Entwicklung von Reaktionsmechanismen für heterogen-katalysierte ...

IWR Universität Heidelberg
Entwicklung von Reaktionsmechanismen
für heterogen-katalysierte Reaktionen
Olaf Deutschmann
Interdisziplinäres Zentrum für Wissenschaftliches Rechnen (IWR), Universität Heidelberg
Im Neuenheimer Feld 368, D-69120 Heidelberg
Tel.: (+49)-6221-54 8886, Fax: (+49)-6221-54 8884
deutschmann@iwr.uni-heidelberg.de
http://reaflow.iwr.uni-heidelberg.de/~dmann
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001
OD_01_101

Objective: Development of appropriate models for
hetereogenous-catalytic reactions
IWR Universität Heidelberg
Courtesy of R.W. Dibble, UC Berkeley
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001
OD_01_102

Complexity of heterogeneous-catalytic reactions: Reaction
rate is specific to the catalyst formulation
IWR Universität Heidelberg
Reaction rate expression depends on:
- catalytic material type and catalyst support,
- type and structure of washcoat,
- method of manufacture,
- surface structures,
- temporal history,
- recrystallisation phenomena,
- solid bulk modification.
Global kinetics
(macroscopic behavior)
k (T,c i
,p 1
,p 2
,...)
Mechanistic approach
(mean field approximation)
k 7
Elementary kinetics
(single microscopic
steps)
k 1
k 2
k 3
k 6
k 4
k 5
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001
OD_01_103

Modeling heterogeneous-catalytic reactions:
Mean field approximation
IWR Universität Heidelberg
Assumptions:
- Adsorbates are assumed to be randomly distributed on the surface
- Surface is viewed as being uniform; the local environment (edges, defects,
terraces, different structures) is not directly taken into account
Reaction rate:
ṡ i =
∑
Ks
k=1
Surface coverage:
θ i = c iσi
Γ
Ng+Ns
∏
ν ik k fk
j=1
c ν jk
′
j
Sticking coefficient:
√
k ads S 0 i 1 RT
=
fk
1 − S 0 i θ v/2 Γ i
τ 2πM i
Rate coefficient:
[
k = A f k kT β −Ea
k exp
k
RT
krk (T )= k fk (T )
Kck (T )
Binding states of adsorption on the surface
vary with the surface coverage of all adsorbed
species.
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001
]
f (θ 1 ,θ 2 ...) =
f(θ 1 ,θ 2 ...)
∏ Ns
i=1
θ µ i k
i exp
[
ɛ θ ]
ik i
RT
OD_01_104

Catalytic combustion of methane over platinum:
Proposed scheme of surface reactions
IWR Universität Heidelberg
D. A. Hickman, L. D. Schmidt, AIChE J. 39
(1993), 1164.
O. Deutschmann, F. Behrendt, and J. Warnatz:
Catal. Today 21 (1994), 461.
Reaction scheme for modeling catalytic ignition of
H2 , CO, CH on Pt in SURFACE CHEMKIN format
4
Reaction A b E(J/mol) Comment
H2 + 2PT(S) => 2H(S) 0.046 0.0 0 STICK, FORD /PT(S) 1/
2H(S) => H2 + 2PT(S) 3.70E+21 0.0 67400 COV /H(S) 0 0 -6000/
H + PT(S) => H(S) 1.00 0.0 0 STICK
O2+ 2PT(S) => 2O(S) 1.80E+21 -0.5 0 DUP
O2+ 2PT(S) => 2O(S) 0.023 0.0 0 STICK, DUP
2O(S) => O2 + 2PT(S) 3.70E+21 0.0 213200 COV /O(S) 0 0 -60000/
O + PT(S) => O(S) 1.00 0.0 0 STICK
H2O + PT(S) => H2O(S) 0.75 0.0 0 STICK
H2O(S) => H2O + PT(S) 1.0E13 0.0 40300
OH + PT(S) => OH(S) 1.00 0.0 0.0 STICK
OH(S) => OH + PT(S) 1.00E13 0.0 192800
H(S) + O(S) = OH(S) + PT(S) 3.70E+21 0.0 11500
H(S) + OH(S) = H2O(S) + PT(S) 3.70E+21 0.0 17400
OH(S)+ OH(S) = H2O(S) + O(S) 3.70E+21 0.0 48200
CO + PT(S) => CO(S) 0.84 0.0 0 STICK, FORD /PT(S) 2/
CO(S) => CO + PT(S) 1.00E+13 0.0 125500
CO2(S) => CO2 + PT(S) 1.00E+13 0.0 20500
CO(S) + O(S) => CO2(S) + PT(S) 3.70E+21 0.0 105000
CH4 + 2PT(S) => CH3(S) + H(S) 0.01 0.0 STICK, FORD/ PT(S) 2.3/
CH3(S)+ PT(S) => CH2(S)s + H(S) 3.70E+21 0.0 20000
CH2(S)s + PT(S) => CH(S) + H(S) 3.70E+21 0.0 20000
CH(S) + PT(S) => C(S) + H(S) 3.70E+21 0.0 20000
C(S) + O(S) => CO(S) + PT(S) 3.70E+21 0.0 62800
CO(S) + PT(S) => C(S) + O(S) 1.00E+18 0.0 184000
Courtesey of L.L. Raja, R.J. Kee, Colorad School of Mines
http://reaflow.iwr.uni-heidelberg.de/~dmann/sm_ch4_ox_1.2_SURFACECHEMKIN
O. Deutschmann, R. Schmidt, F. Behrendt, J. Warnatz: Proc. Comb. Inst. 26 (1996),
1747
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001
OD_00_093

