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    Catalytic Degradation of Polylactic Acid over Al2O3@SiO2 Core-Shell Catalysts
    (Springer, 2021) Akti, Filiz
    Al2O3@SiO2 core-shell catalysts were synthesized by sol-gel method. The core size'control was provided by using of polyethylene glycol (PEG) and glycerol. The shell thickness was optimized by using the different amount of tetraethylorthosilicate (TEOS). The formation of core and shell structures in catalysts was seen in high resolution transmission electron microscopy (HRTEM) images. In some catalysts, the use of PEG caused to formation of a more monodisperse core structure. The particle size of catalysts was observed in the range of 8-12 nm. The BET (Brunauer-Emmett-Teller) surface area and total pore volume of catalysts ranged 440-1014 m(2)/g and 1.28-2.57 cm(3)/g, respectively. In addition, pore diameter reached up to 25 nm. The use of PEG and glycerol improved textural properties. While BET surface area and total pore volume values decreased by the increase of TEOS amount, shell thickness increased a little. Fourier transform infrared (FTIR) spectrums of the pyridine adsorbed catalysts revealed the presence of Lewis and Bronsted acid sites in the catalysts. The catalysts were tested in the degradation of polylactic acid (PLA) by using thermogravimetric analysis (TGA) technique. TGA results showed the degradation temperature of PLA decreased from 353 to 321 degrees C in the presence of catalysts. Activation energy values were calculated using Flynn-Wall-Ozawa method. The activation energy was reduced from 337 to 199 kJ/mol. Pore structure, particle size and acidity of catalysts significantly affected the degradation performance.
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    Effect of kaolin on aluminum loading success in synthesis of Al-SBA-15 catalysts: Activity test in ethanol dehydration reaction
    (Elsevier, 2020) Akti, Filiz
    Aluminum incorporated SBA-15 catalysts were prepared via hydrothermal method using together with aluminum salt and kaolin as aluminum source. Aluminum loading to the SBA-15 structure did not destroy the characteristic peaks of SBA-15 (from X-Ray diffraction (XRD) patterns) and it was led to increase of surface area values. Energy dispersive spectroscopy (EDX) and inductively coupled plasma optical emission spectroscopy (ICP-OES) results demonstrated that increase of kaolin amount positively affected the success of aluminum loading. UV-visible diffuse reflectance (UV-Vis DR) and X-ray photoelectron spectroscopy (XPS) spectra showed that aluminum species were settled in the form of metal oxide. Fourier transform infrared (FTIR) spectra exhibited the characteristic structural bands of SBA-15. Generally the peak intensities of the acid sites increased slightly with the aluminum incorporation and this increase showed mostly at Lewis acid sites. The highest ethanol conversion and ethylene selectivity was observed as 0.95 and 1.00 at 400 degrees C, respectively.
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    Hydrogen generation from hydrolysis of sodium borohydride by silica xerogel supported cobalt catalysts: Positive roles of amine modification and calcination treatment
    (Elsevier Sci Ltd, 2021) Akti, Filiz
    Silica xerogel supported cobalt catalysts were prepared by sol-gel method to hydrogen generation from an alkaline sodium bomhydride solution. The effect of APTES (3-aminopropyl triethoxysilane) modification and calcination treatment was investigated on the structural properties and catalytic activity. The physicochemical properties of the catalysts were evaluated by using XRD (X-ray diffraction), nitrogen adsorption/desorption, TEM/EDX (Transmission electron microscopy/energy dispersive X-ray spectroscopy), XPS (X-ray photoelectron spectroscopy) and FTIR (Fourier transform infrared) analysis techniques. Only the formation of broad amorphous silica was observed from the XRD patterns. APTES modification and calcination treatment led to increasing of surface area and total pore volume values. The surface area, total pore volume and pore diameter values increased up to 752 m(2)/g, 0.693 cm(3)/g and 3.88 nm, respectively. The TEM image of the Co@X-TA-C catalyst showed that cobalt was settled as nanoparticle smaller than 4.0 nm to the structure. The average particle size of this catalyst was determined as similar to 4.5 nm. XPS analysis results demonstrated presence of metallic and oxide cobalt phases. FTIR spectra exhibited bands representing the silica structure and cobalt-silica interaction. The maximum hydrogen generation rate was determined as 100.7 mL.min(-l).g(cat)(-1) for Co@X-TA-C. Kinetic study showed that the hydrolysis of sodium borohydride with Co@X-TA-C catalyst system was a zero-order. The activation energy was found as 15.2 kImol(-1) for this catalyst.
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    The effect of potassium modification on structural properties and catalytic activity of copper and iron containing SBA-16 catalysts for selective oxidation of ethanol
    (Elsevier Ltd, 2019) Akti, Filiz
    Copper and iron SBA-16 catalysts were synthesized using hydrothermal method and modified with potassium. XRD patterns showed that characteristic peaks of SBA-16 for all catalysts did not destroy with metal loading. The metal and potassium loading to SBA-16 structure led to generally the decreasing of specific surface area values. While total pore volume value of SBA-16 increased with copper loading, it decreased with iron loading. Pore diameter values of SBA-16 generally increased with metal loading. It was seen that from TEM images metals settled as nanoparticles to the SBA-16 structure. EDX results demonstrated that potassium modification treatment increased especially the success of metal loading. FTIR spectrums of all catalysts exhibited the characteristic structural bands of SBA-16. It was seen that the peak intensity of both Brønsted and Brønsted + Lewis acid sites of the SBA-16 increased by the metal loading. On the other hand potassium modification improved the acid sites. UV–Vis DR and XPS spectra showed that copper and iron species settled as Cu+2 and Fe+3 form, respectively. The potassium modified catalysts exhibited the highest conversion of 77% and acetaldehyde selectivity of 81% compared to catalysts without potassium modification at reaction temperature of 350 °C. © 2019 Elsevier B.V.
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    Using of Modified SBA-15 Mesoporous Silica Materials for CO2 Capture: A Review
    (Igi Global, 2018) Akti, Filiz
    Carbon dioxide emissions cause global warming, and greenhouse gases and climate change are very serious problems. Mesoporous silica material SBA-15 has been preferred mostly as an ideal adsorbent for CO2 due to its excellent properties such as high surface areas and pore volumes, larger pore diameter, and thicker silica wall. In the literature studies, SBA-15 has been modified by different functional groups and the effects of modification methods on the CO2 adsorption have been investigated. Modified SBA-15 adsorbents showed high CO2 adsorption capacity. The aim of this chapter is to review the use of modified-SBA-15 mesoporous silica materials as adsorbent for CO2 capture.