E2C 2013 – 10/29/2013

Fritz-Haber-Institut der Max-Planck-Gesellschaft

Katharina Mette1, Stefanie Kühl1, Andrey Tarasov1, Robert Schlögl1, Malte Behrens1, Hendrik Düdder2, Kevin Kähler2, Martin Muhler2

1 Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin, Germany

2 Ruhr-University Bochum, Laboratory of Industrial Chemistry, Bochum, Germany

Synthesis and characterization of long-term sintering-stable Ni

catalysts for dry reforming of CH4

anthropogenic emission of CO2: ≈28 Gt/a

CO2 utilized in industry: 20 Mt/a as industrial gas, 110 Mt/a as chemical feedstock

CO2 = attractive option for sustainable utilization of global carbon sources for the

conversion to chemical intermediates

dry reforming of methane (DRM): CO2 + CH4 2 CO + 2 H⇌ 2

ΔH0= 247 kJ/mol

Motivation

2Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin

53%

23%

11%

4%8%

present syngas market: [1]

ammonia

refineries (H2)

methanol

electricity

gas-to-liquids

other

[1] A. van der Drift, H. Boerrigter, ECN Biomass, Coal and Environmental Research, 2006, 1-31.

dry reforming of methane (DRM): CO2 + CH4 2 CO + 2 ⇌

H2 ΔH0= 247 kJ/mol

side reactions:• Boudouard reaction:

2 CO ⇌ C + CO2

ΔH0= -171 kJ/mol• methane pyrolysis:

CH4 ⇌ C + 2H2

ΔH0= 75 kJ/mol ⇨ catalyst deactivation due to coking

high conversion with less side reactions:• high reaction temperature (900 °C)

CO2 conversion to syngas

3Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin

[2] J. Zhang, H. Wang, A. K. Dalai , Journal of Catalysis 249 (2007), 300-310.

Equilibrium constants of reactions

as a function of temperatures:[2]

Goal: Development of a heterogeneous, noble-metal free catalyst for CO2 reforming of CH4

catalyst requirements: high mechanical and thermal resistance

transition metal for CH4 activation

high resistance against coking[3]

CO2 conversion to syngas

4Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin

[3] M. C. J. Bradford, M. A. Vannice, Catal. Rev. - Sci. Eng. 41 (1999) 1.

catalytically active: Ni-based catalysts as well as noble metal-based catalysts

(Rh, Ru, Pd, Pt, Ir)

Ni-based catalysts economical more suitable for commercial applications

5Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin

Synthetic Approach • Ni based catalysts in MgAlOx matrix – basic matrix with

high surface area as well as high temperature stability• obtained from hydrotalcite-like precursor – joint

cation lattice of Ni* with Mg** and Al** in homogeneous compound*active component ** supporting component

Experimental Strategy

Catalyst

Atomic ratio

Ni:Mg:Al

Ni loading[a]

(wt%)

Ni50 50:17:33 55.3

Ni25 25:42:33 30.3

Ni5 05:62:33 6.6

Ni1 01:66:33 1.3

Ni0 00:67:33 0.0 Series of Ni-based catalysts

[a] in final catalyst (after reduction)

controlled co-precipitation of hydrotalcite-like precursors

NixMg0.67-xAl0.33(OH)2(CO3)0.17 m H∙ 2O

with 0 ≤ x ≤ 0.5 (0-50 mol% Ni)

Catalyst Structure

6Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin

XRD: phase pure hydrotalcites

NiMgAlco-

precipitated precursor

Calcined

Reduced

TG, TPO, TPRDefinition of the thermal treatment conditions: Tcalc, Tred.

TG

TG-TPRXRD, XAS, TEM

XRD, SEM

XRD, SEM, XAS

Precursor Calcined (600°)

XRD: nearly amourphous mixed oxides

20 30 40 50 60 70 80

Inte

nsity

/ a.

u.

2 / °

Ni50-600 Ni25-600 Ni5-600 Ni1-600 Ni0-600

NiO ICDD: [47-1049]MgO ICDD: [65-0476]

10 20 30 40 50 60 70 80

Ni50 (50:17:33) Ni25 (25:42:33) Ni5 (05:62:33) Ni1 (01:66:33) Ni0 (00:67:33)

Inte

nsity

/ a.

u.

2 / °

Mg2Al Hydrotalcite ICDD: [89-5434]

Catalyst Structure

7Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin

Reduced at 800°C

Calcined at 600°C

TPR: increasing reduction temperature with decreasing Ni content

SEM: platelet-like morphology still dominant after reduction

200 400 600 800 1000

915 °C

883 °C

744 °C

670 °C

1 mol% Ni

5 mol% Ni

25 mol% Ni

TCD

sig

nal /

a.u

.

