**7. References**


Design of a photocatalytic reactor would work in such a way that in one compartment light is harvested by the semiconductor in order to split water to form H+s and by the transfer of produced protons and electrons, CO2 could be reduced with another catalyst, such as copper, in the other compartment. In this way, with the help of proton exchange membranes and separate reaction centers, interaction between reactants or products and therefore reverse reactions could be prevented by supplying Hs to catalytic compartment at the same time. On the other hand, a high conductance electron membrane would prevent charge

Such a system has already been proposed by Kitano et al. (2007b) for water splitting reaction. Introducing CO2 in the picture will be the next generation modification of the artificial photosynthesis systems. Further refinement of the design will be possible with more understanding about the rates of chemical conversions and the rates of transport.

Photosynthesis and artificial photosynthesis system were compared in this study with an emphasis on charge and H transport which is indicated to be the main reason for the difference in resulting carbon dioxide reduction yields and rates. The gap in artificial systems was found to be in the design of the photocatalytic systems which could be developed with a membrane which would enhance charge separation and H transport. H supply to carbon dioxide reduction centers were found to be limiting the existing photocatalytic carbon dioxide reduction rates, indicating the important role of water splitting in artificial photosynthesis systems. Water being in contact with carbon dioxide on photocatalyst surface was found to act negatively on the methanol formation rates by inhibiting carbon dioxide activation. For a better carbon dioxide reduction with existing photocatalysts, separation of the reaction centers was proposed which would enhance the

This study was funded through The Scientific and Technological Research Council of Turkey (TUBITAK) under research grant numbers: 106Y075 and 107M447. Bahar Ipek

Anpo, M. & Chiba, K. (1992). Photocatalytic Reduction of CO2 on Anchored Titanium-Oxide

Anpo, M.; Yamashita, H.; Ichihashi, Y. & Ehara, S. (1995). Photocatalytic Reduction of CO2

Anpo, M.; Yamashita, H.; Ichihashi, Y.; Fujii, Y. & Honda, M. (1997). Photocatalytic

*Physical Chemistry B*, Vol. 101, No. 14, pp. 2632-2636, ISSN 1089-5647

*Heterogeneous Catalysis*, ISBN 0304-5102, Tokyo, Japan, May 1992

Catalysts, *7th International Symposium on Relations between Homogeneous and* 

with H2O on Various Titanium-Oxide Catalysts. *Journal of Electroanalytical* 

Reduction of CO2 with H2O on Titanium Oxides Anchored within Micropores of Zeolites: Effects of the Structure of the Active Sites and the Addition of Pt. *Journal of* 

would like to acknowledge the support from TUBITAK BIDEB 2228.

*Chemistry*, Vol. 396, No. 1-2, pp. 21-26, ISSN 0022-0728

recombination as illustrated in Figure 4.3.

charge and H transport at the same time.

**6. Acknowledgements** 

**7. References** 

**5. Conclusions** 


Artificial Photosynthesis from a Chemical Engineering Perspective 35

Schulte, K. L.; DeSario, P. A. & Gray, K. A. (2010). Effect of Crystal Phase Composition on

Shustorovich, E. & Bell, A. T. (1991). An Analysis of Methanol Synthesis from CO and CO2

Solymosi, F. & Tombacz, I. (1994). Photocatalytic Reaction of H2O+CO2 over Pure and Doped Rh/TiO2. *Catalysis Letters*, Vol. 27, No. 1-2, pp. 61-65, ISSN 1011-372X Tseng, I. H.; Chang, W. C. & Wu, J. C. S. (2002). Photoreduction of CO2 using Sol-Gel

Umena, Y.; Kawakami, K.; Shen, J. R. & Kamiya, N. (2011). Crystal Structure of Oxygen-

Uner, D.; Oymak, M. M. & Ipek, B. (2011). CO2 Utilization by Photocatalytic Conversion to

VandenBussche, K. M. & Froment, G. F. (1996). A Steady-State Kinetic Model for Methanol

Wang, C. J.; Thompson, R. L.; Baltrus, J. & Matranga, C. (2010). Visible Light Photoreduction

Wang, Z. Y.; Chou, H. C.; Wu, J. C. S.; Tsai, D. P. & Mul, G. (2010). CO2 Photoreduction

Whitmarsh, J.; Govindjee (1999). The Photosynthetic Process, In: *Concepts in Photobiology:* 

Whittingham, C. P. (1974). *The Mechanism of Photosynthesis*, American Elsevier Pub. Co, ISBN

Woan, K.; Pyrgiotakis, G. & Sigmund, W. (2009). Photocatalytic Carbon-Nanotube-TiO2 Composites. *Advanced Materials*, Vol. 21, No. 21, pp. 2233-2239, ISSN 0935-9648 Wu, J. C. S.; Lin, H. M. & Lai, C. L. (2005). Photo Reduction of CO2 to Methanol using

