Catalytic Transformation of CO2 to C1 Products

Christopher Matranga, Molecular Science Division, NETL

Team Members & Collaborators: NETL: Dominic Alfonso, Xingyi Deng, Doug Kauffman, Junseok Lee, Jonathan Lekse, Congjun Wang NETL-RUA: James Lewis (WVU), Ronchao Jin (CMU), Ken Jordan (PITT), Sittichai Natesakhawat (PITT)

‹#›

CO2 Conversion to C1 Industrial Chemicals

Wind-Electric

Solar-Heating Or Photo-driven

Industrial Waste Heat

CO2 H2 Catalyst

H2O

Methanol Methane Formic Acid Formaldehyde

Uses

3 M ton ($720 M)

Approx Yearly Market

25 K Ton1 ($25 M)

3.6 M ton ($1440 M)

484 M ton ($210,000 M)

Leather, Pulp

Urea Resins Phenol Resins

Fuel/MTG Formaldehyde

Fuel Acetic Acid

1 Global Formic Acid Market: 0.5 M Ton ($750 M)

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Project Structure • Photocatalytic Systems

– Heterostructured Photocatalysts for CO2 Reduction – Symmetry Breaking and High Throughput Computational Screening of

Delafossites for the Photocatalytic Reduction of CO2

– Scanning Tunneling Microscopy and Dispersion-corrected Density Functional Theory Studies of TiO2 Surfaces

• Electrocatalytic Systems

– Electronic Structure and Catalytic Activity of Au25 Clusters

• Thermal Catalytic Systems – Atomic Structure and Catalytic Activity of Cu/ZnO-Based Materials

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Technical Barriers for CO2 Utilization Photocatalysts

• Poor optical activity in visible & infrared • Rapid recombination of e- & h+ pairs

prevents useful redox photochemistry • Slow CO2 conversion kinetics • Difficulty controlling product selectivity

from R. Asashi et. al., Science, 293, 269 (2001)

Wavelength (nm)

No activity above ~ 400 nm

UV

hν h+

Red Ox

TiO2

Red Ox

e-

TiO2

–0.5 V (pH 7) B

and gap = 3.2 eV

CO2/CO −0.11 V

O2/H2O 1.23 V

H+/H2 0 V

CO2/(HOOC)2 −0.43 V

CO2/CH4 −0.244 V CO2/CH3OH −0.32 V

EF, SWNT ~ 0.5 V Ener

gy

2013 Merit Review

Plasmonic Heating in Heterostructures for Catalytic CO2 Reduction

Light converted to Thermal energy (ohmic/joule heating)

S. Link, M. A. El-Sayed, J. Phys. Chem. B 103, 4212 (1999); A. O. Govorov, H. H. Richardson, Nano Today 2, 30 (2007), G. Park, D. Seo, H. Song, Langmuir 28, 9003-9009 (2012)

.

−

+

− −

+ +

−

+

− −

+ +

Electric field

Electron cloud

Metal nanoparticle

A “Hybrid” Photo- and Thermal-Catalytic Approach

Light excites collective electron motions (Plasmons)

Optical Activity Controlled by Size/Shape/Composition

Forming Heterostructures Plasmonic

Material

Catalytic Material

2013 Merit Review

Synthesis and Characterization of Plasmonic Au/ZnO Heterostructured Catalysts

+ HAuCl4·xH2O

ZnO Au/ZnO

300 °C

1-3 Au particles/µm2

C. Wang, et al., submitted (2013).

ZnO

25 °C

450 °C E2(high)

2013 Merit Review

Raman Spectroscopy to Estimate Localized Plasmonic Heating

R. Cuscó, et al., Phys. Rev. B 75, 165202 (2007); H. K. Yadav, et al., Appl. Phys. Lett. 100, 051906 (2012); K. Samanta, et al., Phys. Rev. B 75, 035208 (2007); J. Serrano, et al., Phys. Rev. Lett. 90, 055510 (2003); J. Menendez, et al., Phys. Rev. B 29, 2051 (1984).

Temp dependent ZnO phonon peaks used to monitor temperature

ZnO

ZnO

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How Hot? How Localized? 20 nm Au on ZnO Support

•Surface of ZnO Support is Heated •Sample Cell Still Cool to Touch •Heating on/off in microseconds (or less)

Au

ZnO

Light

∞

=∆k

rKIT4

0abs0

2013 Merit Review

Gas sampling port for GC analysis

IR source

IR detector

300 Watt Xe arc lamp

Or

Laser

CO2 + H2O

Cutoff filter

top view

side view

catalyst

catalyst

I0

I0

IT

IT

Photocatalysis Experiments for Activity Evaluation

2013 Merit Review

Visible Light CO2 Reduction with Plasmonic Heating

CO2 + H2 Products

(See next few slides for product distributions)

