Homogeneous Catalysis for C-H Activation and
Other Approaches to Shale Gas Utilization
!
Shannon S. Stahl
!
University of Wisconsin–Madison
!
CH4
H2/CO
H2C CH2
R CH3OH
[O]
(existing)!
What will be the source of aromatics, C4s and propylene?!
Why Homogeneous Catalysis?
!
• !Homogeneous catalysts are used in numerous major industrial processes!
!- !olefin oligomerization, polymerization (ethylene) !
! ! !• metallocenes and other single-site Ti/Zr/Hf!
! ! !• [(P,O)Ni–H]+ (SHOP catalysts)!
! ! !• Cr(EH)
3/Me2pyrrole/AlR3!
!- !hydroformylation (syngas)!
! ! !• Rh/phosphine, HCo(CO)
4 ± phosphine!
!- !aerobic oxidation - Wacker and Mid-Century processes (O
2)!
!- !many others…! !
• !Is Homogeneous vs. Heterogenous Catalysis an appropriate dividing line? !
!Is this an artifact of US academic science (Chemistry vs. Chem. Engr. departments and
associated language barriers)?!
!- !Molecular vs. Nanoparticle vs. Bulk Heterogeneous! !- !Liquid phase vs. gas phase chemistry!
!- !How should single-site supported catalysts (e.g., metallocene and related olefin!
! !polymerization catalysts) and MOFs be classified?!
!
• !This presentatiion will emphasize "molecular" processes and/or concepts!
!- !biological transformations/oxidations reflect this perspective!
! !(enzymes are molecules)!
!- !molecular/atomistic concepts are increasingly relevant and applied to !
α
-Olefin Synthesis and Applications
!
Alpha Olefins Market Analysis By Product (1-Butene, 1-Hexene, 1-Octene), By Application (Polyethylene, Detergent Alcohol, Synthetic Lubricant) And Segment Forecasts To 2020!
Published: March 2015 | ISBN Code: 978-1-68038-356-0!
“Increasing 1-hexene usage in LLDPE
production is expected to drive the market growth over the forecast period.”!
Major Applications!
• LLDPE! • HDPE!
• Detergent Alcohols! • Synthetic Lubricants!
α-Olefin Synthesis!
• Shell Higher Olefin Process (oligomerization/methathesis) - ethylene! • Oligomerization (INEOS) - ethylene!
• Fischer-Tropsch (Sasol) - syngas!
• Butadiene telomerization (Dow) – naphtha cracking! • Ethylene trimerization/tetramerization - ethylene
(Chevron Phillips, Sasol)!
Homogeneous Catalysts!
Selective for primarily! a single alpha olefin!
5.2M tons! 3.7M !
tons!
Discovered in 1930s (Co)
& 1960s (Rh)
– Oxo Process –
Hydroformylation: (
α
-)Olefins and Syngas
!
Linear (and branched) Aldehydes > 18 billion lbs/year
R + H2/CO R H
O H
Discovered in 1955
– Mid-Century and Related Autoxidations –
Radical Chain (Liquid Phase) Aerobic Oxidation of Hydrocarbons
!
H3C
CH3 + 3 O2
Co/Mn/Br
-HO2C
CO2H + 2 H2O
Radical-Chain (Catalytic) Aerobic Oxidation!
> 100 billion lbs/year
In2
nonradical products + O2
also…!
H2C CH2 + 1/2 O2
H3C H O [Pd, Cu]
H2O 2 Cu2+
2 Cu+
H O
CH3
PdII
PdII
OH PdII
H+
H2O
CH2
CH2
2+
+ 2 H+
+
+ H+ Pd0
1/2 O2
CH2 CH2
Discovered in 1959
Wacker Process: Ethylene to Acetaldehyde
!
Regioselective Alkane Activation by Transition Metal Complexes
!
Activation of 1° C-H bond is favored!!! but…!
reactions generally stoichiometric and incompatible with oxidants
or other reagents needed to functionalize the metal-alkyl!
Labinger & Bercaw Nature 2002, 417, 507-514. ! Ir
Me3P
H H
Ir Me3P
H hν
– H2
+ Ir
Me3P
H
110 °C, 14h 1.5:1
+
for M = Rh, only 1° C–H activation
+ CH4 Zr NR
R(H)N R(H)N
R = SiBut 3
Zr
N(H)R R(H)N
R(H)N
CH3
Sc CH3 + 13CH
4 Sc 13CH3 + CH4
Oxidative Addition (Bergman, Graham, Jones, …)!
