Oxidative Dehydrogenation Of Ethylbenzene Research Articles

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.

N, P codoped hollow carbon prisms for efficient oxidative dehydrogenation reaction with both enhanced activity and selectivity

Carbon materials have stimulated tremendous interest in oxidative dehydrogenation (ODH) of alkane to olefin molecules at low temperature. Unfortunately, its further development has been seriously hindered due to the unsatisfactory catalytic performance. To tackle these challenges, nitrogen and phosphorus codoped hollow carbon prisms (NPC) are designed with controllable surface functional groups through supramolecular pre-assembly and substitution reaction from guanine and hexachlorotriphosphazene. The resultant catalysts can achieve both high catalytic activity (63 % conversion) and styrene selectivity (90 %) in ODH of ethylbenzene, outerperforming previous reported carbon-based catalysts. Structural characterizations, kinetics measurements and theoretical results unravel that nitrogen doping can promote nucleophilicity of –CO, thus improving the catalytic activity. The phosphorus doping not only changes reaction rate-determining step from activation of O2 in N-doped carbon to activation of –C–H bond of EB in N,P-codoped carbon, but also inhibits the formation of electrophilic oxygen species, which enhances selectivity of styrene. The current work provides a facile strategy for preparation of functional NPC catalyst and physical–chemical insights on the structure–activity relationship of NPC catalysts, paving the way for further development of the highly efficient non-metallic catalytic systems.

Oxidative dehydrogenation of ethylbenzene on mesoporous carbon catalysts: effect of the active site number on the apparent catalytic activity

SMC-x catalysts demonstrate a distinctive carbon framework containing a significant number of CO active sites for ethylbenzene oxidative dehydrogenation.

Controlling Metal-Oxide Reducibility for Efficient C-H Bond Activation in Hydrocarbons.

Knowing the structure of catalytically active species/phases and providing methods for their purposeful generation are two prerequisites for the design of catalysts with desired performance. Herein, we introduce a simple method for precise preparation of supported/bulk catalysts. It utilizes the ability of metal oxides to dissolve and to simultaneously precipitate during their treatment in an aqueous ammonia solution. Applying this method for a conventional VOx -Al2 O3 catalyst, the concentration of coordinatively unsaturated Al sites was tuned simply by changing the pH value of the solution. These sites affect the strength of V-O-Al bonds of isolated VOx species and thus the reducibility of the latter. This method is also applicable for controlling the reducibility of bulk catalysts as demonstrated for a CeO2 -ZrO2 -Al2 O3 system. The application potential of the developed catalysts was confirmed in the oxidative dehydrogenation of ethylbenzene to styrene with CO2 and in the non-oxidative propane dehydrogenation to propene. Our approach is extendable to the preparation of any metal oxide catalysts dissolvable in an ammonia solution.

Folic Acid-Derived Low-dimensional carbons for efficient oxidative dehydrogenation of ethylbenzene

The oxidative dehydrogenation (ODH) of alkane is one of the most attractive routes in alkane production because of its favourable thermodynamic characteristic. Nitrogen-doped nanocarbons have demonstrated great potential in this reaction due to its cost-effective, high catalytic activity and stability. However, the influence of nitrogen on the catalytic properties of carbon materials is poorly understood due to the complexities of surface oxygen and nitrogen functional groups. Here we derive the performance descriptor that account for the nitrogen-dependent carbocatalysis in ODH reaction. To achieve this, we designed a set of nitrogen-doped nanocarbon materials with tunable nitrogen species by hydrothermal carbonization (HTC) treatment of the biomass folic acid (FA), which are applied in ODH of ethylbenzene. Among them, FA-180-1000 catalyst can achieve high ethylbenzene conversion (up to ∼62 %) and styrene selectivity (∼87 %), outperforming other HTC carbon-based catalysts. Structural characterizations and kinetic analyses revealed that nitrogen doping strongly interferes the charge polarization of CO site via electron transfer between CO, and nitrogen (mainly pyridine nitrogen and graphitic nitrogen) thus enhancing the reactivity of CO. Furthermore, the induction period during reaction process can be shortened by applying of sulfuric acid-assisted HTC method for constructing nitrogen-doped carbon catalyst with low crystallinity. The present work provides new insights into the contribution of nitrogen doping to the ODH reaction of carbon nanocatalysts, as well as guidance for the rational design of carbon catalysts for the conversion of hydrocarbons to high-value chemicals.