OD_01_009
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001
Experiments - detailed data
(spatial & temporal profiles, coverages)
Revised surface
reaction
mechanism
Comparison of experiment and simulation
Experiments - integrated data
(ign.& ext. temperatures,
selectivity, conversion)
Numercial simulation
Reactor models
(including appropriate gas chemistry & transport models)
Sensitivity analysis
=> re-evaluation of cruical kinetic data
Tentative surface
reaction mechansim
BOC-MP
UBI-QEP
Analogy to organometallic
compounds
Transition-State
theory
Heats of adsorption
Surface science
studies
Analogy to gas
phase kinetics
Collision theory
ab-initio
calculations
IWR Universität Heidelberg
Survey of the methodology of the development of a surface
reaction mechanism

Kinetic data for surface reactions at practically relevant
conditions and for technically used catalysts
IWR Universität Heidelberg
Laser-spectroscopic methods such as
SFG (Sum Frequency Generation) can
bridge the pressure and materials gap
=> Quantitative determination of surface
coverage with adsorbed species
R. Kissel-Osterrieder, F. Behrendt, J. Warnatz, U. Metka, H.-R. Volpp, J. Wolfrum. Proc. Combust. Inst. 28 (2000)
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001
OD_00_520

2
OD_01_105
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001
M. Rinnemo, O. Deutschmann, F. Behrendt, B. Kasemo.
Combust. Flame 111 (1997) 312-326
O. Deutschmann, R. Schmidt , F. Behrendt, J. Warnatz.
Proc. Combust. Inst. 26 (1996) 1747-1754
Conditions: T 0
= 298 K, p tot
= 1 bar (94% N 2
), circles: experiment, line: simulation.
α = p H /( p H 2
p O )
α = p H2
/ (p H2
+ p 2
O2
)
α α = p
CH
/( p CH4
/ (p 4 CH4 + p O2
)
320
(a) (b)
300
0.0 0.2 0.4 0.6 0.8 1.0
400
0.0 0.2 0.4 0.6 0.8 1.0
Ignition temperature [K]
500
340
360
600
380
700
400
CH H2 800 4
Ignition temperature [K]
420
440
900
Comparison of measured and calculated ignition temperatures in a stagnation point
flow on a platinum foil heated resistively.
IWR Universität Heidelberg
Catalytic oxidation of hydrogen and methane on platinum:
Ignition temperature

OD_99_314
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001
O. Deutschmann, R. Schmidt, and F. Behrendt. in S. H. Chan (ed.),
Transport Phenomena in Combustion,Vol. 1, p. 166-175, Taylor and
Francis, 1996.
O. Deutschmann, R. Schmidt , F. Behrendt, J. Warnatz, 26th
Symposium (International) on Combustion (1996) 1747-1754
Conditions: H 2
/O 2
mixture (6 % diluted by 94 % N 2
,
p = 1 bar), α = p H2
/(p H2
+p O2
) = 0.5, circles: experiment.
Conditions: CH 4
/O 2
mixture (6 % diluted by 94 % N 2
,
p = 1 bar), α = C CH4
/(p CH4
+p O2
) = 0.5.
Time [s]
Time [s]
10 -5
Surface coverage
10 -1
10 -2
10 -3
10 -4
10 0 550
H(s)
500
Pt(s)
450
400
H2 O(s)
350
Temperature
300
10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0
Surface temperature [K]
Surface coverage
10 0 CO(s) 820
O(s)
C(s)
10 -1
800
Pt(s)
10 -2
780
OH(s)
10 -3
760
H(s)
Temperature
10 -4
740
-10 0 10 20 30 40 50 60 70 80
Surface temperature [K]
IWR Universität Heidelberg
Transient Modeling of Catalytic Ignition of Hydrogen and
Methane Oxidation on Pt: Temperature and Coverage