Sigma-Bond Metathesis (Bercaw, Watson, Marks, …)!
1,2-Addition (Wolczanski, Bergman, …)!
Selective "C–H Functionalization"
!
2000s – Applications to organic chemistry, pharmaceutical synthesis…!
DG H3C
H3C CH3 O
H3C
H3C O
O
O O OH
OH
Jiadifenolide Huw Davies
Emory University
120° C
CH3OH + PtCl42- + 2 HCl CH4 + PtCl62- + H2O
PtCl4
2-!
[O]
!
The
Oxidant
Problem
!
Organometallic Methane Oxidation
!
The Shilov System (1971)
!
PtII Cl Cl
Cl Cl
PtII
Cl Cl
CH3 Cl
PtIV Cl Cl
Cl Cl
2-CH3
Cl
2-CH3OH + H+
CH4 HCl
PtIVCl6
Shilov System
!
+ 25%
conversion
80%
OH HO OH Cl OH
CH
4vs. CH
3OH
k1 k2
k1 ~ k2
cf. H atom abstraction: k1
k2
~ 10-6
C
2H
6vs. C
2H
5OH
H–CH2CH3 > H–CH2CH2OH > H–CH(OH)CH3
→ direct oxidation of ethane to ethylene glycol!
Propanol Oxidation
Biological Methane Oxidation
!
CH4 + O2 + NADH + H+ MMO CH3OH + H2O + NAD+ 45 °C
!
e
–
The
Reductant
Problem
!
Methane Monooxygenase (Fe)
!
Graphic:!
Biological Methane Oxidation
!
CH4 + O2 + NADH + H+ MMO CH3OH + H2O + NAD+ 45 °C
The
Reductant
Problem
!
Methane Monooxygenase (Fe)
!
CH4 + H2O2 → CH3OH + H2O !
O2 + 2 H+ + 2 e– → H
2O2 !
CH4 + 2 H2O → CO2 + 8 H+ + 8 e– !
x 4
!
5 CH4 + 4 O2 → 4 CH3OH + 2 H2O + CO2 !
Biological Aerobic Oxidation
Oxidases
substrate oxidation and
!
dioxygen reduction occur
in
independent
steps
Oxygenases
substrate oxidation coupled
!
to
oxygen atom transfer
!
from dioxygen
!
H2O or!
HgX
2& Pt(bpym)-Catalyzed Oxidation of Methane
!
A. Sen! CH3CH3 + O2 + CO 5% Pd/C CH3CO2H + CO2
H2O (0.1 M HCl)
500 psi 100 psi 100 psi 2.7% yield 1138 TOs
References:!
JACS1992, 114, 7307.! Nature1994, 368, 613.! JACS1997, 119, 6048.!
Acc. Chem. Res.1998, 31, 550.!
in situ H2O2!
production with!
heterogeneous catalyst!
Catalytic "monooxygenase" pathway for ethane oxidation:!
See also:!
R. NeumannJACS2004, 126, 10236.! Methane to Methanol/Acetaldehyde!
Alternative coupled process for methane to acetic acid ("oxidase"-type reactivity): !
Science2003, 301, 814-818.! PdSO4, 180 °C in H2SO4!
H2C CH2 + 1/2 O2
H3C H O [Pd, Cu]
H2O 2 Cu2+
2 Cu+
H O
CH3
PdII
PdII
OH PdII
H+
H2O
CH2
CH2
2+
+ 2 H+
+
+ H+ Pd0
1/2 O2
CH2 CH2
Discovered in 1959
Wacker Process: Ethylene to Acetaldehyde
!
N
Homogeneous "Oxidase" Reactions
O2 + 4 H+ + 4 e- → H
Redox couples can facilitate oxidation reactions with O
2!
•
A!!
Slow steps avoided through the use of synergistic mediators! (Also Fast)!
Fast!
Electrochemical! Kinetics!
Fast ! Aerobic! Oxidation!
Slow! Aerobic! Oxidation!
! Slow!
Electrochemical! Kinetics!
Low Temperature, Direct Conversion of
Natural Gas to Alcohols Using Commercial
Wacker Plant Design
N2
No O2plant required
Inherently Safe
Modified, Commercial Wacker Process
New main
group chemistry
Enables, new low cost process
Methanol Ethanol
Ethylene Glycol Isopropanol Propylene Glycol
Natural Gas
Air
Courtesy of T.B. Gunnoe!
IO3- -based C-H activation reagent/oxidant:
Gunnoe, Groves et al. J. Am. Chem. Soc. 2014, 136, 8393−8401!