Improved O2-assisted styrene synthesis by double-function purification of SWCNT catalyst

The catalytic performance of SWCNT was notably improved in the oxidative dehydrogenation of ethylbenzene (EB) to styrene (ST) upon a double-function purification in one step of the raw SWCNT. This consists of lowering the MeOx concentration and generating surface C=O groups after processing it in nitric acid at controlled conditions, while preserving the structure. The textural improvement was ascribed to the cutting of the tubes/bundles by oxidation and to MeOx removal itself (dilution effect). Both EB conversion and ST selectivity increased with a parallel lowering of the undesired COx selectivity. The conversion was interpreted by the enhancement of the intrinsic properties (i.e., more surface ketonic groups) but also to the higher load of SWCNT in the bed upon purification; both factors contribute to a higher number of active sites (C=O) in the bed for styrene formation. The most purified catalyst underperformed in conversion once the purification altered the SWCNT structure notably. Thus, preserving the structure is an important condition to achieve high conversion and yield. The better selectivity was explained in two ways; more styrene-forming sites (C=O) or less COx-forming sites (uncoated MeOx) in the bed, or both. The styrene yield per catalyst volume was improved by an average of ca. 240 % in comparison to the non-purified SWCNT. Deactivation is critical in maximizing the purification effect on the intrinsic and volumetric yields. In practical terms, the purification method proved to enhance the reaction; the selectivity towards the unwanted COx was significantly lowered with a gain towards styrene, achieving comparable selectivity values as in the conventional process, but operated at much lower temperature.

Influence of heteroatom-doped Fe-carbon sphere catalysts on CO2- mediated oxidative dehydrogenation of ethylbenzene

Distinctly shaping carbon materials together with doping is an excellent approach for tailoring advanced materials. In this study, a series of heteroatom (N, S, P)-doped Fe-carbon sphere catalysts were prepared by a hydrothermal process to explore the effect of unary and binary dopants on the CO2-mediated ethyl benzene oxidative dehydrogenation. Upon doing so, a transformation from quasi to hollow to perfect spheres was observed that takes place due to the increasing hydrolysis rate and attainment of supersaturation. It was shown that each type of heteroatom has a beneficial role in creating specific chemical entities as well as in defining the iron amount of the catalyst. Catalytic activity correlated with XPS and Raman analysis reveal that the direct dehydrogenation of ethylbenzene is controlled by the iron content at low temperatures, while defect sites are the controlling parameter at high temperatures. Under oxidative conditions, the N-doped hierarchical Fe-hollow sphere carbon (Fe-N-C) catalyst shows the highest catalytic performance among all synthesized catalysts due to the cooperative action of pyridinic N species and the Fe3C phase for CO2 activation as well as RWGS reaction promotion.

Tailored Pd/C bifunctional catalysts for styrene production under an ethylbenzene oxidative dehydrogenation assisted direct dehydrogenation scheme

Rational design of efficient ethylbenzene (EB) dehydrogenation catalyst and reaction route is the key scientific challenge for styrene (ST) formation. We reported here a dual-path dehydrogenation (DPDH) route to efficiently convert EB to ST on a Pd/hollow nanocarbon spheres bifunctional catalyst, which exhibited ST formation rate up to 7.11 mmol g−1 h−1 with > 99 % selectivity. Detailed kinetic, isotopic and surface reaction analysis and corresponding DFT calculation suggested that the relatively high intrinsic catalytic activity originated not only from the single atomically dispersed Pd-based coordination structure but also the unique oxidative dehydrogenation (ODH) assisted direct dehydrogenation (DDH) reaction route. In this route, the small amount of H2O produced from ODH effectively lowered the energy barrier for hydrogen generation/desorption via a proton transfer process promoting the DDH process. The present work shed light on the rational design of catalyst and routes for highly efficient alkane dehydrogenation reaction systems.

