Kinetics of Multi‐Step Redox Processes by Time‐Resolved In Situ X‐ray Diffraction

Buelens, Lukas; Galvita, Vladimir; Poelman, Hilde; Detavernier, Christophe; Marin, Guy

doi:10.1002/cite.201600057

Cited by 10 publications

(6 citation statements)

References 32 publications

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“…For the solid‐state diffusion, however, no such dependence was found as the β 2 parameter was not significantly different from zero. In a recent study, it was shown that the kinetic parameters of the optimized shrinking core model, in particular the estimated activation energy for solid‐state diffusion in iron oxides, increases in the following order

{Fe}_{2} {normalO}_{3} true(37 . {5 kJ mol}^{- 1} true) < {Fe}_{3} {normalO}_{4} true({87 kJ mol}^{- 1} true) < FeO true({99 kJ mol}^{- 1} true)

…”

Section: Resultsmentioning

confidence: 99%

“…At later stages in the development, detailed kinetic data are needed within any type of simulation for scale‐up and refined design. Depending on the background of the investigation, different reaction models can be proposed and applied . When solid‐solid diffusion is predominant, often a shrinking core approach is applied …”

Section: Methodsmentioning

confidence: 99%

“…When neglecting both internal and external mass transfer limitations the implementation of these phenomena results in a shrinking core model (Eq. ) where

β_{o} = \frac{d T}{d t}

, represents the ramp rate:

\frac{d {\overset{X}{true}}_{{Fe}^{3 +}}}{d t} = β_{o} \frac{d {\overset{X}{true}}_{{Fe}^{3 +}}}{d T} = \frac{3}{r_{o}} \frac{1}{\frac{1}{k} {true(1 - {\overset{X}{true}}_{{Fe}^{3 +}} true)}^{- \frac{2}{3}} + \frac{b r_{o}}{D} {true(1 - {\overset{X}{true}}_{{Fe}^{3 +}} true)}^{- \frac{1}{3}} - \frac{b r_{o}}{D}} a \frac{C_{{normalH}_{2}, normalb normalu normall normalk}}{C_{{Fe}^{3 +}}^{o}}

…”

Section: Methodsmentioning

confidence: 99%

“…), representing the transformation of MgFe 3+ AlO x to MgFe 2+ AlO x at the interface. D represents a diffusion coefficient, corresponding to the solid‐state diffusion. In this case, D accounts for solid‐state diffusion of lattice oxygen from the unreacted core through the reduced layer to the crystallite surface.…”

Section: Methodsmentioning

confidence: 99%

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Insight in kinetics from pre‐edge features using time resolved in situ XAS

et al. 2017

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The kinetics of reduction of a 10 wt %Fe2O3‐MgAl2O4 spinel were investigated using XRD and time resolved Fe‐K QXANES. The Rietveld refinement of the XRD pattern showed the replacement of Al with Fe in the spinel structure and the formation of MgFeAlOx. The XANES pre‐edge feature was employed to study the reduction kinetics during H2‐TPR (Temperature Programmed Reduction) up to 730°C. About 55% of the Fe3+ in MgFeAlOx was reduced to Fe2+. A shrinking core model, which takes into account both solid‐state diffusion via an oxygen diffusion coefficient, and gas‐solid reaction through a reaction rate coefficient, was applied. The activation energy for chemical reaction showed a linear dependence on the conversion, increasing from 104 to 126 kJ/mol over the course of material reduction. The good accordance between the shrinking core model description and the experimental data indicates that XANES pre‐edge features can be used to correlate changes in material structure and reaction kinetics. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1339–1349, 2018

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{Fe}_{2} {normalO}_{3} true(37 . {5 kJ mol}^{- 1} true) < {Fe}_{3} {normalO}_{4} true({87 kJ mol}^{- 1} true) < FeO true({99 kJ mol}^{- 1} true)

…”

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

“…When neglecting both internal and external mass transfer limitations the implementation of these phenomena results in a shrinking core model (Eq. ) where

β_{o} = \frac{d T}{d t}

, represents the ramp rate:

\frac{d {\overset{X}{true}}_{{Fe}^{3 +}}}{d t} = β_{o} \frac{d {\overset{X}{true}}_{{Fe}^{3 +}}}{d T} = \frac{3}{r_{o}} \frac{1}{\frac{1}{k} {true(1 - {\overset{X}{true}}_{{Fe}^{3 +}} true)}^{- \frac{2}{3}} + \frac{b r_{o}}{D} {true(1 - {\overset{X}{true}}_{{Fe}^{3 +}} true)}^{- \frac{1}{3}} - \frac{b r_{o}}{D}} a \frac{C_{{normalH}_{2}, normalb normalu normall normalk}}{C_{{Fe}^{3 +}}^{o}}

…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Insight in kinetics from pre‐edge features using time resolved in situ XAS

et al. 2017

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“…Fe is clearly the most dynamic element as it returns almost completely to oxidized state (Figure 5A), likely as Fe 3 O 4 phase since CO 2 is not capable of reoxidizing Fe to Fe 2 O 3 . [29] Ni on the other hand, is only partially oxidized, ~35 %, leaving a considerable fraction (~65 %) of metallic Ni (Figure 5C). The lattice constant variation during CO 2 -TPO is quite different from the evolution in TPR: the value as seen from the Fe edge abruptly returns to the original value around 750 K, while the one at the Ni edge maintains its high value throughout the entire TPO (Figure 5B and D).…”

Section: Top)mentioning

confidence: 99%

Trimetallic Catalyst Configuration for Syngas Production

et al. 2022

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Dry reforming of methane (DRM) is a promising catalytic process for syngas production, utilizing and transforming CO 2 to higher density compounds in view of circular economy. The performance of a bimetallic NiFe/MgAl 2 O 4 strongly depends on the initial catalyst state -calcined, reduced or CO 2 -reoxidizedthat corresponds to different structures and is for each state significantly improved by the addition of a low Rh concentration (~1 wt%). In the bimetallic catalyst, reduction is required to form the most active phase, a Ni 3 Fe alloy, showing a CH 4 consumption rate of 0.9 mol s À 1 kg cat À 1 . For the trimetallic NiFeRh, the effect of the initial state is less pronounced, yielding a CH 4 consumption rate of 2.4 mol s À 1 kg cat À 1 after CO 2 -reoxidation. Advanced characterization and modelling were used to gain insights in the trimetallic system and to systematically assess the role of each element. In NiFeRh, reduction leads to the formation of a trimetallic alloy. A subsequent CO 2reoxidation induces partial Fe segregation from the trimetallic alloy, leading to separate Fe 3 O 4 . The latter structure represents the most active state due to the double role that the trimetallic catalyst takes up after H 2 -reduction and CO 2 -reoxidation: improved activity due to highly dispersed NiRh and NiFe alloy particles and carbon removal due to Fe 3 O 4 particles.

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