Aerobic Oxidation Of Ethylbenzene Research Articles

Constructing Cu+ and Lewis acid sites enabling the generation of highly reactive N‑oxyl radical for the efficient aerobic oxidation of alkylarenes

Developing heterogeneous catalytic systems with high performance for the oxygenation of C(sp3)–H bonds to carbonyls using molecular oxygen as the oxidant is highly desirable. In the present research, active Cu+ sites have been efficiently constructed based on layered double hydroxides (LDHs) through in-situ reduction during the coprecipitation. Simultaneously, the formed CuZn(Mg)Al-LDH(R) catalysts demonstrated the characters of increased amount of oxygen vacancy and surface Lewis acid site. The newly synthesized catalysts exhibited higher catalytic performance than the samples prepared via conventional method, and up to 49.4% improvement in specific activity was observed in the aerobic oxidation of ethylbenzene. The mechanism study including a series of control experiments, semi-in-situ FT-IR analysis, and EPR analysis, demonstrated that reactive •O2– species generated via the acceleration of Cu+ species, and activated the NHPI (N-hydroxyphthalimide) molecule to form active PINO (phthalimide N-oxyl) species. The oxygen vacancy was verified to be able to activate O2 molecule and promote the formation of active 1O2 species. The surface Lewis acid site was proposed to interact with NHPI molecule, enabling the generation of highly active PINO species. The catalytic system also has the advantages of catalytical and structural stability, recyclability, and tolerance of wide substrate scope. We believe that the synergistic effect between the highly active sites and Lewis acid sites in catalyst can open up new opportunities for the activation of inert C–H bonds via O2/NHPI system.

Insights into ethylbenzene oxidation catalyzed by transition-metal oxides: Crucial role of hydroperoxide transformation

Selective oxidation of aromatics via a free-radical process is a crucial ingredient in the chemical industry, in which the transformation of hydroperoxide was considered the key step to facilitate the reaction. In this study, the aerobic oxidation of ethylbenzene (EB) to acetophenone (AcPO) catalyzed by carbon nitrides (CNx) supported the transition-metal oxides was performed. Among these catalysts, Co3O4/CNx displayed the highest activity with 48.09 % EB conversion and 77.8 % AcPO selectivity, due to the efficient decomposition of 1-phenylethyl hydroperoxide (PEHP). Notably, in the case of CuO/CNx, the relatively low EB conversion (19.8 %) and high selectivity of AcPO (70.2 %) were observed, while almost no PEHP was detected. Further mechanism investigations revealed that the decomposition of hydroperoxide over CuO/CNx was too fast to generate the reactive free-radicals, which could not efficiently facilitate the propagation steps. Moreover, the addition of tert-butyl hydroperoxide (TBHP) participated in the α-H abstraction of EB and facilitated of radical propagation, showing the distinguished activities over Co3O4/CNx and CuO/CNx.

Fabrication of a magnetic Mn(ii) cross-linked chitosan-amine/glutaraldehyde nanocomposite for the rapid degradation of dyes and aerobic selective oxidation of ethylbenzene.

Owing to the great demand for using sustainable, renewable, and widely available materials in catalytic systems for the conversion of waste/toxic material to high value-added and harmless products, biopolymers derived from natural sources have demonstrated great promise as an alternative to state-of-the-art materials that suffer from high costs and limitations. These have encouraged us to design and fabricate a new super magnetization of Mn-Fe3O4-SiO2/amine-glutaraldehyde/chitosan bio-composite (MIOSC-N-et-NH2@CS-Mn) for advanced/aerobic oxidation process. The morphological and chemical characterization of the as-prepared magnetic bio-composite was assessed using ICP-OES, DR UV-vis, BET, FT-IR, XRD, FE-SEM, HR-TEM, EDS, and XPS techniques. The PMS + MIOSC-N-et-NH2@CS-Mn system was capable of degrading methylene orange (98.9% of removal efficiency) and selectively oxidizing ethylbenzene to acetophenone (conversion 93.70%, selectivity 95.10% and TOF 214.1 (103 h-1) within 8.0 min and 5.0 h, respectively. Moreover, MO was efficiently mineralized (TOC removal of ∼56.61) by MIOSC-N-et-NH2@CS-Mn with 60.4%, 5.20, 0.03 and 86.02% of the synergistic index, reaction stoichiometric efficiency, specific oxidant efficiency, and oxidant utilization ratio in wide pH ranges, respectively. An understanding of its vital parameters and relationship of catalytic activity with structural, environmental factors, leaching/heterogenicity test, long-term stability, inhibitory effect of anions in water matrix, economic study and response surface method (RSM) were evaluated in detail. Overall, the prepared catalyst could be employed as an environmentally friendly and low-cost candidate for the enhanced activation of PMS/O2 as an oxidant. Additionally, MIOSC-N-et-NH2@CS-Mn exhibited great stability, high recovery efficiency, and low metal leaching, which eliminated the harsh condition reaction and supplied practical application performance for water purification and selective aerobic oxidation of organic compounds.

