the mechanism of carbon gasification over a fe-ni catalyst ...16th international congress on...
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16th International congress on Catalysis, Beijing, China, July 3-8, 2016
The mechanism of carbon gasification over a Fe-Ni catalyst
after methane dry reforming
Stavros Alexandros Theofanidis*, Rakesh Batchu, Vladimir V. Galvita, Hilde Poelman and Guy B. Marin
http://www.lct.UGent.be E-mail: [email protected]
*Laboratory for Chemical Technology Technologiepark 914, 9052 Ghent, Belgium
European Research Institute of Catalysis
Carbon characterization
Introduction
• The addition of Fe to Ni catalysts can
improve the catalytic performance as it
combines good redox properties with Fe-Ni
alloy formation upon intimate interaction
between Fe and Ni [1].
Aim
Catalyst preparation and characterization
(B)
Mechanism of carbon oxidation by O2
(C)
•Mg2+
•Al3+
NH4OH Mg2+
Al3+
MgAl2O4 spinel
Calcination
at 1023 K
MgAl2O4
Calcination
at 1023 K
H2O
Fe3+
Ni2+
MgAl2O4
Conclusions
The existence of two different carbon species structures was determined
by RAMAN spectroscopy, XPS and TEM: graphitic and amorphous
CO2 oxidation could remove the carbon species deposited on the
catalyst.
Proposed procedure for catalyst regeneration:
1) Carbon gasification by CO2 (endothermic reaction) in order to
avoid local temperature increase and thus particles migration.
2) Carbon oxidation by O2 in order to remove the carbon species
located far from active metals.
• The mechanism of catalyst regeneration by
CO2 and O2 after methane dry reforming
over a Fe-Ni catalyst.
NiO Fe2O3
Mechanism of carbon gasification by CO2
Amorphous and graphitic-
like carbon.
No carbide formation was
observed.
Used Fe-Ni catalyst (after DRM at 1023 K, 101.3 kPa, CH4/CO2/He= 1.1/1/1, reaction time 1 h).
Operando-XRD during CO2-TPO of used Fe-Ni catalyst (DRM for 1 h, 1023 K,
CH4/CO2/He= 1.1/1/1, total pressure of 101.3 kPa): (A) 2D XRD pattern; (B) CO
produced during carbon species removal as a function of temperature; (C) Integral
intensity variation of (A) for diffraction areas 25.8-26.8o (Graphite), 35.4o-36.4o
(Fe3O4) and 43.7o-44.2o (Fe-Ni alloy).
Schematic representation of carbon species removal by CO2 over
Fe-Ni catalyst. Os: surface oxygen, OL: lattice oxygen. Cm:
carbon deposited on metals, Cs: carbon deposited far from metals.
The carbon illustration is not corresponding to the real carbon
structure.
1) Dissociation of CO2 over Ni followed
by the oxidation of carbon by surface
oxygen.
2) Fe oxidation by CO2 and subsequent
carbon oxidation by Fe oxide lattice
oxygen.
EDX element mapping of Fe-Ni. A) after DRM (1023 K,
CH4/CO2/He= 1.1/1/1, P= 101.3 kPa, TOS= 1 h). (B) after CO2
oxidation (1ml/s of CO2 at 101.3 kPa and 1123 K). Red, green and
blue correspond to carbon, Fe and Ni elements resp.
O2-TPO over different catalyst bed configurations
No evidence of
oxygen spillover
(TAP, O2-TPO)
CO2 response during O2 pulses at TAP reactor at 993 K. (A): 2D view for Fe-Ni,
(B): CO2 molar flow rate produced during selected O2 pulses over Fe-Ni. Fe-Ni
aged by a sequence of 400 CH4 pulses.
Acknowledgement • This work was supported by the FAST industrialization by Catalyst Research and Development (FASTCARD)
project, which is a Large Scale Collaborative Project supported by the European Commission in the 7th
Framework Programme (GA no 604277), by the “Long Term Structural Methusalem Funding by the Flemish
Government” and the Interuniversity Attraction Poles Programme, IAP7/5, Belgian State – Belgian Science
Policy.
References • [1] Theofanidis SA, Galvita VV, Poelman H, Marin GB. Enhanced Carbon-Resistant Dry
Reforming Fe-Ni Catalyst: Role of Fe. ACS Catal. 2015:3028-39.
• [2] Theofanidis, S.A., R. Batchu, V.V. Galvita, H. Poelman, and G.B. Marin, Carbon gasification
from Fe–Ni catalysts after methane dry reforming. Appl. Catal., B, 2016. 185: p. 42-55
D= x2/t ~10-17 m2·s−1,
x: mean traveled distance of
the species (m), x=8-10 nm, D:
diffusion coefficient (m2·s−1).
Temporal Analysis of Products (TAP)
Particles migration followed by carbon gasification
through lattice oxygen.
• In view of the promising results on Fe-
Ni/MgAl2O4 [1] regarding reduced carbon
deposition, this material was used for further
investigation of the catalyst regeneration
mechanism by CO2 and O2 [2].
Experimental conditions:
•20 K/min
•Tmax= 1123K
•10 ml/min
•P= 101.3 kPa
XPS
C1s photoline
•Cm: carbon deposited
on metals
•Cs: carbon deposited
far from metals
•Os: surface oxygen
•OL: lattice oxygen
First metals are oxidized.
Carbon gasification on the active metals results in
local temperature increase.
Graphite