Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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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, SelahattinThe 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, SelahattinIn 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.