Effective routes of stabilization of pyrophoric industrial catalysts

Крылова, А. В.; Ustimenko, G.A.; Nefedova, N. V.; Peev, Todor; Torocheshnikov, N.S.

doi:10.1016/s0166-9834(00)83180-2

Cited by 3 publications

(5 citation statements)

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“…It was showed that carbon dioxide, water vapor, or mixtures of oxidizing agents (oxygen + carbon dioxide + water vapor in different compositions) could be utilized for passivation purposes. 9,10 Investigations on using water vapor as the oxidation agent in iron catalyst passivation were performed. The proposed process was carried out in two stages: In the first stage, the catalyst bed was cooled to 250−200 °C and consequently the catalyst interacted with the mixture of nitrogen and water vapor, whereas in the second stage the catalyst bed was cooled to a temperature below 100 °C and the catalyst was passivated using the classic technique.…”

Section: ■ Introductionmentioning

confidence: 99%

Passivation versus Oxidation of Iron Catalyst with Carbon Dioxide

Ekiert

Arabczyk

2015

J. Phys. Chem. C

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The rate of iron catalyst passivation is strongly limited because the reaction of iron with oxygen is exothermic. It was proposed to perform passivation process using endothermic reaction of Fe oxidation with CO 2 . A thorough insight into the mechanism of the reaction of nanocrystalline iron with carbon dioxide was required. Therefore, oxidation of commercial iron catalyst for ammonia synthesis with CO 2 was investigated (T=300-500 o C, p CO2 =3.75-101.325 kPa). Thermogravimetry, XRD, SEM/EDX and GC were used in measurements.The only solid product of the Fe catalyst oxidation with CO 2 was magnetite Fe 3 O 4 , whereas the only gaseous one -CO. At the initial stage of oxidation of Fe catalyst with CO 2 the process occurred in accordance with the adsorption range model. In this scope, kinetics was described using Langmuir-Hinshelwood model for p CO2 <50 kPa. Above this value the oxidation rate is independent of p CO2 . With the progress of the oxidation process, the surface reaction ceased to be the slowest step, which limited the process rate, and the process started to be driven by gas diffusion in pores. The apparent activation energy was determined as ca. 120kJ/mol.It was assumed, that low temperature oxidation with CO 2 led to creation of magnetite layer, which had no passive properties. The complementary stage of passivation with oxygen at low pressure was needed to obtain a stable, protective oxide layer. However, the time spent on the whole process of passivation was significantly shorter than that in the classic route.

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Section: ■ Introductionmentioning

confidence: 99%

Passivation versus Oxidation of Iron Catalyst with Carbon Dioxide

Ekiert

Arabczyk

2015

J. Phys. Chem. C

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“…This behavior is typical of an operating catalyst, and in fact, some catalysts are too reactive in their active state to be safely transported, and hence established protocols exist to deliver passivated precursor states, which are filled into the reactor and then activated [1,2]. Slight variations in the material define various precursor states of the catalyst, the activated and active states, and the deactivated state.…”

Section: Introductionmentioning

confidence: 99%

The Balance Between Reactivity and Stability of Modified Oxide Surfaces Illustrated by the Behavior of Sulfated Zirconia Catalysts

Klose-Schubert

Jentoft

2011

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The stability of a series of sulfated zirconia catalysts, promoted with up to 2 wt% iron or manganese, in their calcined state was investigated. Phase composition, nature of surface sulfate species, degree of hydroxylation, and butane isomerization activity changed duri ng aging over months in various atmospheres and during milling. The metastability of small oxide particles is discussed, including literature data on alumina, titania and other oxides. Catalytically active fractions of a material easily transition into more stable, less active forms.

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“…[4][5][6] Further investigations showed, that in the reaction between reduced iron catalyst and oxygen of different partial pressures in the range of temperature -195 to -85 °C as well as 450-550 °C the oxidation degree characteristic for passivation process had been obtained, and the oxidized material was no longer pyrophoric. [7][8][9][10][11] The dependence of mass increments vs temperature had the form of a so-called "bell curve". The behavior of the catalyst under oxygen atmosphere was surprising, viz.…”

Section: Introductionmentioning

confidence: 99%

“…However, this procedure is energy- and time-consuming and uses great amounts of nitrogen. Searching for the new methods of iron catalyst passivation some trials to explain the mechanism of this process were undertaken. − Experiments were carried out to study the interaction of oxygen, nitrogen, and hydrogen with the ammonia synthesis catalyst . Initially, it was proposed, that passive layer had been composed of adsorbed water and oxygen monolayer formed as a result of the reaction between oxygen added and hydrogen left in catalyst after its reduction during activation process.…”

Section: Introductionmentioning

confidence: 99%

“…Initially, it was proposed, that passive layer had been composed of adsorbed water and oxygen monolayer formed as a result of the reaction between oxygen added and hydrogen left in catalyst after its reduction during activation process. However, it has been found later that the passive layer with the multilayer structure was formed. − Further investigations showed, that in the reaction between reduced iron catalyst and oxygen of different partial pressures in the range of temperature −195 to −85 °C as well as 450−550 °C the oxidation degree characteristic for passivation process had been obtained, and the oxidized material was no longer pyrophoric. − The dependence of mass increments vs temperature had the form of a so-called “bell curve”. The behavior of the catalyst under oxygen atmosphere was surprising, viz.…”

Section: Introductionmentioning

confidence: 99%

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Studies of the Oxidation of Nanocrystalline Iron with Oxygen by means of TG, MS, and XRD Methods

2008

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The oxidation of the nanocrystalline iron containing small amounts of structural promotersssuch as aluminum, calcium, and potassium oxidesshas been studied. The oxidation processes were carried out under atmospheric pressure at pure oxygen atmosphere at various temperatures in the range of 573-773 K, in the differential tubular reactor with thermogravimetric (TG) measurement. Nanocrystalline promoted iron did not reveal the pyrophority under pure oxygen atmosphere at temperatures higher than 573 K. The oxide layer stable at a given temperature was formed and protected the iron against further oxidation. The higher oxidation temperature, the thinner was the oxide layer. X-ray diffraction analysis (XRD) and Mo ¨ssbauer spectroscopy (MS) were used to characterize the oxidized samples in order to determine the structure of formed oxides. The XRD analysis proved the magnetite structure of obtained iron oxides. The Mo ¨ssbauer studies revealed that magnetite layer formed at temperatures higher than 573 K had got the disturbed structure, derived from aluminum ions incorporation into the tetrahedral sites of magnetite's lattice. The ratio of the number of iron atoms to the number of aluminum atoms located in tetrahedral sites was 2:1 whereas the ratio of the number of iron atoms located in tetrahedral sites to the number of iron atom located in octahedral sites was 1:3.

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Effective routes of stabilization of pyrophoric industrial catalysts

Cited by 3 publications

References 0 publications

Passivation versus Oxidation of Iron Catalyst with Carbon Dioxide

Passivation versus Oxidation of Iron Catalyst with Carbon Dioxide

The Balance Between Reactivity and Stability of Modified Oxide Surfaces Illustrated by the Behavior of Sulfated Zirconia Catalysts

Studies of the Oxidation of Nanocrystalline Iron with Oxygen by means of TG, MS, and XRD Methods

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