Yamashita, H.; Nishiguchi, H.; Kamada, N.; Anpo, M.; Teraoka, Y.; Hatano, H.; Ehara, S.;

Catalyst. *Journal of Catalysis*, Vol. 161, No. 1, pp. 1-10, ISSN 0021-9517 Varghese, O. K.; Paulose, M.; LaTempa, T. J. & Grimes, C. A. (2009). High-Rate Solar

Approach. *Surface Science*, Vol. 253, No. 1-3, pp. 386-394, ISSN 0039-6028 Singal, H. R.; Talwar, G.; Dua, A. & Singh, R. (1995). Pod Photosynthesis and Seed Dark CO2

Vol. 20, No. 1, pp. 49-58, ISSN 0250-5991

*Environmental*, Vol. 37, No. 1, pp. 37-48, ISSN 0926-3373

*Letters*, Vol. 9, No. 2, pp. 731-737, ISSN 1530-6984

*Chemistry Letters*, Vol. 1, No. 1, pp. 48-53, ISSN 1948-7185

*a-General*, Vol. 380, No. 1-2, pp. 172-177, ISSN 0926-860X

3373

60, ISSN 0028-0836

Delhi

0926-860X

142-162, ISSN 1758-2083

9780444195524 , New York

the Reductive and Oxidative Abilities of TiO2 Nanotubes under UV and Visible Light. *Applied Catalysis B-Environmental*, Vol. 97, No. 3-4, pp. 354-360, ISSN 0926-

on Cu and Pd Surfaces by the Bond-Order-Conservation Morse-Potential

Fixation Support Oil Synthesis in Developing Brassica Seeds. *Journal of Biosciences*,

Derived Titania and Titania-Supported Copper Catalysts. *Applied Catalysis B-*

Evolving Photosystem II at a Resolution of 1.9 A. Nature, Vol. 473, No. 7345, pp. 55-

Methane and Methanol. *International Journal of Global Warming*, Vol. 3, No. 1-2, pp.

Synthesis and the Water Gas Shift Reaction on a Commercial Cu/ZnO/Al2O3

Photocatalytic Conversion of CO2 and Water Vapor to Hydrocarbon Fuels. *Nano* 

of CO2 Using CdSe/Pt/TiO2 Heterostructured Catalysts. *Journal of Physical* 

using NiO/InTaO4 in Optical-Fiber Reactor for Renewable Energy. *Applied Catalysis* 

*Photosynthesis and Photomorphogenesis,* Singhal, G.S.; Renger, G.; Sopory, S. K.; Irrgang, K. D. & Govindjee, Narosa Publishing House, ISBN 0-7923-5519-9, New

Optical-Fiber Photoreactor. *Applied Catalysis a-General*, Vol. 296, No. 2, pp. 194-200,

Kikui, K.; Palmisano, L.; Sclafani, A.; Schiavello, M. & Fox, M. A. (1994).


Indrakanti, V. P.; Schobert, H. H. & Kubicki, J. D. (2009). Quantum Mechanical Modeling of

Inoue, T.; Fujishima, A.; Konishi, S. & Honda, K. (1979). Photoelectrocatalytic Reduction of

Ipek, B. (April 2011). Photocatalytic Carbon Dioxide Reduction in Liquid Media. M.Sc.

Jitaru, M. (2007). Electrochemical Carbon Dioxide Reduction- Fundamental and Applied

Kaneco, S.; Shimizu, Y.; Ohta, K. & Mizuno, T. (1998). Photocatalytic Reduction of High

Ke, B. (2001). *Photosynthesis: Photobiochemistry and Photobiophysics*, Kluwer Academic

Kitano, M.; Matsuoka, M.; Ueshima, M. & Anpo, M. (2007a). Recent Developments in

Kitano, M.; Takeuchi, M.; Matsuoka, M.; Thomas, J. A. & Anpo, M. (2007b). Photocatalytic

Photocatalysts. *Catalysis Today*, Vol. 120, No. 2, pp. 133-138, ISSN 0920-5861 Koci, K.; Mateju, K.; Obalova, L.; Krejcikova, S.; Lacny, Z.; Placha, D.; Capek, L.;

Koci, K.; Obalova, L.; Matejova, L.; Placha, D.; Lacny, Z.; Jirkovsky, J. & Solcova, O. (2009).

Meyer, T. J. (2008). Catalysis - The Art of Splitting Water. *Nature*, Vol. 451, No. 7180, pp. 778-

Ovesen, C. V.; Clausen, B. S.; Schiotz, J.; Stoltze, P.; Topsoe, H. & Norskov, J. K. (1997).

