Ethylbenzene Conversion Research Articles

Extra-framework cations promoted zeolite-encaged cobalt catalysts towards efficient ethylbenzene dehydrogenation

The transformation of ethylbenzene to styrene through direct dehydrogenation is essential process in chemical industry, indispensable for the synthesis of polymers and plastics. Herein, faujasite zeolite encaged cobalt catalyst with potassium ion as the extraframework cations, namely K-Co@Y, is reported to be a robust catalyst for ethylbenzene direct dehydrogenation, showing ethylbenzene conversion of ∼45 % and styrene selectivity of ∼95 % simultaneously under employed conditions. The superior performance of K-Co@Y in comparison with Na-Co@Y is attributed to the effective modulation of zeolite-encaged Co2+ species by extraframework K+ ions, which increases the electron density of cobalt sites and facilitates CH bond activation. Although coke deposits cause gradual deactivation, the structural integrity of K-Co@Y can be well preserved during the dehydrogenation reaction and the performance can be full restored via a simple calcination regeneration step, making K-Co@Y an eligible catalyst for long-term running in the continuous regeneration mode. This study highlights the vital role of extraframework cations in zeolite-encaged single-site catalysts for target chemical transformations and opens up a new way to modulate the performance of zeolite catalysts.

Hybridizing engineering strategy of decatungstate III: Transition metal modified carbon quantum dot-regulated photo-catalytic oxidation performance of decatungstate

The selective oxidation of hydrocarbons (RH) by dioxygen (O2) is a very important method for industrial production of bulk oxygen-containing compounds, However, due to the high chemical inertness of RH and O2, achieving this reaction under mild conditions still faces significant challenges. This paper discloses an efficient hybridizing engineering (HE) strategy of decatungstate (DT) with 3d transition metal ions (Mn+=Ni2+, Co2+ or Cu2+)-modified carbon quantum dots (Mn+/CQD) as the dopants. Compared to pure CQD, The Mn+/CQD can more efficiently combine with DT anion to fabricate a high-quality hybrid via electrostatic interactions, thereby bestowing the hybrid with an enhanced visible light response especially the separation efficiency of photo-generated charge pairs. Furthermore, the above hybridization effects of Mn+/CQD on DT anion can be fine-tuned and gradually improved with a change of the metal ion from Cu2+, Co2+ to Ni2+, along with a continuous enhancement of the hybrid's photo-catalytic efficiency in the visible light- triggered selective oxidation of ethylbenzene with O2 in acetonitrile. The best Ni2+/CQD-doped TBADT can achieve ca. 48% ethylbenzene conversion and 87.6% acetophenone selectivity in the presence of 2 M HCl, and it also shows a much higher photo-catalytic activity for the photo-oxidation of toluene, cyclohexane and benzyl alcohol compared to pure TBADT. The HE strategy with Mn+/CQDs as the cationized hybridizers is much superior to that with pure CQD or Ni2+ as the hybridizer in hoisting the photo-catalytic performance of DT.

Deep learning with local spatiotemporal structure preserving for soft sensor development of complex industrial processes

Data-driven soft sensors have emerged as indispensable tools for predicting quality variables in complex industrial processes because of their cost-effectiveness and ease of maintenance. In particular, soft sensors based on deep learning have been utilized in extensive research and successful applications in recent years. However, traditional deep learning methods capture hierarchical data features by minimizing global fitting errors, neglecting the local structural characteristics implied in the original data. In this paper, we propose a new deep learning method for soft sensor development. Utilizing autoencoders as the foundational architecture of our network, a new semisupervised strategy is adopted for layerwise pretraining optimization. On the one hand, more representative data features are extracted by maintaining the local spatiotemporal structure of the data; on the other hand, layer-by-layer supervised learning is employed to identify the critical features that are aligned with the ultimate task, which aids in obtaining the optimal network parameters and improving the resulting prediction accuracy. Subsequently, a local spatiotemporal structure-preserving stacked semisupervised autoencoder (LSP-SuAE) is established. To evaluate the feasibility and effectiveness of the proposed approach, experiments are carried out in a real industrial process. A soft sensor based on the LSP-SuAE is developed to predict the rate of ethylbenzene conversion during the dehydrogenation of styrene. The experimental results demonstrate that, compared to five other common or similar data-driven modeling methods, LSP-SuAE exhibits higher prediction accuracy and better stability.

