Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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2002 - 200912010 - 20143

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Author: search.filters.author.Yilmaz, Selahattin

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Now showing 1 - 4 of 4
  • Master Thesis
    Development of Tungsten Loaded and Zirconia Incorporated Mesoporous Catalysts for Esterification of Palmitic Acid With Cetyl Alcohol
    (Izmir Institute of Technology, 2014) Mutlu, Vahide Nuran; Yılmaz, Selahattin; Yilmaz, Selahattin
    In this study, it was pursued to develop acidic mesoporous catalysts for esterification of cetyl alcohol by palmitic acid. For this, Zr incorporated SBA-15 was prepared by hydrothermal synthesis. Zr-SBA-15 was used both as a catalyst support and as a catalyst itself. WO3 loading onto the Zr-SBA-15 was performed by incipient wetness impregnation. Additionally, WO3-ZrO2 catalyst was prepared by co-precipitation with two different contents of WO3 (15 wt% and 20 wt%). The reaction tests were carried out in mesitylene under reflux conditions. Zr was incorporated into SBA-15 successfully. The surface areas of Zr-SBA-15 and WO3/Zr-SBA-15 catalysts were significantly higher than that of WO3-ZrO2. Loading of WO3 decreased the surface area of Zr-SBA-15. The acidity of the WO3/Zr-SBA-15 with 15 wt% WO3 was higher than that of with 20 wt% WO3. Moreover, increasing the calcination temperature from 700 to 800 oC resulted in the increase of acidity. The activity of the catalysts differed. The only product obtained was cetyl palmitate. Under the test conditions it was found that the reaction rate was not limited by equilibrium. Zr-SBA-15 provided the highest conversion (64 %) which corresponded to cetyl palmitate yield of 63% among other mesoporous catalysts because of its high surface area (600.3 m2/g) and acidity (0.152 mmol NH3/g cat). This catalyst did not show leaching. WO3/Zr-SBA-15 based catalys tests showed that catalyst activity increased by increasing calcination temperature. This was atributed to better dispersion of W. The conversion of cetyl alcohol did not change much with more W loading.
  • Master Thesis
    Investigation of Catalytic Activity and Selectivity of Pd and Ni Loaded Clinoptilolite Rich Natural Zeolite for Citral Hydrogenation
    (Izmir Institute of Technology, 2002) Uçar, Şule; Yilmaz, Selahattin
    The preparation of active and selective clinoptilolite rich natural zeolite supported palladium and nickel catalysts for the liquid phase hydrogenation of citral was investigated. The catalysts were prepared by impregnation and ion exchange methods. Catalytic activity and selectivity tests were performed in a semi-batch reactor for different calcination temperatures, pressures, stirring rates, reaction temperatures, amount of catalysts, ethanol sources, catalyst metal loadings and catalysts preparation methods. Catalyst deactivation was also investigated. The characterization results showed that clinoptilolite was the major mineral in natural zeolite used as catalyst and catalyst support. It was thermally stable up to 440°C and its stability improved with Pd and Ni loading. Catalysts with loading of 0.72, 2.42, 5.63 % Pd and 3.12 % Ni were prepared by impregnation method. One catalyst was prepared by Pd ion exchange (5.66 %). Surface areas of the catalyst samples changed with calcination temperature, method of metal loading, amount of metal loading. A calcination temperature of 430°C and catalyst metal loading of 2.42 % Pd provided the largest surface area (38.96 m2/g) among the catalysts prepared by impregnation. The catalyst prepared by ion exchange had a much more larger surface area (49.46 m2/g) than those prepared by impregnation. The product distribution changed with catalysts prepared by different methods, catalyst metal loadings, catalyst calcination temperatures and reaction temperatures. The results showed that the Pd catalyst prepared by impregnation favoured the hydrogenation of the conjugated double bond of citral, giving citronellal as the primary hydrogenation products, whereas the amounts of unsaturated alcohols were very minor. High selectivity to citronellal was obtained for the catalyst calcined at 430°C containing 2.42 % Pd. The product distribution and the reaction rates were affected significantly by the reaction temperature (80, 100 and 120°C). The highest selectivity to citronellal (88 %) and the yield of citronellal (87 %) were obtained at 120°C. Higher reaction rates were observed as temperature increased. Increasing the amount of the catalyst in the reaction medium (150, 250 and 400 mg/100mL) affected the reaction rates, selectivity and the yield of citronellal. The highest amount of citronellal yield (91 %) was obtained when the reaction was carried out in the presence of the largest amount of the catalyst (400 mg/100 mL) used in this study. Different product distributions were obtained with various ethanol sources. Higher yields and selectivities were obtained with more pure solvent. Product distribution changed with catalyst metal loading. First increased significantly by changing catalyst loading from 0.72 to 2.42 % Pd and then rised slowly when metal loading changed from 2.42 to 5.63 % Pd. This was attributed to active metal surface area and its dispersion. Impregnated Pd catalysts regained their activities and selectivities upon regeneration. Ni impregnated catalyst showed a different product distribution. It showed a lower activity for a given temperature. Overall selectivities of the best Pd catalyst and Ni catalysts were similar. Pd catalyst prepared by ion exchange gave different products and its selectivity to citronellal was the lowest. This was attributed to the metal and catalyst surface interactions.
