newly characterized BVMO (BVMO4) from a strain of Dietzia towards sulfide- and aldehyde substrates have been studied. BVMO4 could react with sulfides containing an aromatic group. The presence of a substituent on the aromatic group was tolerated when they were in the meta- and para position and the oxidations yielded predominantly the (R)-sulfoxides. Similarly, BVMO4 displayed a higher activity for aldehydes containing a phenyl group, but long aliphatic aldehydes, namely octanal and decanal, were also accepted as substrate by this enzyme. The major oxidation products of the aldehyde substrates were the respective carboxylic acids in contrast to formate ester that was obtained in most of the previous reports. The Baeyer–Villiger oxidation of the substrate 2-phenylpropionaldehyde was studied in further detail and the corresponding acid product was obtained with good regio- and enantioselectivity. This is a unique feature for BVMO4 and is of great interest for further exploration of an alternative biocatalytic process.