IR study of reaction of 2‐butene adsorbed on deuterated ZSM‐5 and mordenite

The dehydrogenation of ethylbenzene to styrene was studied over single-crystalline iron oxide model catalyst films grown epitaxially onto Pt(111) substrates. The role of the iron oxide stoichiometry and of atomic surface defects for the catalytic activity was investigated by preparing single-phased Fe₃O₄(111) and α-Fe₂O₃(0001) films with defined surface structures and varying concentrations of atomic surface defects. The structure and composition of the iron oxide films were controlled by low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES), the surface defect concentrations were determined from the diffuse background intensities in the LEED patterns. These ultrahigh vacuum experiments were combined with batch reactor experiments performed in water–ethylbenzene mixtures with a total gas pressure of 0.6 mbar. No styrene formation is observed on the Fe₃O₄ films. The α-Fe₂O₃ films are catalytically active, and the styrene formation rate increases with increasing surface defect concentration on these films. This reveals atomic surface defects as active sites for the ethylbenzene dehydrogenation over unpromoted α-Fe₂O₃. After 30 min reaction time, the films were deactivated by hydrocarbon surface deposits. The deactivation process was monitored by imaging the surface deposits with a photoelectron emission microscope (PEEM). It starts at extended defects and exhibits a pattern formation after further growth. This indicates that the deactivation is a site-selective process. Post-reaction LEED and AES analysis reveals partly reduced Fe₂O₃ films, which shows that a reduction process takes place during the reaction which also deactivates the Fe₂O₃ films.     

Understanding heterogeneous catalysis on an atomic scale: a combined surface science and reactivity investigation for the dehydrogenation of ethylbenzene over iron oxide catalysts

In order to study the dehydrogenation of ethylbenzene to styrene, epitaxial iron oxide model catalyst films with Fe₃O₄(111), -Fe₂O₃(0001) and KFe _x O _y (111) stoichiometry were prepared in single crystal quality on Pt(111). They were investigated using surface science techniques before and after atmospheric pressure reaction experiments in a newly designed single crystal flow reactor. As expected from low-pressure measurements, Fe₃O₄(111) is catalytically inactive. The catalytic activity of -Fe₂O₃(0001) starts after an activation period of about 45 min. After that, the surface is essentially clean but shows a high concentration of defects. On the potassium-promoted films, however, the activation period is much longer, the activity then is higher and the surface gets covered completely with carbon and oxygen during reaction. This indicates a different reaction pathway on the promoted films with a carbon–oxygen species as catalytically active species.     

Novel Perovskite-Type Oxide Catalysts for Dehydrogenation of Ethylbenzene to Styrene

We investigated novel LaMnOx perovskite-oxide (ABO₃) catalysts for effective catalytic dehydrogenation of ethylbenzene to produce styrene monomer. Comparison with industrial Fe–K catalyst, our La_0.8Ba_0.2Mn_0.6Fe_0.4O_3-δ catalyst showed higher activity. Results show that the A-site in perovskite-type oxides affected catalytic dehydrogenation activities and that the B-site affected stability of the activities.     

Distribution of alkaline promoters within the structure of iron oxide catalyst for dehydrogenation

Along with potassium, cesium is an efficient promoter of catalytic activity of iron oxide catalysts for dehydrogenation of olefins and alkylaromatic hydrocarbons. In the reaction medium, a catalyst is a ferrite system consisting of potassium β″-polyferrite, potassium and cesium monoferrites, and magnetite. The character of the distribution of alkaline promoters within the catalyst structure is studied to provide the theoretically substantiated calculation of the optimal composition of this type of catalysts. The preferred location of cesium ions is shown to be the structure of β″-polyferrite of K_{2 ? z} Cs _z Fe²⁺Fe ₁₀ ³⁺ O₁₇ composition. The catalytic activity of this system with different contents of cesium in the dehydrogenation of ethylbenzene to styrene (flow-type reactor; 0.1 MPa; 600°C; hourly space velocity of ethylbenzene, 1 h^?1; ethylbenzene : steam weight ratio, 1 : 3) was tested. The maximum specific rate of styrene formation is attained at a Cs : Fe ratio in the interval 0.023–0.027, corresponding to the coefficient z = 0.26–0.30. It is impractical to introduce more cesium. Theoretical propositions for targeted transporting of a promoting agent to a given phase of a catalytically active ferrite system are developed. The content of expensive cesium compounds in iron oxide catalyst is optimized.     

