Elucidating the role of adsorbed states of hydrogen, water and carbon dioxide over TiO2 and Pd/TiO2

Download

index.pdf

Date

2020

Author

Yılmaz, Begü

Metadata

Show full item record

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Item Usage Stats

368
views

240
downloads

Artificial photosynthesis studies aim to utilize solar energy for conversion of CO2 into valuable organics using H2O; however, developments in the area are far from realistic level applications due to the low production rates. In order to understand the mechanism, CO2 and H2O adsorption isotherms over TiO2 P25 were investigated by using a volumetric chemisorption technique with and without an illumination source. Adsorption isotherms revealed indirect evidences on local temperature rise on the surface indicating photo-induced thermal chemistry upon charge recombination. Desorption was observed during CO2 adsorption over TiO2 P25 under illumination. Calculation of adsorbed amounts according to estimation for local temperature rise (to 160°C) on the surface yielded a reasonable adsorption isotherm under illumination. Similarly, H2O adsorption isotherm under illumination showed Langmuir type of adsorption isotherm indicating presence of only strongly bound molecules under illumination. In this study, weakly adsorbed molecules were claimed to be desorbed due to local temperature rise on the catalyst surface upon charge recombination resulting in similar chemistry with heating of the sample cell to 150°C. Additionally, the attempts on direct heat release measurement upon charge recombination via microcalorimeter were explained. Moreover, H2 and CO2 adsorption isotherms over Pd/TiO2 surface were investigatedusing a chemisorption manifold connected to a Setaram C80 microcalorimeter to understand the effect of presence of precious metal on TiO2 support. 0.5% Pd/TiO2 showed relatively well dispersed palladium on support. Enhanced CO2 adsorption observed on 0.5% Pd/TiO2 was related to increase in oxygen vacancy concentration due to spilled hydrogen during the reduction of surface. Evidences for presence of palladium bulk on 2.0% Pd/TiO2 were presented via H2-TPR results, especially. According to these evidences, it is understood that the effect of heat release upon charge recombination on chemistry is highly underrated in literature. The local temperature rise can affect the chemistry significantly;however, uncontrollable temperature conditions are not desired. Last but not least, metal hydrogen systems over metal oxide support can offer a strategy for enhanced reduction reactions by utilizing stored hydrogen on surface.

Subject Keywords

Photocatalysis., Keywords: Photocatalysis, CO2 adsorption, H2O adsorption, TiO2 P25, Pd/TiO2

URI

http://etd.lib.metu.edu.tr/upload/12625253/index.pdf
https://hdl.handle.net/11511/45511

Collections

Graduate School of Natural and Applied Sciences, Thesis

Suggestions

OpenMETU
Core

Elucidating the role of adsorption during artificial photosynthesis: H2O and CO2 adsorption isotherms over TiO2 reveal thermal effects under UV illumination Üner, Deniz; Yılmaz, Begüm (2022-06-01) Adsorption measurements of CO2 and H2O over TiO2 surfaces in dark and under illumination were carried out to reveal the ensuing bottlenecks of the initial steps of the artificial photosynthesis reaction. When the adsorption isotherms of both CO2 and H2O were measured under illumination, the results were comparable to isotherms measured at higher temperatures in dark. This evidence is interpreted as the presence of hot spots, due to charge carrier recombination reactions. Differential heat of adsorption meas...
A new economic feasibility approach for solar chimney power plant design Okoye, Chiemeka Onyeka; Solyali, Oguz; Taylan, Onur (2016-10-15) Solar chimney power plants have been accepted as one of the promising technologies for solar energy utilization. The objective of this study is to propose an effective approach to simultaneously determine the optimal dimensions of the solar chimney power plant and the economic feasibility of the proposed plant. For this purpose, a two-stage economic feasibility approach is proposed based on a new nonlinear programming model. In the first stage, the proposed optimization model which determines the optimal pl...
Analysis of carbon dioxide sequestration in shale gas reservoirs by using experimental adsorption data and adsorption models Merey, Sukru; Sınayuç, Çağlar (2016-11-01) For carbon dioxide (CO2) sequestration in depleted shale gas reservoirs or CO2 injection as an enhanced shale gas recovery technique, it is important to understand the adsorption mechanism in these reservoirs. In this study, experimental adsorption measurements for Dadas shale samples were conducted at 25 degrees C, 50 degrees C, and 75 degrees C up to approximately 2000 psia by using pure CO2 (maximum adsorption capacity 0.211 mmol/g at 25 degrees C) and pure methane (CH4) (maximum adsorption capacity 0.04...
A methodology to assess suitability of a site for small scale wet and dry CSP systems Uzgoren, Eray; Timur, Eray (2015-06-25) This study presents a methodology to assess suitability of a site for small scale concentrated solar power (CSP) systems for its energy conversion efficiency and make-up water requirement. Energy conversion efficiency of CSPs relies not only on the level of direct solar radiation but also on the performance of the cooling system. Regions with high solar potential have to deal with heat rejection at elevated temperatures which causes reduced energy conversion efficiencies due to high condenser temperatures. ...
Numerical modeling and performance analysis of solar-powered ideal adsorption cooling systems Taylan, Onur; Baker, Derek Keıth; Department of Mechanical Engineering (2010) Energy consumption is continuously increasing around the world and this situation yields research to find sustainable energy solutions. Demand for cooling is one of the reasons of increasing energy demand. This research is focused on one of the sustainable ways to decrease energy demand for cooling which is the solar-powered adsorption cooling system. In this study, general theoretical performance trends of a solar-powered adsorption cooling system are investigated using TRNSYS and MATLAB. Effects of differ...

Citation Formats

B. Yılmaz, “Elucidating the role of adsorbed states of hydrogen, water and carbon dioxide over TiO2 and Pd/TiO2,” Thesis (M.S.) -- Graduate School of Natural and Applied Sciences. Chemical Engineering., Middle East Technical University, 2020.