Approaching Catalysis from First Principle with

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Kingston, ON 15 - 18 June, 2008
Tuesday June 17 830-930 am
Tom Ziegler Department of Chemistry University
of Calgary-Calgary,Alberta,Canada T2N 1N4
Approaching Catalysis from First Principle
with Density Functional Theory
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Atomistic Theory
400 B.C
John Dalton (1766-1844)
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Atomic Theory
Niels Bohr (1885-1962)
Ernst Rutherford (1871-1937)
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The underlaying physical laws necessary for
the mathematical theory ofand the whole of
Chemistry are thus completely known, and
the Difficulty is only that the exact application
of The laws leads to equation much too
complicated to solve
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Electronic Structure Theory and Potential Energy
Surfaces Wave function methods
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JACOBS LADDER OF DFT
QUANTUM
MECHANICAL HEAVEN
Rung 5
Hyper-GGA
Rung 4
Meta-GGA
Rung 3
GGA
Rung 2
Rung 1
LDA
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JACOBS LADDER OF DFT
QUANTUM
MECHANICAL HEAVEN
Rung 5
Hyper-GGA
Rung 4
Meta-GGA
Rung 3
GGA
Rung 2
Rung 1
LDA
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ADF

• Solves Kohn-Sham equations
• Properties
• NMR, EFG, EPR, Raman, IR, UV/Vis, NLO, CD,
• Potential energy surfaces (transition states,
  geometry optimization)
• Environment effects
• QM/MM, COSMO
• Relativistic effects
• Scalar relativistic effects, spin-orbit coupling
• Transition and heavy metal compounds
• Uses Slater functions

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Olefin Polymerization
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Applications of Polyolefins
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Wold Plastic Production
Total production 110 billion pounds (2003)
15000 T more at end of this talk
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1980- The Metallocene Revolution
Brinzinger/Kaminsky
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The Metallocene Revolution
Hans Brintzinger
Walter Kaminsky
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Theoretical Chemists Joins the Revolution
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Early View of Metallocene Catalysts
Complete separation of ion-pair
Cation the active species
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Early Calculations on Metallocene Catalysts
All catalysts active
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Realistic View of Metallocene Catalysts
Pre-catalyst
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Activation Step
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Model Reduction
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Modes of attack
Ziegler et al. C.R. Chimie, 2005,8.
Vanka et al. Topics in Catalysis, 34,143
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Simulation of Cis-Attack
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Simulation of Trans-Attack
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Simulation of Termination
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Structures of the Cationic Catalyst Systems
I
phosphinimide
siloxy
Kitamide
Nova Catalysts
Stephan et al. Organometallics 2005.24,
Bis(phosphinimide)
Constrained geometry
Vanka,K. et al. Isr.J.Chem.2003,42
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Anions
Xu,Z. et al.Organometallics,2000
Vanka et al. Topics in Catalysis, 34,143
tetrakis(pentafluorophenyl)borane
Methyl Tris(pentafluorophenyl)borane
Methide--tetramethylaluminum methylalumoxane
Methide-methylalumoxane
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Correlation between Insertion Barriers (Cis
Approach)and Ion-pair Separation Energies
III
Vanka,K. et al. Isr.J.Chem.2003,42
Xu,Z. et al.Organometallics,2001,21,2444
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Dependence of Ion-Pair Separation on Nature of
Catalyst
Xu,Z. et al.Organometallics,2001,21,2444
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Relation between bond order and activity
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Accomplishments to date for group-4 metals
Nova Catalysts
phosphinimide
siloxy
Kitamide
Bis(phosphinimide)
Constrained geometry
New more active catalysts with more
electron-donating ligands. Stephan,
Organometallics 2004, 23,5240
New more active catalysts based on
Zirconium Stephan, Organometallics 2004,23,1562
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ZIEGLER-NATTA COORDINATION POLYMERIZATION
Karl Ziegler 1898-1973
Giulio Natta 1903-1979
The Nobel Prize in Chemistry 1963
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MgCl2
Support for Ziegler- Natta hetero- generous polyme
rization catalyst
Planes of Mg sandwiched between Planes of Cl
M.Serh,P.M.Margl,T.Ziegler Macromol. 2002,35,7815
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MgCl2 Support
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Vacant Sites on MgCl2 Support
4-coordinated exposed magnesium
M.Serh,P.M.Margl,T.Ziegler Macromol. 2002,35,7815
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Vacant Sites on MgCl2 Support
5-coordinated exposed magnesium
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Free Energy Selection of Possible Species
M.Serh,P.M.Margl,T.Ziegler Macromol. 2002,35,7815
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Vacant Sites on MgCl2 Support
Corradini Site
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Vacant Sites on MgCl2 Support
Edge Site
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Vacant Sites on MgCl2 Support
Slope Site
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Free Energy Selection of Possible Species
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CorradiniMg(II) Ti(III)26.9
Binding of methylation product
EdgeMg(II) Ti(III)24.9
CorradiniTi(II) Ti(III)40.0 kcal/mol
Edge Ti(II) Ti(IV)26.3 Ti(III)35.2 kcal/mol
SlopeMg(II) Ti(III)26.8
Mg(II)
Ti(II)
Slope Ti(II) Ti(IV)25.6 Ti(III)42.9 kcal/mol
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TiCl3-alkyl and MgCl2
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Ethylene insertion into Ti(III)-alkyl bond on
MgCl2
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Termination Ti(III) and MgCl2
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Termination on Ti(III) and MgCl2
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Reduce number of active sites with base
0 active sites
2 active sites
2 active sites
M.Seth,T.Ziegler Macromol. 2004,37,9191
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Four different sides
M.Seth,T.Ziegler Macromol. 2004,37,9191

