On the mechanism of photocatalytic CO2 reduction with water in the gas phase

The mechanism of photocatalytic reduction of CO2 with H2O over Pt-TiO2 films produced by the sol-gel deposition over glass beads was investigated. The accumulation of significant amount of carbonaceous intermediate on the surface followed by deactivation indicated the rate limiting reaction is the water splitting reaction, similar to the natural photosynthetic systems. When gas phase hydrogen was allowed in the system, the carbonaceous intermediates were converted to methane at rates higher than the artificial photosynthesis conditions. In the presence of hydrogen, formation of methane reaction proceeded in the dark albeit at lower rates. The progress of the reaction is very similar to the natural photosynthetic reactions however the rates are seven orders of magnitude slower than the reactions in the natural photosynthetic processes. Furthermore, the role of spilled over hydrogen in the reaction was also demonstrated.


The deactivation behavior of the TiO2 used as a photo-catalyst for benzene oxidation
Üner, Deniz (1999-01-01)
In this study, the deactivation behavior of TiO2 as a photocatalyst for benzene decomposition to carbon dioxide and water was investigated. The effect of space time on the benzene and carbon dioxide conversions were monitored. Benzene conversion and carbon dioxide production rates were not correlated, indicating accumulation of a carbon containing intermediate on the surface. This intermediate was blocking the active sites at a stiochiometry of 1 C:1 site. High space times favored the production of carbon d...
Investigation of precursor sequence and post-annealing effects on the properties of Cu2SnZnSe4 thin films deposited by the elemental thermal evaporation
Bayrakli, O.; Terlemezoğlu, Makbule; Gullu, H. H.; Parlak, Mehmet (IOP Publishing, 2017-08-01)
Cu2ZnSnSe4 (CZTSe) thin films were deposited onto soda lime glass substrates by thermal evaporation using the pure elemental sources. The influence of the sequential deposition order of Zn and Sn precursor layers for different evaporation cycles were investigated. In situ annealing at 400 degrees C under Se evaporation was applied to promote conversion of precursor layers to quaternary compound structure and additionally, subsequent post-annealing processes under nitrogen atmosphere at 450 degrees C was car...
Dye sensitized artificial photosynthesis in the gas phase over thin and thick TiO2 films under UV and visible light irradiation
Ozcan, O.; Yukruk, F.; Akkaya, E. U.; Üner, Deniz (2007-02-15)
Perylene diimide based organic sensitizers capable of electron generation under illumination were used to initiate gas phase photo reduction reactions on TiO2 thin and thick film surfaces. For comparison [Ru(Bpy)(3)](2+) dye sensitizers were also studied. The photo reduction Of CO2 was carried out under static conditions in the gas phase. TiO2 films were coated on hollow glass beads via a sol-gel procedure. Pt was incorporated on the films either by adding the precursor salt in the sol, Pt(in), or by wet im...
On the Electrochemical Reduction Mechanism of CaWO4 to W Powder
Erdogan, Metehan; Karakaya, İshak (2012-08-01)
The reduction mechanism of CaWO4 to W in molten eutectic CaCl2-NaCl electrolyte has been studied. Cyclic voltammetry and constant potential electrolysis tests were performed to determine the reversible cell potential. Analyses of the experimental results revealed that at least 2.2 V was required to compensate the potentials for the accompanying cell reaction and the electrode polarizations. A cell reaction was proposed by associating the experimental results and the Gibbs energy changes of the possible reac...
On the Limits of Photocatalytic Water Splitting
İpek Torun, Bahar; Üner, Deniz (2019-01-01)
The major drawbacks on the limited H2 and O2 evolution activities of one-step photocatalytic water splitting systems are given here with the emphasis on charge recombination, back-oxidation reactions, and mass transfer limitations. Suppression of these unwanted phenomena is shown to be possible with the usage of small crystal-sized photocatalysts with low defect concentrations, presence of phase junctions, selection of co-catalyst that would be active for H2 evolution but inactive for O2 reduction, coating ...
Citation Formats
D. Üner, “On the mechanism of photocatalytic CO2 reduction with water in the gas phase,” CATALYSIS TODAY, pp. 82–88, 2012, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/46536.