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[Display omitted] • A new bizeolite Pt/ZSM-5:ZSM-12/Al 2 O 3 catalyst was designed for C-8 aromatics isomerization. • ZSM-5/ZSM-12 based Pt catalyst allows both intra- and intermolecular isomerization routes. • Ethylbenzene and m -xylene conversions over ZSM-5+ZSM-12 based catalyst are higher than over an industrial counterpart. A bizeolite catalyst based on ZSM-5 and ZSM-12 was designed to maximize the yield of valuable aromatics from ethylbenzene (EB) rich feedstocks for the first time. The catalyst Pt/ZSM-5:ZSM-12/Al 2 O 3 was characterized by X-ray diffraction (XRD), nitrogen physisorption, temperature-programmed desorption of ammonia (TPD-NH 3), transmission and scanning electron microscopy (TEM and SEM), X-ray fluorescence analysis (XRF), Fourier-transformed infrared spectroscopy (FTIR) and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The catalyst and its components were tested in isomerization of an industrial C-8 aromatic cut (C8-Ar) and feedstocks with high EB content. The catalyst demonstrated higher conversion of EB and m -xylene (MX) compared with an industrial catalyst and higher selectivity to dealkylation products. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synthesis of polymer-silica hybrid supported Co (II) and Cu (II) catalysts. • Characterization by BET, CHNS, SEM-EDX, FTIR, and TGA techniques. • Evaluation of catalytic activity by ethylbenzene oxidation at various reaction conditions. • Study of kinetic parameters and reusability test. Polymer-silica hybrid support (SA-2-AMPS-SiO 2) was synthesized and Co (II), Cu (II) metals were loaded over hybrid support by incipient impregnation technique. Oxidation of ethylbenzene was carried out for testing catalytic activity of catalysts at different reaction conditions i.e. the mole ratio of ethylbenzene to TBHP and reaction temperature. The main oxidation product was acetophenone along with benzaldehyde as the minor product and the highest ethylbenzene conversion (83.65 %) was attained at a 1:4 mol ratio of ethylbenzene to TBHP and temperature at 100 °C. The reusability of the catalysts was also determined and results showed that they can be easily reused three times without much loss in their structural and catalytic properties. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Defect-rich Ce 1-x Zr x O 2 was synthesized via the urea-assisted hydrothermal method. • The largest amount of CO was released by pulsing CO 2 over reduced Ce 0.5 Zr 0.5 O 2. • Ce 0.5 Zr 0.5 O 2 showed the highest ethylbenzene conversion over 72% for CO 2 -ODEB. • The activity of Ce 1-x Zr x O 2 for CO 2 -ODEB strongly depends on its redox property. • The stability of Ce 1-x Zr x O 2 for CO 2 -ODEB is promoted by the deposited coke. Abstract The zirconium doped ceria (Ce 1-x Zr x O 2 , x = 0.0, 0.1, 0.3, 0.5, 0.9, and 1.0) was synthesized via the urea-hydrolysis assisted hydrothermal method by using (NH 4) 2 Ce(NO 3) 6 and ZrO(NO 3) 2 ·2H 2 O as the precursors. The structural and textural properties of the oxides were characterized with pertinent techniques, and the materials were evaluated as catalysts for the oxidative dehydrogenation of ethylbenzene with carbon dioxide (CO 2 -ODEB) under the conditions of 550 °C, 0.1 MPa, CO 2 to ethylbenzene molar ratio of 20, and W/F = 8.07 g-cat·h∙mol−1. Characterization results indicate that the single-phase cubic solid solution was formed in the cases of Ce 0.9 Zr 0.1 O 2 , Ce 0.7 Zr 0.3 O 2 , and Ce 0.5 Zr 0.5 O 2. In contrast, separated tetragonal and monoclinic phases of ZrO 2 were present over Ce 0.1 Zr 0.9 O 2 besides the solid solution. Moreover, the relative content of defects over the surface of Ce 1-x Zr x O 2 was continuously increased with x, but the highest amount of reducible Ce4+ was obtained over Ce 0.5 Zr 0.5 O 2. Reaction results indicate that Ce 1-x Zr x O 2 was effective for CO 2 -ODEB, and the highest conversion of ethylbenzene was obtained over Ce 0.5 Zr 0.5 O 2. The activity of Ce 1-x Zr x O 2 for the titled reaction is determined by both the amount of the reducible Ce4+ and the easy oxidation of Ce3+ by CO 2 over the catalyst. The inhibition of the coke via the oxidation of Ce3+ by CO 2 and its promotional effect on the activity are responsible for the stability of the catalyst for CO 2 -ODEB. [ABSTRACT FROM AUTHOR]