Ozcan, O.; Yukruk, F.; Akkaya, E. U. & Uner, D. (2007). Dye Sensitized Artificial

Sahibzada, M.; Metcalfe, I. S. & Chadwick, D. (1998). Methanol Synthesis from CO/CO2/H2

*B-Environmental*, Vol. 89, No. 3-4, pp. 494-502, ISSN 0926-3373

23, (October 2009), pp. 5247-5256, ISSN 0887- 0624

277, No. 5698, pp. 637-638, ISSN 0028-0836

42, No. 4, pp. 333-344, ISSN 1311-7629

Publishers, ISBN 0-7923-6334-5, Dordrecht

Ankara, Turkey

ISSN 1010-6030

pp. 1-14, ISSN 0926- 860X

pp. 239-244, ISSN 0926-3373

779, ISSN 0028-0836

297, ISSN 0926-3373

133-142, ISSN 0021- 9517

174, No. 2, pp. 111-118, ISSN 0021- 9517

CO2 Interactions with Irradiated Stoichiometric and Oxygen-Deficient Anatase TiO2 Surfaces: Implications for the Photocatalytic Reduction of CO2. *Energy & Fuels*, Vol.

Carbon-Dioxide in Aqueous Suspensions of Semiconductor Powders. *Nature*, Vol.

Thesis, Chemical Engineering Department, Middle East Technical University,

Topics (Review). *Journal of the University of Chemical Technology and Metallurgy*, Vol.

Pressure Carbon Dioxide using TiO2 Powders with a Positive Hole Scavenger. *Journal of Photochemistry and Photobiology a-Chemistry*, Vol. 115, No. 3, pp. 223-226,

Titanium Oxide-Based Photocatalysts. *Applied Catalysis a-General*, Vol. 325, No. 1,

Water Splitting using Pt-Loaded Visible Light-Responsive TiO2 Thin Film

Hospodkova, A.; & Solcova, O. (2010). Effect Of Silver Doping on The TiO2 for Photocatalytic Reduction of CO2. *Applied Catalysis B-Environmental*, Vol. 96, No. 3-4,

Effect of TiO2 Particle Size on the Photocatalytic Reduction of CO2. *Applied Catalysis* 

Kinetic Implications of Dynamical Changes in Catalyst Morphology During Methanol Synthesis over Cu/ZnO Catalysts. *Journal of Catalysis*, Vol. 168, No. 2, pp.

Photosynthesis in the Gas Phase over Thin and Thick TiO2 Films under UV and Visible Light Irradiation. *Applied Catalysis B-Environmental*, Vol. 71, No. 3-4, pp. 291-

over Cu/ZnO/Al2O3 at Differential and Finite Conversions. *Journal of Catalysis*, Vol.


**3** 

*Iran* 

**Manganese Compounds as Water Oxidizing** 

*Chemistry Department, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan,* 

Artificial photosynthesis is an umbrella term but it could be introduced as a research field that attempts to mimic the natural process of photosynthesis and uses sunlight to oxidizing and reducing different compounds. In this process, we could assume water as one of the compounds that could be reduced and (or) oxidized to hydrogen and (or) oxygen, respectively. Water splitting is the general term for a chemical reaction in which water is

 Production of hydrogen fuel from electrolysis of water would become a practical strategy if we could find a ''super catalyst'' for water oxidation reaction (Bockris, 1977). Super catalyst means a stable, low cost, efficient and environmentally friendly catalyst. The water oxidation half reaction in water splitting is overwhelmingly rate limiting and needs high over-voltage (~1V) that results the low conversion efficiencies when working at current densities required, also at this high voltage, other chemicals will be oxidized and this would be environmentally unacceptable for large-scale hydrogen production (Bockris, 1977). Thus, a significant challenge in the sustainable hydrogen economy is to design a water oxidizing

In past few years, there has been a tremendous surge in research on the synthesis of various metal compounds aimed at simulating water oxidizing complex (WOC) of photosystem II (PSII) (Liu et al., 2008; Kanan, M.W. & Nocera, 2008; Cady et al., 2008; Yagi & Kaneko, 2001; Ruttinger & Dismukes, 1997). Of these materials, the Co, Ru and Ir compounds have been shown to be an effective catalyst for water oxidation. However, most of the compounds are

Particular attention has been given to the manganese compounds aimed at simulating the WOC of PSII (Umena et al., 2011) not only because it has been used by *Nature* to oxidize water but also because manganese is cheap and environmentally friendly. In this chapter we consider manganese compounds as structural or (and) functional models for the WOC of PSII

There are many mono, di, tri and tetra nuclear manganese complexes as structural models

**1. Introduction** 

catalyst.

decomposed to oxygen and hydrogen (Pace, 2005).

**2. Water Oxidizing Catalysts in artificial photosynthesis** 

expensive and often relate to potentially carcinogenic salts.

**2.1 Structural models for biological Water Oxidizing Complex** 

for the WOC in PSII (Mullins & Pecoraro, 2008).

**Catalysts in Artificial Photosynthesis** 

Mohammad Mahdi Najafpour

Photocatalytic Reduction of CO2 with H2O on TiO2 and Cu/TiO2 Catalysts. *Research on Chemical Intermediates*, Vol. 20, No. 8, pp. 815-823, ISSN 0922-6168

