energy chemical industry catalysis...conditions: 1mm co,0.1 m nbu 4clo 4 in acetonitrile n,...
TRANSCRIPT
FUELS (~90%)
CHEMICALS (~10%)
Syngas Methanol Ethylene Propylene Butadiene Benzene, Aromatics
FUELS (90% ?)
CHEMICALS (10% ?)
Ethanol Glycerol Carbohydrates Seed Oils Lignin
Fossil Resources (1800’s – present)
Renewable Resources (Energy and Feedstocks of Future?)
silk, cotton, wool Cellulose acetate Rayon Polylactide (PLA) Polyhydroxy- alkanoates (PHA)
Polyethylene Polypropylene Polybutadiene PET PVC
Energy Chemical Industry Catalysis
“The Electron Economy”: Energy Conversion/Storage Waymouth, Chidsey, GCEP
Liquid Fuels + O2
CO2, H2O
H2 + O2
HEAT
WORK
Low Free Energy Electrons
High Free Energy Electrons
Chemical Energy Conversion
“The Electron Economy”: Energy Conversion/Storage Waymouth, Chidsey, GCEP
fuel oxygenH+
motore- e-motor
reductioncatalyst
oxidationcatalyst
graphiticcarbonelectrode
graphiticcarbonelectrode
polymerelectrolytemembrane(PEM)
H2
2 H+ + 2 e-
O2
2 H2O
4H+ + 4 e-
Polymer-Electrolyte-Membrane Fuel Cell (PEM)
Electrocatalysis at Stanford Waymouth, Chidsey, Stack Kanan (Chemistry) Jaramillo, Norskov (Chem. Eng.)
CH3OH+ H2O
CO2+ 6 e- + 6 H+
Electrocatalytic Efficiency: Potential
0.0 0.2 0.4 0.6 0.8 1.0 1.2
bestexistingoxygen
O2
bestexistingoxygen
O2workheat heat
Oxidant
oxygenO2
Fuel
reversiblepotentials
E0H+/H2
E0CO2+H2O/CH2
E0O2/H2O
hydrocarbon(CH2)n
bestexisting
methanolCH3OH
bestexisting
hydrogenH2
How much work can be obtainedand heat avoided
with discrete electrocatalysts?
free energy converted
to work
free energy wasted as heat of fuel oxidation
free energy wasted as heat of O2 reduction
heat
heatwork
Electrochemical Potential (V vs. H+/H2)
H2
2 H+ + 2 e-
CH3OH+ H2O
CO2+ 6 e- + 6 H+
O2 4 e- + 4 H+
2 H2O
Pt electrode
O C
CO2
H Hn H+
CH3 OH
Oe
O CO
-2.2 V
H H H H
H2O
C
OH2O
CO2
Energy Storage: Opportunities and Challenges
Reversible Generation of Fuels:
2 e- + 2 H+ H2
CO2 + 6 e- + 6 H+ CH3OH + H2O
high overpotential for CO2 reduction
Pt electrode
HHHH
HH2 H+
overpotential for CH3OH oxidation
Energy Storage: Opportunities and Challenges
HCO2HCO2 + 2 e- + 2 H+
H2C=O + H2OCO2 + 4 e- + 4 H+
CO2 + 6 e- + 6 H+ CH3OH + H2O
CO2 + 3H2
HCO2H 2H2
CH3OH H2O
H2C=O H2 + H2O8.9 kcal/mol6.6 kcal/mol
-4.3 kcal/mol
0 kcal/mol
Δ G°
(6 e- + 6 H+)
E° (V vs NHE)
-0.194
-0.071
0.031
As this reaction is thermoneutral (when R = R’),
it occurs at the reversible electrochemical potential
Transfer Hydrogenation: Insights for Reversible Electroatalysts
K ~ 1
Transfer Hydrogenation: Alcohol is oxidized by a ketone
Proposed Mechanism Proposed Electrocatalytic
Mechanism
OH
HR'R'
O
R R+
OH
HRR
O
R'R'+
Haack, K. J.; Hashiguchi, S.; Fujii, A.; Ikariya, T.; Noyori, R., ACIEE 1997, 36 (3), 285-288.
RuX N
R R
H
RuX N
R R
H
HHO
R R
OH
HRR
OH
HR'R'
O
R'R'
RuX N
R R
H
RuX N
R R
H
HH
OH
H
O
- 2 H+
- 2 e -
RuX N
R R
H
OH
HR'R'
Transfer Hydrogenation: Strategies for CO2 Activation and Reduction
• Metal Hydrides will activate and Reduce CO2
• Hypothesis: Outer-sphere Bifunctional Activation of CO2 preferred
Ru
NTs N
R R
H
HH RuN P
Ph2N
Ph2P
H
Ru
O N
R R
H
HH
N Co NCCH3
2+
NNOC Mo HOC
ORRR
R
CO
H
HH
Transfer Hydrogenation: Insights for Reversible Electroatalysts
Transfer Hydrogenation: Reversible Transfer of H2 between ketone and alcohol
Ph
O
H
OH
Ph H
O O+ +
H
TOF 20 h-1 113 h-1 6 s-1 0.03 h-1
Kristin Brownell
Kate Waldie
Tomo Seki
Sungkwan Kim
Noyori, Ikariya Baratta
0.7 h-1
Megan Buonauito, Anthony DeCrisci Tom Jaramillo
Ru(OH)x /Oxidized Ti electrode
Electrocatalytic Oxidation of MeOH
RuHN O
on graphite electrode
CH3
OHH O
O
H
or CO
+ 4 e- + 4 H+
0
10
20
30
40
50
0 0.2 0.4 0.6 0.8 1 1.2
400 rpm 800 rpm 1600 rpm 3000 rpm
E / V vs. NHE
curr
ent /µA
Edge plane graphite electrode, 1M NaClO4, 0.01 M phosphate buffer, pH = 11.5
overpotenial: ~1.2 V (pH 11.5)
Brownell, Chidsey, Waymouth, Zare, J. Am. Chem. Soc., 2013, 135,14299.
