the mechanism of carbon gasification over a fe-ni catalyst ...16th international congress on...

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: StavrosAlexandros.Theofanidis@UGent.be

*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