Guanine biomolecule derived nitrogen-doped carbon for efficient oxidative dehydrogenation performance

Biomolecule self-assembly shows great potential in the preparation of ordered functional materials. Here, we prepare a gauzy NC material via water guiding guanine biomolecule self-assemble, which exhibits the better ethylbenzene conversion (∼50%), styrene selectivity (∼91%) and long-term stability (>40 h) in ODH of ethylbenzene to styrene than that of guanine solid self-assembly produced NC (38% conversion vs. 88% selectivity) sample. The study shows that water not only facilitates guanine biomolecule self-assembly to form more stable octamer structure but restrains vertical growth of guanine, and resultant NC-1000-12 h holds high density active sites and outstanding oxidation resistance, thus enhancing NC catalytic performance. Overall, current work provides a new understanding on preparation of highly efficient NC materials through supramolecular self-assembly strategy.

Synthesis of carbon nanotubes via CCVD of ethylbenzene over SrFe12O19/SiO2 oxide and their application for photodegradation of the remazol red dye

Carbon-based materials have stood out due to their variety of applications such as photocatalysis. Thus, strontium hexaferrite dispersed in silica was prepared by the Pechini method and used as a catalyst in the ethylbenzene reaction to produce carbon filaments and subsequent application in the photodegradation of the remazol red dye. The presence of SrFe12O19, α-Fe2O3 and amorphous silica phases was confirmed in the XRD (X-ray diffraction), Raman and XPS (X-ray photoelectron spectroscopy) analysis. The SEM (scanning electron microscopy) and TEM (transmission electron microscopy) results of the fresh oxides indicate cluster and sponge-like morphology. The formation of carbon filaments was observed by SEM analysis as a result of catalytic chemical vapor deposition (CCVD) of ethylbenzene. TEM images confirm the generation of multi-walled carbon nanotubes with an average diameter of 27.9 nm. Besides the presence of the SrFe12O19 and SiO2 phases, the diffractograms of the samples after the reaction shows the formation of graphite carbon and Fe0, confirming the reduction of α-Fe2O3 which was also verified in the TPR-H2 profile. The growth of nanotubes occurs from metallic iron, considering that the tip of the tube contains only iron, according to EDS (energy-dispersive X-ray spectroscopy) results. The Raman spectrum exhibited the characteristic D and G bands of carbon, where the ID/IG ratio decreased with increasing temperature. The reaction with the best catalytic performance achieved an average ethylbenzene conversion of 99 % and was more selective to ethene (∼93 %) at 650 °C. Furthermore, it was possible to carry out a simple theoretical-computational study regarding the distribution of the sites in a 2D plane by constructing maps and proposing a mechanism for the formation of carbon nanotubes from the ethylbenzene conversion. Finally, the obtained materials were applied in the remazol red dye degradation, achieving complete degradation in 15 min for the material synthesized at 650 °C.

Supported copper nanoarchitecture for selective ethylbenzene oxidation (EBO) reaction

Copper-based (Cu-NP) uniformly dispersed on various inorganic supports (alumina, silica, titania, and zirconia) were prepared by the reverse microemulsion technique. These nanoparticles were used for the selective oxidation of ethylbenzene (EB) to produce acetophenone (AP) as the main product in the presence of Tert‑butyl hydroperoxide(TBHP) as an oxidant. This study focused on creating Cu-nanoparticles evenly dispersed on alumina using varying Cu-loadings (5 %, 10 %, and 15% wt.) and Brij-35 as the surfactant. The resulting catalytic material was characterized using various physicochemical techniques like XRD, FESEM, HRTEM, XPS and physisorption techniques. Various parametric studies were conducted, such as the effects of temperature, catalyst support, catalyst loading, and TBHP loading to optimize the EB conversions and AP selectivity. Among the various catalyst loadings, 15 % CuO/Al2O3 (15 % of the copper content) nanocomposites showed exceptional performance, with the highest EB conversion rate (99.7 %) and AP selectivity (98.5 %) compared to other nanocomposites. The catalyst's stability and recyclability over four cycles were attributed to the strong copper oxide-alumina interaction. These findings suggest that this nanocomposite material is a promising candidate for catalytic applications, offering high selectivity and consistent EB conversion rates.