Green Light Green Light

Determining Reaction Pathways

2013 Merit Review

Rxn Products

CO

CH4

Thermodynamic Prediction

Experiment

Selectivities

Reaction scheme 1: CO2 + H2 CO + H2O (Reverse water-gas shift (RWGS)) Reaction scheme 2: CO2 + H2 CO + H2O (RWGS) CO2 + 3H2 CH3OH + H2O (Methanol synthesis) Reaction scheme 3: CO2 + H2 CO + H2O (RWGS) CO + 3H2 CH4 + H2O (CO-methanation) Reaction scheme 4: CO2 + H2 CO + H2O (RWGS) CO2 + 3H2 CH3OH + H2O (Methanol synthesis) CO + 3H2 CH4 + H2O (CO-methanation)

Pathways CO2 + H2 Products

CH4

CH4 Au/ZnO

Temperature Programmed Reaction in Dark Confirm Rxn Mechanism

CO

CO Au/ZnO

Dar

k R

eact

ions

Li

ght R

eact

ions

Light Reactions

Dark R

eactions

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Demonstrating Scalability One Simple Plasmonic Reactor Run in Two Different Modes

Fixed Bed Mode Fluidized Bed Mode

Gas Out

Gas In

¼ or 3/8” Quartz Tube

Light

Top Down View

Cross Section View

Gas In

Gas Out

Catalyst Coated On Wall

Light

Top Down View

Gas Out

Gas In

Longitudal View

Fluidize Bed w/Mechanical

Vibration

‹#›

Project Structure • Photocatalytic Systems

– Heterostructured Photocatalysts for CO2 Reduction – Symmetry Breaking and High Throughput Computational Screening of

Delafossites for the Photocatalytic Reduction of CO2

– Scanning Tunneling Microscopy and Dispersion-corrected Density Functional Theory Studies of TiO2 Surfaces

• Electrocatalytic Systems

– Electronic Structure and Catalytic Activity of Au25 Clusters

• Thermal Catalytic Systems – Atomic Structure and Catalytic Activity of Cu/ZnO-Based Materials

Technical Barriers for CO2 Electrocatalysis

• Large overpotentials required • Low Efficiency • Poor product selectivity • Parasitic H2 evolution

Ener

gy

Reaction Coordinate

Possible Electrode Processes

J. Electroanal. Chem. 2006, 594, 1

Challenge Identify a high efficiency catalyst with low overpotential and good

product selectivity

Technical Issues

CO2

CO2−

CH3OH CH4

HCOOH

H2

CO

Closely Spaced Products

Activ

atio

n B

arrie

r

Barrier = Overpotential = Cost!

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Atomically Precise Aun clusters (n < ~200)

18 SR-ligand groups * From R. Jin, Nanoscale, 2010, 2, 343–362

Spans sizes between molecules & “traditional” nanomaterials

Au3 – Au13 Au23 – Au28 Larger Au

NPs

Unique quantized electronic structure

No plasmons

Molecular like orbitals

High fraction of surface atoms for catalysis

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Au25 (SR)18 Crystal Structure

Zhu et, al. J. Am. Chem. Soc. 2008, 130, 5883-5885.

12 “Shell” (ligand) Au atoms. 18 SR-ligand groups

Au25 carries a ground state negative charge

Au13 “core”

Au S

(−S−Au−S−Au−S−)6 “shell” Au25 cluster

1 nm

TOA counterion balances charge in crystal structure

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Reversible Optical Bleaching in Presence of CO2

0.0

0.1

0.2

0.3

0.4

0.0

0.2

0.4

0.6

0.8

1.0

1.2

3.3 3.0 2.7 2.4 2.1 1.8 1.5 1.2 0.9-0.01

0.00

0.01

-0.60.00.61.2

400 650 900 11501400

a'abc

a'a

b

Abso

rban

ce

N2 PurgedCO2 Sat'd

c

Norm

aliz

ed P

L (1

06 a.u

.)

∆ A

bs

Energy (eV)

∆ P

L (1

05 a.u

.)

Wavelength (nm)

Reversible bleaching due to charge redistribution

Experimental

Kauffman, et, al. J. Am. Chem. Soc. 2012, 134, 10237−10243.

HOMO − 4HOMO − 3HOMO − 2

HOMO − 5

HOMO − 1

LUMO + 2LUMO + 1

LUMO

HOMO

E

EgE a' b ca

Electronic Structure

Energy level diagram reproduced from Schatz & Jin et. al. JACS 2008, 130 (18), pp 5883–5885

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CO2 Physisorption Reversibly Perturbs Electronic Structure

-0.06

-0.05

-0.04

-0.03

-0.02

-0.01

0.00

0.01∆

e−

Core

Three-fold O One-fold O One-fold C

Au Atoms Shell

Au Atoms

Shell S Atoms

CO2 Adsorption Configuration

Three-fold O Coordination

One-fold O Coordination

One-fold C Coordination

Adsorption Pocket

Binding Energies

~ 80 – 140 meV

Kauffman, etl, al. J. Am. Chem. Soc. 2008, 130, 5883-5885.