Redox catalysts based on amorphous porous carbons

A modular synthesis concept to prepare a library of mainly amorphous porous carbons has been developed. The carbons show – while keeping the textural properties nearly unchanged - systematically varied features such as the content of nitrogen, oxygen, iron and graphitic species, respectively. These individual features and the cross-relations between them were characterized with respect to applications of the carbons as reactants or catalysts in different test reactions, namely the temperature-programmed oxidation (TPO), the oxidation of sulphurous acid (OSA), the electrochemical oxygen reduction reaction (ORR) and the oxidative dehydrogenation of ethylbenzene (ODH), respectively. The carbon materials show striking similarities in terms of catalytic activity in TPO, OSA and ORR, respectively. The influence of individual nitrogen species and graphitic species on the catalytic behaviour was analyzed in detail. Pyrrole-like nitrogen species are obviously beneficial for the activation of molecular oxygen in different test reactions while pyridine-like species do not affect the catalytic behaviour. Graphitic species do not significantly influence the catalytic activity of otherwise amorphous carbons. For ODH, it was shown that nitrogen functionalities enhance the overall catalyst deactivation by catalysing the destruction of active sites. • A library of carbon catalysts with systematically varied features was developed. • The catalysts were used for comparative studies on different redox-reactions. • Carbon catalysts show striking similarities in terms of activity in TPO, OSA and ORR. • Pyrrole-like nitrogen is obviously beneficial for the activation of molecular oxygen. • Graphitic species do not significantly influence the catalytic activity of the carbons.

Preferential adsorption of CO2 on cobalt ferrite sites and its role in oxidative dehydrogenation of ethylbenzene

Preferential adsorption of CO2 on cobalt ferrite sites and its role in oxidative dehydrogenation of ethylbenzene

Oxidative dehydrogenation on nanocarbon: Polydopamine hollow nanospheres as novel highly efficient catalysts

Ethylbenzene oxidative dehydrogenation (EB ODH) reactions with nanocarbon as catalysts exhibit promising prospects as green and sustainable chemical industrial process. The present work reported the design and synthesis of polydopamine hollow nanospheres (PDA HNSs) carbon-based catalysts via a polymerization & carbonization method using silica as hard templates. The proposed PDA HNSs catalysts exhibit a high surface area of 641.6 m2 g−1 with the surface oxygen and nitrogen content up to 6.3% and 9.5%, respectively. It shows exceptional catalytic performance towards EB ODH reaction, which is even better than the commercial nanocarbon materials, such as carbon nanotubes, from the viewpoint of the apparent activity (EB conversion at 61.6%), the intrinsic activity (7.7 × 10−4 s−1) and the activation energy (42.5 kJ/mol), although they share the same catalytic active sites of ketonic carbonyl/quinone groups and reaction kinetics, such as rate determining step and reaction orders.

Electrochemical Denitrification and Oxidative Dehydrogenation of Ethylbenzene over N-doped Mesoporous Carbon: Atomic Level Understanding of Catalytic Activity by 15N NMR Spectroscopy

Spherical mesoporous carbon (with a particle size in the range of 40–75 μm) was synthesized by nanoreplication of a hard silica template using sucrose as the carbon precursor. The mesoporous carbon...

On mechanism of formation of SBA-15/furfuryl alcohol-derived mesoporous carbon replicas and its relationship with catalytic activity in oxidative dehydrogenation of ethylbenzene

Abstract A series of CMK-3-like carbon replicas was synthesized by precipitation polycondensation of furfuryl alcohol in an aqueous slurry of SBA-15 at a polymer/SiO2 mass ratio of 0.50–2.00. Changes in textural and structural parameters of SBA-15 after polymer deposition were studied by N2 adsorption and X-ray diffraction. Morphology of the replicas was investigated by transmission electron microscopy, while their surface composition was determined by temperature-programmed desorption and X-ray photoelectron spectroscopy. The mechanism of deposition of poly(furfuryl alcohol) (PFA) onto silica surface was elucidated. It was found that PFA accumulates in SBA-15 pores randomly; certain channels are completely filled, while others remain partially empty. The incomplete filling of mesopores results in “pseudo-CMK-3” structures featuring the bimodal porosity (the typical mesopores of CMK-3 are accompanied by broader ones formed by the coalescence of adjacent partially hollow pores). The total filling of pores with PFA leads to the formation of good-quality CMK-3. The carbon replicas exhibited the presence of abundant amounts of superficial oxygen-containing moieties. These entities are responsible for high activity of the materials in the oxidative dehydrogenation (ODH) of ethylbenzene, bringing evidence supporting the mechanism of active coke, considered as governing the catalytic performance of carbon materials in ODH of alkanes.

