Premium
Insight in kinetics from pre‐edge features using time resolved in situ XAS
Author(s) -
Dharanipragada N.V.R.A.,
Galvita Vladimir V.,
Poelman Hilde,
Buelens Lukas C.,
Marin Guy B.,
Longo Alessandro
Publication year - 2018
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.16017
Subject(s) - xanes , kinetics , spinel , rietveld refinement , x ray absorption spectroscopy , diffusion , chemical kinetics , chemistry , activation energy , redox , analytical chemistry (journal) , reaction rate , thermodynamics , materials science , crystallography , crystal structure , spectroscopy , absorption spectroscopy , inorganic chemistry , metallurgy , catalysis , physics , biochemistry , chromatography , quantum mechanics
The kinetics of reduction of a 10 wt %Fe 2 O 3 ‐MgAl 2 O 4 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 MgFeAlO x . The XANES pre‐edge feature was employed to study the reduction kinetics during H 2 ‐TPR (Temperature Programmed Reduction) up to 730°C. About 55% of the Fe 3+ in MgFeAlO x was reduced to Fe 2+ . 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