Hybrid materials consisting of few-layer sp 2 carbon supported on Al 2 O 3 can potentially display comparable performance with nanodiamonds for the oxidative dehydrogenation of ethylbenzene. The hybrid structure could be easily prepared by fast coking method using ethanol as a precursor and ɣ-Al 2 O 3 with high specific surface areas as a template. In this case, ɣ-Al 2 O 3 plays the role of 3D support for depositing few-layer graphene-like structure. The hybrid structure exhibiting similar structure with nanodiamonds calcined at high temperature is further used as a metal-free catalyst for the oxidative dehydrogenation of ethylbenzene to styrene. The yield rate of styrene normalized by the specific area on Al 2 O 3 @C is 0.044 mmol m −2 h −1 (TOF = 4.13 h −1 ) which is two times of that on nanodiamonds (0.020 mmol m −2 h −1 , TOF = 3.27 h −1 ). Considering the low cost process and good catalytic performance, the hybrid nanostructure may be a promising candidate to be applied in the oxidative dehydrogenation of ethylbenzene. [ABSTRACT FROM AUTHOR]

Hybrid materials consisting of graphene and nanodiamonds (NDs) can potentially display not only the individual properties of ND and graphene, but also those resulting from synergism when they closely interact. Herein, synergistic effects between ND and few-layer-graphene (FLG) containing between 5 and 20 layers of graphene are examined. The ND/FLG composite was prepared by mixing a suspension of FLG in ethanol with NDs. In this case, FLG plays the role of 2D support for dispersing ND clusters while NDs acting as a nano-spacer for partly preventing the re-stacking of the FLG sheets. The as-synthesized hybrid material was further used as metal-free catalyst for the steam-free direct dehydrogenation (DH) of ethylbenzene (EB) to styrene (ST). The DH activity obtained on the ND/FLG catalyst was benchmarked with other catalysts, i.e. commercial K-promoted Fe-based catalysts and carbon-based catalysts. The ND/FLG catalyst exhibits the highest DH activity among the tested catalysts, especially with a dehydrogenation specific rate as high as 19 mmol ST g ND −1 h −1 along with a selectivity toward styrene up to 95% at reaction temperature at 600°C. The catalyst displays a relatively high stability as a function of time on stream while the deactivated catalyst can be easily regenerated by an oxidative treatment in mild temperature conditions. [ABSTRACT FROM AUTHOR]

Carbon based catalysts for the oxidative dehydrogenation of ethylbenzene were prepared by a template assisted route. Using that synthesis procedure, the carbons could be modified systematically regarding their surface area and composition (namely the amount of nitrogen). Mesoporous silica and porous concrete, respectively, were used as the hard templates, whereas an aqueous solution of sucrose was the carbon source. Nitrogen was introduced by urea which partially replaced the sucrose in the solution. The materials were characterized by means of nitrogen adsorption at −196 °C, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and tested as catalysts in the oxidative dehydrogenation (ODH) of ethylbenzene. The catalytic activity was discussed with regard to the textural properties and the nitrogen content in the carbon catalysts. [ABSTRACT FROM AUTHOR]

The surface of CMK-3 carbon, synthesized by the reversible replication of mesoporous silica (SBA-15) using poly(furfuryl alcohol) as a carbon precursor, was activated by wet oxidation with an aqueous solution of HNO3 or H2O2. The process was performed at 50 °C using solution containing different concentrations of the oxidizing agent. It was found that during the modification no significant changes in textural and structural properties of CMK-3 replica occurred. However, the treatment resulted in the formation of appreciable amounts of surface species containing oxygen. XPS and DRIFT spectroscopy allowed to identify and quantify the surface functional groups. Their stability was studied by TG-FTIR measurements. CO and CO2 were found as main gaseous products evolved during thermal decomposition under inert atmosphere. Finally, the modified samples were tested in the catalytic oxidative dehydrogenation of ethylbenzene to styrene at 350 °C in the presence of oxygen as an oxidizing agent (at O2/ethylbenzene molar ratio of 1.0 and 3.0). At the beginning of the catalytic run, the highest styrene yield and selectivity was achieved at the lower O2 content over the catalysts treated with nitric acid. Nevertheless, all studied catalysts underwent a gradual deactivation due to coke formation and changes in the distribution of surface moieties. [ABSTRACT FROM AUTHOR]

