Reduction of Carbon Dioxide catalyzed by Amine and Pyridinium

40 Pages·2014·2.19 MB·English

by  Chao Crazz

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