Entwicklung von Reaktionsmechanismen für heterogen-katalysierte ...
Entwicklung von Reaktionsmechanismen für heterogen-katalysierte ...
Entwicklung von Reaktionsmechanismen für heterogen-katalysierte ...
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IWR Universität Heidelberg<br />
<strong>Entwicklung</strong> <strong>von</strong> <strong>Reaktionsmechanismen</strong><br />
<strong>für</strong> <strong>heterogen</strong>-<strong>katalysierte</strong> Reaktionen<br />
Olaf Deutschmann<br />
Interdisziplinäres Zentrum <strong>für</strong> Wissenschaftliches Rechnen (IWR), Universität Heidelberg<br />
Im Neuenheimer Feld 368, D-69120 Heidelberg<br />
Tel.: (+49)-6221-54 8886, Fax: (+49)-6221-54 8884<br />
deutschmann@iwr.uni-heidelberg.de<br />
http://reaflow.iwr.uni-heidelberg.de/~dmann<br />
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001<br />
OD_01_101
Objective: Development of appropriate models for<br />
hetereogenous-catalytic reactions<br />
IWR Universität Heidelberg<br />
Courtesy of R.W. Dibble, UC Berkeley<br />
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001<br />
OD_01_102
Complexity of <strong>heterogen</strong>eous-catalytic reactions: Reaction<br />
rate is specific to the catalyst formulation<br />
IWR Universität Heidelberg<br />
Reaction rate expression depends on:<br />
- catalytic material type and catalyst support,<br />
- type and structure of washcoat,<br />
- method of manufacture,<br />
- surface structures,<br />
- temporal history,<br />
- recrystallisation phenomena,<br />
- solid bulk modification.<br />
Global kinetics<br />
(macroscopic behavior)<br />
k (T,c i<br />
,p 1<br />
,p 2<br />
,...)<br />
Mechanistic approach<br />
(mean field approximation)<br />
k 7<br />
Elementary kinetics<br />
(single microscopic<br />
steps)<br />
k 1<br />
k 2<br />
k 3<br />
k 6<br />
k 4<br />
k 5<br />
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001<br />
OD_01_103
Modeling <strong>heterogen</strong>eous-catalytic reactions:<br />
Mean field approximation<br />
IWR Universität Heidelberg<br />
Assumptions:<br />
- Adsorbates are assumed to be randomly distributed on the surface<br />
- Surface is viewed as being uniform; the local environment (edges, defects,<br />
terraces, different structures) is not directly taken into account<br />
Reaction rate:<br />
ṡ i =<br />
∑<br />
Ks<br />
k=1<br />
Surface coverage:<br />
θ i = c iσi<br />
Γ<br />
Ng+Ns<br />
∏<br />
ν ik k fk<br />
j=1<br />
c ν jk<br />
′<br />
j<br />
Sticking coefficient:<br />
√<br />
k ads S 0 i 1 RT<br />
=<br />
fk<br />
1 − S 0 i θ v/2 Γ i<br />
τ 2πM i<br />
Rate coefficient:<br />
[<br />
k = A f k kT β −Ea<br />
k exp<br />
k<br />
RT<br />
krk (T )= k fk (T )<br />
Kck (T )<br />
Binding states of adsorption on the surface<br />
vary with the surface coverage of all adsorbed<br />
species.<br />
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001<br />
]<br />
f (θ 1 ,θ 2 ...) =<br />
f(θ 1 ,θ 2 ...)<br />
∏ Ns<br />
i=1<br />
θ µ i k<br />
i exp<br />
[<br />
ɛ θ ]<br />
ik i<br />
RT<br />
OD_01_104
Catalytic combustion of methane over platinum:<br />
Proposed scheme of surface reactions<br />
IWR Universität Heidelberg<br />
D. A. Hickman, L. D. Schmidt, AIChE J. 39<br />
(1993), 1164.<br />
O. Deutschmann, F. Behrendt, and J. Warnatz:<br />
Catal. Today 21 (1994), 461.<br />
Reaction scheme for modeling catalytic ignition of<br />
H2 , CO, CH on Pt in SURFACE CHEMKIN format<br />
4<br />
Reaction A b E(J/mol) Comment<br />