• Higher insertion
• barriers

2. Much higher Termination barriers
Molecular weights Slope 88.000 Edge 209.000
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Stochastic Appoaches
1,2 Propylene re
1,2 Propylene si
2,1 Propylene re
2,1 Propylene si
M.Seth,T.Ziegler Macromol. 2004,37,9191
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Stochastic Appoaches
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Observed Experimental Molecular Wight Distribution
Experimental Weight Distribution
Z.Flisak ,T.Ziegler Macromol. 2005,38,9872
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Observed Experimental Molecular Wight Distribution
Experimental Weight Distribution
Z.Flisak ,T.Ziegler Macromol. 2005,38,9872
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Calculated Molecular Wight Distribution for
Second Site
Z.Flisak ,T.Ziegler Macromol. 2005,38,9872
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Calculated Molecular Wight Distribution for Third
Site
Z.Flisak ,T.Ziegler Macromol. 2005,38,9872
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Calculated Molecular Wight Distribution for
Fourth Site
Z.Flisak ,T.Ziegler Macromol. 2005,38,9872
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Calculated Total Molecular Wight Distribution
Different T and different P(Et)/P(Prop)
Exp.
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Summary Ziegler-Natta catalysis

• Be able to describe the molecular weight
  destribution
• For so

Comparison between theory and experiment difficult
Better experimental characterization of sites
needed
Combined QM and stochastic approach of some use -
but expensive
76
The Fe-catalyzed F-T synthesis of Hydrocarbons A
DFT study
Fischer-Tropsch synthesis An Introduction
(2n1) H2 n CO ? CnH2n2 n H2O 2n H2 n CO ?
CnH2n n H2O CO H2O ? CO2 H2 2 CO ? C CO2
77
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Fischer-Tropsch synthesis An Introduction
First discovered by Sabatier and Sanderens in
1902
Fischer and Tropsch reported in 1923 the
synthesis of liquid hydrocarbons with high oxygen
contents from syngas on alkalized Fe catalyst
(Synthol synthesis)
(2n1) H2 n CO ? CnH2n2 n H2O 2n H2 n CO ?
CnH2n n H2O CO H2O ? CO2 H2 2 CO ? C CO2
Øyvind Vessia, Project Report, NTNU, 2005.
Commercialized by Shell (Malaysia), Sasol (S.
Africa) and Syntroleum (USA)
78
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Mechanisms of F-T synthesis
CO insertion mechanism (Pichler and Schultz
(1970s))
Enol mechanism (Emmett et al. (1950s))
insertion
A
A
B
condensation
C
B
C
79
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Mechanisms of F-T synthesis
Most widely accepted carbene mechanism (Fischer
Tropsch (1926))
How is methane formed?
A
B
How do the C1 units couple?
Maitlis et al. JACS 124, 10456 (2002)
C
F
E
How does the chain grow?
D
80
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Methods of Computations

