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 • Introduction • Catalysis

• Historical Background • Catalyst and Kinetic Energy • Catalytic Cycle

• CO2 Reduction

• Water Gas Shift Reaction • Introducing CO2 Reduction Catalysts

• Methods

• Synthesis of Catalysts and Chemical Environments • CV and Theory • IR-SEC

• Results

• Smieja • Franco • Riplinger • Fischer-Tropsch

• Conclusions

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• Jöns Jakob Berzelius (1835, Swedish chemist)

• Wilhelm Ostwald (1909 Nobel Prize in Chemistry)

• 20th Century

Catalytic Power (history)

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

• Rate of Reaction

• Pathway

• Activation Energy(Ea)

• Equilibrium

http://en.wikipedia.org/wiki/Catalysis#mediaviewer/File:CatalysisScheme.png (accessed 11/1/14)

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Catalyst

• Rate of Reaction

• Pathway

• Activation Energy(Ea)

• 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 6

CH3OH methanol 7

CH4 methane 2

CO carbon monoxide many

J. Chem. Educ., 1958, 35 (9), 446-449

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CO2 Reduction

http://newenergyandfuel.com/wp-content/uploads/2010/12/Products-From-CO2-Reforming.gif (accessed 11/1/14)

CO2 + 2 H+ + 2 e- → CO + H2O

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Green Chemistry with Carbon Dioxide

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Water Gas Shift Reaction (WGSR)

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CO2 + H2 = H2O + CO

Water Gas Shift Reaction (WGSR)

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CO2 + H2 = H2O + CO

Water Gas Shift Reaction (WGSR)

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Chiang et al. Inorg. Chem., 2005, 44, 9007-9016; J. Chem. Educ., 1958, 35 (9), 446-449

CO2 Reduction 15

• Catalytic Hydrogenation

• Complex Metal Hydrides

• Electrochemical Reduction

• Photocatalysis

• Biological reduction

- Carbon Monoxide DeHydrogenase: CODH

_dioxide#mediaviewer/File:TiO2nanotube.jpg (accessed 11/1/14); M. Asadi, Nat. Commun., 2014, 5; http://www.ratbehavior.org/im

Electrochemical Reduction

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TiO2 films MoS2 flakes

Fe-porphyrin

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

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B. A. Parkinson, P. F. Weaver, Nature, 1984, 309, 148-149

Biological Reduction

Carbon Monoxide DeHydrogenase (CODH)

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Synthesis of Catalysts

• Smieja Study

• Riplinger Study

(white)

M=Re (white crystal), Mn (orange crystal) (yellow)

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

(yellow)

Franco et al. Chem. Commun., 2014, 00, 1-3; Chiang et al. Inorg. Chem., 2005, 44, 9007-9016

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• Franco Catalyst

• Why use a proton-assisted process?

• Sustained catalysis in homogeneous solution even in the absence of Brønsted acids

• Reduce the large overpotentials required for multi-electron catalysis, specifically during protonation

• Long durability in solution and high selective conversion of CO2 into CO at relatively low potentials

Chemical Environments

• Addition of protons through a variety of acids (H2O, TFE, MeOH)

• Changes to atmospheric environment

• Exposure to CO2

• Inert conditions (N2, Ar)

• Addition of different metals to ligands (Mn, Re, Pd, Rh, Ni, Fe, Co)

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Cyclic Voltammetry

• What is Cyclic Voltammetry?

• Provides insights into both the kinetic and thermodynamic details of many chemical systems via redox reactions

• Includes a working electrode, reference electrode, counter electrode, and supporting electrolyte

• Types: homogenous and heterogeneous

• Dependent on scan rate, concentration and pH

Marken et al. Electroanalytical Methods, 2010, 2, 57-105

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Theory Behind CV

• 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

• Reversibility determined by ratio between anodic and cathodic, peak current densities

• Internal standard consists of ferrocene, because it is completely reversible!

• Counter electrode applies current to system to keep voltage constant as the chemical system absorbs electrons

• 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

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Infrared-Spectroelectrochemistry (IR-SEC)

• A compliment to cyclic voltammetry

• Resolves the ambiguity of voltammetric data due to equilibrium of fast/slow steps on a voltammetric timescale in both the forward and backward direction

• Combines the thermodynamic data obtained from IR and the kinetic data obtained from CV

Marken et al. Electroanalytical Methods, 2010, 2, 57-105; Smieja et al. Inorg. Chem. 2013, 52, 2484-2491

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Smieja Results • Increased response as more equivalents of acid

were added to the CV cell

• The stronger the acid, the stronger the catalytic response

• Activated catalytic species: [Mn(bpy-tBu)(CO)3]-

• Mn(bpy-tBu)(CO)3 Br in MeCN under an Ar atmosphere

• Less overpotential than its Re counterpart

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Franco Catalyst

• Contains two acidic OH groups close to the metal centre, which showed a sustained catalytic response in homogeneous solution in the absence of acids

• Under a CO2 atmosphere in anhydrous MeCN

• 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

• 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

• 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

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Fischer-Tropsch Process • Originated from need of liquid fuels by Germany

during World War II

• Syngas from Water Shift Gas Reaction to Hydrocarbons

• Involves CO activation, C-C coupling, hydrogenation and desorption of the hydrocarbon product

• “hydrogen mediated catalytic reductive polymerization of carbon monoxide”

• Atomic details are still unclear for these steps

• Exothermic reaction, increasing heat release with longer hydrocarbon chains

• 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

Conclusions

• Increasing interest in the industrial and academic communities

• A way to use a harmful greenhouse gas for synthesis of industrial compounds (CH4, CO, CH2O, Syngas)

• Multiple studies

• Purification and concentration of CO2 from the atmosphere to use the harmful levels of this greenhouse gas for energy storage

• Continue the approach to local proton sources on chelate ligands and mimicking naturally occurring catalytic systems

• 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/

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