Optical Bleaching Results from Reversible Charge Redistribution

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CO2 + 2H+ 2e− → CO + H2O E0 = −0.103 V (RHE)

0.0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 -1.40

20

40

60

80

100

CO H2

Fa

rada

ic E

ffici

ency

/ %

E / V (RHE)

Unprecented Catalytic Efficiency

0.0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 -1.410-3

10-2

10-1

100

CO H2

Form

atio

n Ra

te /

mm

ol c

m-2 Au

hr-1

E / V (RHE)

E 0

CB+ Nafion + Au25

CB Support

Sonicate

Au25 CO2 Products + n e−

Working Electrode (cathodic voltage)

Catalyst Layer Drop Cast

Kauffman, etl, al. J. Am. Chem. Soc. 2008, 130, 5883-5885.

No appreciable Ea , ~ 100 % Selectivity

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Comparison to other Au Materials

0.0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 -1.40

10

20

30

40

50

j / m

A cm

−2 Au

E (V vs. RHE)

2 nm AuAu25

5 nm AuBulk Au

0.0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 -1.4

10-3

10-2

10-1

100

Au2 nm / CB

CO F

orm

atio

n Ra

te (

mm

ol c

m-2 Au

hr-1

)E (V vs. RHE)

E 0

Au25 / CB

Au5 nm / CBBulk Au

Thermodynamic Limit

Kauffman, etl, al. J. Am. Chem. Soc. 2008, 130, 5883-5885.

Demonstrating Scalability

Anode Compartment

CO2 saturated electrolyte

Lid with sampling port

Pt Counter Electrode

Reference Electrode

Au25/CB on GC Electrode

Nafion Membrane

Proof-of-Concept in Small H-Cell Scaled-Up Flowing H-Cell Reactor

CO2 saturated electrolyte in

Nafion membrane

Lid with Headspace Sampling Port

Au25 on carbon foam

Reference electrode

electrolyte out

to anode compartment

Working electrode

e−

CO2

CO

Continuous Flow Electrochemical Reactor

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Summary • Visible light plasmonic heating can be used to

convert CO2 into CH4, CO, and other products • Catalytic mechanism is “photothermal”

• Au25 exhibits spontaneous electronic coupling to

CO2

• Au25 shows unprecendented catalytic efficiency towards CO2 conversion

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Charge Redistribution Impacts Electron Transfer to CO2

0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 -1.4

-2.0

0.0

2.0

4.0

6.0

8.0

Potential

Au-1/ -225

Au0 / -125

∆E1

∆E2

Calibrated vs. Fc/Fc+

Current

Au+1 / 025I (

µA)

E (V vs. SHE)

Cathodic

*Open Circuit

Small but statistically significant anoidic shift to + oxidizing potentials Consistent with e- depletion of HOMO donating levels

∆ = 21 ± 2 mV > 99% CL

Kauffman, etl, al. J. Am. Chem. Soc. 2008, 130, 5883-5885.

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General Catalytic Approaches For CO2 Conversion

Photochemical Catalytic Conversion

Electrochemical Catalytic Conversion

Thermal Catalytic Conversion

Thermally Initiated Reactions

Solar-Thermal Reactors Waste/Plasmon Heat

For Energy Input

Traditional Catalysts Make Near Term

Deployment More Realistic

Photochemical Generation

of electrons/holes or plasmonic heating

Sun Provides Energy Input

Emerging Technology Utilizing TiO2 and Other

Photocatalysts

Electrochemical Generation of electrons/holes

Geothermal, Wind, or Waste Electricity

Provides Energy Input

Emerging Technology Utilizing Cu, Cu-oxide And Other Catalysts

Lower Risk Higher Risk

Basic R&D Applications R&D

Investigating “Quantum Alloys” with Computational & Experimental Screening

Au22Ag3

S Ag Au

-223.4

-223.2

-223.0

-222.8

-222.6

-222.4

stable

n = 30 n = 36 n = 59 n = 3 n = 31 n = 11

Ener

gy /

eV

n = 6

least

stablemost

400 700 1000 1300

3.3 3.0 2.7 2.4 2.1 1.8 1.5 1.2 0.90.00

0.05

0.10

0.15

0.20

0.25

0.0

1.0

2.0

3.0

4.0

b'

Energy / eV

Wavelength / nm

a'

Au22 Ag3 Au25

c

b

Abso

rban

ce /

a.u.

a

PL In

tens

ity /

105 a

rb. u

nits

0.9 0.6 0.3 0.0 -0.3 -0.6 -0.9 -1.2 -1.5

+1/0 0/-1

4 µA

Au25

Au22Ag3

Cur

rent

/ µA

Potential / V (vs. SHE)

-1/-2

0/-1+1/0

-1/-2

Occupied orbital

Unoccupied orbital

•DFT Screens ~176 alloy compositions

•Au22Ag3 predicted to be stable & confirmed experimentally

Computational Experimental Optical Properties

Electronic Structure