Microkinetic modelling of the dehydrogenation of ethylbenzene to styrene over unpromoted iron oxides

Schüle, Achim; Shekhah, Osama; Ranke, Wolfgang; Schlögl, Robert; Kolios, Grigorios

doi:10.1016/j.jcat.2005.01.013

Cited by 22 publications

(16 citation statements)

References 24 publications

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“…Concerning the mechanism of catalytic dehydrogenation of ethylbenzene to styrene over iron oxides this is a remarkable result. In model catalysis experiments over Fe 2 O 3 [4,35] it was found that the H formed on the surface reduces the catalyst to Fe 3 O 4 . However, the produced amount of styrene and thus also of hydrogen was by about two orders of magnitude higher than explainable by a stoichiometric reduction reaction with oxygen from the catalyst.…”

Section: H At On Feo(111) -Discussionmentioning

confidence: 99%

Autocatalytic partial reduction of FeO(111) and Fe3O4(111) films by atomic hydrogen

Huang

Ranke

2006

Surface Science

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The interaction of atomic hydrogen with thin epitaxial FeO(111) and Fe3O4(111) films was studied by TDS, XPS and LEED. On the thin, one Fe-O bilayer thick FeO film, partial reduction occurs in two steps during exposure. It ends after removal of ¼ monolayer (ML) of oxygen with a 2´2 pattern appearing in LEED. This FeO0.75 film is passive against further reduction. The first reduction step saturates after removal of ~0.2 ML and shows autocatalytic kinetics with the oxygen vacancies formed during reduction causing acceleration. The second step is also autocatalytic and is related with reduction to the final composition and an improvement of the 2´2 order. A structure model explaining the two-step reduction is proposed. On the thick Fe3O4 film, irregular desorption bursts of H2O and H2 were observed during exposure. Their occurrence appears to depend on the film quality and thus on surface order. Because of the healing of reduction-induced oxygen vacancies by exchange of oxygen or iron with the bulk, a change of the surface composition was not visible. The existence of partially reduced oxide phases resistant even to atomic hydrogen is relevant to the mechanism of dehydrogenation reactions using iron oxides as catalysts.Key words: Low energy electron diffraction, X-ray photoelectron spectroscopy, temperature programmed desorption, catalysis, surface chemical reaction, hydrogen atom, iron oxide IntroductionIron oxides, widespread in nature, are of interest to many scientific disciplines from geology to biology [1]. The reduction of iron oxides is inevitable in many processes, such as metallurgy, corrosion, and heterogeneous catalysis. It was long found that the very rapid dissolution of the passive iron oxides film on iron involves a reductive mechanism [2]. The surface reduction, together with coke formation, is responsible for the deactivation of the iron oxide-based catalyst for the dehydrogenation of ethylbenzene to styrene [3,4]. Because of their relevance for corrosion processes, the reduction of iron oxides in solution has been extensively studied and a clear understanding of the mechanism and kinetics is acquired [5]. However, fundamental understanding of of iron oxide reduction by gas phase hydrogen is poor.Most fundamental understanding of the gas-solid interactions comes from surface science studies of relevant model systems under ultra-high-vacuum (UHV) conditions. Very little is known about the interaction of hydrogen with well-characterized single-crystal iron oxides. The nearly stoichiometric, well ordered a-Fe 2 O 3 (0001) surface is inert towards molecular hydrogen at room temperature and interaction occurs only at defects [6]. Thus it is difficult to approach the reduction of iron oxides by employing molecular hydrogen. The reason is, of course, the high dissociation energy of H 2 (432 kJ/mol). Atomically adsorbed hydrogen, OH groups or protons are formed in catalytic dehydrogenation reactions or during electrochemical reduction. Therefore it makes sense to study the interaction of surfaces...

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Section: H At On Feo(111) -Discussionmentioning

confidence: 99%

Autocatalytic partial reduction of FeO(111) and Fe3O4(111) films by atomic hydrogen

Huang

Ranke

2006

Surface Science

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“…The depth of the qualitative and quantitative insight already gained was used to design a microkinetic model177 of the reaction based on experimental observations. In contrast to earlier attempts that followed the approach given above with an active center of unspecified nature, in this study a model of a catalyst is used that boasts both oxidic as well as carbon‐based active centers with the generation of these active centers explicitly taken into account.…”

Section: Case Study Of the Dehydrogenation Of Ethylbenzene Over Irmentioning

confidence: 99%

Heterogeneous Catalysis

2015

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“…Iron (hydr)oxides have been widely used as catalysts in various heterogeneous catalytic processes such as Haber-Bosch to produce ammonia (Bogdanov et al, 1990;Holme, 1997), the Fischer-Tropsch hydrocarbon synthesis (Moodley et al, 2010;Dong et al, 2011;, steam reforming (Matsuoka et al, 2006;Gong et al, 2009), water-gas shift (Basinska et al, 2006;Datta et al, 2011), ethylbenzene dehydro-genation to produce styrene monomers (Schüle et al, 2005;Li & Shanks, 2011), water splitting for hydrogen production (Lin et al, 2011;Pereira et al, 2011a), aerobic oxidation of organic compounds to produce new products for the fine chemical industry (Menini et al, 2008(Menini et al, , 2011 and in advanced oxidation processes (AOPs) to oxidize pollutants in water and soils (He et al, 2002;Andrade et al, 2009;Silva et al, 2009;Botas et al, 2010;Hu et al, 2011;Rodriguez et al, 2011;Sreethawong & Chavadej, 2011;Vicente et al, 2011).…”

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confidence: 99%

Iron oxide catalysts: Fenton and Fentonlike reactions – a review

2012

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Iron is the fourth most common element by mass in the Earth's crust and forms compounds in several oxidation states. Iron (hydr)oxides, some of which form inherently and exclusively in the nanometre-size range, are ubiquitous in nature and readily synthesized. These facts add up to render many Fe (hydr)oxides suitable as catalysts, and it is hardly surprising that numerous studies on the applications of Fe (hydr)oxides in catalysis have been published. Moreover, the abundant availability of a natural Fe source from rocks and soils at minimal cost makes the potential use of these as heterogeneous catalyst attractive.Besides those Fe (hydr)oxides that are inherently nanocrystalline (ferrihydrite, Fe5HO8.4H2O, and feroxyhyte, δ’-FeOOH), magnetite (Fe3O4) is often used as a catalyst because it has a permanent magnetization and contains Fe in both the divalent and trivalent states. Hematite, goethite and lepidocrocite have also been used as catalysts in their pure forms, doped with other cations, and as composites with carbon, alumina and zeolites among others.In this review we report on the use of synthetic and natural Fe (hydr)oxides as catalysts in environmental remediation procedures using an advanced oxidation process, more specifically the Fenton-like system, which is highly efficient in generating reactive species such as hydroxyl radicals, even at room temperature and under atmospheric pressure. The catalytic efficiency of Fe (hydr)oxides is strongly affected by factors such as the Fe oxidation state, surface area, isomorphic substitution of Fe by other cations, pH and temperature.

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Microkinetic modelling of the dehydrogenation of ethylbenzene to styrene over unpromoted iron oxides

Cited by 22 publications

References 24 publications

Autocatalytic partial reduction of FeO(111) and Fe3O4(111) films by atomic hydrogen

Autocatalytic partial reduction of FeO(111) and Fe3O4(111) films by atomic hydrogen

Heterogeneous Catalysis

Iron oxide catalysts: Fenton and Fentonlike reactions – a review

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