H2 + 2PT(S) => 2H(S) 0.046 0.0 0 STICK, FORD /PT(S) 1/<br />
2H(S) => H2 + 2PT(S) 3.70E+21 0.0 67400 COV /H(S) 0 0 -6000/<br />
H + PT(S) => H(S) 1.00 0.0 0 STICK<br />
O2+ 2PT(S) => 2O(S) 1.80E+21 -0.5 0 DUP<br />
O2+ 2PT(S) => 2O(S) 0.023 0.0 0 STICK, DUP<br />
2O(S) => O2 + 2PT(S) 3.70E+21 0.0 213200 COV /O(S) 0 0 -60000/<br />
O + PT(S) => O(S) 1.00 0.0 0 STICK<br />
H2O + PT(S) => H2O(S) 0.75 0.0 0 STICK<br />
H2O(S) => H2O + PT(S) 1.0E13 0.0 40300<br />
OH + PT(S) => OH(S) 1.00 0.0 0.0 STICK<br />
OH(S) => OH + PT(S) 1.00E13 0.0 192800<br />
H(S) + O(S) = OH(S) + PT(S) 3.70E+21 0.0 11500<br />
H(S) + OH(S) = H2O(S) + PT(S) 3.70E+21 0.0 17400<br />
OH(S)+ OH(S) = H2O(S) + O(S) 3.70E+21 0.0 48200<br />
CO + PT(S) => CO(S) 0.84 0.0 0 STICK, FORD /PT(S) 2/<br />
CO(S) => CO + PT(S) 1.00E+13 0.0 125500<br />
CO2(S) => CO2 + PT(S) 1.00E+13 0.0 20500<br />
CO(S) + O(S) => CO2(S) + PT(S) 3.70E+21 0.0 105000<br />
CH4 + 2PT(S) => CH3(S) + H(S) 0.01 0.0 STICK, FORD/ PT(S) 2.3/<br />
CH3(S)+ PT(S) => CH2(S)s + H(S) 3.70E+21 0.0 20000<br />
CH2(S)s + PT(S) => CH(S) + H(S) 3.70E+21 0.0 20000<br />
CH(S) + PT(S) => C(S) + H(S) 3.70E+21 0.0 20000<br />
C(S) + O(S) => CO(S) + PT(S) 3.70E+21 0.0 62800<br />
CO(S) + PT(S) => C(S) + O(S) 1.00E+18 0.0 184000<br />
Courtesey of L.L. Raja, R.J. Kee, Colorad School of Mines<br />
http://reaflow.iwr.uni-heidelberg.de/~dmann/sm_ch4_ox_1.2_SURFACECHEMKIN<br />
O. Deutschmann, R. Schmidt, F. Behrendt, J. Warnatz: Proc. Comb. Inst. 26 (1996),<br />
1747<br />
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001<br />
OD_00_093
OD_01_009<br />
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001<br />
Experiments - detailed data<br />
(spatial & temporal profiles, coverages)<br />
Revised surface<br />
reaction<br />
mechanism<br />
Comparison of experiment and simulation<br />
Experiments - integrated data<br />
(ign.& ext. temperatures,<br />
selectivity, conversion)<br />
Numercial simulation<br />
Reactor models<br />
(including appropriate gas chemistry & transport models)<br />
Sensitivity analysis<br />
=> re-evaluation of cruical kinetic data<br />
Tentative surface<br />
reaction mechansim<br />
BOC-MP<br />
UBI-QEP<br />
Analogy to organometallic<br />
compounds<br />
Transition-State<br />
theory<br />
Heats of adsorption<br />
Surface science<br />
studies<br />
Analogy to gas<br />
phase kinetics<br />
Collision theory<br />
ab-initio<br />
calculations<br />
IWR Universität Heidelberg<br />
Survey of the methodology of the development of a surface<br />
reaction mechanism
Kinetic data for surface reactions at practically relevant<br />
conditions and for technically used catalysts<br />
IWR Universität Heidelberg<br />
Laser-spectroscopic methods such as<br />
SFG (Sum Frequency Generation) can<br />
bridge the pressure and materials gap<br />
=> Quantitative determination of surface<br />
coverage with adsorbed species<br />
R. Kissel-Osterrieder, F. Behrendt, J. Warnatz, U. Metka, H.-R. Volpp, J. Wolfrum. Proc. Combust. Inst. 28 (2000)<br />
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001<br />
OD_00_520
2<br />
OD_01_105<br />
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001<br />
M. Rinnemo, O. Deutschmann, F. Behrendt, B. Kasemo.<br />
Combust. Flame 111 (1997) 312-326<br />
O. Deutschmann, R. Schmidt , F. Behrendt, J. Warnatz.<br />
Proc. Combust. Inst. 26 (1996) 1747-1754<br />
Conditions: T 0<br />
= 298 K, p tot<br />
= 1 bar (94% N 2<br />
), circles: experiment, line: simulation.<br />