• ? Fe system (less extensively studied than Co and
  Ru)
• ? Surface energy Fe(100) Fe(110) lt Fe(111)
• ? Spin-polarized periodic DFT with plane-wave
  basis sets (VASP)
• ? PW91 exchange-correlation functional at GGA
  level
• ? Vanderbilts ultra-soft pseudopotentials
• Energy cutoff 360 eV
• k-point sampling of Brillouin zone
• ? 5-layer p(2 ? 2) slabs mimicking Fe(100)
  surface separated by 10 Å vacuum layer

81
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Methanation on Fe(100) Surface
? General reaction network for CH4 formation
(including all byproducts such as CO2, H2O, H2CO
and CH3OH)
Lo and Ziegler, J. Phys. Chem. C 111, 11012 (2007)
A
H
G
B
F
I
C
D
E
J
L
K
82
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Reactive intermediates on Fe(100) surface
? Three adsorption sites available on-top,
bridge and hollow sites ? Determine the most
preferred adsorption sites ? Calculate the
binding energies at various surface coverage
Lo and Ziegler, J. Phys. Chem. C 111, 11012 (2007)
Reference Lo and Ziegler, J. Phys. Chem. C 111,
11012 (2007)
83
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Chemisorption of CO Kinetics
Lateral interaction crucial factor affecting the
adsorption kinetics of CO
Desorption barrier decreases with ?
Activation barrier increases with ?
CO is less strongly bound at higher ?
Increase In free energy With 4 kcal For each 100K
Calculations predict full coverage by CO?
Something is missing
ENTROPY !
Lo and Ziegler, J. Phys. Chem. C 111, 11012 (2007)
84
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Chemisorption of CO Entropic contribution
Different components of entropy for a gaseous
molecule can be computed using statistical
thermodynamics
Generally speaking, one can write the total
entropy as a sum (reference Surf. Sci. 600, 2051
(2006))
This term will be completely lost because of the
assumption that the adsorbed species is immobile
This term is small compared to the rotational
entropy, and is thus neglected
This term mostly vanishes during adsorption for
immobile species but it is not possible to
compute such quantity for adsorbed molecules, and
is thus assumed zero after adsorption (crude
approximation)
85
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Chemisorption of CO Kinetics
Lateral interaction crucial factor affecting the
adsorption kinetics of CO
Desorption barrier decreases with ?
Activation barrier increases with ?
CO is less strongly bound at higher ?
Calculations predict full coverage by CO?
Something is missing
ENTROPY !
Lo and Ziegler, J. Phys. Chem. C 111, 11012 (2007)
86
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Dissociation of CO Coverage dependence
Lateral interaction affects the CO dissociation
Eact generally increases
0.06 kcal/mol
C O becomes less stable w.r.t. CO
CO dissociation is suppressed at ? 0.75 ML
Lo and Ziegler, J. Phys. Chem. C 111, 11012 (2007)
87
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Phenomenological kinetic simulation of CO
addition and dissociation
Langmuir-Hinshelwood approach all sites in (2x2)
units are energetically homogeneous
Simulation parameters COAr (119) gas at 1 atm
28 hours _at_ 150 and 473 K
Results
_at_ 150 K 50 CO 50 vacancy no C and O
_at_ 473 K 27 CO 27 vacancy 23 C 23 O
Lo and Ziegler, J. Phys. Chem. C 111, 11012 (2007)
88
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Formation of carbon filaments on iron surface
Fe is active catalyst for the Boudouard reaction
Boudouard reaction assists the formation of coke
on Fe(100) in the absence of H2
Reference Lo and Ziegler, J. Phys. Chem. C 111,
11012 (2007)
89
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Formation of CHx species on iron surface
Fe is active catalyst for the CHx formation
Reaction of C and H on Fe(100) in the absence of
CH2
CH2
C
CH
CH
CH
CH
