Browsing by Author "Oktar, Nuray"

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Biofuel Production From Model Bio-Oil: Impact of Perovskite-Based Catalysts and Metal Oxide Mixtures on Upgrading and Selectivity
(Springer, 2026) Ozcan, Merve Celik; Dogu, Doruk; Oktar, Nuray
Biofuel production was conducted using model bio-oil to examine the upgrading performance of perovskite-based and metal oxide catalysts. Bare and Ce, Co, Sr, Mo, and tungstophosphoric acid-doped LaFeO3 perovskite-based catalysts were synthesized via sol-gel method. The bio-oil upgrading activity of commercial La2O3, alpha-Fe2O3, and alpha-Fe2O3/La2O3 metal oxide catalysts compared to LaFeO3-based catalyst was also investigated. Catalyst properties were characterized by XRD, TGA/DTG, N-2 adsorption/desorption, SEM-EDX, FTIR, DRIFTS, and Raman techniques. Activity tests were performed at 400 degrees C at under atmospheric pressure. A model bio-oil mixture was formulated with hydroxy propanone/formic acid/furfural (2:4:3 mass ratio), and a dilution ratio of 30:70 (bio-oil mixture/alcohol) was applied. Ethanol and methanol were examined as co-reactants. Ethanol-assisted upgrading resulted in higher deoxygenation efficiency and enhanced iso-paraffin selectivity compared to methanol. Increasing the calcination temperature of LaFeO3 from 700 to 800 degrees C improved crystallinity and raised the overall bio-oil conversion from 69.4 to 83.4%. The bare LaFeO3 catalyst calcined at 800 degrees C exhibited high iso-paraffin selectivity (69.4 vol%) and oil-phase selectivity (80.3%). The superior upgrading performance of LaFeO3 was attributed to its orthorhombic perovskite lattice structure and mild surface acidity, favoring cracking, deoxygenation, and coke suppression. Ce-doped LaFeO3 (x = 0.1) enhanced oxygen mobility and promoted olefin selectivity resulting in the highest overall bio-oil conversion (83.8%). At higher Ce contents (x = 0.2), CeO2 side-phase formation promoted naphthene selectivity. In contrast, Sr-, Co-, and Mo-doped LaFeO3 catalysts showed higher oxygenated content. Compared with alpha-Fe2O3/La2O3 mixed catalyst, which exhibited 16.0 wt% coke formation, LaFeO3 showed low coke deposition (0.24 wt%). Long-term stability testing of LaFeO3 revealed only a very small amount of carbon formation (1.39 wt%) and no catalyst deactivation. Similar product distributions were obtained in both short-term and long-term tests. [GRAPHICS]
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.