Highlights: [•] Addition of Cs2O to Cs-X enhances the activity but decreases the styrene selectivity. [•] Addition of ZrB2O5 to Cs2O/Cs-X enhances the activity and the styrene selectivity. [•] Transfer hydrogenation of styrene with methanol is main pathway to ethylbenzene. [•] Grinding Cs2O/Cs-X with ZrB2O5 followed by calcination yields efficient catalyst. [Copyright &y& Elsevier]

Highlights: [•] The characteristics of “ideal” bifunctional Pt/zeolite catalysts were specified. [•] High hydrogenating/acid balance for having acid olefin rearrangement as rate limiting. [•] Low number of H+ between Pt sites to avoid multistep olefin transformation. [•] Favourable location of active H+ sites: no diffusion and steric constraints. [•] Low H+ site concentration for limiting the demanding ethylbenzene disproportionation. [Copyright &y& Elsevier]

Abstract: In this work, a pulse plant has been used to study the redox properties, activity and coke generation of four catalysts in ethylbenzene dehydrogenation to produce styrene. CO2 was used as weak oxidant. A physicochemical and structural characterization was carried out in order to verify possible changes in the catalysts after the tests. The experiments consisted of a reduction test with H2, oxidation with CO2, reaction with ethylbenzene, regeneration with CO2 and coke combustion and reoxidation with O2. These experiments were carried out at three temperatures (450, 500 and 550°C). With the catalyst that exhibited the best results, MnO2–ZrO2, additional experiments with different oxidation states were carried out in order to determine the influence on its activity and redox properties to assess the feasibility of using CO2 as a regenerating agent during the ethylbenzene dehydrogenation reaction. [Copyright &y& Elsevier]

Abstract: Highly graphitized multiwalled carbon nanofibers (CNFs) were used as a carbon-based model catalyst to study the oxidative dehydrogenation (ODH) of ethylbenzene. Their stability as well as the evolution of catalytic performance as well as structural and textural properties under robust operation conditions were studied. The catalyst was characterized by TEM, TPO, XPS, and N2 physisorption techniques. Highly ordered CNFs provide a low initial catalytic activity owing to the low degree of surface functionalization. The rate of ethylbenzene conversion increases by factor of 5 as the catalyst is exposed to the reaction conditions at 475°C for a period of 30h time on stream. A similar catalytic performance is obtained after short-term oxidation treatment of the pristine CNFs. The in situ formation of surface defects is attributed to the activation of the catalyst, whereas the generation of an active carbonaceous deposit on the catalyst surface is found to be less relevant. [Copyright &y& Elsevier]

Abstract: Dehydrogenation is a widely exploited route for large scale production of pure olefins. Its industrial application is however complicated by clashing kinetic and thermodynamic constraints. A commercial bubbling fluidized bed technology for isobutylene production from isobutane has been developed to solve these constraints. An economically attractive implementation was achieved by defining an optimal synergy between chromia alumina catalyst design and reactor engineering. The fluidized bed know-how developed has also led to the development of a revolutionary technology for the production of styrene from ethylbenzene using a riser reactor and a gallium based catalyst. [Copyright &y& Elsevier]

Abstract: Multi-walled carbon nanotubes were synthesized by chemical vapor deposition method using SBA-15 as a template under methane and carbon dioxide as carbon sources. As-synthesized multi-walled carbon nanotubes were treated by NaOH at 80°C to remove the template and retain the Ni and Co metals. The multi-walled carbon nanotubes supported (Co and Ni) were used as catalysts. The catalysts were characterized by SEM, TEM, XRD, Raman and SEM-EDX. The catalytic activity was investigated for the dehydrogenation of ethylbenzene at different oxidants and temperatures. CNTs-Co-10 showed the highest styrene selectivity (92.3%) at 450°C and ethylbenzene conversion (93.5%) at 700°C with a higher styrene yield (80.6). The catalyst also showed a high thermal stability. [Copyright &y& Elsevier]