TlIII, PbIV, BiV, IIII-based C-H activation reagent/oxidant:
Periana, Ess et al. Science2014, 343, 1232-1237
T. Brent Gunnoe!
Radical Chain (Aerobic) Oxidation of Hydrocarbons
!
Bromine as a recyclable "chain carrier"!
(CH
4, C
2H
6, …)
!
Lorkovic, et al. !
Radical Chain (Aerobic) Oxidation of Hydrocarbons
!
Bromine as an
O
2-recyclable
"chain carrier"
!
McFarland, Science, 2012, 338, 340-342. ! Alkane bromination:!
Alkyl bromide conversion !
to valuable products:!
Pt(bpym)-Catalyzed Oxidation of Methane vs. Ethane
!
Periana et al.!
Science1998, 280, 560-564.! CH4 + H2SO4 + SO3 CH3OSO3H + H2O + SO2
[Pt(bpym)X2]
HgX
2& Pt(bpym)-Catalyzed Oxidation of Methane
!
CH4 + 2 Hg(O3SCF3)2 CH3O3SCF3 + HO3SCF3 + Hg2O3SCF3)2
alternative solvents: H2SO4 and CF3CO2H
CH4 + 2 H2SO4 CH3OSO3H + 2 H2O + SO2 180 °C
100% !!
50% conversion, 85% selectivity: 43% yield
180 °C HO3SCF3
HgII
Periana/Catalytica, 1993!
50% conversion, 85% selectivity: 43% yield!
90% conversion, 81% selectivity: 70% single-pass YIELD !!! CH4 + 2 H2SO4 CH3OSO3H + 2 H2O + SO2
200 °C PtII
Periana/Catalytica, 1998!
N N
N N
PtII X
X PtII =
Periana et al. Science1993, 259, 340-343.! Periana et al. Science1998, 280, 560-564.
!
Notes!
• H2SO4 is the oxidant!
• the organic ligand remains stable in hot, fuming sulfuric acid! • the Pt(II) complex is thermodynamically stable!
HgX
2& Pt(bpym)-Catalyzed Oxidation of Methane
!
Step 1: CH4 + 2 H2SO4
Step 2: CH3OSO3H + H2O
Step 3: SO2 + 1/2 O2 + H2O
Net Rxn: CH4 + 1/2 O2
CH3OSO3H + 2 H2O + SO2
CH3OH + H2SO4
H2SO4
In principle. . .
CH3OH
multi-stage aerobic oxidation of alkanes... !
Step 1: 2 CH4 + 5 H2SO4
Step 2: CH3CO2SO3H + H2O Step 3: 4 SO2 + 2 O2 + 4 H2O
Net Rxn: 2 CH4 + 2 O2
CH3CO2SO3H + 7 H2O + 4 SO2
CH3CO2H + H2SO4
4 H2SO4
CH3CO2H + 2 H2O
Catalytica/Periana Pt(bpym) Catalyst
!
% One-Pass RH Conversion!
%
These catalysts all generate radicals
k1 << k2
+ OCM!
Methane Sulfonation!
Economic Window: k1 >> k2
courtesy of R. A. Periana!
R–H
R–OH
First-generation
Pt(bpym)-Catalyzed Oxidation of Methane vs. Ethane
!
Periana and coworkers!
J. Am. Chem. Soc.2014, 136, 10085−10094!
CH3–CH3 + H2SO4 + SO3 CH3 OSO3H HO3S OSO3H [Pt(bpym)X2]
CH4 + H2SO4 + SO3 CH3OSO3H + H2O + SO2
[Pt(bpym)X2]
Gunnoe, Herring, Trewyn; J. Am. Chem. Soc. 2016, 138, 116-125.!
Low Temperature Electrocatalytic
Oxidation of CH
4
OMC-4Bp-Pt-Cl2 Electrocatalysis provides a unique opportunity
Oxidative C–C Coupling
!
#2 polyimide resin!
!
high thermal and chemical resistance, high electrical insulating properties
and high mechanical strength!
CO2Me
Oxidative Dehydrogenation of Saturated C–C Bonds
!
R R' + H
2O cat. PdII
+ 1/2 O2
H H
R' R
O
2as the hydrogen acceptor
!
R
R'
X
L
nPd
IIH
Hydride
Elimination
β
-L
nPd
IIX
2HX
X
L
nPd
IIR
R'
H
H
R
R'
H
C–H
Activation
L
nPd
L
nPd
0HX
2 HX
O
O
O
2H
2O
2Oxidative Dehydrogenation
!