CH3
CH2
CH3
CH4
Reference Lo and Ziegler, J. Phys. Chem. C 111,
11012 (2007)
90
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Thermodynamic PES of CH4
? Stability of CHn assuming the infinite
separation approximation
? For Fe(100), Co(0001) and Ru(0001), CH is the
most thermodynamically stable intermediate
? For Fe(110), surface carbide is the most
preferred species
? CH is likely the most abundant active C1
species on Fe(100) while CH, CH2 and CH3 have
significant coverage on Co under the F-T
conditions
? A possible F-T mechanism proceeding via CH
coupling reaction
Reference Lo and Ziegler, J. Phys. Chem. C 111,
11012 (2007) Gokhale and
Mavrikakis, Prep. Pap. - Am. Chem. Soc. Div. Fuel
Chem. 50, U861 (2005) Gong,
Raval and Hu, J. Chem. Phys. 122, 024711 (2005)
Ciobica et al., J. Phys. Chem.
B 104, 3364 (2000)
91
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Temperature effects on the rate of CH4 formation
Simulations including both CO and H2 at
industrial reaction conditions
P(CO)/P(H2)1/3
Reference Lo and Ziegler, J. Phys. Chem. C 111,
11012 (2007) Lox and
Froment, Ind. Eng. Chem. Res. 32, 61 (1993) 32,
71 (1993)
92
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Pressure effects on the rate of CH4 formation
(a)
? The rate of CH4 formation exhibits a strong
dependence on the partial pressures of CO and H2
p(CO) 0.2 Mpa T525 K
? Fixed pressures of CO and H2 p(CO) 0.2 MPa,
p(H2) 0.9 MPa.
? The computed rates are much higher than the
experimentally observed values
(b)
? Reason the coupling of C1 fragments is ignored
in all simulations
p(H2) 0.9 Mpa T525
Reference Lo and Ziegler, J. Phys. Chem. C 111,
11012 (2007) Lox and
Froment, Ind. Eng. Chem. Res. 32, 61 (1993) 32,
71 (1993)
93
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
C-C bond coupling reactions on Fe(100) surface
To figure out the origins of the product
selectivity of ethane/ethylene mixture
(c)
(e)
(d)
15
13
5
9
2
1
4
10
12
6
8
14
3
11
7
(f)
(a)
(b)
(e)
(c)
(d)
Lo and Ziegler, J. Phys. Chem. C 111, 13149 (2007)
94
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Thermodynamic stability of C2 species
Lo and Ziegler, J. Phys. Chem. C 111, 13149 (2007)
95
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Kinetics of the C-C coupling reactions on Fe(100)
With this information we may construct the
kinetic profile for the formation of ethane
ethylene
C-C bond coupling reactions are usually
kinetically demanding processes
Reference Lo and Ziegler, J. Phys. Chem. C 111,
13149 (2007)
96
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Kinetic profile of ethane formation
The formation of CH3CH3 is kinetically feasible
The rate-determining step is the C CH2 coupling
reaction
The C CH step has to overcome a much higher
barrier (gt 29 kcal/mol), and is thus less likely
Lo and Ziegler, J. Phys. Chem. C 111, 13149 (2007)
97
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
General chain propagation reactions on Fe(100)
surface
Very complicated processes because of a large
number of active surface species
For Co and Ru, the following mechanisms have been
proposed
Information obtained from previous sections C
and CH are the most abundant surface
species CCH, CCH2 and CCH3 are stable C2
fragments on Fe(100)
98
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
C-C bond coupling reactions
Coupling reactions with C-CHn fragments are
generally endothermic ? important only at high
reaction temperatures
Reactions between C and CHCH2/CH-CH3 and CH2CH3
possess lower activation barriers on Fe
Reactions between CH/CH2 and CHCH2/CH-CH3 or
CH2CH3 possess higher activation barriers on Fe
Therefore, the carbide route should be the
dominant mechanism in the Fe-catalyzed F-T
synthesis (thermodynamically favorable but
kinetically demanding)
99