Abstract: Zeolites La,Na-Y are important catalysts for industrial FCC units due to their acidic properties and stability. The ethylbenzene disproportionation on this zeolite was suggested as a standard test reaction for acidic zeolites by the Catalysis Commission of the International Zeolite Association (IZA). The present work provides solid-state 13C NMR spectroscopic evidence that various amounts of reactants inside the supercages of zeolites La,Na-Y obviously affect the catalytic behavior of ethylbenzene reaction. At 453K, diphenylethane was only detected on zeolite La,Na-Y with three ethylbenzene molecules per supercage. This intermediate, however, did not occur on samples with low loading (1 or 2 EB molecules per supercage). On zeolite La,Na-Y loaded with one molecule ethylbenzene per supercage, dealkylation and realkylation of ethylbenzene occurred at 548K without any side-reactions. However, side-reactions of oligomerization, hydride transfer, and aromatization were observed on samples with high ethylbenzene loading, which promotes the catalyst deactivation. In addition, the zeolites La,Na-Y with high loadings of ethylbenzene show a higher reactivity and more complex reaction mechanisms. [Copyright &y& Elsevier]

Abstract: This paper describes dehydrogenation reaction of ethylbenzene to styrene with CO2 over iron oxide-based catalysts. Three catalysts of Fe2O3–MgO/γ-Al2O3, Fe2O3/MgAl2O4 and MgFe0.1Al1.9O4 with the same molar ratio of Mg/Fe/Al were prepared by impregnation and sol–gel methods. At 580°C, the ethylbenzene conversion over MgFe0.1Al1.9O4 kept a value of 40% during the time on stream of 20h, whereas that over Fe2O3/MgAl2O4 decreased rapidly from initial 50.0% to 27.4%. The properties of the catalysts were characterized by several techniques such as N2 adsorption/desorption, X-ray diffraction, thermogravimetry, energy dispersive X-ray spectroscopy, Fourier transform-infrared spectroscopy, 57Fe Mössbauer spectroscopy, temperature-programmed reduction, and temperature-programmed desorption of NH3 and CO2. It was found that the iron species of these catalysts are different. In MgFe0.1Al1.9O4, all Fe3+ species are incorporated in the spinel lattice. MgFe0.1Al1.9O4 shows high catalytic activity and stability in ethylbenzene dehydrogenation reaction with CO2. Moreover, the weak surface acidity of MgFe0.1Al1.9O4 prevents from the carbon formation during the reaction. [ABSTRACT FROM AUTHOR]

Abstract: The effect of graphitization of carbon nanotubes (CNTs) on the oxidative dehydrogenation of ethylbenzene to styrene was studied. An elimination of functional groups was observed by treating the catalyst under inert gas at temperatures below 1100°C, while its microstructure and reactivity in TPO experiments did not change significantly. A decrease in the initial catalytic performances was observed, but the functional groups can be regenerated during the catalytic reaction, thus leading to a significant improvement in the catalytic activity. Annealing CNTs above 1500°C leads to a well graphitisized wall structure of CNTs with a nearly oxygen-free surface with a low number of defects. The obtained samples show low but stable catalytic performances, indicating that the oxygenated active sites cannot be regenerated on this well-organized and low defective surface. [Copyright &y& Elsevier]

Abstract: Cyclam type macrocyclic ligand was tethered onto mesoporous silica surface through N-functionalization of the cyclam. The mesoporous silica was synthesized directly with in-built chloropropyl functional group by applying microwave synthesis approach and the cyclam ligand was tethered via the surface substitution reaction of the chloro group. The tethered cyclam ligand was proven to facilely accommodate Co(III) cation into its cavity. This Co(III)cyclam-functionalized mesoporous silica showed good catalytic activity in the aerial oxidation of ethylbenzene to give acetophenone as the major product, which exceeded 60%. The presence of pyridine ligand which bounded to the axial sites of the tethered Co(III)cyclam complex enhanced the activity of the catalyst with sustaining the selectivity. [Copyright &y& Elsevier]