Wills, M., et.al JOC 1997, 62 (15), 5226-5228.
4 electron oxidation with a rate of 1 MeOH s-1
• Ru(OH)x/Titanium electrodes: Catalytic transfer hydrogenation • Electrochemical oxidation of 2-propanol to acetone: bulk electrolysis
• mild conditions (25oC, neutral pH), low Ru loadings • Faradaic efficiencies above 95% with TOF ~ 0.6 hr-1 • Recyclability of electrode with only 20% reduction in activity and efficiency • Onset potential approximately 1000 mV vs RHE, overpotential ~ 870 mV
Heterogeneous Transfer Hydrogenation Catalysts: Ru(OH)x on anatase TiO2
Buonaiuto, M.; DeCrisci, A.; Jaramillo, Waymouth, manuscript in preparation
CH
O
HH
H
CR
O
R'
80oC1 atm N2/Ar C
H
O
R'R
H
CH
O
H
Ru(OH)x/TiO2
O
TiO
Ti
ORu
OTi
ORu
OH
O
TiO
Ti
ORu
OTi
ORu
OH H
H
CH
O
HH
H
CH
O
H
2H+, 2e-
CR
O
R'
CH
O
R'R
H
OR
Mizuno N. Chem. Eur. J. 2008,14, 11480.
Deposit Ruthenium onto Titanium Electrodes
Titanium
<10nm TiO2 amorphous
Submonolayer Ru(OH)x/Titanium foil
Reactivity ü 2-propanol electrooxdation to acetone under N2 ü Chemical Transferhydrogenation of acetophenone
under Mizuno conditions
Electrooxidation
CTH
20 nm TiO2
Ru Ru O
O
O
O
O
O
O
O
O
O
Ru(OH)x/TiO2 2.1%Ru
Our Approach: Ru(OH)x Electrocatalysis on Oxidized Titanium foils
Entry R1 R2 ΔG°298K (kcal/mol)
Exp. Calc.
1 CH3 CH3 -3.1 -2.4
2 CH3 n-C5H11 -2.7 -2.1
3 CH3 C6H5 -4.0 -5.7
4 CO2 - -10.5
Thermodynamics of Ketone/CO2 Insertion: Experiment and Calculations
Kate Waldie
Srinivasan Ramakrishnan. TeraChemTM (Todd Martinez)
Level of Theory: ωB97xD/6311g*(C,H,N,O,P)/LANL2DZ(Ru)/SMD(THF)
• Fast, reversible insertion of Ketones
• Fast insertion of CO2, irreversible
Theory Experiment
R1 R2
ORuN
NO
PPΔG298K
Ph2
Ph2
R1HR2 H
H
RuN
NH
PP
Ph2
Ph2
HH
d8-THF
1-H
R R
RuN
NO
PPΔG298K
Ph2
Ph2
H
HH
RuN
NH
PP
Ph2
Ph2
HH
d8-THFC OO
O
R R
0.0
+5.0
-8.7 -10.5
+6.5 11
1-H + CO2
12
13 1-OCHO
TS11-12 +11.0 TS12-13
+10.8
Insertion Pathway: CO2
RuN
NH
PPh2
Ph2P
H HCO
O
Cooperative Addition of Ru-H and N-H to CO2
+6.8
+14.9 +17.2
+10.2 +13.7
+7.5
0.0 -2.4 1-OiPr
10
TS7-8 8
9 1-NH + iPrOH
7
1-H + CH3(CO)CH3
+15.8 TS8-9
0.0
+5.0
-8.7 -10.5
+6.5 11
1-H + CO2
12
13 1-OCHO
TS11-12 +11.0 TS12-13
+10.8
(a)
(b)
Insertion Pathways: Acetone and CO2
4-OiPr (-6.5)
2-OiPr (+0.4)
1-OiPr (-2.4)
3-OiPr (-9.1) 2-OCHO (-7.4)
4-OCHO (-14.5)
3-OCHO (-15.3)
1-OCHO (-10.5)
0.0
1-H 2-H 3-H 4-H
acetone or CO2
+
RuN
NX
PN
Ph2
H2
HH
X = H (2-H) OiPr (2-OiPr) OCHO (2-OCHO)
RuN
NX
PP
Ph2
Ph2
HH
X = H (1-H) OiPr (1-OiPr) OCHO (1-OCHO)
RuN
NX
NN
H2
H2
HH
X = H (4-H) OiPr (4-OiPr) OCHO (4-OCHO)
X = H (3-H) OiPr (3-OiPr) OCHO (3-OCHO)
RuN
NX
NP
H2
Ph2
HH
Theory: Predictions for More Effective Catalysts Crucial Role of the cis and trans ligands
Electrochemical Generation of Metal Hydrides:
(MeO)3P
CoI
P(OMe)3
CoIII
(MeO)3PP(OMe)3
