UKCCSC Meeting, 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 Photon as energy source (Photochem) Electricity as energy source (Electrochem) One electron process is unfavorable Multi-electron transfer catalysts CO 2 + e - CO 2 - E = 1.9 V ( vs NHE at pH 7) CO 2 + H + + 2e - HCO 2 - E = 0.49 V CO 2 + 2H + + 2e - CO + H 2 O E = 0.53 V CO 2 + 6H + + 6e - CH 3 OH + H 2 O E = 0.38 V Comments Inorg. Chem. 1997, 19, 67 Coord. Chem. Rev. 1999, 185, 373

CO 2 Reduction If Nature Can Do It, Why Can't We?

Artificial photosynthesis for CO 2 reduction typically requires a photosensitizer, a catalyst and an electron donor Products are CO, formate, and H 2

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

- CO, formate, carbonate are produced - BUT: low turnover numbers, catalyst poisoning, by-products George, M. W., et al. (1996) Organometallics 15,

Reaction of the catalytically active species with CO 2 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,

CO 2 is the solvent and reagent Achieve solvent density comparable to conventional solvents Tuneable Properties Why operate in scCO 2 ? T c = 304 K P c = 72.9 atm

Problem:Most metal carbonyls are insoluble in non-polar solvents! Solution : C 9 H 19 chains Soluble in non-polar solvents!

Investigate photophysics/photochemistry in conventional solvents and scCO 2 Test catalytic ability of new complexes in scCO 2 Feedback into rational catalyst design

PROBE SAMPLE DETECTOR PUMP IR UV TRIR Spectroscopy Kinetic studies of mechanisms from picosecond ( s) to seconds 50 ns charge separation h In n-heptane similar excited state to un-substituted complex

v

Conclusions Solvent coordination is a problem in existing Re-bpy CO 2 reduction catalysts CO 2 soluble analogue may overcome this problem – work in scCO 2 Currently examining mechanism with TRIR spectroscopy We will start testing catalytic ability shortly

Mike George Etsuko Fujita / Dave Grills John Gavey

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 –CO 2 + 2H 2 O CH 3 OH + O 2 –CO 2 + CH 4 CH 3 COOH If we can do this, then we can do what Nature does