EFRC
Chemistry in the Center for CatalyticHydrocarbon Functionalization:Fundamental Studies Relevant to Catalystsfor C-H Functionalization
EFRC
Scripps Energy and Materials Center
CH4CH4
H2OH2O
N2N2
CO2CO2
O2O2
EnergyEnergy
FertilizerFertilizerCommodityChemicalsCommodityChemicals
FuelsFuels
Energy SecurityEnergy Security
SustainabilitySustainability
EFRC
Team
Gunnoe/UVA
Vedernikov/UM
Periana/TSRI
Groves/Princeton
Trewyn/Ames
Ess/BYU
Goddard/Caltech Cundari/UNT
Crabtree/Yale
Meyer/UNC
Homogeneous catalysis and organometallic chemistry
Electrochemistry and electrocatalysis
Bioinorganic chemistry and enzymatic chemistry
Computational chemistry and quantum mechanics
Materials chemistry (nanomaterials, electrodes surfaces, etc.)
Natural Gas(CH4)
Electricity
Natural gas
CO2
Materials
Fuels
An Economy Based on Natural Gas
Natural gas
CO2
CH + ½ O2 COH
Next GenerationCatalysts
Why natural gas?
EFRC
Extensive Natural Gas Reserves5
Energy Facts 2011 5
• Stranded gas is a shorter term, less demanding opportunity
• Gas could be at zero or negative cost
• Smaller, less expensive portable GTL units could process smaller NG reserves
• Less demanding requirements could accelerate implementation
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Flared Gas is an Immediate Need
• Gas at negative value• Require small Inexpensive GTL Units
• ~25% of US needs is flared
• Current high Temperature, syngas technology too expensive and complex for these applications
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CH4
Electricity
Natural gas
CO2
Materials
Fuels
Implementing the Natural Gas Economy
Natural gas
CO2
CH3OH The future
IntermediateFeedstock
Technologies known or in development
Why Methanol (DME)?
EFRC
Current technology to convert CH4 to Liquids
70% yield!
Mature technology!
Practiced at fuel scale!
Uses only AIR as the co‐reagent!
~25%900oC
MeOH
NaturalGas
Air
Synthesis Gas (CO/H2)
~60% MeOH
Fuels
Chemicals, CO, H2
Power
Fischer–Tropsch
Key to cost reduction is lower capital cost!
8
Selectivity of any new process must be >~80 – 90%!
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Technology Needed
NaturalGas
AirMeOH
Direct, Selective,Lower Temperature Methane Oxidation
Fuels
Chemicals
Power
CH4 + ½ O2 CH3OH
250 oC
Goal: >50% reduction in costrelative to existing technology
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The ChallengeSlide 10
of 69
H3C-H + ½ O2 H-CH2-OH CO2 + H2O
Utilize catalyst to activate (increase reactivity) of RH
Utilize catalyst to activate (increase reactivity) of O2
MinimizeEFRC
High Selectivity by Minimizing Product Oxidation
RH gas
RH lig ROHlig ROPlig
CO2 gas CO2 gas
Kp
k2
k1
k3P
Poor selectivity without “protection” since k2 > k1
High selectivity with “protection” if Kp >> 1 and k1 >> k3 << k2
P group needs to be inexpensive, stable and easily recycled
11
The strategy capitalize on reactivity of OH groupProduct protection strategy
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Commercial Wacker Process for Partial Oxidation of Ethylene
C2H4 + Ox+ H2O CH3CHO + H2Ox C2H4 + Ox+ H2O CH3CHO + H2Ox H2Ox + ½ O2 Ox + H2OH2Ox + ½ O2 Ox + H2O
Ox = 2Cu2+Ox = 2Cu2+Pd2+
Homogeneous catalysis
EFRC
Wacker Process Design can be Utilized for Partial Oxidation of CH4
CH4 + ½ O2 CH3OH
H2Ox + ½ O2 Ox + H2OH2Ox + ½ O2 Ox + H2O
13
CH4 + Ox+ H2O CH3OH + H2Ox CH4 + Ox+ H2O CH3OH + H2Ox
• Selective Partial oxidation• Lower capital and operating costs• Lower temperature• Gas/Liquid system• No air separation• Inherently safer• Easily scalable
• PdII is not effective
• New homogeneous (molecular) catalyst design
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Minimum Metrics for Measure Success
Key engineering guidelines >90% Product Selectivity >20% Methane conversion per pass Temperature >200oC but < 300oC Reactor volumetric productivity (STY) ~10‐6 mol/cc.sec Inexpensive product separation
Key Catalyst Guidelines TOF ~1 s‐1
TON >103
Can molecular catalysts meet these targets??
