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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.
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.