Pd-Catalyzed Dehydrogenation of Cyclohexanones to Phenols!
Izawa, Pun, Stahl Science, 2011,333, 209.!
catalyst!
Pd(TFA)2 /
N NMe2
O O OH
R R R
[Pd], O2 [Pd], O2
– H2O – H2O
"Interrupted" Dehydrogenation of Cyclohexanones:!
Diao, Stahl JACS 2011, 133, 14566.! catalyst!
Pd(DMSO)2(TFA)2!
O O OH
R R R
[Pd], O2 [Pd], O2
– H2O – H2O
O O
O OH
Molecular PdII!
Species! NanoparticlesSoluble Pd! ! Heterogeneous PdAggregates! !
fast! moderate! inactive!
slow! moderate! inactive!
(kinetic burst)!
(induction period)!
(steady-state! turnover)!
(steady-state! turnover)!
X
!
Non-Oxidative Hydrocarbon Conversion
!
Activation of 1° C-H bond is favored!!! but…!
reactions generally stoichiometric and incompatible with oxidants
or other reagents needed to functionalize the metal-alkyl!
Labinger & Bercaw Nature 2002, 417, 507-514. !
Oxidative Addition (Bergman, Graham, Jones, …)!
Sigma-Bond Metathesis (Bercaw, Watson, Marks, …)!
1,2-Addition (Wolczanski, Bergman, …)!
Sadow & Tilley!
A NSF Center for Chemical Innova=on CHE‐1205189
cellulose
hemicellulose
lignin
waste oil
CO + H
2n
-alkanes
Stochas(c Distribu(on Fischer ‐
Tropsch
GAS
FUEL (Diesel)
C
nX
(not useful
as
fuel) HIGH-MW
3 9 19
Alkane Metathesis:
Diesel from Any Carbon Source
!
Gas, Coal, Shale, Tar Sands, Biomass…
hydrocracking alkane
metathesis
n-Alkanes are ideal transportation fuel (C10-C19 diesel): !
Burns more cleanly than oil-based fuels. Reduces CO
emissions and particulate matter!
Diesel engines 30 - 40% more efficient than !
Alkane Methathesis via Tandem Catalysis
!
Goldman, A. S. et al, Science, 2006, 312, 257.!
U.S. Patent 7,902,417, issued March 8, 2011!
Alan Goldman Maurice Brookhart Richard Schrock
Comparable rates ! but desired ! MW-selectivity achieved with tBuPCP, !
Subtle catalyst variations are key:!
PtBu2
Schrock!
catalyst!
From Ethylene and Alkanes to Aromatics
!
Lyons, T. W. et al. J. Am. Chem. Soc. 2012, 134, 15707-15711.
Brookhart, et al. “Synthesis of para-xylene and toluene.” (2012) WO 2012061272 A2.
Maurice Brookhart (iPr)2P Ir P(iPr)2
Brookhart, Goldman, et al. Nature Chemistry, 2011, 3, 167-171.
(CH2)nH
O PiPr 2
PiPr 2 Ir
170 °C (CH2)nH
+ (CH2)nH
R R
Alan Goldman Maurice Brookhart
[Cr] Catalyst
Phillips Process
Dehydrogenation
2 H2
major minor
Feedstock
3
catalyst
250 °C 250 °C
Opportunities for Homogeneous Catalysis
!
1.
Oxygen management and reactivity
!
a. Sacrificial reductant?!
b. O
2-Recyclable co-oxidant (Br2, NOx, etc.)!
2.
Oxidative vs. Non-Oxidative Transformations
!
a. Reactions with ethylene (selective oligomerization)!
b. Dehydrogenative coupling, aromatization!
c. Methane as a C1 source!
d. Oxygenation reactions !
e. Oxidative C–C coupling (fundamentals, practical opportunities?)!
f. Oxidative dehydrogenation!
3.
Broader exploration of "Extreme" conditions (homogen. catal. perspective)
!
a. Strong acid solvents!
b. "High" temperature (200 °C)!
c. Stable ligands to prevent catalyst decomp., oxidatively stable !
!(previous examples: pincers, bpym)!
4.
Electrocatalysis and other tools
!
a. A (new) tool for catalyst development and understanding!
b. Practical application opportunites? (smaller scale plants to avoid flaring)!
5.
Funding – to reinvigorate the field
!
a. Small-team grants but programmatically interconnected – e.g., req'd participation in
annual/bi-annual workshop/symposium!
b. Active industrial engagement (consultation, funding?)!