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Metrics to Measure Success
Engineering Guidelines Avoid explosive mixtures >20% Methane conversion per pass >90% Product Selectivity >20% Oxidant conversion per pass Non‐corrosive materials for inexpensive reactor construction Facile product isolation Pressure <500 psig Temperature >200oC but < 300oC Reactor volumetric productivity (STY) ~10‐6 mol/cc.sec = [cat] x TOF
Key Catalyst Guidelines TOF ~1 s‐1 TON >103 Catalyst concentration of 1 mM at TOF = 1 s‐1 to be cost effective At 1:1 gas:liquid should generate 2M MeOH in ~1.5 hr
Periana, J. Mol. Cat., 2004, 22, 7
The ChallengeSlide 17
of 69
H3C-H + ½ O2 H-CH2-OH CO2 + H2O
Utilize catalyst to activate (increase reactivity) of RH
Utilize catalyst to activate (increase reactivity) of RH
Need to minimize
Basis for Focus on Molecular Catalysts
Well Defined
Full Molecular Model
Poor Catalyst Separation
Very Selective
Fast below 250oC
Full synthetic Control
“Rational” Design
Inexpensive Heat Transfer
Gas‐Liquid or Gas‐Solid
Inexpensive Reactors
Low Operating Costs
Unstable above 250oC
Emerging
TSRI Confidential
Expensive EFRC
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CatalystDesign
QuantumChemistry
CatalystTesting
RapidScreening
Molecularcatalysts
Can Integrate Modern Tools to Reduce time to Market
PredictiveModel
Mechanisticstudies
Approaches to Catalyst Design20
CH4 + ½ O2 CH3OH
LnMX
[LnMO]+
½ O2
CH4+ X‐
CH3OH
½ O2+ HX
LnMX
LnM‐CH3
HX
CH4 CH3OH
Activatedintermediate Activated
intermediate
X‐
CH4 NOT “INVOLVED”O2 NOT “INVOLVED”
O2 ActivationCH Activation
Avoid free radicals
EFRC
LMX Catalysts Identified by “Theoretical Chemistry”
(In + Hsolv) / n
z/r (Å)
H+
Fe3+
Cr3+
La3+
Co3+Mn3+
Cu2+
Sn2+
Cr2+
Rh3+
Ni2+
Tl3+
Au1/3+Pt2+
Cd2+ Pb2/4+
Hg2+
Pd2+
Ag+Cu+
In+
Ti4+
I+Xe2+
Borderline RedoxElectrophiles
Hard RedoxElectrophiles
Bi3/5+Ir+
Rh+
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Several Effective Electrophilic Catalysts Operate by Electrophilic CH Activation
STY ~ 10‐7 mol/cc.sec
~1M methanol
Stable
>90% Selectivity
~80% methane conversion
All Catalysts operate by CH Activation
N N
N NPt
Cl
Cl
Science, 1998
Hg(II)/H2SO4
Science, 1993
I+/H2SO4
Chem Commun2002
Pd(II)/H2SO4
Science, 2003
Au(III)/H2SeO4
Angew Chem. E.2004
Cat220oC, 2.5 hrs
150 ml 98% H2SO4500 psig ~ 1M
CH4 + H2SO4CH3OH + H2O + SO2
22
Acid solvent is essential!!
Soft, Redox active electrophilesEFRC
EFRC
Catalysts inhibited by Products in Strong Acid Solvents
6 7 8 9 10 250
0.5
1.5
2.0
2.5
100
3.0
H+
(1960)
Hg2+
Fuels?
Chemicals?
Ho of D2SO4 solvent
K x 10
4s‐1
Need second generation catalysts!
N N
N NPt
Cl
Cl
Cost comparable to existing MeOH. Not applicable to large fields
Stranded gas?
