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CO2 Reduction
Catalysts and Catalysis
CHEM 462
Kristina Goldstein
Soomin Park
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Why does CO2 matter?
https://www.skepticalscience.com/breathing-co2-carbon-dioxide.htm (accessed 11/1/14)
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Why does CO2 matter?
http://theenergycollective.com/nrdcswitchboard/299251/strong-climate-action-requires-moving-away-fossil-fuels (accessed 11/1/1
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Outline
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Introduction
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Catalysis
• Historical Background
• Catalyst and Kinetic Energy
• Catalytic Cycle
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CO2 Reduction
• Water Gas Shift Reaction
• Introducing CO2 Reduction Catalysts
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Methods
• Synthesis of Catalysts and Chemical Environments
• CV and Theory
• IR-SEC
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Results
• Smieja
• Franco
• Riplinger
• Fischer-Tropsch
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Conclusions
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Catalytic Power
(history)
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Jöns Jakob Berzelius (1835, Swedish chemist)
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Wilhelm Ostwald (1909 Nobel Prize in Chemistry)
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20th Century
http://en.wikipedia.org/wiki/Jöns_Jacob_Berzelius#mediaviewer/File:Jöns_Jacob_Berzelius_daguerreotype.jpg (accessed 11/1/1
http://en.wikipedia.org/wiki/Wilhelm_Ostwald#mediaviewer/File:Wilhelm_Ostwald.jpg (accessed 11/1/14)
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Catalyst
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Rate of Reaction
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Pathway
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Activation Energy(Ea)
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Equilibrium
http://en.wikipedia.org/wiki/Catalysis#mediaviewer/File:CatalysisScheme.png (accessed 11/1/14)
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Catalyst
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Rate of Reaction
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Pathway
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Activation Energy(Ea)
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Equilibrium (Keq)
http://en.wikipedia.org/wiki/Catalysis#mediaviewer/File:CatalysisScheme.png (accessed 11/1/14)
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Catalytic Cycle
http://en.wikipedia.org/wiki/Catalytic_cycle#mediaviewer/File:Catcycle.png (accessed 11/1/14)
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CO2 Reduction
(1958)
Chemical Formula
Name
# of articles
HCO2H
formic acid
5
HCHO
formaldehyde
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CH3OH
methanol
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CH4
methane
2
CO
carbon monoxide
many
J. Chem. Educ., 1958, 35 (9), 446-449
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CO2 Reduction
CO2 + 2 H+ + 2 e- → CO + H2O
http://newenergyandfuel.com/wp-content/uploads/2010/12/Products-From-CO2-Reforming.gif (accessed 11/1/14)
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Green Chemistry with Carbon Dioxide
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Water Gas Shift Reaction
(WGSR)
CO2 + H2
=
H2O
+ CO
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Water Gas Shift Reaction
(WGSR)
CO2 + H2
=
H2O
+ CO
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Water Gas Shift Reaction
(WGSR)
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CO2 Reduction
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Catalytic Hydrogenation
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Complex Metal Hydrides
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Electrochemical Reduction
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Photocatalysis
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Biological reduction
- Carbon Monoxide DeHydrogenase: CODH
Chiang et al. Inorg. Chem., 2005, 44, 9007-9016; J. Chem. Educ., 1958, 35 (9), 446-449
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Electrochemical Reduction
MoS2 flakes
TiO2 films
Fe-porphyrin
_dioxide#mediaviewer/File:TiO2nanotube.jpg (accessed 11/1/14); M. Asadi, Nat. Commun., 2014, 5; http://www.ratbehavior.org/im
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Transition Metals
Complexes
C. Riplinger at el, 2014, http://pubs.acs.org.lib-ezproxy.tamu.edu:2048/doi/pdf/10.1021/ja508192y
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Photocatalysis
B. A. Parkinson, P. F. Weaver, Nature, 1984, 309, 148-149
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Biological Reduction
Carbon Monoxide DeHydrogenase (CODH)
Synthesis of Catalysts
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Smieja Study
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Riplinger Study
M=Re (white crystal),
Mn (orange crystal)
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(yellow)
(white)
Smieja et al. Inorg. Chem. 2013, 52, 2484-2491; Riplinger et al. J. Am. Chem. Soc. 2014 (Just Accepted Manuscript)
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Synthesis Continued
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Franco Catalyst
(yellow)
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Why use a proton-assisted process?