Oxidative Dehydrogenation of Ethylbenzene over Cu1-x Co x Fe2O4 Catalyst System: Influence of Acid–Base Property

A series of Cu–Co ferrites with the general formula Cu_1-x Co _x Fe₂O₄ (x = 0, 0.25, 0.50, 0.75 and 1.0) was prepared by a low-temperature hydroxide coprecipitation route. The catalyst systems were characterized by adopting various physicochemical techniques. The acid–base properties were studied in detail, and the catalytic activity as well as the selectivity for oxidative dehydrogenation of ethylbenzene was compared for various compositions. FTIR adsorption of pyridine is carried out to understand the relative acidity of various compositions of the systems. IR studies of spinel surface with adsorbed CO₂ and adsorption studies of electron acceptors such as 7,7,8,8-tetracyanoquinodimethane, 2,3,5,6-tetrachloro-1-4-benzoquinone and p-dinitrobenzene are carried out to evaluate the nature of basic sites and the strength and distribution of electron donor sites present on the spinel surface. It is found that acidity (basicity) of the Cu_1-x Co _x Fe₂O₄ spinel system increases (decreases) from x = 0 to 1. A good correlation was found between the activity for this reaction and the surface acid–base properties of the catalysts. Intermediate compositions show better catalytic performance, among which x = 0.50 is superior and demonstrates an intermediate acid–base character. It was observed that dehydrogenation of ethylbenzene to styrene proceeds mainly on an acid–base pair site.     

Optimum ratio of K2O to CeO2 in a wet-chemical method prepared catalysts for ethylbenzene dehydrogenation

Fe₂O₃–K₂O–CeO₂ catalysts with various ratios of K₂O to CeO₂ were prepared by the wet-chemical method. Their phase compositions, reducibility, valence states of elements and catalytic activities for ethylbenzene dehydrogenation were studied. The results demonstrated that when the weight ratio of K₂O: CeO₂ was 1.40, the catalyst had highest ethylbenzene conversion and styrene selectivity, which were attributed to the optimization of active phase content and electron transfer ability, etc. Further, higher CeO₂ content not only enhanced styrene selectivity, but also prolonged the life cycle of catalysts.     

SO2 promoted oxidative dehydrogenation of ethylbenzene

It has been demonstrated that SO₂ acts as an efficient dehydrogenation agent in the conversion of ethylbenzene to styrene in the presence of alkali and alkaline earth metal oxide doped alumina and titania catalysts. Development of these catalysts, which give styrene yields of greater than 80% per pass, is described in the paper. The catalysts allow the use of close to stoichiometric amounts of sulphur dioxide, are active in the presence of steam diluent and show low deactivation with time. The effect of varying process conditions such as temperature, reactant concentration and diluent amount is also described.     

Dehydrogenation of ethylbenzene to styrene over Fe2O3/Al2O3 catalysts in the presence of carbon dioxide

An Fe₂O₃ (10 wt%)/Al₂O₃ (90 wt%) catalyst prepared by a coprecipitation method was found to be effective for dehydrogenation of ethylbenzene to produce styrene in the presence of CO₂ instead of steam used in commercial processes. The dehydrogenation of ethylbenzene over the catalyst in the presence of CO₂ was considered to proceed both via a one-step pathway and via a two-step pathway. CO₂ was found to suppress the deactivation of the catalyst during the dehydrogenation of ethylbenzene. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dehydrogenation of ethylbenzene to styrene over Fe2O3/Al2O3 catalysts in the presence of carbon dioxide

Thermodynamic consideration of the dehydrogenation of ethylbenzene clearly indicates that the equilibrium yield of styrene for the dehydrogenation in the presence of CO₂ is much higher than that for the dehydrogenation in the presence of steam. A two-step pathway for the dehydrogenation in the presence of CO₂ appears to provide higher equilibrium yield of styrene at a given temperature. The amount of energy required for the new process using CO₂ is much lower than that for a typical present commercial process using steam. An Fe₂O₃(10 wt.%)/Al₂O₃(90 wt.%) catalyst prepared by a coprecipitation method was found to be effective for the dehydrogenation of ethylbenzene to produce styrene in the presence of CO₂.     