Improved catalytic properties of Co3O4-impregnated La2O3/MgO over Co3O4/MgO catalyst in the oxidative dehydrogenation of ethylbenzene

A series of lanthanum oxide (La2O3—2–14 wt%)-encapsulated Co3O4/MgO catalysts and bare Co/MgO solid oxides were prepared by wetness impregnation method. Among all catalysts, La2O3-promoted Co3O4/MgO (CM) was found to be remarkable in terms of superior promotional effect of La oxide species. Therefore, La2O3-incorporated Co3O4/MgO (LCM) catalysts afforded unusual catalytic activity efficiency with respect to high EB conversion and styrene selectivity due to the synergistic effect of Co–La species. By contrast, bare Co3O4/MgO solid oxide (CM) catalyst afforded low EB conversion with mild catalytic activity due to the absence of promotional role of La oxide.

On the catalytic role of superficial VOx species and coke deposited on mesoporous MgO replica in oxidative dehydrogenation of ethylbenzene

Mesoporous MgO was synthesized by the nanoreplication method using CMK-3 carbon as a hard template and magnesium nitrate as a metal oxide precursor. The produced support was modified with different amounts of ammonium metavanadate solution. Various distributions of V-containing species on the MgO surface were found by XRD, low-temperature adsorption of N2, TEM, XPS and UV–vis-DR spectroscopy. At low V loadings isolated VO4 dominated. Increasing V content resulted in clustering of VO4 species and the formation of Mg3V2O8 crystallites. As found in temperature-programmed reduction (H2-TPR), the latter phase was clearly harder in reduction by H2 compared to highly dispersed VO4 forms. The developed materials appeared to be very active catalysts of oxidative dehydrogenation of ethylbenzene (ODH). The optimal catalytic performance was observed for the sample containing 10 wt% of vanadium. The initial ethylbenzene conversion of 63.6% at selectivity to styrene of 86.9% was achieved at temperature as low as 500 °C. A notable influence of carbonaceous deposit formed during the ODH reaction on the catalytic activity was discussed, including presentation of both coexisting superficial reaction mechanisms. A reasonable regeneration procedure to recover lost activity was developed.

Radical-Mediated Difunctionalization of Styrenes

Styrene, an extremely important compound in the chemical industry, is mainly produced by the dehydrogenation or oxidative dehydrogenation of ethylbenzene. Transformation of this raw organic material to more useful fine organic chemicals is a very significant topic. Recently, the radical difunctionalization of styrene has become a powerful and efficient tool for organic synthesis. This strategy can introduce two substituents into a styrene molecule in one step via addition to the C=C bond, enhancing the molecular complexity in a single operation with good selectivity and wide functional group compatibility.1 Introduction2 C-Centered Radicals3 CF3 and Other Polyfluoroalkyl Radicals4 N-Centered Radicals5 P-Centered Radicals6 O-Centered Radicals7 S-Centered Radicals8 Other-Atom-Centered Radicals9 Conclusion and Perspective

Role of Cobalt Oxide-Based Catalysts for Styrene Production: A Review on Significance of Various Promoters, Calcination Temperature, Chemical Behavior of Support Materials and Synthesis Procedure