CATA
LYST RAT
E
10‐3
Process Economics Show that this is not applicable to Large Fields24
Vent
Methanol
Nitrogen
Air
Natural Gas
H2O/SO2
H2SO4
Mechanistic Studies Show that Systems Operate by CH Activation
CH4
H2SO4
CH Activation
SO2 + 2 H2O3 H2SO4
H2O
N N
HN NPt
X
CH3
X
Cl
X = HSO4
+
N N
N NPt
Cl
Cl
CH3OH
Sol2+
2 X-sol
N N
HN NPt
Cl
[Sol]
- HCl
Sol = H2SO4
X-sol
1/2 O2 H2O
Pt[Sol]CH3
+
X-sol
N N
HN N
N N
HN NPt
[Sol]CH3
X
Cl +
HX
[CH3OH2]+
o]RH[TOF HHN N
NNPt
Cl
CH3
H
+2
1.55 1.73
2.17
25
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Current Proposed Reaction Mechanism
28 kcal/mol
Coordination is Rate determining
H2SO4 facilitatescoordination and cleavage
26
EFRC
Several Possible Mechanisms: A, B, C and D27
N
N
HN
N
XPtIV
CH3
X
X
+
X-
N
N
HN
N
XPtII
CH3
+
X-
N
N
HN
N
XPtII
X
+
X-
1
2
3
N
N
HN
N
XPtIV
X
X
X
+
X-
4
CH4
HX k6
k-6
k5
H2SO4 + 2 HXSO2 + 2 H2O
k2
CH3X + HX
k3
H2SO4 + 2 HX
SO2 + 2 H2Ok4k-4
k1k-1
CH4
HX
X = Cl-, HO3SO-
Original mechanism, A,Is wrong. Reactions proceeds by pathway D.
Can we get 103 increase?
27
EFRC
New Catalyst Designs
N
NN
N Pt
Cl
N
N
NN
N Ir
ClCl
Cl
RhO O
OOL
ORh
O
R
L
PtO O
OO
L
+
OsO O
OOL
L
N
N Ir
XX
X
OPt
N
TFA
TFA
O
N N
N NIr
OH2
Cl
IrO O
OO
CH3
N
N NPt
OH2
Cl
Rates too low
Very stable
28
EFRC
Approaches to Catalyst Design29
CH4 + ½ O2 CH3OH
LnMX
[LnMO]+
½ O2
CH4+ X‐
CH3OH
½ O2+ HX
LnMX
LnM‐CH3
HX
CH4 CH3OH
Activatedintermediate Activated
intermediate
X‐
CH4 NOT “INVOLVED”O2 NOT “INVOLVED”
O2 ActivationCH Activation
Avoid free radicals
29
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Ni-CoM-dependent Methanogenesis
S. W. Ragsdale and C. WilmottJ. Am. Chem. Soc. 2011, 133, 5626
30
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MNN N
N
O
L
HCH3
MNN N
N
O
L
H CH3
MNN N
N
O
L
H HCH3
MNN N
NL
CH3
H2O
HO
MNN N
NL
HO-CH3
Strategies for the oxygenation of strong C-H bonds
MNN N
CH3
O
L
HCH3
MNN N
O
L
H
H3C-CH3
HO-CH3
MNN N
O
L
H
OCH3
H2OH+
?
31
EFRC
Methane Activation by Rhodium Porphyrins
Wayland B. JACS, 1990; DiMagno, S. G. J. Am. Chem. Soc. 2000; Han, Y. Z.; Sanford, M. S.; England, M. D.; Groves, J. T. Chem. Comm. 2006, 549‐551; Sanford, M.S.; Groves, J.T. Angew. Chemie 2004, 116, 598‐600.
32
EFRC
Several Effective Electrophilic Catalysts Operate by Electrophilic CH Activation
STY ~ 10‐7 mol/cc.sec
~1M methanol
Stable
>90% Selectivity
~80% methane conversion
All catalysts operate by CH Activation
N N
N NPt
Cl
Cl
Science, 1998
Hg(II)/H2SO4
Science, 1993
I+/H2SO4
Chem Commun2002
Pd(II)/H2SO4
Science, 2003
Au(III)/H2SeO4
Angew Chem. E.2004
Cat220oC, 2.5 hrs
150 ml 98% H2SO4500 psig ~ 1M
CH4 + H2SO4CH3OH + H2O + SO2
33
Applicable to flared gas? EFRC
Summary and Future Directions34
Molecular catalysts that operate in solution at lower temperature by CH activation has been shown to be effective and potential practical for conversion of methane to methanol
High selectivity observed in these systems can be attributed to fast reaction at lower temperatures and reaction without the involvement of free‐radicals, and reversible protection
Issues such as cost, stability, separations, etc. can be addressed through catalyst modifications, changes in solvents, oxidants, etc.
A key basis for effectiveness of molecular catalysts is that detailed atomistic models can be obtained that together with a wide variety of synthetic tools utilized to “rationally” design improved catalysts.
An important focus is increasing catalyst rate by ~103
To speed up discovery, the iterative loop of synthesis, characterization, testing and study must be accelerated
An important strategy to accelerating progress while minimizing risk is to leverage efforts directed at the other small molecules, O2 ,N2, CO2 and H2O
EFRC