Abstract: Direct synthesis route was developed to support TiO2–ZrO2 binary metal oxide onto the carbon templated mesoporous silicalite-1 (CS-1). Metal hydroxide modified carbon particles could play a role as hard template and simultaneously support metal components on the mesopores during the crystallization of zeolites. Such supported TiO2–ZrO2 binary metal oxides (TZ/CS-1) showed better resistance to deactivation in the oxidative dehydrogenation of ethylbenzene (ODHEB) in the presence of CO2. These catalysts were found to be active, selective and catalytically stable (10h of time-on-stream) at 600°C for the dehydrogenation of ethylbenzene (EB) to styrene (Sty). [Copyright &y& Elsevier]

Abstract: The ethylbenzene dehydrogenation in the presence of steam is the dominant technology for styrene production, one of the most important high value chemicals. The most widely used industrial catalyst comprises potassium-promoted iron oxide, which deactivates with time, due to potassium loss. In order to find alternative free-potassium catalysts, the effect of lanthanum on hematite-based catalysts was studied in this work. Samples with different amounts of lanthanum and prepared with different precipitants (ammonium hydroxide, sodium carbonate and sodium hydroxide) were obtained. It was found that lanthanum led to the production of solids with small particles when ammonium hydroxide was used, a fact which was assigned to lanthanum species on the surface where they keep the hematite particles apart avoiding sinterization. On the other hand, bigger particles were produced when sodium hydroxide and sodium carbonate are used, which resulted in solids with small specific surface areas. This was related to the sodium species which covered the surface impairing the lanthanum action. The most promising catalyst was that prepared with ammonium hydroxide and with La/Fe=0.1, which showed the highest specific activity and the highest activity per area. In this solid, lanthanum acts as a structural promoter. [Copyright &y& Elsevier]

Abstract: Activated carbons have found several applications as catalysts and as catalytic supports. They can be useful in the ethylbenzene dehydrogenation to produce styrene, a high value chemical. In order to produce alternative catalysts for this reaction, the preparation of spherical activated carbon-supported copper was studied in this work. Solids with two different amounts of copper were prepared, characterized and evaluated in the ethylbenzene dehydrogenation in the presence of carbon dioxide. It was noted that some copper species were weakly adsorbed on the solid and were removed from the solid during the reaction causing the collapse of the structure. The weakly bonded copper species did not affect the activity but improved the yield to styrene and decreased the production of benzene and toluene. On the other hand, the more strongly bonded species contributed to the activity and to the stability of the catalyst. The solid with the lowest amount of copper was the most promising one, since it showed high activity and resistance against deactivation, being able to work up to 600°C. [Copyright &y& Elsevier]

Abstract: SnO2–ZrO2 nanocomposite catalysts with different compositions ranging from 0 to 100% of SnO2 were prepared at room temperature by co-precipitation method using aqueous ammonia as a hydrolyzing agent. X-ray diffraction, transmission electron microscopic characterization revealed the SnO2–ZrO2 nanocomposite behavior. Acid–base properties of these catalysts were ascertained by temperature-programmed desorption (TPD) of NH3 and CO2. Both acidic and basic sites distribution of the nanocomposite catalysts is quite different from those of respective single oxides (SnO2 or ZrO2). Catalytic activity of these nanocomposite catalysts for ethylbenzene dehydrogenation (EBD) to styrene in the presence of excess CO2 was evaluated. The change in the acid–base bi-functionality of the nanocomposite catalysts in comparison with single oxides had profound positive influence in enhancing the catalytic activity. [Copyright &y& Elsevier]

Abstract: Alumina-supported V0.43Sb0.57 oxide (VSb/Al) and MgO-modified alumina-supported V0.43Sb0.57 oxide catalysts (VSb/Mg n Al with Mg/Al atomic ratio, n =0.1, 0.3 or 0.5) have been tested for the dehydrogenation of ethylbenzene with carbon dioxide as an oxidant. Their catalytic behaviors were interpreted by results of several catalyst characterization methods. The decrease in the surface acidity of the VSb/Mg n Al catalysts due to modification of alumina with MgO favors the prolonged time-on-stream activities. However, the addition of relatively large amounts of MgO (n =0.3 or 0.5) causes substantial decrease in their surface areas, reducibility of active vanadium oxide component and, consequently, ethylbenzene conversion. These negative factors did not become apparent for the most efficient VSb/Mg0.1Al system demonstrating high and stable catalytic activity. [Copyright &y& Elsevier]