Unravelling a complex catalyst deactivation in which selectivity affects conversion: oxygen-assisted styrene synthesis at industrially-relevant conditions

The oxidative dehydrogenation of ethylbenzene (EB) into styrene (ST) has been proposed as an alternative to the conventional energy-consuming synthesis of styrene. Various types of catalysts have been reported as promising for the reaction under industrially-relevant conditions. However, they show a complex deactivation behaviour. The EB conversion and the ST selectivity decay, with an increased COx selectivity. This phenomenon was investigated by means of experimental data and reaction model analysis, using two reference inorganic catalysts. The active catalyst is the deposited coke (ODH-coke) and not directly the inorganic material. The coke is formed in the initial reaction phase and promoted by the Lewis acid sites of the inorganic material. The reaction shows an activation period in which the ODH-coke is deposited and the EB conversion reaches a maximum where O2 is fully converted. From that point onwards, the reaction model is applicable and the experimental data fit very well with low standard deviations. The model explains that the EB conversion′s decay with time on stream is associated to changes in the selectivity. Hence, EB conversion is not an independent parameter. This simplifies the understanding of this complex deactivation; the deactivating parameter is the selectivity. At this moment, we cannot discriminate between increased COx and decreased ST, or both effects, because both routes are competitive. This case represents a new type of catalyst deactivation behaviour, in which selectivity affects conversion.

Manipulation of Electronic Effect and Assembly Architecture to Invoke Oxidation of Ethylbenzene by Hierarchical Co3O4 Wreaths.

A high-performance transition-metal oxide catalyst can be designed by appropriately integrating the concepts of morphology regulation and electronic structure modulation. In this work, hierarchical Co3O4 wreaths (CCW) enriched with oxygen vacancies (Ov) were facilely constructed for the selective oxidation of ethylbenzene (EB) to acetophenone (AP). Under the screened optimal reaction conditions, the CCW catalyst can offer a 79.1% conversion of EB (ri = 0.244 mol gcat-1 h-1) accompanied by a selectivity of 92.3% to AP. The good reaction performance can be attributed to the cooperation of defect engineering and architecture design, which can synergistically facilitate the EB oxidation performance by augmenting the intrinsic reactivity and accessibility of active sites. This work presents a reliable route to construct a high-performance transitional metal oxide catalyst via manipulation of electronic effect and assembly architecture for the selective oxidation of EB and beyond.

Simulating Gas-Solid Phase Isomerization of C8 Aromatics Affected by Catalyst Shapes in Fixed Bed Reactors with Particle-Resolved CFD Approach

Paraxylene (PX) is essential for producing polyethylene terephthalate fibers. We conduct particle-resolved CFD simulations, coupled with our reaction kinetics, on a fixed bed reactor randomly filled with catalyst shapes including sphere, cylinder, trilobe and quadrilobe to enlarge PX productivity in the catalytic isomerization of C8 aromatics. Our findings reveal the effects of catalyst shapes on velocity, concentration, temperature fields, and pressure drop. Although all catalyst shapes present particle utilization above 70 %, trilobes and quadrilobes show superior PX yield and ethylbenzene conversion due to their larger surface area and reduced mass transfer distance. Yet, among these catalysts, trilobes have twice the pressure drop of the others for complex geometric surface. Therefore, quadrilobes are more practical as their higher bed voidage, smaller pressure drop, better reactivity for desired reactions, and lower adiabatic temperature rise. This work provides guidance for catalyst design and process optimization to enhance PX productivity in aromatic isomerization.