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Thermodynamic stability of reactive C3 fragments
Kcal/mol
Reference Lo and Ziegler, J. Phys. Chem. C (to
be submitted)
Lo and Ziegler, J. Phys. Chem. C
111(2008),submitted
100
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Plausible reaction scheme of chain propagation
According to the computed C-C bond coupling
reaction barriers, the following possible
reaction scheme leading to the formation of
propane and propylene can be deduced
The kinetic profiles for the production of
propane and propylene can be obtained if the
activation energies for all these hydrogenation
reactions are known
Reference Liu and Hu, J. Am. Chem. Soc. 124,
11568 (2002).
101
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Kinetic potential energy surface for propane
formation
Lo and Ziegler, J. Phys. Chem. C 111,
2008,submitted
102
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Kinetic potential energy surface for propane
formation
Lo and Ziegler, J. Phys. Chem. C 111,
2008,submitted
103
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Propane/Propylene selectivity in the F-T synthesis
The formation of propane and propylene can be
traced back to CCHCH3
The production of propylene is more kinetically
controlled in the first step, while the path
leading to CHCH2CH3 intermediate is endothermic
Turnover may occur at CHCH2CH3 either proceeding
further to form propyl and propane, or undergoing
dehydrogenation to yield CCH2CH3 that is then
transformed into propylene (thermodynamic
selectivity)
Selectivity toward propylene is thus attributed
to the thermodynamically driven turnover of
CHCH2CH3
Lo and Ziegler, J. Phys. Chem. C 111,
2008,submitted
104
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Overall reaction scheme of the F-T synthesis
Combining all information collected in previous
sections, a reasonable reaction mechanism for the
F-T synthesis on Fe can be constructed
Next coupling
Lo and Ziegler, J. Phys. Chem. C 111,
2008,submitted
105
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
CO dissociation channel Fe(100) v.s. Fe(310)
Two stable configurations are located on Fe(310)
4f and 4f2
Barrier for CO activation on Fe(310) edge is
lowered compared to that on flat Fe(100) at 0.250
ML surface coverage
At higher coverage, the Fe(310) 4f2 becomes the
most feasible path, having the barrier of only
22.7 kcal/mol, and a large exothermicity of 12.1
kcal/mol
It is estimated that for an Fe catalyst with 10
Fe(310) steps by surface area, the resulting
percentage of adsorbed CO undergoing
decomposition becomes
(compared to 50 for Fe(100) surface)
Lo and Ziegler J. Phys. Chem. C. 2008 112
3692-3700
106
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Use of Alloys
1. H2 activation
Lo and ZieglerJ. Phys. Chem. C 2008, 112,
3667-3678
2. CO activation
J. Phys. Chem. C. (Article) 2008 112(10)
3679-3691.
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The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Conclusions
The process of Co hydrogenation on Fe catalyst
has been investigated computationally, and the
associated kinetics has been explored.
CO addition on Fe(100) has been controlled by the
entropy lost during the process, and in maximum
50 of the surface active sites can be occupied.
The most abundant C1 species on Fe(100) is CH,
but the chain initiation takes place making use
of CH2 instead.
The carbide mechanism, in which C inserts into
surface CnHm units, is found to be more
thermodynamically feasible than the well-known
alkenyl or alkylidene mechanisms.
The activity of Fe catalyst in the F-T synthesis
can be improved by introducing surface defects,
such as steps, or doping of other metals.
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New Orleans National Meeting
35nd ACS National Meeting April 6-10, 2008 New
Orleans, Louisiana