Abstract: MnO2-ZrO2 binary oxide catalytic system was applied for the effective utilization of CO2 as an oxidant in the ethylbenzene dehydrogenation (EBD) to styrene monomer (SM). MnO2-ZrO2 oxides were prepared by co-precipitation method and characterized as solid solution mixture having surface area more than 1002 g−1. 10% MnO2-ZrO2 mixed oxide catalyst exhibited conversion of 73% with the selectivity of 98% at 650°C. The MnO2-ZrO2 binary oxides were X-ray amorphous whereas the individual oxides (MnO2 and ZrO2) having much lower surface areas were crystalline in nature. As a result, MnO2-ZrO2 binary oxides exhibited greatly elevated catalytic activity for the conversion of ethylbenzene (EB) than those of individual oxides in the presence of CO2. However, in the absence of CO2 poor catalytic activity and stabilities were observed. Gradual enhancement of activities were demonstrated in the higher CO2 to EB ratios. Hence, CO2 had a profound role as a soft oxidant by improving both activity and stability in the EBD over MnO2-ZrO2 mixed oxide catalysts. [Copyright &y& Elsevier]

Abstract: The molecular designed dispersion (MDD) method was used for the modification of SBA-15 with vanadium oxide. Vanadyl acetylacetonate was grafted on the support surface at different VO(acac)2 concentrations in a toluene solution, and then converted into the VO x /SBA-15 catalysts at elevated temperatures. The thermal transformation of surface species was studied by FTIR-PAS spectroscopy. The obtained materials were characterized with respect to their texture (BET), metal dispersion (FT-Raman and UV–vis-DR) and reducibility (H2-TPR). It was found that only isolated V5+ species were present in the samples with a low V loading. The catalyst with the highest V content showed the presence of polymeric V5+ species, which appeared to be easier reducible compared to the isolated form of V. The VO x /SBA-15 samples were tested as catalysts in the oxidative dehydrogenation of ethylbenzene to styrene in the presence of N2O. An increase in the catalytic activity with raising the V content was observed. It was however prove that monomeric V5+ species were considerably more active and selective in the styrene formation than oligomeric ones. [Copyright &y& Elsevier]

Abstract: The paper contains a short review on the impact of in situ 13C and 1H MAS NMR to the elucidation of the mechanisms of alkylaromatics transformation over zeolite catalysts. The studies of deuterated benzene and cumene transformations over protonic forms of zeolites are considered to account for the mechanisms of H/D exchange in the aromatic ring and alkyl chain. The investigations of 13C label transfer in the course of the rearrangements of specifically labeled benzene, cumene, n-propylbenzene and ethylbenzene are reviewed to provide deeper insight in the mechanisms of transalkylation, disproportionation, skeletal and nonskeletal rearrangements of alkyl chain, fragmentation and dealkylation/alkylation over zeolites. The main factors controlling selectivity of zeolite catalysts in alkylbenzenes transformations are established. [Copyright &y& Elsevier]

Abstract: The objective of this work is to study the behaviour of V-Sb-Ti mixed oxides in the ODH of ethylbenzene and to compare these results with those previously reported for the partial oxidation of toluene with the same catalysts. The solids, with nominal compositions VSbO4, VSb0.8Ti0.2O4 and V0.8SbTi0.2O4, were prepared by solid-state reaction. Catalytic tests were carried out in a fixed-bed reactor using ethylbenzene and air as reactants. A relation between the dehydrogenation function of the solids and their Sb/V surface ratios was established. The higher Sb/V surface ratio the higher selectivity to styrene but pointing out the participation of Sb sites in the H-abstraction step. Comparison between toluene and ethylbenzene oxidation results has confirmed that the reaction rate is independent of the hydrocarbon used in the feed and controlled by the reoxidation of the catalyst. Besides, at the same conversion level, selectivity to total oxidation products is lower when ethylbenzene is used as reactant, due to the formation of a stable dehydrogenated product, styrene, which competes with oxygen for the chemisorption on Lewis acid sites. [Copyright &y& Elsevier]