STUDY OF CATALYTIC BEHAVIOURS OF THE SPINEL STRUCTURE NdxMg1- xAl2O4 COMPOSITION WITH ZSM-5 ZEOLITE IN ETHYLBENZENE DISPROPORTIONATION

Nanosized (10–15 nm) powders of spinel structures NdxMg1–xAl2O4 were obtained by low-temperature combustion of aluminium, magnesium, neodymium nitrate solutions, diethylmalonate, and hydrazine monohydrate with further calcination of nanopowders at 1000 °C, which were used in the preparation of catalytic compositions with ZSM-5 zeolite. The obtained catalytic compositions were characterized by X-ray diffraction, pyridine adsorption, and low-temperature nitrogen adsorption. The acidic properties and porosity of the catalysts were altered by controlling the concentration of nanopowder (1.0–7.0 wt.%) in the catalytic composition. The interaction of the modifier with HZSM-5 zeolite leads to a decrease in specific surface area and pore volume, as well as reduse of strong Bronsted acid sites (B) and an increase in the concentration of medium Lewis acid sites (L), resulting in a change in the B/L ratio from 3.61 to 0.23. The ongoing variations contributed mainly to an enhancement of the para-selectivity of the catalytic composition in the ethylbenzene disproportionation reaction. The catalytic composition of 5% Nd0.1Mg0.9Al2O4 with a pore volume of 0.15 cm3/g and an acid site B/L ratio of 0.27 demonstrates a maximum selectivity to p-diethylbenzene of 75.6% with a conversion of ethylbenzene of 23.7%.

Cobalt and nitrogen co-modified hollow periodic mesoporous organosilica spheres for selective oxidation of aryl alkanes

Hollow periodic mesoporous organosilica spheres (HPMOs) have stimulated great research interest owing to its unique organic–inorganic hybrid skeleton. In this work, HPMOs were synthesized by hydrothermal method, and then cobalt and nitrogen co-doped carbon catalyst was prepared by using HPMOs as supports. The optimal catalyst (Co-Nx/HPMOs-D) performed excellent activity in the selective oxidation reaction of aryl alkanes, with the conversion of ethylbenzene up to 97.0% and the selectivity of acetophenone was 98.9%, which was attributed to the Co-Nx active species and the unique HPMOs supports. The unique amphiphilic property of Co-Nx/HPMOs-D could better facilitate the adsorption and diffusion of organic substrates in the aqueous phase. The addition of dicyandiamide not only enhanced the nitrogen content in the catalyst, but also promoted the conversion of pyrrolic-N to pyridinic-N during the pyrolysis process, thus strengthened the interaction between the substrate and cobalt and improved the stability of the catalyst. This work presented a green and environmentally friendly method for the preparation of HPMOs and a facile strategy to obtain high performance catalysts for selective oxidation of aryl alkanes.

Redox oxidative dehydrogenation of ethylbenzene over Mn–Al–O composites using active lattice oxygen at moderate temperatures

Oxidative dehydrogenation (ODH) of ethylbenzene is a promising process for styrene production. However, its application is limited by product overoxidation and purification requirements due to the co-feeding of mild oxidants. Herein, we report a facile manganese-based catalyst (K/Mn3O4-Al2O3) and achieve competitive styrene selectivity of 88 % and ethylbenzene conversion of 95 % at 450 ℃ (84 % yield vs. ∼ 60 % yield in commercial dehydrogenation process at 600 ℃) under a cyclic redox ODH scheme. The introduction of Al2O3 into MnOx restructures composite oxides and depresses bulk lattice-oxygen migration for the partial oxidation of ethylbenzene. The surface modification using potassium creates reactive sites and regulates surface properties, achieving ethylbenzene activation and high conversions. Highly active lattice oxygen in catalysts after bulk and surface modifications selectively converts ethylbenzene to styrene and water. This study provides an understanding of roles of manganese-based catalysts in styrene generation and offers a strategy to modulate lattice oxygen on catalysts.

