Browsing by Author "Dogu, Doruk"

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Comparison Between Gas Phase and Electrochemical Nitridation of 8ysz Under Nitrogen Atmosphere To Produce Nitride Conducting Solid Electrolytes
(Elsevier, 2024) Ozturk, Onur; Dogu, Doruk
Ammonia is one of the most used chemicals in the world. It is commonly synthesized by the Haber-Bosch process which requires high temperature (450-500 degrees C) and pressure (up to 300 bar). This process is thermodynamically limited and causes environmental problems due to CO2 emissions caused by the production of H2 required by this process from fossil fuels. Electrocatalytic processes using oxide and proton-conducting electrolytes are gaining interest for ammonia production to overcome these limitations. Although both methods overcome many of the problems associated with the Haber-Bosch process, due to strong N-N triple bonds selectivity towards ammonia decreases. This is because the reaction occurs on the same side of the membrane electrode assembly, namely the cathode electrode, where nitrogen is fed in the gas phase and nitrogen bonds should be broken to react with hydrogen ions readily available on the electrolyte surface. Since N-N bond cleavage requires very high energy, hydrogen ions generally recombine to form H2 before the nitrogen can be ionized. Nitride conducting electrolytes can be an answer to this problem because in their use nitrogen ionization and ammonia synthesis reactions occur at different electrodes and nitrogen is fed to the reaction site in the ionic form which is more active for the reaction. This study focuses on two alternative methods for the production of nitride conducting solid electrolytes by nitridation of 8 % Yttria Stabilized Zirconia (8YSZ). Two different methods for nitridation were studied: gas phase powder nitridation and electrochemical nitridation of YSZ electrolytes. This study shows that although gas phase nitridation of YSZ powders at high temperatures under nitrogen is not efficient, electrochemical nitridation of YSZ electrolytes is a highly promising method to produce nitride conducting electrolytes.
Influence of Synthesis Parameters on the Structural Formation of Mayenite via the Citrate Sol-Gel Method
(Tubitak Scientific & Technological Research Council Turkey, 2025) Eryildirim, Busra; Oktar, Nuray; Dogu, Doruk
Mayenite (Ca12Al14O33) has remarkable properties such as high oxygen mobility, ionic conductivity, and catalytic activity. It has many different applications, including oxide-conducting electrolytes, fluorescent lamps, moisture sensors, hydrogen-permeable membranes, oxygen pumps, hydrogen storage, and catalysis. However, pure and homogeneous mayenite synthesis parameters have not yet been fully explored. This study examines the effect of synthesis parameters including metal salt (MS) to citric acid (CA) molar ratios (1:1 and 1:2), pH (0.4-2), and calcination temperature (900-1200 degrees C) in citrate sol-gel method on the crystal structure of mayenite. Synthesized materials were examined by thermogravimetric (TG), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, N2 adsorption-desorption, scanning electron microscopy (SEM), inductively coupled plasma-optical emission spectrometry (ICP-OES), Fourier-transform infrared spectroscopy (FTIR), and pyridine adsorbed diffuse reflectance Fourier-transformed infrared spectroscopy (DRIFTS) analyses. The results show that all 3 parameters contribute to the mayenite phase formation and different impurity phases can be observed depending on the synthesis parameters. With no pH adjustment and an MS to CA ratio of 1, other phases of calcium aluminate mostly form. Mayenite becomes the main phase by doubling the CA amount. Besides CA, pH is also an important factor in mayenite synthesis. When the pH was adjusted to 2 with the MS to CA ratio at 1:1, mayenite was formed as the main phase, but other phases of calcium aluminate were also observed in the structure. XRD results show that all parameters studied influence the crystal structure of the final material, including the calcination temperature. This study shows that pure mayenite can be synthesized with a calcination temperature of 1200 degrees C, at a pH of 2, and the MS to CA molar ratio of 1:2.
Citation - WoS: 1
Outperformance of CaO-Incorporated Alumina-Supported Pd Catalysts in Methanol Decomposition
(Springer, 2025) Eryildirim, Busra; Oktar, Nuray; Dogu, Doruk
This study aimed to investigate the impact of CaO incorporation to alumina-supported Pd catalysts on the methanol decomposition reaction. For this purpose, mayenite, alumina and/or calcium oxide-supported Pd catalysts were synthesized. The synthesized catalysts were characterized by XRD, FTIR, Laser Raman spectroscopy, N2 adsorption-desorption, pyridine adsorbed DRIFTS, CO2-TPD, XPS, SEM-EDS, and ICP-OES techniques. Catalytic activity tests were carried out over a 6 h reaction period in the range of 100-400 degrees C. The results of the characterization and activity tests showed that the addition of CaO had significant effects on the physicochemical properties of the catalyst as well as on the catalytic activity. By adding CaO to the alumina support material, the acidity was reduced, thus reducing the selectivity for dimethyl ether (DME) formation, which is significantly high for the 1Pd@Al2O3 catalyst, and increasing the H2 and CO selectivity. The mayenite-supported catalyst (1Pd@SGM), which contains alumina and calcium oxide in its unique crystal structure, showed an excellent catalytic performance close to complete methanol conversion with DME selectivity below 1% at 400 degrees C. In the stability test carried out at 350 degrees C for 6 h with 1Pd@Al2O3, 1Pd@SGM, and 1Pd@48CaO@Al2O3 catalysts used in the temperature scan, it was concluded that all catalysts were stable and 1Pd@SGM catalyst showed higher catalytic activity than the others.