Stability of Fe2O3/MgAl2O4 for CO2 utilization

in super-dry reforming of CH4

Lukas Buelens1, A. Dharanipragada1, V.V. Galvita1, H. Poelman1, G.B. Marin1

EUROPACAT 2017, FLORENCE, 27-31 AUGUST 2017

1Laboratory for Chemical Technology

Step 2: inert + 4CaCO3 + 3Fe ⇄ 4CaO + Fe3O4 + 4CO + inert

Δ𝑟𝐻1023𝐾° = +212 𝑘𝐽 𝑚𝑜𝑙𝐶𝑂2

−1 Δ𝑟𝐺1023𝐾° = +23.8 𝑘𝐽 𝑚𝑜𝑙𝐶𝑂2

−1

Step 1: CH4 + 3CO2 + Fe3O4 + 4CaO ⇄ 2H2O + 3Fe + 4CaCO3

Δ𝑟𝐻1023𝐾° = −103 𝑘𝐽 𝑚𝑜𝑙𝐶𝑂2

−1 Δ𝑟𝐺1023𝐾° = −32.4 𝑘𝐽 𝑚𝑜𝑙𝐶𝑂2

−1

Introduction: super-dry reforming of CH4

Fe3O4

3Fe

4CaCO3

4CaO

inert

4CO2

4CO+

inert

CH4

+CO2

2CO + 2H2

2H2O2CO2

Ni

2CO2

methane dry reforming

chemical

loop 1

chemical

loop 2

Science (2016), 354: 449-452. 2/13

combination of

3 processes

CH4CO2

CO2

H2OH2O

CO2

Ni

Fe3O4

CaO

CO

inert

CO

inert CO

CO

Ni

CaCO3

Fe

Step 1 Step 2

T = 1023 K

Ni: reforming catalyst

Fe3O4: oxygen carrier

CaO: CO2 sorbent

Introduction: super-dry reforming of CH4

Fe3O4

3Fe

4CaCO3

4CaO

inert

4CO2

4CO+

inert

CH4

+CO2

2CO + 2H2

2H2O2CO2

Ni

2CO2

Science (2016), 354: 449-452. 3/13

RWGS: 2H2 + 2CO2 ⇄ 2H2O + 2CO

CH4 + 3CO2 + inert ⇄ 4CO + 2H2O + inertΔ𝑟𝐻1023𝐾

° = +109 𝑘𝐽 𝑚𝑜𝑙𝐶𝑂2−1

Δ𝑟𝐺1023𝐾° = −8.6 𝑘𝐽 𝑚𝑜𝑙𝐶𝑂2

−1

→ Method for valorization of C1 feedstocks (CH4 and CO2) through CO production

T = 1023 Kp = 1 atm

→ Isothermal combination of catalytic methane dry reforming and chemical looping

Focus of

this work

Iron oxide as oxygen carrier

High capacity for CO2 conversion into CO

Abundantly available (low cost)

Environmentally sound

However…

Rapid deactivation through sintering

Formation of FeAl2O4 (MgFe2O4) leads to continuous deactivation

Incorporation of Fe in the MgAl2O4 spinel

Stability and performance of Fe2O3/MgAl2O4 over several days?

Fe3O4

3Fe 4CO2

4CO4H2

4H2O

→ addition of textural promoter such as Al2O3 (MgO)

→ use of MgAl2O4 promoter

4/13

Introduction: oxygen carrier

J. Mater. Chem. A (2015), 3: 16251-16262.

Introduction

Material synthesis

Activity tests

Characterization

Conclusions

5/13

Outline

One-pot co-precipitation of Fe(NO3)3, Mg(NO3)2 and Al(NO3)3 using NH4OH

3 different materials: X-Fe2O3/MgAl2O4 (with X = 10, 30, 50 w%)

Denoted as 10FMA, 30FMA and 50FMA

NH4OH

Fe(NO3)3

Mg(NO3)

2Al(NO3)3

Fe(OH)3

Mg(OH)2

Al(OH)3

Fe(OH)3

Mg(OH)2

Al(OH)3

NH4NO3

co-precipitation ageing

(overnight, RT)

filtration drying

(overnight, 393 K)

calcination

(4h at 1023 K)

H2O

H2O

H2O

H2ONH4NO3

6/13

NH4NO3

Material synthesis

50FMA 30FMA 10FMA

H2 CO2inert inert

1 min 2 min 1 min 2 min

10% in He 40% in He100% He 100% He

Step response: 100, 200, 500 and 1000 redox cycles (1 min 10% H2 in He; 2 min purging in 100%

He; 1 min 40% CO2 in He; 2 min purging in 100% He) were performed using 50Fe2O3/MgAl2O4,

30Fe2O3/MgAl2O4 and 10Fe2O3/MgAl2O4 at p = 1.013 bara, T=1023 K, Ftot = 2.35 10-4 mol s-17/13

Activity tests: 1000 redox cycles

Fe3O4

3Fe 4CO2

4CO4H2

4H2ORedox cycle (1023 K, 1 atm)

stabilization after

300 redox cycles

stabilization after

500 redox cyclesmost stable

± 28% of CO

yield retained

± 31% of CO

yield retained

± 84% of CO

yield retained

10FMA

10FMA

30FMA

50FMA

threshold crystallite size below

which STYCO,max is constant?

10FMA

8/13

10FMA

30FMA

50FMA

Characterization: N2 adsorption

Superior morphological

stability of 10FMA

different behavior of 10FMA

than 30FMA and 50FMA

Application as redox

active catalyst support

30FMA50FMA

10FMA

30FMA

50FMA

10FMA

Mg(Fe,Al)2O4

FeAl2O4

MgAl2O4

30FMA

50FMA

10FMA

Mg-Fe-Al-O diffraction peak

→ well reproduced with bimodal crystallite size

(2 Gaussians, Scherrer’s equation)

Various Mg(Fex,Al1-x)2O4 phases

range for reliable dXRD estimations

sintering

Fe remains present in the spinel

phase, even after 1000 redox cycles

Fe3O4 - 8.396Å

MgFe2O4 - 8.369Å

9/13

Characterization: X-ray diffraction (Mg-Fe-Al-O spinel)

10FMA

30FMA

50FMA

Small crystallites: dotted lines

Large crystallites: dashed lines

10FMA

30FMA

50FMA

Fe-rich

zone

Enrichment of Fe along the

surface of Mg-Fe-Al-O spinel

Indicates low surface tension between

Fe-rich phase and Mg-Fe-Al-O spinel 10/13

Characterization: STEM-EDX

10Fe2O3/MgAl2O4

Stable redox properties and morphology over 1000 redox cycles

50Fe2O3/MgAl2O4

Redox activity stabilizes after 300 redox cycles, despite deterioration of

morphological properties

STEM-EDX analysis suggests a good interaction between the Fe-rich phase and

the Mg-Fe-Al-O spinel

X-Fe2O3/MgAl2O4

Fe remains (partially) incorporated in the spinel, even after 1000 redox cycles

promising oxygen carrier for CO2 conversion or redox active catalyst support

promising oxygen carrier for CO2 conversion

11/13

Conclusions

Institute for the Promotion of Innovation through Science and

Technology (IWT) in Flanders

Flemish government for long-term structural funding (Methusalem)

Interuniversity Attraction Poles (IAP) from BELgian Science Policy

Office (Belspo)

Fund for Scientific Research Flanders FWO (Project: G004613N)

12/13

Acknowledgements

Thank you

13/13