α = p H /( p H 2<br />
p O )<br />
α = p H2<br />
/ (p H2<br />
+ p 2<br />
O2<br />
)<br />
α α = p<br />
CH<br />
/( p CH4<br />
/ (p 4 CH4 + p O2<br />
)<br />
320<br />
(a) (b)<br />
300<br />
0.0 0.2 0.4 0.6 0.8 1.0<br />
400<br />
0.0 0.2 0.4 0.6 0.8 1.0<br />
Ignition temperature [K]<br />
500<br />
340<br />
360<br />
600<br />
380<br />
700<br />
400<br />
CH H2 800 4<br />
Ignition temperature [K]<br />
420<br />
440<br />
900<br />
Comparison of measured and calculated ignition temperatures in a stagnation point<br />
flow on a platinum foil heated resistively.<br />
IWR Universität Heidelberg<br />
Catalytic oxidation of hydrogen and methane on platinum:<br />
Ignition temperature
OD_99_314<br />
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001<br />
O. Deutschmann, R. Schmidt, and F. Behrendt. in S. H. Chan (ed.),<br />
Transport Phenomena in Combustion,Vol. 1, p. 166-175, Taylor and<br />
Francis, 1996.<br />
O. Deutschmann, R. Schmidt , F. Behrendt, J. Warnatz, 26th<br />
Symposium (International) on Combustion (1996) 1747-1754<br />
Conditions: H 2<br />
/O 2<br />
mixture (6 % diluted by 94 % N 2<br />
,<br />
p = 1 bar), α = p H2<br />
/(p H2<br />
+p O2<br />
) = 0.5, circles: experiment.<br />
Conditions: CH 4<br />
/O 2<br />
mixture (6 % diluted by 94 % N 2<br />
,<br />
p = 1 bar), α = C CH4<br />
/(p CH4<br />
+p O2<br />
) = 0.5.<br />
Time [s]<br />
Time [s]<br />
10 -5<br />
Surface coverage<br />
10 -1<br />
10 -2<br />
10 -3<br />
10 -4<br />
10 0 550<br />
H(s)<br />
500<br />
Pt(s)<br />
450<br />
400<br />
H2 O(s)<br />
350<br />
Temperature<br />
300<br />
10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0<br />
Surface temperature [K]<br />
Surface coverage<br />
10 0 CO(s) 820<br />
O(s)<br />
C(s)<br />
10 -1<br />
800<br />
Pt(s)<br />
10 -2<br />
780<br />
OH(s)<br />
10 -3<br />
760<br />
H(s)<br />
Temperature<br />
10 -4<br />
740<br />
-10 0 10 20 30 40 50 60 70 80<br />
Surface temperature [K]<br />
IWR Universität Heidelberg<br />
Transient Modeling of Catalytic Ignition of Hydrogen and<br />
Methane Oxidation on Pt: Temperature and Coverage
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Catalytic oxy-dehydrogenation of ethane: Interaction of<br />
transport and <strong>heterogen</strong>eous and homogeneous reactions<br />
IWR Universität Heidelberg<br />
Platinum coated monolith, 1cm in length<br />
Autothermal<br />
Residence time: 5 ms<br />
Ethylene selectivity: > 70%<br />
M. Huff and L. D. Schmidt: AIChE J. 42 (1996), 3484<br />
A. S. Bodke, D. A. Olschki, L. D. Schmidt, E. Ranzi: Science 285 (1999), 712<br />
The two-dimensional simulation of a single monolith channel is coupled with detailed<br />
gas-phase and surface reaction mechanisms.<br />
D.K. Zerkle, M.D. Allendorf, M. Wolf, O. Deutschmann. J. Catal.196 (2000) 18<br />
C2 H 6 , O 2<br />
C 2<br />
H 6<br />
+O 2<br />
C 2<br />
H 6<br />
+H -> C 2<br />
H 5<br />
+H 2<br />
C2 H 5 +M -> C 2 H 4 +H+M<br />
C2 H 6 + H 2 O<br />
Heat<br />
Shield<br />
H, C, O<br />
H2 O+Heat<br />
+C 2<br />
H 4<br />
+CO 2<br />
+CO<br />
H, O, CH x<br />
, C H 2<br />
, CO, CH 4,<br />
C 2<br />
H 4<br />
Alumina-Supported Platinum Catalyst<br />
Heat<br />
Shield<br />
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001<br />
OD_01_106
OD_01_107<br />
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001<br />
R. Kissel-Osterrieder, F. Behrendt, J. Warnatz, U. Metka, H.-R. Volpp, J. Wolfrum: Experimental and Theoretical Investigation<br />
