The aim of this study is to investigate and reveal challenges in
photocatalytic CO2 reduction tests performed in liquid media. Effect of test conditions in photocatalytic studies are often underestimated with an assumption of negligible mass transfer limitations in observed rate results. In this study, effect of mass transfer limitations in liquid phase photocatalytic tests was revealed with stirring rate and gas hold-up time experiments performed with Pt/TiO2 and Cu/TiO2 catalysts. In addition, apparent activation energies of 12 and 19.5 kJ/mol found with Pt/TiO2 and Cu/TiO2 catalysts respectively indicate diffusion
limitations which favor back oxidation reactions resulting in low reduction yields.
Photocatalytic CO2 reduction reaction is named as Artificial Photosynthesis even though present artificial system does not have sophisticated transport and membrane systems which natural systems have. Similarities and differences between artificial and natural photosynthesis are studied in order to present ideas to improve present photocatalytic rates.
Kinetic and microkinetic modeling of catalytic methanol production from CO2 hydrogenation on Cu surfaces were performed in order to have an idea about kinetic limitations at photocatalytic systems. Calculations were performed at
temperatures and pressures at which photocatalytic studies are conducted. The results indicated that water has an inhibitory effect on methanol formation rates and higher pressures could be implemented in photocatalytic systems for higher rates. Another implication drawn from degree of rate control calculations is that H formation step plays an important role underlying the importance of water splitting in CO2 reduction reactions.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/12613183/index.pdf |
| Date | 01 April 2011 |
| Creators | Ipek, Bahar |
| Contributors | Uner, Deniz |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | M.S. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for public access |
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