H
H
(MeO)3P
CoIII
P(OMe)3
2 +
e e
Hydrogen Evolution Rxn, Electrogeneration of M-H: CpCo complexes
Koelle, Inorg. Chem.1986, 2689
2 H+ H2-1.15 V, pH 5
water
(MeO)3P
Co
P(OMe)3
Proposed Reactivity:
Synthetic Target: Redox-active ligand to facilitate generation of Metal Hydride
Challenge: Neg potentials to reduce Co(III)
N Co NCCH3
2+
NN
N CoIII NCCH3
2+
NN
N CoII
NN
N CoIII H
+
NN
H+
2 e -
-‐3.0 -‐2.5 -‐2.0 -‐1.5 -‐1.0 -‐0.5 0.0 0.5
-‐60
-‐40
-‐20
0
20
40
60
80
Currnet (µA
)
E /V vs F c /F c +
[C pC o(A zpy)(C H3C N )][C lO
4]2
[C pC o(bpy)(C H3C N )][C lO
4]2
E1/2
1= -‐0 .158V
Ec
1= -‐0.186V
E1
a= -‐0.130V
E1/2
1= -‐1 .822V
Ec
2= -‐1.860V
Ea
2= -‐1.784V
E Ea1 Ec
1 E1/21 Ea
2 Ec2 E1/2
2 Ec3
Azpy V -0.130 -0.186 -0.158 -1.784 -1.860 -1.822 N.A. Bpy V -0.377 -0.442 -0.407 -0.976 -1.052 -1.014 -2.617
CVs of [CpCo(Azpy)(MeCN)][ClO4]2
N CoIIINCMe
2ClO4
N
N CoIIINCMe
2ClO4
NN
azpy
bpy
• 2 electron reduction of Co(III) at – 0.15 V
-‐2.5 -‐2.0 -‐1.5 -‐1.0 -‐0.5 0.0 0.5
-‐100
-‐80
-‐60
-‐40
-‐20
0
20
40
60
80Current (µA
)
E /V vs F c /F c +
1mM C o, 0mM ac id 1mM C o, 1mM ac id 1mM C o, 3mM ac id 1mM C o, 5mM ac id 1mM C o, 7mM ac id 1mM C o, 9mM ac id 1mM C o, 11mM ac id
Electrocatalytic Reduction of H+ with [CpCo(azpy)(CH3CN)][ClO4]2
Conditions: 1mM Co,0.1 M NBu4ClO4 in acetonitrile N, DMF/DMFH+, Scan rate 100 mV/s (In N2 glovebox )
Kim, Waldie, Ingram, Waymouth, Inorg. Chem., 2014, submitted for publication
2 H+ + 2 e- H2
N Co NCCH3
2+
NN
ElectroReduction of [CpCo(azpy)(CH3CN)][ClO4]2
CoIN
N N
CoIIN
N N
CoIII
NCMeN
N N
2+2 e-
diamagnetic
CoIII
NCMeN
NNH
+
+ H+
not CoIII
HN
NN
+
CoIII
NCMeN
N N
2+2 e-
diamagnetic
Molecular Designs for Electrocatalysts
• Transfer Hydrogenation Catalysts Alcohol Electrooxidation Catalysts
• Theory and Experiment Critical for Molecular Design
• Rapid and Reversible Ketone Reduction
• Rapid and Reversible CO2 Activation and Reduction
• Facile Electrogeneration of Metal Hydrides at low overpotential
• Need Better Molecular Understanding:
• Electronic Communication: Ligand e- reservoirs (redox-active ligands) and Metals • Coupled Proton / Electron Transfers
Kate Waldie, Kevin Chung, Tim Blake, Andrew Ingram, Tyler Stukenbroeker, James Flanagan, Wilson Ho, Megan Buonaiuto, Young Chang, Colin McKinlay, Xiangyi Zhang, Wei-Wei Wu, Dr. Tomo Seki, Dr. Andrey Rudenko Prof. Eun Joo Kang Srini Ramakrishnan Dr. Jelena Samonina-Kosicka
Collaborators Prof. Chris Chidsey (Stanford) Prof. Tom Jaramillo (Stanford) Prof. Todd Martinez (Stanford) Prof. Dick Zare (Stanford) Dr. James Hedrick (IBM) Julia Rice, Hans Horn (IBM) Prof. Paul Wender (Stanford)
DOE, National Science Foundation ONR, GCEP (Stanford Global Climate and Energy Program) Center For Molecular Analysis and Design (Stanford Chemistry)