Promotional effect and mechanism of SiO2 on Cr-Al2O3 catalysts for N2O-assisted oxidative dehydrogenation of ethylbenzene

A series of Cr-SiO2-Al2O3 (abbreviated as Cr-Si-Al) catalysts were synthesized using an evaporation induced self-assembled (EISA) method and applied to the N2O-assisted dehydrogenation of ethylbenzene (EB), offering a versatile solution for greenhouse gas recycling and a novel pathway for styrene (ST) production. Notably, the Cr-5Si-Al catalyst calcinated at 850 °C exhibited remarkable performance with a high EB conversion of 71% and a good ST selectivity of 62%, resulting in an optimal ST yield of nearly 44%. To elucidate the impact of calcination temperature and reveal the underlying promoting mechanism, numerous types of characterization particularly in-situ DRIFTS were used. Results indicated that the Cr-5Si-Al-850 catalyst possessed a distinctively ordered mesoporous structure, which improved the specific surface area and facilitated the dispersion of active species. The interaction among the multiple species in the catalyst was enhanced under the high calcination temperatures, leading to an increased ratio of Cr6+ and Oα, and thus promoting the dehydrogenation of EB. Furthermore, in situ DRIFTS revealed two favorable reaction pathways: one involving the reaction between adsorbed N2O and EB, and the other involving the reaction between adsorbed EB and N2O. These pathways led to the formation of a similar intermediate, observed at a wavenumber of 1285 cm−1. The improved adsorption of EB played a pivotal role in the excellent catalytic performance of the Cr-5Si-Al-850 catalyst.

Coupled Interface and Oxygen-Defect Engineering in Co3O4/CoMoO4 Heterostructures toward Active Oxidation of Ethylbenzene.

The catalytic oxidation of ethylbenzene (EB) is a promising route to produce acetophenone (AcPO). Unfortunately, it remains a great challenge to achieve the highly efficient oxidation of EB under solvent-free conditions using molecular oxygen as the sole oxidant. In this contribution, we present a facile strategy to construct hierarchical oxygen vacancy-rich Co3O4/CoMoO4 heterostructures (Vö-CCMO), which delivers a high yield value of 74.5% at 83.2% conversion of EB and selectivity of 89.6% to AcPO. Both experimental studies and theoretical calculations substantiate the important role of oxygen-defect engineering triggered by the modified chemistry environment at the interfaces between the biphasic phases, which contributes to the good catalytic performance. This work illustrates a promising paradigm for the exploit of advanced catalysts toward boosting EB oxidation reaction in a more practical way.

ДЕГИДРИРОВАНИЕ ЭТИЛБЕНЗОЛА В ПРИСУТСТВИИ ЖЕЛЕЗООКСИДНЫХ КАТАЛИЗАТОРОВ, ПРОМОТИРОВАННЫХ КАЛИЕМ, ЦЕРИЕМ И МОЛИБДЕНОМ: КИНЕТИЧЕСКОЕ МОДЕЛИРОВАНИЕ