Abstract: In this work, the oxidative dehydrogenation (ODH) of ethylbenzene to styrene reaction over an activated carbon felt was studied by experiments of mass spectrometry coupled to a quasi in situ XPS system. These experiments permit to deepen into the mechanism of the aforementioned reaction. The results obtained allow us to conclude that carbonyl-quinone and hydroxyl groups are involved in the ODH. The amount of both types of oxygen groups increases when the ethylbenzene conversion to styrene increases. Therefore, the reaction seems to take place through the carbonyl-quinone/hydroxyl and styrene/ethylbenzene redox couples, confirming that carbonyl-quinone are the active phase in this oxidative dehydrogenation. [Copyright &y& Elsevier]

Abstract: The oxidative dehydrogenation (OD) of ethylbenzene (EB) has been investigated over different catalysts of xCaO/SiO2 and yP/xCaO/SiO2 composition. It has been shown that the texture characteristics of initial SiO2 exert an important influence on the activity of catalysts obtained on their basis. Higher conversion of ethylbenzene and selectivity on styrene are observed in the case of macroporous silica gels. The yield of styrene and quantity of carbon deposits (CD) in the initial reaction period are increased symbately. In the stationary reaction period achievable in 1–6h after beginning of reaction, depending on texture characteristics of catalysts, maximal conversion of EB and minimal rate of accumulation of carbon deposits are observed over catalyst surface. In this period of process catalytically active system represents carbon deposits formed over catalyst surface and inclusive various carbonyl-containing groups. Catalysts are not passive carriers on which carbon deposits are formed; on the contrary, structure and catalytic activity of carbon deposits strongly depend on composition, texture characteristics and acid–base properties of used catalysts. [Copyright &y& Elsevier]

Abstract: Nanocarbons (multiwalled carbon nanotubes (CNTs) and onion-like carbon) are tested for the oxidative dehydrogenation (ODH) of ethylbenzene to styrene. The catalytic performances are compared with these using carbon black and graphite as catalysts. The tested nanocarbons are catalytic active in the reaction. The highest yield is achieved by using onion-like carbon as catalyst. The combustion stability of graphite, carbon nanotubes and onion-like carbons gives stable catalytic performances on stream. The comparison of onion-like carbons as a model catalyst with other carbon materials gives the criteria for efficient carbon catalyst. A reaction model for oxidative dehydrogenation on carbon catalysts is proposed too. Our findings provide a new perspective for the application of nanostructured carbon materials. [Copyright &y& Elsevier]

Abstract: Hydrogenation of diethylbenzenes in the liquid phase was studied at 358–418K and 2–6MPa over 16.7% Ni/Al2O3. The reactivity of diethylbenzene isomers was dependent on the mutual position of the substituents and decreased in the following order: 1,3->1,4->1,2-. The apparent activation energies were ca. 60kJ/mol. The cis-to-trans ratio of the corresponding saturated products exhibited only a weak dependence on temperature and hydrogen pressure. [Copyright &y& Elsevier]

Silica-supported tungstophosphoric acid (SPW) with Keggin structure in liquid phase alkylation of benzene with ethylene and transalkylation of benzene with diethylbenzene was studied. The structures of SPW were characterized by nitrogen adsorption, FT-IR, and XRD; and the acidic properties characterized by pyridine adsorption FT-IR, NH3-TPD, and Hamett indicators. Tungstophosphoric acid (PW) maintains its Keggin structure in SPW. PW is finely dispersed on the support as the loading less than 30 wt.%. SPW has both Brönsted (B) and Lewis (L) acid sites with B acid sites predominantly. The L acid sites are derived from the chemical interaction between the protons of PW and the hydroxyl groups of silica. The amount and acid strength of surface acid sites of SPW increase as the loading increased. Liquid phase alkylation indicated that catalytic activity of SPW is associated with amount and strength of surface acid sites and dispersivity of PW. Highly dispersed PW is much more effective than bulky solid ones. Liquid phase transalkylation showed that catalytic activity of SPW is determined by amount and strength of surface acid sites. SPW with large amount and strong acid strength of surface acid sites as well as relatively large specific surface areas has high activity in both alkylation and transalkylation. SPW is very active and selective in both alkylation and transalkylation. [Copyright &y& Elsevier]

