Reduction of Carbon Dioxide catalyzed with Amine and Pyridinium Organic Seminar – Spring 2014 Pengchao Hao Annual Global Fossil-Fuel Carbon Emission http://cdiac.ornl.gov/trends/emis/glo_2010.html Photochemical conversion of CO to fuel 2 3 www.thinkprogress.org/climate 2 Major strategies to reduce CO 2 CO reduction 2 Photochemical Electrocatalytic reduction reduction Electrode (Metal/ Photosensitizer Semi-conductor) Light Electricity/light Seminar Outline Part A: Redesigning amine to improve existing CO photochemical reduction 2  Why is stoicometric amount of sacrificial reductant (Et N) needed? 3  Design a regenerable amine  Experimentally recycle the amine Part B: Use of pyridinium to improve CO electrocatalytic reduction 2  High overpotential problem for electrochemical CO reduction’s 2  The magic effect of Pyridinium  Debate about the mechanism of RDS among several research groups Difficulties of CO reduction 2 Thermodynamic and kinetic aspects CO + e− → CO •− ∆Go = 43.9 kcal/mol 2 2 r ∆Go r kcal/mol CO + 4H+ + 4e- → HCHO + H O ∆Go = 11.78 kcal/mol 2 2 r CO + 2H+ + 2e- → HCO H ∆Go = 9.19 kcal/mol 2 2 r CO + 2H+ + 2e- → CO + H O ∆Go = 5.54 kcal/mol 2 2 r 0 CO + 6H+ + 6e- → CH OH + H O ∆Go = -4.2 kcal/mol 2 3 2 r Morris, A. J.; Fujita, E. Acc. Chem. Res.2009, 42, 1983 2 Types of photochemical CO reduction catalysts 2 Type 1 Type 2 *P = Photosensitizer Nomally, Ru(bpy) 2+ 3 Cobalt (II) Tetraaza-macrocyclic Catalyst Rhenium Catalyst Turnover #: 532 Quantum yield: 38% (CO) Consume stoichiometric amount of Et N and produce waste! 3 (moles of Products)*2 QY= Moles of photon absorbed Morris, A. J.; Fujita, E. Acc. Chem. Res. 2009, 42, 1983; Lehn, J. Chem. Soc., Chem. Commun1983, 536. Why does Et N become waste? 3 Generation of radical ion pair Level of theory: Photocatalyst: MP2/aug-cc-pVDZ//MPWB1K/aug-cc-pVDZ [Et N•+, CO •−] 3 2 8 Carpenter, B., J. Phys. Chem. A. 2007, 111, 3721 Why does Et N become waste? 3 Three possible pathways Level of theory: Photocatalyst: MP2/aug-cc-pVDZ//MPWB1K/aug-cc-pVDZ [Et N•+, CO •−] 3 2 9 Carpenter, B., J. Phys. Chem. A. 2007, 111, 3721 Why does Et N become waste? 3 The main reaction pathway Level of theory: Photocatalyst: MP2/aug-cc-pVDZ//MPWB1K/aug-cc-pVDZ [Et N•+, CO •−] 3 2 10 Carpenter, B., J. Phys. Chem. A. 2007, 111, 3721