On the deactivation of Fe,K/active carbon catalysts in the course of oxidative dehydrogenation of ethylbenzene with carbon dioxide

Highly active and selective Fe₂O₃–K₂O/C_act catalysts for oxidative dehydrogenation of ethylbenzene with CO₂ undergo deactivation. The course of deactivation up to a loss of 95% activity is described, and related to the formation of an inactive carbonaceous deposit. The catalysts and deposits were characterized after various times-on-stream (TOS) by textural, structural and chemical analysis, as well as by temperature-programmed decomposition and oxidation. XPS spectra of O 1s and K 2p confirmed the removal of OH and diminishing of carbonyl groups, as well as segregation of K₂CO₃ onto the surface. Prolonged TOS, at temperatures above 500°C caused removal of heteroatoms from the carbonaceous deposits and even the appearance of graphitized structure in XRD patterns. It was found that the activity depended almost linearly on the amount of and the decrease in surface area. An excess of CO in relation to styrene in the product distribution suggests that the deposit is formed owing to styrene polymerization, and further dehydrogenation, on the catalyst surface. This revised version was published online in August 2006 with corrections to the Cover Date.     

Dehydrogenation of ethylbenzene over TiO2-Fe2O3 and ZrO2-Fe2O3 mixed oxide catalysts

The mixed metal oxides TiO₂-Fe₂O₃ and ZrO₂-Fe₂O₃ were examined as potential catalysts for the dehydrogenation reaction of ethylbenzene. The acidic and basic properties and surface area, pore volume and pore size distribution of these catalysts were measured. The catalytic activities can be correlated very well with the surface area and the acidity and basicity of ZrO₂-Fe₂O₃ catalysts. However, for TiO₂-Fe₂O₃ catalysts, the surface area, the amount of acidic and basic sites and TiFe₂O₅ crystallinity are all important factors affecting the catalytic activities for ethylbenzene dehydrogenation. A synergistic effect was found for the TiO₂-Fe₂O₃ and ZrO₂-Fe₂O₃ catalyst system and also for the TiO₂-Fe₂O₃-ZrO₂ system, i.e. the activities of these catalysts can be ranked in the following order: TiO₂-Fe₂O₃-ZrO₂>TiO₂-Fe₂O₃ >ZrO₂>Fe₂O₃>TiO₂. Meanwhile, all of these catalysts showed higher activities than the conventional potassium-promoted iron catalysts.     

Microwave-assisted catalytic oxidative dehydrogenation of ethylbenzene on iron oxide loaded carbon nanotubes

The catalytic performance of multi-walled carbon nanotubes (MWCNTs) modified by iron oxide has been investigated for oxidative dehydrogenation of ethylbenzene in an integral fixed-bed reactor conventionally-heated and under microwave-assisted conditions. The morphology and microstructural characteristics of the obtained composites before and after the catalytic reaction were characterized by transmission electron microscopy and X-ray diffraction. The content 3wt.% of iron oxide supported on MWCNTs was found optimal in respect of the ethylbenzene conversion and styrene selectivity. All prepared composites were found more selective in a microwave field in the temperature range 380-450 °C. The transformation of Fe₂O₃ into Fe nanocrystals encapsulated by polyhedral graphite shells was observed only under microwave-assisted reaction conditions.     

Dehydrogenation of ethylbenzene in the presence of CO2 using a catalyst synthesized by polymeric precursor method

Catalysts of iron oxide dispersed on Al or Si oxides were prepared via a polymeric precursor derived from the Pechini method and tested in the dehydrogenation of ethylbenzene in the presence of CO₂, in order to contribute with the studies of this reaction. The catalysts were characterized by thermogravimetric analysis (TG), temperature-programmed reduction (TPR), X-ray diffraction (DRX) and temperature-programmed desorption of CO₂ (TPD-CO₂). Analysis of the spent catalysts by TG and Fourier transformed infrared spectroscopy (FT-IR) pointed to the contribution of CO₂ to the coke deposition. The catalytic results suggest that the high initial ethylbenzene conversion is due to the contribution of basic sites, and the CO₂ adsorption in the basic site (lattice oxygen) may compete with the oxidative dehydrogenation of ethylbenzene. Although CO₂ provides the appropriate conditions to lower the consumption of the basic site, it is not able to promote the Fe²⁺ oxidation or to regenerate the basic site (lattice oxygen) in the iron oxide dispersed on Al or Si oxide catalysts.     