Symposium on Roles of Catalysis in Fuel
Cells Division for Petrochemistry
Organizers Umit S. Ozkan Jingguang G
Chen Presiding Thursday April 10, 2008, 1145
am. -1215 PM. Morial Convention Center, Room
Rm. 208
N.Galea, D.Knapp, E.Kadantsev, M.Shiskin,
T.Ziegler Department of Chemistry University
of Calgary,Alberta, Canada T2N 1N4
Studying SOFC anode activity with DFT
Suggestions for coke reduction and the effects of
hydrogen sulfide adsorption
109
Solid Oxide Fuel Cell CH4
The problem of coking

• CH4 4O2- ? 2H2O CO2 8e- (Direct
  Oxidation,coaking)
• CH4 H2O ? CO 3H2 (Steam Reforming Reaction)
• H2/CO O2- ? H2O/CO2 2e- (Oxidation Reaction)
• Molecular hydrogen or methane gas is typical
  anode fuel.
• CH4 adsorbs on Ni anode surface and decomposes,
  blocking adsorption sites with graphene, most
  stable form of carbon.

110
Triple Phase Boundary (TPB) Reactions
Pre-activation on Ni
Nickel/YSZ YSZ
Electrolyte
Anode
Cathode
2O2- 2O2-
O2(g)
2O2-
4e-
Burning on oxygen rich YSZ
Activation on Ni
Nickel
2H O2 ----gt H2O 2e-
H2 --gt 2H
YSZ
CH4-x (8-x)/2 O2- ---gt CO2(4-x)/2H2O(8-x)e-

CH4 --gt xHCH4-x
Oxygen rich YSZ
C(Coke)
111
Surface Calculations CH4
Steps and Terraces
Stepped (211) - C
Planar (111) - C

• Two classes of active adsorption sites.
• Stepped surfaces more reactive than planar
  surfaces.
• Supercell 3 layers, 2x2(planar) or 2x3(stepped)
  surface.

112
Calculations CH4
Computational Details

• Vienna Ab Initio Package (VASP). ADF BAND
• Projector augmented wave (PAW) method. Frozen
  core (BAND)
• Generalized gradient approximation (GGA)
  functional PBE96.
• Planar (111) Surfaces 2x2 unit cell, with 3
  layers.
• Stepped (211) Surfaces 3x3 unit cell, with 3
  layers.
• Theoretical equilibrium bulk lattice constants,
  aO(Ni) is 3.52? and aO(Cu) is 3.61?.
• 10? vacuum region between slabs.
• Cu(111) 5 x 5 x 1 Monkhorst-Pack k-point mesh.
• Other Surfaces 4 x 4 x 1 Monkhorst-Pack k-point
  mesh.
• Kinetic energy (wave function) cutoff energy is
  25Ry 340eV.
• Charge density (augmentation) cutoff energy is
  50Ry 680eV.
• Energies converged to 10-3eV.
• TS and reaction barriers calculated using the
  nudged-elastic band (NEB) method.
• MatLab mathematical software package.

N.Galea,D.Knapp,T.Ziegler Journal of Catalysis
247 (2007) 20-33
113
Ni(111) and Ni(211) Surfaces Adsorption and
Decomposition of CH4
Decomposition of CH4 on steps and terraces of Ni
(b)
(a)

• Theoretical literature Nørskov.
• Planar surface implies that coking should not
  occur.
• Stepped surface energies illustrating final
  exothermic dissociation reaction is driving force
  of coke formation.

Graphene
114
Ni(111) Ni(211)
Decomposition of CH4 on steps and terraces of Ni
N.Galea,D.Knapp,T.Ziegler Journal of Catalysis
247 (2007) 20-33
115
Graphene
Graphen formation

• Carbon is adsorbed at step base, resulting in
  formation of graphene (coke) layer on (111)
  terrace. Ni and hexagonally structured carbon
  atoms lie parallel to one another.
• Graphene island of finite size
• is required for stability.
• Blocking all step sites is
• NOT needed to prevent formation.
• Sparse covering of promoter atoms (e.g. gold,
  sulfur, alkali) or replacing Ni with Cu can
  hinder coke formation.