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Sustained catalysis in homogeneous solution even in the absence of Brønsted acids
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Reduce the large overpotentials required for multi-electron catalysis, specifically during
protonation
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Long durability in solution and high selective conversion of CO2 into CO at relatively low
potentials
Franco et al. Chem. Commun., 2014, 00, 1-3; Chiang et al. Inorg. Chem., 2005, 44, 9007-9016
Chemical Environments
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Addition of protons through a variety of acids (H2O,
TFE, MeOH)
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Changes to atmospheric environment
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Exposure to CO2
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Inert conditions (N2, Ar)
Addition of different metals to ligands (Mn, Re, Pd,
Rh, Ni, Fe, Co)
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Cyclic Voltammetry
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What is Cyclic Voltammetry?
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Provides insights into both the
kinetic and thermodynamic
details of many chemical
systems via redox reactions
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Includes a working electrode,
reference electrode, counter
electrode, and supporting
electrolyte
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Types: homogenous and
heterogeneous
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Dependent on scan rate,
concentration and pH
Marken et al. Electroanalytical Methods, 2010, 2, 57-105
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Theory Behind CV
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Rate of the homogeneous electron transfer step
can be determined based on the measurement
of peak potential and peak current data as a
function of scan rate
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Reversibility determined by ratio between
anodic and cathodic, peak current densities
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Counter electrode applies current to system to
keep voltage constant as the chemical system
absorbs electrons
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Internal standard consists of ferrocene,
because it is completely reversible!
Ohm’s Law: V=IR
Position of electrodes matter due to effects of
IR(ohmic) drop
Marken et al. Electroanalytical Methods, 2010, 2, 57-105
Infrared-Spectroelectrochemistry
(IR-SEC)
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A compliment to cyclic
voltammetry
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Resolves the ambiguity of
voltammetric data due to
equilibrium of fast/slow steps
on a voltammetric timescale
in both the forward and
backward direction
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Combines the thermodynamic
data obtained from IR and the
kinetic data obtained from CV
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Marken et al. Electroanalytical Methods, 2010, 2, 57-105; Smieja et al. Inorg. Chem. 2013, 52, 2484-2491
Smieja Results
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Increased response as more equivalents of acid
were added to the CV cell
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The stronger the acid, the stronger the catalytic
response
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Activated catalytic species: [Mn(bpy-tBu)(CO)3]•
Mn(bpy-tBu)(CO)3 Br in MeCN under an Ar
atmosphere
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Less overpotential than its Re counterpart
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Franco Catalyst
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Contains two acidic OH groups close to the metal
centre, which showed a sustained catalytic
response in homogeneous solution in the absence
of acids
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Under a CO2 atmosphere in anhydrous MeCN
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Partial stabilization of intermediate due to
interaction between OH-Br and O-N(bpy)
2-/3- reduction wave due to formation of a metal
hydride
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Protons required for the catalytic process are
supposed to be supplied by the Hofmann
degradation of the supporting electrolyte, or
hydrogen abstraction from the solvent
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Formation of HCOOH and CO confirm the
presence of competing pathways and the
hypothesis of hydride formation
Franco et al. Chem. Commun., 2014, 00, 1-3
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Catalytic Activation
Riplinger et al. J. Am. Chem. Soc. 2014
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CO/H2 Generation
Riplinger et al. J. Am. Chem. Soc. 2014
Fischer-Tropsch Process
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Originated from need of liquid fuels by Germany
during World War II
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Syngas from Water Shift Gas Reaction to
Hydrocarbons
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Involves CO activation, C-C coupling,
hydrogenation and desorption of the hydrocarbon
product
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“hydrogen mediated catalytic reductive
polymerization of carbon monoxide”
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Atomic details are still unclear for these steps
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Exothermic reaction, increasing heat release with
longer hydrocarbon chains
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Different metal centers contribute to different
hydrocarbon formations
Interest motivated by economic viability,
environmental and energy security concerns
Olusola et al. RSC Adv., 2012, 2, 7347–7366
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Conclusions
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Increasing interest in the industrial and academic communities
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A way to use a harmful greenhouse gas for synthesis of
industrial compounds (CH4, CO, CH2O, Syngas)
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Multiple studies
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Purification and concentration of CO2 from the atmosphere to use
the harmful levels of this greenhouse gas for energy storage
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Continue the approach to local proton sources on chelate ligands
and mimicking naturally occurring catalytic systems
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Application of a solar cell to power catalysis, and separation of
byproducts
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Questions ?
(accessed 2NOV2014) http://inhabitat.com/northwestern-university-develops-more-efficient-organic-solar-cell-using-algorithm-based-on-natural-evolution/