Kinetics of the dehydrogenation of ethylbenzene to styrene over unpromoted and K-promoted model iron oxide catalysts

The dehydrogenation of ethylbenzene to styrene over unpromoted and potassium-promoted model iron oxide catalysts has been studied using ultrahigh vacuum techniques in conjunction with elevated pressure reaction kinetics. Model iron oxide catalysts were prepared by oxidizing a polycrystalline Fe sample that was subsequently dosed with metallic potassium. At 875 K the unpromoted catalyst exhibited a turnover frequency of 5×10^–4 molecules/ site s and an activation energy of 39 kcal/mol, both in excellent agreement with the results found for an analogous iron oxide powder catalyst. Potassium promotion increased the turnover frequency to 1.0×10^–3 molecules/site s and lowered the activation energy to 36 kcal/mol for the dehydrogenation reaction. Similarities between the activation energies on the unpromoted and promoted catalysts indicate that the active site is the same on both catalysts. Creation of the active site was dependent upon the formation of an Fe³⁺ metastable species, consistent with the formation of a KFeO₂ phase, upon the addition of potassium.     

Oxidative dehydrogenation of 4-vinylcyclohexene into styrene over ZrO2 catalyst promoted with Fe2O3 and CaO

The oxidative dehydrogenation of 4-vinylcyclohexene (VCH) into styrene was carried out in the presence of oxygen over a ZrO₂ catalyst promoted with Fe₂O₃ and CaO. Intrinsically, ZrO₂ showed high dehydrogenation activity, which resulted in 80% styrene selectivity with 45% conversion at 425 °C and LHSV 3 h⁻¹. When the ZrO₂ was further promoted with calcium and iron, CaO/Fe₂O₃/ZrO₂, the highest styrene selectivity of 88.9% was obtained as well as the lowest deactivation. The deactivation of catalyst was prohibited properly through the introduction of oxygen in the reactant together with the modification of Fe₂O₃/ZrO₂ with CaO. The CaO/Fe₂O₃/ZrO₂ showed constant catalytic activity and selectivity for more than 50 h without deactivation. The selectivity of styrene was strongly influenced by the mole ratio of O₂/VCH and 95% selectivity with 80% conversion was obtained at O₂/VCH mole ratio of 6 over Fe₂O₃/ZrO₂. It is thought that the oxidative dehydrogenation proceeds through the dehydrogenation (DH) of ring-hydrocarbon of VCH followed by selective combustion of hydrogen (SHC) and the high selectivity of styrene was achieved by the bi-functional role of ZrO₂ for DH and SHC reactions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Oxidative Dehydrogenation of Ethylbenzene with Carbon Dioxide over Metal-Doped Titanium Oxides

Various metal-doped (Fe, V, Zr, Mg) titanium oxides were prepared by an acid-catalyzed sol–gel method and their properties as catalysts were investigated for oxidative dehydrogenation of ethylbenzene in the presence of carbon dioxide. The characterization techniques, XRD, BET, TGA were employed to analyze the features of catalyst. Fe₃Ti catalyst was found to be quite effective among the catalysts tested at 823 K, 39.8% ethylbenzene conversion and 98% styrene selectivity were acquired.     