The direct CO2 oxidative dehydrogenation of ethyl benzene (ODH-EB) is a great potential for the production of valuable styrene monomer. In contrast, past/present styrene (ST) synthesis is mainly obtained from oxidative dehydrogenation of ethyl benzene (EB) and being transformed into pilot scale under CO2 atmosphere. It was due to few unresolved restrictions existed in the synthesis of styrene monomer using the steam assisted process and commercial ST production technology. These problems are being rectified by ODH-EB process using CO2 as a soft oxidant. Therefore, ODH of EB is well-known high temperature process to convert the EB (petroleum by product) into valuable ST monomer through the utilizing of CO2. Present study clearly explains the concise history of dehydrogenation process used to convert EB to ST monomer, which is essential feedstock in the wide range of industrial commodities production. In this discussion we majorly devoted to design, development and synthesis of different Co based catalysts by applying different support materials such as SiO2, MgO, MgAl2O4 and γ-Al2O3 respectively. Moreover, this study extensively deals with chemical behavior of oxidants, utilization of viable active promoters and its characteristics features in the oxidative dehydrogenation process. Different reaction mechanisms in the ODH of EB process to describe CO2 utilization as well as surface styrene monomer formation and evaluation of other by products were discussed widely in this review paper. The surface acidic and basic chemistry of various support materials, its preparation, utilization and its catalytic activity applications have been discussed. Acidic–basic textural properties of different solid oxide support materials have been extensively illustrated through incorporation of variety active metallic oxide and promoters. The catalyst activity evaluation in ODH of EB process as well as plausible reaction mechanism of styrene monomer formation has been explained.

Oxidative dehydrogenation on nanocarbon: Effect of heteroatom doping

Kinetic analysis is a powerful and effective strategy to reveal the physical-chemical nature of the promotion effect of heteroatoms to nanocarbon catalysts. The present work reported the mechanistic and kinetic analysis of ethylbenzene oxidative dehydrogenation (ODH) reactions on heteroatom (N or B) doped and undoped carbon nanotube (CNT) catalysts via active site titration, kinetic isotope effect and single reactant surface reaction experiments etc. The physical-chemical meanings behind the elementary step rate and equilibrium constants were revealed and applied for interpretations of the promotion effect of heteroatoms at molecular level. Nitrogen doped CNT exhibited both higher rate and equilibrium constants for C–H bond dissociation and O2 adsorption than undoped one via facilitating the electron transfer process. The evolution of the active sites could be quantitatively described with rate equation via the theory of most abundant surface intermediates, which provides in depth understandings on the mechanism and structure-function relations in carbon catalyzed redox reactions.

Oxidative Dehydrogenation of Ethylbenzene into Styrene by Fe-Graphitic Catalysts.

Carbon-based catalysts have attracted much attention for the dehydrogenation (DH) of organic molecules, due to their rich active sites, high conversion efficiency, and selectivity. However, because of their poor stability at high operation temperature and relatively high cost, their practical applications have been limited. Here, we report a simple ball-milling-induced mechanochemical reaction which can introduce iron (Fe) and different functional groups (mostly stable aromatic C═O after heat-treatment) along the edges of graphitic nanoplatelets. The resulting Fe-graphitic nanoplatelets (Fe-XGnPs, X = H, C, N, or V) provide active sites for the oxidative dehydrogenation (ODH) of ethylbenzene into styrene. Among them, Fe-NGnPs (X = N) displayed the highest performance for styrene production at low temperature (∼11.13 mmol g-1 h-1, 450 °C) with high selectivity and durability.

Oxidative dehydrogenation of ethylbenzene on nanocarbon: Kinetics and reaction mechanism

Active site titration, kinetic analysis, isotope and temperature programmed surface reaction experiments have been applied to reveal the nature of nanocarbon catalyzed alkane oxidative dehydrogenation reactions. The catalytic reaction involves the redox cycle of ketonic carbonyl-hydroxyl pairs on nanocarbon materials, during which the substrate of ethylbenzene (EB) dehydrogenates to product styrene, and the molecular oxygen re-oxidizes the catalysts yielding water. The rate equation based on the mechanistic interpretations of the catalytic reactions provides intrinsic rate or equilibrium constants, which have their specific physicochemical meanings and could be directly linked to the catalytic process. The proposed rate equation could also accurately describe the effects of reactant (EB or O2) pressures and isotopomers (deuterated-EB or 18O2) on rate data, and provide a quantitative analysis on the evolution and content of surface intermediates on carbon catalysts, which is a reliable descriptor of the intrinsic reactivity and essential to establish the structure-function relations for carbon catalyzed redox reactions.