Sample Temperature / °C

50 mol% Ni

Catalyst Structure

8Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin

Variation of Ni content: small Ni particles at 1000°C well dispersed in Mg-Al oxide

matrix

Ni5Ni25

900°C 1000°C

Ni50-red: Stable microstructure up to 900°C.*

50mol% Ni after reduction: SEM: platelet-like morphology

still dominant TEM: small Ni nanoparticles

dispersed in oxide matrix – sintering at 1000°C

Ni50-red

NiX after reduction at 1000°C

*recently published: K. Mette, S. Kühl, H. Düdder, K. Kähler, A. Tarasov, M. Muhler, M. Behrens, ChemCatChem 2013 in press: DOI: 10.1002/cctc.201300699

Catalyst Structure

9Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin

CatalystNi

loading[a]

(wt%)

Ni particle size

(TEM) / nm

Ni surface area / m2/gcat

Ni dispersion /

%

Ni50 55.3 19.4 ± 2.2 6.0 4.8

Ni25 30.3 8.0 ± 1.7 5.0 2.5

Ni5 6.6 9.5 ± 2.1 3.0 6.9

Ni1 1.3 - 0.1 1.0

Ni0 0.0 - 0.0 0.0

decreasing specific Ni surface area (SA) with decreasing Ni content – high embedment of Ni particles

Ni5: highest Ni dispersion

Strong support effect on Ni embedment.

[a] in final catalyst (after reduction)

Activity in DRM Coke formation

spent catalyst

Catalytic tests, TG of carbon depositionTPO of spent catalyst

TEM

10

Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin

DRM: CO2 + CH4 2 CO + 2 H⇌ 2

ΔH0= 247 kJ/mol

Activation: 4%H2 in Ar, 5Kpm, 1000°C (Ni0: 900°C)

DRM: 240 Nml/min 40% CO2 / 32% CH4 / Ar, T= 900°C, 10 h

50mol% Ni

catalyst highly active in DRM almost stable performance for

100h time on stream deactivation:

Activity in Dry Reforming of Methane

6%100%)(CHX

)(CHX1

42h

4100h

X(CH4) ≈ 75%

• accessible Ni-SA responsible for activity• coke formation - no direct correlation to Ni content• lowest coking for Ni5 (sample with highest Ni dispersion)

0 10 20 30 40 500

1

2

3

4

5 specific activity at 900°C

r(C

H4)

/ m

mo

l/(s

gC

at)

Ni /mol%

0

5

10

15

20

25

30

35

CO2 formation during TPO

CO

2 / mm

ol/g

Cat

Ni0

high activity at 900 °C

11

Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin

Higher activity with increasing Ni content.

Linear correlation between activity and available Ni metal surface area.

Variation of Ni content

Activity in Dry Reforming of Methane

0 2 4 60

1

2

3

4

5

r(C

H4)

/ m

mo

l/(s

gC

at)

Ni surface area / m2/gCat

Ni50

Ni5

Ni25

Ni0Ni1

0 2 4 6 810

15

20

25

30

35

Ni0

Ni1

Ni5

Ni25Ni50

Ni dispersion / %

O2 c

on

sum

ptio

n /

mm

ol/g

cat

12

Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin

Activity in Dry Reforming of Methane

High Ni dispersion is mitigating coke deposition.

O2 consumption (TPO)

TEM spent samplesNi50

Ni0

Ni25

Ni5

amorphousgraphitic

Graphitic + filamenteous C

type of carbon species changed with Ni content: only high Ni contents produce

filaments Ni5 forms only graphtic C

Carbon amount and species are influenced by catalyst composition.

Coking Investigations

Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Abteilung Anorganische Chemie, Berlin 13

Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Abteilung Anorganische Chemie, Berlin 14

Strong dependence of coking rate on temperature and Ni content.

Coking InvestigationsTHERMOBALANCE (in situ DRM):40% CO2, 32% CH4, 28% Ar, 120ml/min

• in situ TG: carbon formation during DRM monitored • higher coking rate at 800°C and for Ni50• DRM – showing continuous carbon formation despite stable performance

0 1 2 3 4 5 6 7 8 999

100

101

102

103

Ni5

Ni5

ma

ss /

%

time / h

800°C 900°C

0 1 2 3 4 5 6 7

100

110

120

130

140

150

160

Ni5Ni5

Ni50

ma

ss /

%

time / h

800°C 900°C

Ni50

Conclusion

15

noble metal free Ni/MgAlOx catalysts developed from phase pure NiMgAl hydrotalcite-like precursor

small Ni particles embedded in MgAl oxide matrix with stable microstructure at high temperatures

highly active in DRM with linear correlation to specific Ni metal surface area

coking rate strongly depends on reaction temperature and Ni content

direct correlation of carbon amount to Ni dispersion Ni5 most attractive catalyst: showing a compromise of

activity and carbon formation – interplay of dispersion and embedment

Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin

Acknowledgement

16

Fritz-Haber-Institut der Max-Planck-Gesellschaft, Abteilung Anorganische Chemie, Berlin

Hendrik DüdderKevin KählerMartin Muhler

Thank you for your attention !

Frank GirgsdiesMichael HäveckerJasmin AllanGisela Weinberg

Robert SchlöglMalte BehrensKatharina MetteAndrey Tarasov

in the framework of CO2RRECT Project (FKZ 01RC1006)

Reduced catalysts

17

Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin

30 40 50 60 70 80

Ni5

Ni1Ni 0

Reduced at 1000 °C in 5% H2/Ar

mol.% Ni

Inte

nsity

/ a.

u.

2 / °

Ni50

Ni25

*

* *

MAl2O

4MO

Ni

M= Ni, Mg

*

• XRD: metallic Ni, poorly crystalline oxidic matrix

DRM calculations

18

Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin

Comparison to thermodynamic equilibrium