Phenomenological‐based kinetics modelling of dehydrogenation of ethylbenzene to styrene over a Mg3Fe0.25Mn0.25Al0.5 hydrotalcite catalyst

This communication reports a mechanism‐based kinetics modelling for the dehydrogenation of ethylbenzene to styrene (ST) using Mg₃Fe_0.25Mn_0.25Al_0.5 catalyst. Physicochemical characterisation of the catalyst indicates that the presence of basic sites Mg²⁺O^2? on the catalysts along with Fe³⁺ is responsible for the catalytic activity. The kinetics experiments are developed using a CREC Fluidised Riser Simulator. Based on the experimental observations and the possible mechanism of the various elementary steps, Langmuir–Hinshelwood type kinetics model are developed. To take into account of the possible catalyst deactivation a reactant conversion‐based deactivation function is also introduced into the model. Parameters are estimated by fitting of the experimental data implemented in MATLAB. Results show that one site type Langmuir–Hinshelwood model appropriately describes the experimental data, with adequate statistical fitting indicators and also satisfied the thermodynamic restraints. The estimated heat of adsorptions of EB (64 kJ/mole) is comparable to the values available in the literature. The activation energy for the formation of ST (85.5 kJ/mole) found to be significantly lower than that of the cracking product benzene (136.6 kJ/mole). These results are highly desirable in order to achieve high selectivity of the desired product ST. © 2012 Canadian Society for Chemical Engineering     

High Performance of Fe–K Oxide Catalysts for Dehydrogenation of Ethylbenzene to Styrene with an aid of ppm-order Pd

Styrene is manufactured industrially through catalytic dehydrogenation of ethylbenzene on Fe–K oxide-based catalysts. It was invented by Süd-Chemie Group that the activity of the industrial ethylbenzene dehydrogenation catalysts (Styromax) based on the oxides of Fe and K is highly promoted by the addition of small amount (hundreds ppm-order) of precious metals such as Pd. The present work is intended to elucidate the role of Pd on the Fe–K catalyst empirically by use of a periodical pulse technique from a mechanistic point of view. The oxidative dehydrogenation was faster than the simple dehydrogenation, and it proceeded by consuming the surface lattice oxygen in the catalyst. The lattice oxygen was subsequently supplied from steam. Palladium added to the Fe–K oxide catalysts was found to enhance the rate of regeneration (supplying) of the lattice oxygen, although it hardly changed the rate of dehydrogenation of ethylbenzene or consumption of surface lattice O^2? anions. This study demonstrated that steam works not only as a diluent but also as a reactant to form hydrogen and lattice oxygen.     

Amorphous porous MxTi mixed oxides as catalysts for the oxidative dehydrogenation of ethylbenzene

The properties of different metal‐oxide‐doped porous titanium oxides as catalysts for the oxidative dehydrogenation of ethylbenzene were investigated. Amorphous porous mixed oxides based on the amorphous titania matrix with selected metal ion centers as active sites have been prepared by an acid‐catalyzed sol–gel method. The dehydrogenation of ethylbenzene was studied in a continuous gas phase flow reactor under different reaction temperatures at ambient pressure. Among the 23 catalysts studied the amorphous porous AM‐Cr₅Ti mixed oxide is the most promising catalyst. At 350 °C a 75% selectivity to styrene at a 29% conversion of ethylbenzene was obtained. BET, HRTEM, XRD, GC, MS, TGA and optical microscopy were employed to characterize the fresh and used AM‐Cr₅Ti catalyst. This revised version was published online in August 2006 with corrections to the Cover Date.     

Reaction Coupling of Ethylbenzene Dehydrogenation with Nitrobenzene Hydrogenation

The chemical equilibrium for the coupling of ethylbenzene dehydrogenation with nitrobenzene hydrogenation, to produce styrene and aniline simultaneously, has been calculated on the basis of the Soave–Redlich–Kwong equation of state. The dehydrogenation of ethylbenzene in the presence of nitrobenzene over the catalysts -Al₂O₃, ZSM-5, activated carbon and platinum supported on activated carbon has been carried out at 400 °C. The effects of Pt loading and the pretreatment of the catalysts have been investigated. It has been revealed that the conversion of ethylbenzene can be greatly improved by the reaction coupling due to the elimination of the hydrogen produced in the reaction by the hydrogenation of nitrobenzene. Platinum supported on the activated carbon has been suggested as a suitable catalyst. The best results with ethylbenzene conversion of 33.8% and styrene selectivity of 99.2% were obtained over Pt(0.02 wt%)/AC at 400 °C. Moreover, such process is also energetically favored since the necessary process heat to drive the ethylbenzene dehydrogenation can be provided by the coupling with the exothermic nitrobenzene hydrogenation reaction.