(Pictorial representation of surface)
116
Cu(111) and Cu(211) Surfaces Adsorption and
Decomposition of CH4
Decomposition of CH4 on steps and terraces of Cu

• Activity of copper in the dissociation of methane
  will be poor.
• Carbon cokes will not form on copper surfaces.
• Consistent with experimental SOFC observations.

Galea et al. Journal of Catalysis 247 (2007) 20-33
N.Galea,D.Knapp,T.Ziegler Journal of Catalysis
247 (2007) 20-33
117
Cu(111) and Cu(211) Surfaces Adsorption and
Decomposition of CH4
Decomposition of CH4 on steps and terraces of Cu

• Activity of copper in the dissociation of methane
  will be poor.
• Carbon cokes will not form on copper surfaces.
• Consistent with experimental SOFC observations.

Galea et al. Journal of Catalysis 247 (2007) 20-33
N.Galea,D.Knapp,T.Ziegler Journal of Catalysis
247 (2007) 20-33
118
Cu(111) and Cu(211) Surfaces Adsorption and
Decomposition of CH4
Decomposition of CH4 on steps and terraces of Cu

• Activity of copper in the dissociation of methane
  will be poor.
• Carbon cokes will not form on copper surfaces.
• Consistent with experimental SOFC observations.

Galea et al. Journal of Catalysis 247 (2007) 20-33
N.Galea,D.Knapp,T.Ziegler Journal of Catalysis
247 (2007) 20-33
119
Cu(111) and Cu(211) Surfaces Adsorption and
Decomposition of CH4
Decomposition of CH4 on steps and terraces of Cu

• Activity of copper in the dissociation of methane
  will be poor.
• Carbon cokes will not form on copper surfaces.
• Consistent with experimental SOFC observations.

Galea et al. Journal of Catalysis 247 (2007) 20-33
N.Galea,D.Knapp,T.Ziegler Journal of Catalysis
247 (2007) 20-33
120
Cu(111) and Cu(211) Surfaces Adsorption and
Decomposition of CH4
Decomposition of CH4 on steps and terraces of Cu

• Activity of copper in the dissociation of methane
  will be poor.
• Carbon cokes will not form on copper surfaces.
• Consistent with experimental SOFC observations.

Galea et al. Journal of Catalysis 247 (2007) 20-33
N.Galea,D.Knapp,T.Ziegler Journal of Catalysis
247 (2007) 20-33
121
Cu(111) Cu(211)
Decomposition of CH4 on steps and terraces of Cu
N.Galea,D.Knapp,T.Ziegler Journal of Catalysis
247 (2007) 20-33
Galea et al. Journal of Catalysis 247 (2007) 20-33
122
Step Edge - Cu-Ni(211) Adsorption and
Decomposition of CH4
Decomposition of CH4 on Cu-steps and Ni-terraces
Galea et al. Journal of Catalysis 247 (2007)
20-33
Copper
(a)

• Cu surface segregation occurs as Cu has a lower
  surface energy than Ni.
• Likely that Ni steps that nucleate C formation
  are blocked by Cu atoms, exposed terrace Ni sites
  contribute to activity.
• Endothermic C production on alloy, with
  reasonable activity.

123
S-Ni(211)
Decomposition of CH4 on S-steps and Ni-terraces
Galea et al. Journal of Catalysis 247 (2007) 20-33
N.Galea,D.Knapp,T.Ziegler Journal of Catalysis
247 (2007) 20-33
124
100 Step Au/S-Ni(211) Adsorption and
Decomposition of CH4
Decomposition of CH4 on (S,Au,S) steps and
Ni-terraces
Sulfur or Gold
(a)

• Small amounts of sulfur / gold can discourage the
  adsorption of carbon at the step by blocking edge
  sites, mimicking the nature of the planar nickel
  surface.

