Autocatalytic Reduction of Hematite with Hydrogen under Conditions of Surface Control: A Vacancy-Based Mechanism

Elhamid, M. H. Abd; Khader, Mahmoud M.; Mahgoub, Ar.; Anadouli, B. E. El; Ateya, B. G.

doi:10.1006/jssc.1996.0175

Cited by 19 publications

(5 citation statements)

References 9 publications

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“…All these parameters have an influence on the rate-limiting step, and therefore, different rate-limiting steps lead to different apparent activation energies. By summarizing the results of previous studies, as given in table 4 [33,[35][36][37][38][39][40][41][42], it can be found that the apparent activation energy obtained when the reaction experimental conditions are similar to the reaction conditions in this study are also relatively consistent.…”

Section: 𝑘 = 𝐴𝑒supporting

confidence: 70%

Effect of water vapor on the reduction kinetics of hematite powder by hydrogen-water vapor in different stages

Mao

Fan

et al. 2023

J min metall B Metall

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The powder of hematite sample was isothermally reduced with hydrogen-water vapor gas mixture at 1023K-1273K. The results indicated that the overall reduction process of hematite could be separated into three stages (Fe2O3-Fe3O4-FeO-Fe) to respectively study. At 1023K, the average reaction rate dropped by 53.6% in the stage 1 when the water vapor content of gas reactant rose from 0% to 50%, and it decreased by about 77.2% in the stage 2. However, in the stage 3, when the water vapor content only increased from 0% to 20%, it decreased by about 78.1%. Besides, the average reaction rate had a roughly negative linear relationship with the water vapor content, and the results further shown that the effect of water vapor on the reduction reaction increased with increasing reaction temperature at all stages of the reduction reaction. The microstructure of reduction products showed that it still had some holes, which the channel for hydrogen diffusion was not seriously blocked. In order to further clarify the influence of water vapor in the reduction stage, different models were considered, and the range of apparent activation energy of different stages obtained by model fitting was about 20-70 kJ/mol, which also confirmed the absence of solid-state diffusion phenomenon.

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Section: 𝑘 = 𝐴𝑒supporting

confidence: 70%

Effect of water vapor on the reduction kinetics of hematite powder by hydrogen-water vapor in different stages

Mao

Fan

et al. 2023

J min metall B Metall

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“…The method is well-known in industrial molybdenum metallurgy, 32,33 and was previously used to engineer disorder and atomic defects in various materials. 34,35 The discussion below is divided into two major parts: the description of the structure of the investigated materials followed by the detailed assessment of their electrocatalytic activity for the reduction of dinitrogen to ammonia under various conditions.…”

Section: Resultsmentioning

confidence: 99%

Is Molybdenum Disulfide Modified with Molybdenum Metal Catalytically Active for the Nitrogen Reduction Reaction?

Hodgetts

Chatti

et al. 2020

J. Electrochem. Soc.

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Inspired by the previously published theoretical findings, the present work aims to assess the electrocatalytic activity of molybdenum(IV) sulfide modified with metallic molybdenum for the nitrogen reduction reaction in aqueous electrolyte solution (0.1 M Li2SO4; pH 3) and in aprotic [C4mpyr][eFAP] ionic liquid electrolyte at ambient temperature. The material of interest was synthesized via a high-temperature partial reduction of MoS2, while electrocatalytic tests followed a previously established robust protocol, which in particular involves strict control over any NH3 and NO3 −/NO2 − contamination at every key step. As expected, no activity was found in aqueous solutions. In aprotic medium, the formation of small amounts of ammonia at low rates was observed and was found to strongly depend on the water concentration and applied potential. However, the amount of electrochemically generated NH3 always reached a particular limit and did not increase further, even when the N2 pressure was increased from 1 to 16 bar. The results suggest rapid blockage of the surface of the investigated electromaterial with NH3, which prevents its operation as a catalyst for the ammonia electrosynthesis.

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“…We can write the conductivity (as function of heating time t ) in the form where e is the electronic charge, μ is the electronic mobility, and n is the density of conducting electrons. This is somewhat of a simplification as during reduction both surface and bulk oxygen anions are removed as water 27–30. The bulk oxygen is essentially always in the form of oxide ions, O 2− .…”

Section: Resultsmentioning

confidence: 99%

Reduction kinetics of ceria surface by hydrogen

Al-Madfa

Khader

Morris

2004

Int J of Chemical Kinetics

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Powdered cerium dioxide (ceria, CeO 2 ) as compressed, sintered pellets, of porosity 16.4% and density 5.99 g cm −3 , were treated in hydrogen flow at 1 atm and various temperatures to effect reduction. The electrical conductivity was measured in situ during the reduction process. The conductivity increased continuously during the hydrogen treatment because of the creation of anion vacancies and accompanying small polaron electrons. The conductivitytime relationship exhibits three distinct regions indicated as I, II, and III. For each of steps I and II, the conductivity increases exponentially with the reduction. It is suggested from the kinetic analysis of the data that region I is due to desorption of adsorbed oxygen states. Region II appears to be the reduction of surface lattice oxygen. The kinetics of the reactions in both regions I and II obey first-order rate laws with similar activation energies of 86 and 115 kJ mol −1 , respectively. Thermogravimetric experiments were used to determine the time needed to remove one monolayer of adsorbed oxygen from the surface. This could be used to estimate the activation energy of the desorption process at 95 kJ mol −1 -close to the value measured by conductivity measurements. After completing the surface reduction the electrical conductivity subsequently increased slowly during region III. This step is assigned to a diffusion-controlled process during which the bulk of the pellets are reduced. 1 H MASNMR and in situ PXRD experiments confirmed the chemical nature of each of the three steps. C

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Autocatalytic Reduction of Hematite with Hydrogen under Conditions of Surface Control: A Vacancy-Based Mechanism

Cited by 19 publications

References 9 publications

Effect of water vapor on the reduction kinetics of hematite powder by hydrogen-water vapor in different stages

Effect of water vapor on the reduction kinetics of hematite powder by hydrogen-water vapor in different stages

Is Molybdenum Disulfide Modified with Molybdenum Metal Catalytically Active for the Nitrogen Reduction Reaction?

Reduction kinetics of ceria surface by hydrogen

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