12345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901234567890123456789012123
12345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901234567890123456789012123
12345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901234567890123456789012123
12345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901234567890123456789012123
12345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901234567890123456789012123
12345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901234567890123456789012123
12345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901234567890123456789012123
12345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901234567890123456789012123
12345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901234567890123456789012123
12345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901234567890123456789012123
12345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901234567890123456789012123
12345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901234567890123456789012123
12345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901234567890123456789012123
12345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901234567890123456789012123
12345678901234567890123456789012123456789012345678901234567890121234567890123456789012345678901212345678901234567890123456789012123
Catalytic oxy-dehydrogenation of ethane: Interaction of
transport and heterogeneous and homogeneous reactions
IWR Universität Heidelberg
Platinum coated monolith, 1cm in length
Autothermal
Residence time: 5 ms
Ethylene selectivity: > 70%
M. Huff and L. D. Schmidt: AIChE J. 42 (1996), 3484
A. S. Bodke, D. A. Olschki, L. D. Schmidt, E. Ranzi: Science 285 (1999), 712
The two-dimensional simulation of a single monolith channel is coupled with detailed
gas-phase and surface reaction mechanisms.
D.K. Zerkle, M.D. Allendorf, M. Wolf, O. Deutschmann. J. Catal.196 (2000) 18
C2 H 6 , O 2
C 2
H 6
+O 2
C 2
H 6
+H -> C 2
H 5
+H 2
C2 H 5 +M -> C 2 H 4 +H+M
C2 H 6 + H 2 O
Heat
Shield
H, C, O
H2 O+Heat
+C 2
H 4
+CO 2
+CO
H, O, CH x
, C H 2
, CO, CH 4,
C 2
H 4
Alumina-Supported Platinum Catalyst
Heat
Shield
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001
OD_01_106

OD_01_107
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001
R. Kissel-Osterrieder, F. Behrendt, J. Warnatz, U. Metka, H.-R. Volpp, J. Wolfrum: Experimental and Theoretical Investigation
of CO-Oxidation on Platinum: Bridging the Pressure and the Materials Gap, Proc. Combust. Inst. 28 (2000)
Conditions: CO: 15 sccm; O 2 : 30 sccm, Ar: 105 sccm at a total pressure of 20 mbar
CO coverage
1
0.8
0.6
0.4
0.2
0
300 400 500 600 700 800
temperature [K]
CO 2
-flux [sccm]
14
12
10
8
6
4
2
0
300 400 500 600 700 800
temperature [K]
The CO oxidation on polycrystalline Pt is modelled by a two-adsorption site model.
The predicted CO surface coverage is compared with data derived from optical sumfrequency
generation (SFG) vibrational spectroscopy.
IWR Universität Heidelberg
Site heterogeneity of catalytic surfaces: Extension of the
mean-field approximation leads to different sub-mechanisms

Lateral adsorbate interactions: Monte Carlo simulations of
the elementary surface processes
IWR Universität Heidelberg
Spatio-temporal patterns in catalytic oxidation of CO on platinum; 2D resolution of the
non-homogeneous layers of adsorbed species
Pt(110), PEEM, 0.2 x 0.3 mm 2 , T = 427 K,
p O2 = 32·10 -3 mbar, p CO 3·10 -3 mbar, ∆t = 4.1/ 30 s
Target pattern on Pt(100), ∆t = 10 s, 1000 x 1000 lattice, 0.25 x 0.25 mm 2 ,
T = 490 K, p O2 = 50·10 -3 mbar, p CO 1.5·10 -3 mbar
S. Jakubit, H.H. Rotermund, W. Engel, A.von Oertzen,
G. Ertl. Phys. Rev. Lett. 65 (1990) 3013
R. Kissel-Osterrieder, F. Behrendt, J. Warnatz. Proc. Combust. Inst. 28
(2000)
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001
OD_01_108

Summary and Outlook
IWR Universität Heidelberg
Multi-step mechanisms for simple heterogeneous-catalytic reactions such as
- oxidation of H 2
, CO, CH 4
, C 2
H 6
on noble metals
- NO reduction on noble metals (3WCC)
- methanol and ammonia synthesis
Advanced experimental techniques help to overcome the pressure and materials gap
- high pressure STM
- nonlinear laser methods such as SFG and SHG
Challenges
- Still too little is known about the elementary steps, in particular at high pressure
- Combination of the experimental observations of single elementary steps
to the overall picture of the catalyst
- Coupling of the detailed reaction mechanisms with the macroscopic processes
(mass and heat transport in the surrounding reactive flow, the washcoat, and the
solid bulk)
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001

Danksagung
IWR Universität Heidelberg
Daniel Chatterjee, Dr. Chrys Correa, Oliver Grosshans, Dr. Ralf Kissel-Osterrieder, Stefan Kleditzsch, Dr. Luba
Maier, Renate Schwiedernoch, Steffen Tischer, Dr. Markus Wolf (IWR, Universität Heidelberg)
Dr. Uwe Metka, Dr. Hans-Robert Volpp, Prof. Jürgen Wolfrum (PCI, Universität Heidelberg)
Dr. David K. Zerkle (Los Alamos National Lab.)
Prof. Jürgen Warnatz (IWR, Universität Heidelberg)
Deutsche Forschungsgemeinschaft (DFG) (Sachbeihilfen, SFB 359)
Forschungsverbund Verbrennungskraftmaschinen e.V. (FVV)
Bundesland Baden-Württemberg
J. Eberspächer GmbH & Co.
Conoco Inc.
US Department of Energy
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001
OD_00_110