Solvent-free oxidation of benzyl C-H to ketone with Co-Ni layered double hydroxide as the catalyst and O2 as the sole oxidant.

The aerobic oxidation of ethylbenzene is an effective way to produce acetophenone, in which solvent-free conditions and oxygen as the sole oxidant are the best choice. At present, the catalytic activity and selectivity are still at an unsatisfactory level, because efficient catalysts need to achieve both C-H bond activation and O2 activation. In this work, the 2-methylimidazole-induced hydrolysis strategy was used to prepare a new class of CoNi-layered double hydroxide (CoNi-LDH) materials with different metal ratios. High-Resolution Transmission Electron Microscopy (HRTEM) showed that CoNi-LDH had obvious weak crystallinity and a thin lamellar structure. X-ray Photoelectron Spectroscopy (XPS) reveals the consistency between the content of the M-O component in the host layer and the proportion of Co3+, among which CoNi-LDH with a feed ratio (Co : Ni) of 2 : 1 (Co2Ni-LDH) has the highest M-O content and Co3+ ratio. The formation of M-O is due to the H-vacancy generated by the breaking of the hydroxyl group, which can be used for the H abstraction of C-H bonds. The redox effect caused by M2+/M3+ facilitates the transfer of electrons, which promotes the activation of O2 to the superoxide radical anion (˙O2-). Thereby, Co2Ni-LDH shows the highest catalytic activity for the oxidation of ethylbenzene. Under solvent-free conditions and with oxygen as the sole oxidant, 97.8% conversion of ethylbenzene and 98.8% selectivity of acetophenone can be obtained. The excellent catalytic performance is related to the structure of CoNi-LDH, and is also the best when compared with the reported results. Various types of aromatic hydrocarbons containing benzyl C-H bonds can be effectively oxidized by CoNi-LDH to produce the corresponding ketone products.

Catalyst Performance of the Calcined Products of CoAl Layered Double Hydroxide in the Aerobic Oxidation of Ethylbenzene

Catalyst Performance of the Calcined Products of CoAl Layered Double Hydroxide in the Aerobic Oxidation of Ethylbenzene

The Role of Co-ZSM-5 Catalysts in Aerobic Oxidation of Ethylbenzene

Various forms of cobalt catalysts have been studied extensively for selective aerobic oxidation of hydrocarbons. However, it remains unclear whether cobalt can directly activate molecular oxygen under mild reaction conditions. Here we investigated the catalytic roles of cobalt in ethylbenzene oxidation with and without a hydroperoxide initiator. The contribution of different cobalt species was studied by varying the metal loading on Co-impregnated ZSM-5 samples. Quantitative EPR was used to determine the impact of cobalt catalysts on the free radical concentrations. This work provided strong evidence that cobalt, in several different forms, catalyzes hydrocarbon oxidation by facilitating peroxy bond cleavage, instead of direct oxygen activation.

Organosuperbase dendron manganese complex grafted on magnetic nanoparticles; heterogeneous catalyst for green and selective oxidation of ethylbenzene, cyclohexene and oximes by molecular oxygen

