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UKCCSC Meeting, 18 - 19 April 2007 Nottingham

UKCCSC Meeting, 18 - 19 April 2007 Nottingham. Long Term Utilisation To develop, for the first time, catalysts which allow photocatalytic reduction to be performed in supercritical CO 2. Prof M. George / A. Cowan. Strategy for CO 2 Reduction. Reduction of CO 2 requires energy

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UKCCSC Meeting, 18 - 19 April 2007 Nottingham

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  1. UKCCSC Meeting, 18 - 19 April 2007 Nottingham Long Term Utilisation To develop, for the first time, catalysts which allow photocatalytic reduction to be performed in supercritical CO2 Prof M. George / A. Cowan

  2. Strategy for CO2 Reduction • Reduction of CO2 requires energy  Photon as energy source (Photochem)  Electricity as energy source (Electrochem) • One electron process is unfavorable  Multi-electron transfer catalysts CO2 + e- CO2- E = -1.9 V (vs NHE at pH 7) CO2 + H+ + 2e- HCO2- E = -0.49 V CO2 + 2H+ + 2e- CO + H2O E = -0.53 V CO2 + 6H+ + 6e- CH3OH + H2O E = -0.38 V Comments Inorg. Chem. 1997, 19, 67 Coord. Chem. Rev. 1999, 185, 373

  3. CO2 Reduction If Nature Can Do It, Why Can't We? http://photoscience.la.asu.edu

  4. Artificial photosynthesis for CO2 reduction typically requires a photosensitizer, a catalyst and an electron donor • Products are CO, formate, and H2

  5. TEA TEA+ charge separation hu Charge separation • Co macrocycles • Ni macrocycles • Cobalt and Iron porphyrins, Phthalocyanines and corroles • Ru(bpy)2(CO)X • Re(bpy)(CO)3X • Ni(bpy)32+

  6. George, M. W., et al. (1996) Organometallics15, 3374-3387 - CO, formate, carbonate are produced - BUT: low turnover numbers, catalyst poisoning, by-products

  7. Reaction of the catalytically active species with CO2 is very slow • Solvent binds to the “vacant site” • -Low turnover numbers, catalyst poisoning, by-products Hayashi, Y., Kita, S., Brunschwig, B. S. & Fujita, E. (2003) J. Am. Chem. Soc.,125, 11976-11987.

  8. Why operate in scCO2 ? Tc = 304 K Pc= 72.9 atm • CO2 is the solvent and reagent • Achieve solvent density comparable to conventional solvents • Tuneable Properties

  9. C l N O C C9H19 chains R e O C N C O • Problem: Most metal carbonyls are insoluble in non-polar solvents! • Solution:  Soluble in non-polar solvents!

  10. Investigate photophysics/photochemistry in conventional solvents and scCO2 • Test catalytic ability of new complexes in scCO2 • Feedback into rational catalyst design

  11. PUMP UV hu charge separation 1977 1951 PROBE IR 2052 SAMPLE D DETECTOR OD = 0.05 2022 1925 1906 2100 2050 2000 1950 1900 1850 TRIR Spectroscopy Kinetic studies of mechanisms from picosecond (10-12 s) to seconds 50 ns In n-heptane similar excited state to un-substituted complex

  12. v

  13. Conclusions • Solvent coordination is a problem in existing Re-bpy CO2 reduction catalysts • CO2 soluble analogue may overcome this problem – work in scCO2 • Currently examining mechanism with TRIR spectroscopy • We will start testing catalytic ability shortly

  14. Mike George • Etsuko Fujita / Dave Grills • John Gavey

  15. Future aims • A fundamental challenge is the replacement of the “sacrificial” electron donors by species that will lead to useful (or benign) chemicals in their own right • CO2 + 2H2O  CH3OH + O2 • CO2 + CH4  CH3COOH • If we can do this, then we can do what Nature does

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