The present work is devoted to assessing the effect of the chemical composition of iron oxide catalysts promoted with potassium, cerium and molybdenum on their activity, quantified as ethylbenzene conversion, and selectivity of ethylbenzene dehydrogenation and interpreting the results obtained using kinetic modeling. The concentrations of the components of the reaction mixture, the conversion of ethylbenzene and selectivity of the ethylbenzene dehydrogenation were experimentally determined in the presence of synthesized iron oxide catalysts. A kinetic model of the process has been developed in the form of a system of differential equations that describes changes of the reaction system components concentration according to the mass action law. The experimental concentrations of the reaction mixture components, the ethylbenzene conversion and selectivity were described by the kinetic model by the use in the model of the following type of dependencies of the reaction rate coefficients on temperature: k i = k i0 T n i exp⁡(- B i T m i ) , where ki0, Bi, ni, mi are coefficients independent of temperature; T is the process temperature, K. As a result of kinetic modeling, the following patterns were established. The rate of the forward reaction of ethylbenzene dehydrogenation C6H5-C2H5 ⇆ C6H5-C2H3 + H2 is much greater than the rate of the reverse reaction, so chemical equilibrium in the ethylbenzene dehydrogenation reaction is not achieved. The effect of the reverse reaction on the kinetics of the ethylbenzene dehydrogenation process is minimal. The rate of the direct reaction of ethylbenzene dehydrogenation C6H5-C2H5 ⇆ C6H5-C2H3 + H2 is much higher than the rates of the reactions C6H5-C2H5 → C6H6 + C2H4 and C6H5-C2H5 + H2 →C6H5-CH3 + CH4. In this regard, the conversion of ethylbenzene is determined by the rate coefficient of the forward reaction in the reversible reaction of ethylbenzene dehydrogenation C6H5-C2H5 ⇆ C6H5-C2H3 + H2. The selectivity is determined by the ratio of the rate (or the ratio of the rate coefficient) of the direct reaction of ethylbenzene dehydrogenation C6H5-C2H5 ⇆ C6H5-C2H3 + H2 to the sum of the rates (or the sum of rate coefficient) of the direct reaction of ethylbenzene dehydrogenation and the dealkylation reaction of ethylbenzene C6H5-C2H5 ⇆ C6H6 + C2H4. It has been shown that an increase of the ethylbenzene conversion can be achieved, first of all, by promoting the iron oxide catalyst with the potassium compound. Pre-exponential factors and activation energies for all iron oxide catalysts promoted with the potassium compound do not change when cerium or molybdenum compounds are introduced into the catalyst, that is, in the process under consideration, the contribution of cerium and molybdenum compounds to the chemical properties of the iron oxide catalyst is insignificant.

КИНЕТИЧЕСКИЙ АНАЛИЗ ТЕХНОЛОГИЧЕСКИХ КРИТЕРИЕВ ЭФФЕКТИВНОСТИ ПРОЦЕССА ОКИСЛЕНИЯ ЭТИЛБЕНЗОЛА В ПРИСУТСТВИИ КОМПЛЕКСОВ ДИБЕНЗО-18-КРАУН-6 ЭФИРА С ХЛОРИДАМИ CA, SR, BA

A kinetic scheme is proposed that is common to the processes of ethylbenzene oxidation and ethylbenzene hydroperoxide decomposition in the presence of dibenzo-18-crown-6 ether complexes with Ca, Sr, and Ba chlorides. The scheme includes reactions of the formation of intermediate adducts from components of the reaction mixture and catalyst molecules, classical reactions of initiation, propagation and termination of the chain, reactions of initiation and propagation of the chain with the participation of intermediate adducts, and molecular reactions (includingthose with the participation of intermediate adducts).Basedonexperimentaldataandtheproposedscheme, akineticmodelwasmade.The kinetic model, written in the form of nonlinear differential equations according to the mass action law describes in time the rate of change of the concentrations of all components of reaction mixtures for ethylbenzene oxidation and ethylbenzene hydroperoxide decomposition in the presence of dibenzo-18-crown-6 ether complexes with Ca, Sr, Ba chlorides. As a result of solving the inverse kinetic problem using the zero-order direct search method, the values of reaction rate coefficients were found where the kinetic model reproduces the experimental values of the concentrations of all components of the reaction mixtures of the processes under consideration within the average relative error of 25%.As a result of the analysis based on the kinetic model, it was established that the conversion of ethylbenzene in the process of its oxidation is most affected by the reaction of ethylbenzene with the ethylbenzene peroxyl radical (target reaction).Using the kinetic model, the following was shown: 1) the values of the conversion of ethylbenzene, depending on the nature of the catalyst, line up in a row that corresponds to a number of values of the reaction rates of ethylbenzene with ethylbenzene peroxyl radical; 2) the model qualitatively reproduces the trend of selectivity changes when changing the catalyst.

Green and efficient catalytic oxidation of ethylbenzene to acetophenone over cobalt oxide supported on a carbon material derived from sugar.