The dehydrogenation of ethylbenzene to styrene was performed in the presence of carbon dioxide instead of steam over a series of alumina supported catalysts, which was believed to be an energy-saving and environmentally friendly process. The effects of active components, promoters, textural properties and other preparation parameters on the catalyst behaviors were examined. The results indicated that the conversion of ethylbenzene could be greatly improved by the reaction coupling due to the simultaneous elimination of hydrogen produced from the dehydrogenation, and vanadium supported on alumina with chromium as promoter was suggested to be promising catalysts. With the catalyst VCr/Al2O3, high ethylbenzene conversion (about 50%) and selectivity to styrene (95–99%) at lower temperature (550 °C) was achieved with reasonable stability (>70 h). The main cause of catalyst deactivation is the coke deposition, which may be alleviated in the presence of carbon dioxide. The catalytic activity of V/Al2O3 can be resumed completely after burning the coke by air or diluted air. Moreover, the catalyst characterization showed that high ratio of mesopore in the γ-Al2O3 support could benefit the catalyst activity and stability. [Copyright &y& Elsevier]

Alumina-supported vanadium oxide, VOx/Al2O3, and binary vanadium–antimony oxides, VSbOx/Al2O3, have been tested in the ethylbenzene dehydrogenation with carbon dioxide and characterized by SBET, X-ray diffraction, X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction and CO2 pulse methods. VSbOx/Al2O3 exhibited enhanced catalytic activity and especially on-stream stability compared to VOx/Al2O3 catalyst. Incorporation of antimony into VOx/Al2O3 increased dispersion of active VOx species, enhanced redox properties of the systems and formed a new mixed vanadium–antimony oxide phase in the most catalytically efficient V0.43Sb0.57Ox/Al2O3 system. [Copyright &y& Elsevier]

The catalytic dehydrogenation of ethylbenzene to produce styrene is an important industrial process because it is used in the manufacture of resins, synthetic rubber and plastics. The most used catalysts for this process are iron oxides containing potassium and chromium oxides. These catalysts show high activity and selectivity but deactivate with time on-stream in the industrial units, mainly due to the loss of potassium. On the other hand, the storage of the exhausted catalytic materials causes environmental damage because of the toxicity of chromium compounds. In order to find non-toxic and potassium-free catalysts, the effect of aluminum and the salt precursor on the properties of iron oxides was investigated in this work. The catalysts showed high specific area, were resistant to reduction and were potassium-free; these features can prevent their deactivation. Also, they showed higher activity and selectivity than hematite and were no harmful for the environment. In these catalysts aluminum acts both as textural and structural promoter. Among the starting salt precursors studied (nitrate, sulfate and chloride), the iron chloride was the most efficient one, producing active and selective catalysts with high resistance against deactivation. [Copyright &y& Elsevier]

Catalyst development for non-stationary redox application is still time consuming. A new method for high-throughput screening of catalysts under non-steady-state conditions is introduced enabling catalyst screening with >50 samples per day. The new method was applied to the oxidative dehydrogenation of ethylbenzene (ODEB) performed by alternately feeding ethylbenzene and oxygen. A highly selective mixed metal oxide catalyst (composition K2O (0.3 wt.%)/V2O5 (16 wt.%)/MgO) was found which converts ethylbenzene into styrene with an overall yield of 80.2% obtained by adding up both the wt.% ethylbenzene and the oxygen pulse. Selectivities in the ethylbenzene pulse amounted up to 98%. Mechanistic investigations reveal that the reaction does not proceed in a typical redox type mode. [Copyright &y& Elsevier]

Huge improvements towards the development of environmentally friendly processes have been achieved in the alkylations of aromatics with olefins, since the last four or five decades. Particularly, much efforts have been devoted to the research of solid catalysts adequate to substitute mineral or Lewis acids and free bases traditionally employed as catalysts in the acid or base catalyzed alkylations. Here we review the options industrially worthy of note in the alkylations of benzene and toluene for the production of ethylbenzene (EB), cumene, linear alkyl benzene and cymene. We also discuss features of different zeolites as a function of their activity and selectivity in the reactions considered. [Copyright &y& Elsevier]

Abstract: The dehydrogenation of ethylbenzene over alumina-supported vanadium–antimony oxide catalyst has been studied under different atmospheres such as inert nitrogen, steam, oxygen and carbon dioxide as diluent or oxidant. Among them, the addition of CO2 gave the highest styrene yield (up to 82%) and styrene selectivity (up to 97%) along with stable catalytic performance. Carbon dioxide plays a beneficial role as a selective oxidant in improving the catalytic behavior through the oxidative pathway. [Copyright &y& Elsevier]