of CO-Oxidation on Platinum: Bridging the Pressure and the Materials Gap, Proc. Combust. Inst. 28 (2000)<br />
Conditions: CO: 15 sccm; O 2 : 30 sccm, Ar: 105 sccm at a total pressure of 20 mbar<br />
CO coverage<br />
1<br />
0.8<br />
0.6<br />
0.4<br />
0.2<br />
0<br />
300 400 500 600 700 800<br />
temperature [K]<br />
CO 2<br />
-flux [sccm]<br />
14<br />
12<br />
10<br />
8<br />
6<br />
4<br />
2<br />
0<br />
300 400 500 600 700 800<br />
temperature [K]<br />
The CO oxidation on polycrystalline Pt is modelled by a two-adsorption site model.<br />
The predicted CO surface coverage is compared with data derived from optical sumfrequency<br />
generation (SFG) vibrational spectroscopy.<br />
IWR Universität Heidelberg<br />
Site <strong>heterogen</strong>eity of catalytic surfaces: Extension of the<br />
mean-field approximation leads to different sub-mechanisms
Lateral adsorbate interactions: Monte Carlo simulations of<br />
the elementary surface processes<br />
IWR Universität Heidelberg<br />
Spatio-temporal patterns in catalytic oxidation of CO on platinum; 2D resolution of the<br />
non-homogeneous layers of adsorbed species<br />
Pt(110), PEEM, 0.2 x 0.3 mm 2 , T = 427 K,<br />
p O2 = 32·10 -3 mbar, p CO 3·10 -3 mbar, ∆t = 4.1/ 30 s<br />
Target pattern on Pt(100), ∆t = 10 s, 1000 x 1000 lattice, 0.25 x 0.25 mm 2 ,<br />
T = 490 K, p O2 = 50·10 -3 mbar, p CO 1.5·10 -3 mbar<br />
S. Jakubit, H.H. Rotermund, W. Engel, A.<strong>von</strong> Oertzen,<br />
G. Ertl. Phys. Rev. Lett. 65 (1990) 3013<br />
R. Kissel-Osterrieder, F. Behrendt, J. Warnatz. Proc. Combust. Inst. 28<br />
(2000)<br />
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001<br />
OD_01_108
Summary and Outlook<br />
IWR Universität Heidelberg<br />
Multi-step mechanisms for simple <strong>heterogen</strong>eous-catalytic reactions such as<br />
- oxidation of H 2<br />
, CO, CH 4<br />
, C 2<br />
H 6<br />
on noble metals<br />
- NO reduction on noble metals (3WCC)<br />
- methanol and ammonia synthesis<br />
Advanced experimental techniques help to overcome the pressure and materials gap<br />
- high pressure STM<br />
- nonlinear laser methods such as SFG and SHG<br />
Challenges<br />
- Still too little is known about the elementary steps, in particular at high pressure<br />
- Combination of the experimental observations of single elementary steps<br />
to the overall picture of the catalyst<br />
- Coupling of the detailed reaction mechanisms with the macroscopic processes<br />
(mass and heat transport in the surrounding reactive flow, the washcoat, and the<br />
solid bulk)<br />
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001
Danksagung<br />
IWR Universität Heidelberg<br />
Daniel Chatterjee, Dr. Chrys Correa, Oliver Grosshans, Dr. Ralf Kissel-Osterrieder, Stefan Kleditzsch, Dr. Luba<br />
Maier, Renate Schwiedernoch, Steffen Tischer, Dr. Markus Wolf (IWR, Universität Heidelberg)<br />
Dr. Uwe Metka, Dr. Hans-Robert Volpp, Prof. Jürgen Wolfrum (PCI, Universität Heidelberg)<br />
Dr. David K. Zerkle (Los Alamos National Lab.)<br />
Prof. Jürgen Warnatz (IWR, Universität Heidelberg)<br />
Deutsche Forschungsgemeinschaft (DFG) (Sachbeihilfen, SFB 359)<br />
Forschungsverbund Verbrennungskraftmaschinen e.V. (FVV)<br />
Bundesland Baden-Württemberg<br />
J. Eberspächer GmbH & Co.<br />
Conoco Inc.<br />
US Department of Energy<br />
O. Deutschmann, XXXIV. Jahrestreffen Deutscher Katalytiker / Fachtreffen Reaktionstechnik, Weimar, 21.-23.3.2001<br />
OD_00_110