The use of biomass as a carbon source to support metal oxides has significant advantages in environmental protection and reducing the cost of the catalyst. The critical point lies on the development of highly active and recyclable catalysts. In this study, sugar was used as a carbon source, and cobalt oxide was loaded via an in situ method and an impregnation method to prepare the catalyst, respectively. The catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, Raman, in situ electron paramagnetic resonance (in situ EPR) and N2 adsorption-desorption. The characterization results show that the macroporous carbon-supported cobalt oxide catalyst prepared by the in situ method contains CoOx nanoparticles on the support, but the dispersion of cobalt oxide on the support is more uniform compared with the catalyst prepared by the impregnation method. The catalytic performance of the prepared catalyst was evaluated through the oxidation of ethylbenzene (EB) to acetophenone (AP) as a probe reaction. Under the optimized reaction conditions, temperature (T) = 80 °C, m(catalyst) : m(EB) = 0.15, n(H2O2) : n(EB) : n(KBr) = 14.4 : 1 : 0.1, t = 8 h, and V(EB) : V(CH3COOH) = 1 : 10, the conversion of EB and the selectivity of AP were 84.1% and 81.3%, respectively. CoOx/SC-10-in situ exhibits improved reactivity of EB oxidation owing to cobalt ions on the carbon support that promote the free radical and acid catalytic reaction pathway. The cobalt oxide catalyst supported by biomass carbon has decent recycling and regeneration ability, which provides a new idea for the application of biomass.

Cobalt Encapsulated in Nitrogen-Doped Graphite-like Shells as Efficient Catalyst for Selective Oxidation of Arylalkanes.

Selective oxidation of ethylbenzene to acetophenne is an important process in both organic synthesis and fine chemicals diligence. The cobalt-based catalysts combined with nitrogen-doped carbon have received great attention in ethylbenzene (EB) oxidation. Here, a series of cobalt catalysts with metallic cobalt nanoparticles (NPs) encapsulated in nitrogen-doped graphite-like carbon shells (Co@NC) have been constructed through the one-pot pyrolysis method in the presence of different nitrogen-containing compounds (urea, dicyandiamide and melamine), and their catalytic performance in solvent-free oxidation of EB with tert-butyl hydrogen peroxide (TBHP) as an oxidant was investigated. Under optimized conditions, the UCo@NC (urea as nitrogen source) could afford 95.2% conversion of EB and 96.0% selectivity to acetophenone, and the substrate scalability was remarkable. Kinetics show that UCo@NC contributes to EB oxidation with an apparent activation energy of 32.3 kJ/mol. The synergistic effect between metallic cobalt NPs and nitrogen-doped graphite-like carbon layers was obviously observed and, especially, the graphitic N species plays a key role during the oxidation reaction. The structure-performance relationship illustrated that EB oxidation was a free radical reaction through 1-phenylethanol as an intermediate, and the possible reaction mechanistic has been proposed.

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.

Bridging Effect of Carbon Nitride with More Negative Conduction Potential and Halogens Promotes the Liquid-Phase Oxidation of Aromatic C-H Bonds.

The selective oxidation of benzyl C-H bonds of alkyl aromatic hydrocarbons under solvent-free conditions by using heterogeneous catalysis is a challenging task. In this work, we designed a carbon nitride photocatalyst with a high charge separation efficiency and a directed charge transfer path, which was doped with Ni and Br in the carbon nitride skeleton. Br was deposited directionally onto the electron-rich Ni surface traps to form a bond with Ni, which acted as a charge transfer bridge connecting CN and Br, resulting in a bridging effect. Photogenerated electrons were transferred from Ni target to Br, and electrons were aggregated to form a directional charge transfer path, thereby enhancing the photocatalytic performance of CN. The photocatalyst was utilized for the selective oxidation of ethylbenzene at room temperature, atmospheric pressure, and solvent-free conditions. Under batch conditions simulating solar irradiation, the conversion of ethylbenzene was 43.3% and the selectivity of the product acetophenone was up to 92.0%. With the continuous flow strategy, the conversion of ethylbenzene was increased to 52.4 and 48.1%, respectively, while the selectivity reached 92.7 and 91.0%, and the reaction time was reduced from 24 to 2.1 h. The catalyst was also found to be broadly applicable for the selective oxidation of C-H bonds in the benzyl position of alkyl aromatic hydrocarbons.