  • Master Thesis
    An Investigation of Activities and Selectivities of Hzsm-5 and H-Ferrierite Zeolites Modified by Different Methods in N-Butene Isomerization
    (Izmir Institute of Technology, 2010) Kılıç, Emre; Yilmaz, Selahattin
    In this study the synthesis and preparation of active and selective zeolite catalysts for the skeletal isomerization of 1-butene to iso-butene reaction were investigated. Since this reaction occurs on the acid sites, acidity of the catalyst plays important role on catalyst activity and isobutene selectivity. The acidity of synthesized HZSM-5, commercial Ferrierite (H-FER) and HZSM-5-C zeolite catalysts were modified by chemical liquid deposition (CLD) using tetraetyhyl orthosilicate (TEOS), SiCl4 and triaminopropyltriethoxysilane (3-amino), alkali, acid and ammoniumhexafluorosilicate treatment methods. Reaction tests were performed in a fixed bed reactor at 375 0C at weight hour space velocities of 22 h-1. SiCl4 deposition dramatically decreased the total acidity and surface area, both conversion and selectivity of the catalysts whereas TEOS increased selectivity. The highest selectivity (81.2 %) among CLD agents, were obtained by H-FER modified by TEOS 1 hour 1 cycle. Mild alkali treatment slightly decreased the acidity, which increased selectivity for H-ZSM5 from 57 to 60. However severe alkali treatment decreased the selectivity of the catalysts since some acid sites increased after this treatment. Acid treatment significantly decreased the surface area, acidity and caused dealumination. As a result catalyt activity decreased by 10 %. However, selectivity to isobutene changed slightly. Pre-alkali treatment before acid treatment decreased the dealumination effect, so this increased the selectivity; for H-ZSM5 from 57 to 66. AHFS treatment decreased the acidity slightly without affecting other properties. This increased the selectivity of H-ZSM5 from 58 to 87. The highest selectivity values were obtained for AHFS treatment among all modifications.
  • Master Thesis
    An Investigation of Catalyt Preparation Conditions and Promoter Loading (sn) Effects on Activity and Selectivity of Pt Catalyists in Citiral Hydrogenation
    (Izmir Institute of Technology, 2010) Depboylu, Can Okan; Yilmaz, Selahattin
    In this study, citral hydrogenation reaction in liquid phase over silica gel supported Pt and PtSn catalysts were studied. It was desired to hydrogenate carbonyl group (C.O) selectively to produce valuable unsaturated alcohols, namely nerol, geraniol and citronellol. Pt/SiO2 catalysts were prepared by impregnation method while PtSn/SiO2 catalysts were prepared by catalytic reduction (CR), co-impregnation (CI) and successive impregnation (SI) methods. Pt loading over silica gel support was 1 % (w/w). For bimetallic catalysts, the (Sn/Pt) loading ratios were varied as 0.3, 0.5 and 0.7. The effects of parameters investigated in the present study included catalyst activation temperature (350 °C, 450 °C), calcination temperature (400 °C, 500 °C), solvent type (ethanol, 2-pentanol), catalyst activation without calcination, washing of catalyst with 0.1 M NaOH solution, Pt precursor type (hexachloroplatinic acid, platinum II acetylacetonate (PAA)) and Sn loading ratio. For Pt/SiO2 catalysts, maximum citral conversion (89 %) was achieved at lower activation (350 °C) and calcination (500 °C) temperatures when PAA was used. Increasing the activation temperature to 450 °C decreased the citral conversion to 52 % but increased the selectivity to unsaturated alcohols (nerol and geraniol) (SNE+GE) from 8 % to 60 %. It was observed that the lower activation temperature provided higher citral conversion but lower selectivity to unsaturated alcohols. Washing of catalyst and using of 2-pentanol prevented the acetal formation. Catalyst activated without calcination step gave lower conversion (20 %) and SNE+GE of 30 %. For bimetallic catalyst (PtSn/SiO2), maximum citral conversion was observed as 91.1 % when catalyst was prepared by CR method and calcined at 500 °C. Higher citral conversion and selectivity to unsaturated alcohols were achieved at the higher calcination temperature and higher reduction temperature. CR method was the most appropriate preparation method for bimetallic catalysts compared to CI and SI. An optimum of activity (91.1 %) and selectivity (89.7 %) was found at a Sn/Pt ratio 0.5.