N.Galea,D.Knapp,T.Ziegler Journal of Catalysis
247 (2007) 20-33
Galea et al. Journal of Catalysis 247 (2007) 20-33
125
A. Conclusions CH4

• Our research theoretically studies methods used
  experimentally to block step sites and reduce
  graphitic carbon formation.
• Propensity to coking of Ni surface explained by
  strong adsorption of C atoms at step edge,
  followed by graphene growth over terrace sites.
• Thermodynamic energies and kinetic barriers of
  methane ads.n and dis.n on Cu surfaces are high,
  explaining poor activity and lack of coke.
• Cu-Ni alloys, where Cu blocks step sites, the
  catalyst retains activity due to Ni, while C
  formation remains endothermic due to Cu.
• S-Ni stepped surface (and Au) demonstrates that
  step blocking renders step sites inactive to
  methane dis.n and forces ads.n onto terrace
  sites.
• Galea, N.M. Knapp, D. Ziegler, T. J. Catal.
  2007, 247, 20.

126
Triple Phase Boundary (TPB) Reactions
Pre-activation on Ni
Nickel/YSZ YSZ
Electrolyte
Anode
Cathode
2O2- 2O2-
O2(g)
2O2-
4e-
Burning on oxygen rich YSZ
Activation on Ni
Nickel
2H O2 ----gt H2O 2e-
H2 --gt 2H
YSZ
CH4-x (8-x)/2 O2- ---gt CO2(4-x)/2H2O(8-x)e-

CH4 --gt xHCH4-x
Oxygen rich YSZ
M.Shishkin N.Galea,D.Knapp,T.Ziegler, work in
progress
127
Triple Phase Boundary (TPB) Reactions
Activation on YSZ
Nickel/YSZ YSZ
Electrolyte
Anode
Cathode
2O2- 2O2-
O2(g)
2O2-
4e-
Activation and burning on oxygen rich YSZ
Nickel
YSZ
H2O2- ----gt H2O 2e-
Oxygen rich YSZ
CH4 4 O2- ---gt CO22H2O8e-
M.Shishkin N.Galea,D.Knapp,T.Ziegler, work in
progress
128
Triple Phase Boundary (TPB) Reactions
Activation on YSZ
Nickel/YSZ YSZ
Electrolyte
Anode
Cathode
2O2- 2O2-
O2(g)
2O2-
4e-
Zr
9-YSZ
Nickel
O
YSZ
Oxygen rich YSZ
Y
M.Shishkin N.Galea,D.Knapp,T.Ziegler, work in
progress
129
Molecular Hydrogen Adsorption onOxygen Rich YSZ

• Initial adsorption of H2(g) on 9-YSZ is
  energetically more favourable than on nickel.
• TS energy barriers all lt 5 kcal/mol.

M.Shishkin N.Galea,D.Knapp,T.Ziegler, work in
progress
130
Methane adsorption on Oxygen rich YSZ initial
stage.
M.Shishkin N.Galea,D.Knapp,T.Ziegler, work in
progress
131
Methane adsorption on Oxygen rich YSZ Second
stage.
132
Third stage formaldehyde decomposition on oxygen
enriched YSZ surface.
133
Methane adsorption on oxygen deficient YSZ
surface.
134
B. Conclusions CH4

• It might be possible to construct anodes of
  inactive conductors and electrolytes that can
  oxydize fuels
• .

M.Shishkin N.Galea,D.Knapp,T.Ziegler, work in
progress
135
(No Transcript)
136
Collaborators
Dr. Tebikie Habtu
Dr. Dongqi Wang
Dr. Simone Tomasie
137
Classical Ziegler-Natta Catalysts
Zygmunt Flisak (PDF)
Michael Seth (PDF)
138
The Fe-catalyzed F-T synthesis of hydrocarbons A
DFT study
Acknowledgments
? Dr. John Lo ? Department of Chemistry,
University of Calgary ? The Western Canada
Research Grid (Westgrid) ? Alberta Ingenuity Fund
139
Acknowledgements

• Thank You!
• Financial support was provided by the Alberta
  Energy Research Institute and the Western
  Economic Diversification Department.
• Calculations were carried out on WestGrid
  computing resources, funded in part by the
  Canadian Foundation for Innovation, Alberta
  Innovation and Science, BC Advanced Education,
  and the participating research institutions.

140
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