Magnetic Fe3O4 nanoparticles as a support were modified with an amino-terminated organosilicon and cyanoric choloride ligands. The novel manganese complex was grafted on modified magnetic support (Mn(II)-Met@MMNPs). The nanocatalyst structure, particle size, morphology and surface properties was well characterized by elemental analysis, ICP-AES, AAS, EDS, FT-IR, SEM, TEM, DLS, VSM, TGA, XRD and XPS. In order to develop an effective heterogeneous nanocatalyst for eco-friendly aerobic, highly active and selective catalytic reactions, synthesized nanocatalyst was applied in oxidation of various organic compounds. The catalytic performance of the manganese nanocatalyst in the aerobic oxidation of ethylbenzene (EB), cyclohexene (CYHE) and various aldoximes and ketoxime were studied. Selective aerobic oxidation of EB and CYHE and various oximes were catalyzed by the Mn-nanocatalyst using N-hydroxyphthalimide (NHPI) with molecular oxygen as the green oxidant without the need of any reducing agent, and respectively the acetophenone (AcPO) as a benzylic product, 2-cyclohexene-1-one (CYHEO) as an allylic product and corresponding carbonyl compounds were obtained. The oxidation process has been optimized for Mn-nanocatalyst by considering the effect of different parameters such as the ratio and amount of Mn-nanocatalyst/NHPI, reaction time and solvent for achieving maximum conversion and selectivity to products. Due to their significant low cost, informal preparation, easy magnetically separation from reaction mixture, excellent catalytic performance, simple recovery and reusability without any metal leaching, the Mn-nanocatalyst has huge application prospect in selective and green oxidation process.

Manganese-containing hollow TS-1: Description of the catalytic sites and surface properties for solvent-free oxidation of ethylbenzene

Hollow MnOx/TS-1 catalyst was prepared by dissolution-recrystallization and impregnation method, and its catalytic activity was evaluated in aerobic oxidation of ethylbenzene under solvent-free conditions. Tetrahedral Ti4+ and MnOx species homogeneous dispersed on the hollow TS-1 surface and strong favourable synergic interactions between them occurred, which supported by the comprehensive analysis of XRD, N2 physical adsorption, TEM, FTIR, UV–vis, XPS and Raman spectroscopy. The virtue of such synergic effect was reflected in a catalytic efficiency enhancement of valuable ketone and alcohol products (TOF=137h−1): MnOx/TS-1 catalyst showed about 2.2 times higher activity compared to MnOx/Silicalite-1 references. Furthermore, the Mn species content and calcination temperature of the MnOx/TS-1 catalyst presented significant effects of lower-nuclearity Mn species on the structural, chemical, and catalytic properties. Based on the theoretical calculations, the reaction mechanism was proposed where the cleavage of the longer methylene CH bond (1.0935Å) of ethylbenzene and OO bond (1.5267Å) of alkyl hydroperoxide over the OTiOMn sites is a key step to yield radical continuously for recycle.

Comparative Catalytic Activity of Metal-Containing Catalysts of Different Nature in the Liquid-Phase Aerobic Oxidation of Ethylbenzene

The article describes an impact of metal-containing compounds - carbon nanofiber of platelet type, ferrocene and naphthenate Co on the aerobic oxidation of ethylbenzene. It has been established that all types of the added compounds reveal significant catalytic activity in the oxidation of ethylbenzene and may be ordered as: ferrocene > naphthenate Co ≥ carbon nanofiber. The authors guess that the results obtained are helpful to design new catalytic oxidation process profile of diesel fraction rich by aromatics.

Manganese nanocatalyst and N-hydroxyphthalimide as an efficient catalytic system for selective oxidation of ethylbenzene, cyclohexene and oximes under aerobic condition

The catalytic activity of the nano-manganese-catalyst in the aerobic oxidation of ethylbenzene, cyclohexene and oximes were evaluated without the need of any reducing agent, using N-hydroxyphthalimide (2-Hydroxy-1H-isoindole-1,3-dione; NHPI) under oxygen pressure. The oxidation of ethylbenzene and cyclohexene to acetophenone and 2-cyclohexene-1-one using N-hydroxyphthalimide (2-Hydroxy-1H-isoindole-1,3-dione; NHPI) under oxygen atmosphere in the presence of a SiO2/Al2O3-supported manganese catalyst occurs with conversions of 95 and 99% and selectivities of 99%. The supported manganese is also a suitable and efficient catalyst for the oxidative deprotection of oximes to the corresponding carbonyl compounds. A mild and efficient method has been optimized for manganese catalysts by considering the effect of various parameters such as the reaction time and the amount of catalyst, the temperature and the reusability of the catalyst after several runs without modification. Moreover, some possible mechanisms for the oxidation of ethylbenzene, cyclohexene and oximes have been proposed.

Liquid phase oxidations using novel surface functionalised silica supported metal catalysts

Metal species supported on a surface functionalised silica gel are active heterogeneous catalysts for the liquid phase, room temperature epoxidation of cyclohexene and the aerobic oxidation of ethylbenzene.