Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Dimethyl Ether Production From Methanol Over Silica-Alumina Catalysts(01. Izmir Institute of Technology, 2021) Tarancı, Ecem; Şeker, ErolThis study aims to investigate the effect of acidic properties of acidic catalysts on the activity, which is required to produce dimethyl ether from methanol. In this study, silica-alumina (SiO2/Al2O3) catalysts with different compositions which are 25/75 wt.%, 50/50 wt.%, 75/25 wt.%, and 3 different calcination temperatures which are 500°C, 700°C, and 900°C were synthesized by the sol-gel method for the methanol dehydration to dimethyl ether reaction. In the further stages of the study, some changes were made in the catalyst formulations of the most active and the least active catalysts in terms of catalytic performance to modify acidic properties. In this regard, the peptizer acid of silica-alumina catalysts was changed from HNO3 to H2SO4, or 0.1 g of ZSM-5 zeolite was added to the silica-alumina sol mixture step. The NH3-TPD analysis was used to understand the acidic properties of all synthesized SiO2/Al2O3 catalysts. The reaction temperatures were 300°C and 400°C for both 30 min. The study has shown that there was a decrease in the acidity of the catalysts calcined at 900°C is observed. The activity of 75%SiO2-25%Al2O3 catalyst decreases significantly as the calcination temperature increases. The activities of all catalysts calcined at 500°C are close to each other, whereas there is a big difference in activity between 25%SiO2-75%Al2O3 and 75%SiO2-25%Al2O3 catalysts calcined at 900°C. As evidence of the NH3-TPD results, 25/75 wt.% catalyst calcined at 900°C was the most active catalyst with approximately 97% methanol conversion, while 75/25 wt.% catalyst calcined at 900°C was the least active catalyst with 63% conversion at 400°C. The 50/50 wt.% catalyst calcined at 900°C is also a very active catalyst with over 90% conversion. While sulfuric acid and/or zeolite exchange increased the performance of the least active catalyst, it did not reveal much difference in the most active catalysts. In addition, the addition of ZSM-5 zeolite increased the acidic strength of the catalysts. All synthesized catalysts are active for methanol dehydration. The DME selectivity for all catalysts is approximately 100%.Master Thesis Grawth and Electrical Characterization of High Purity Carbon Nanotubes(Izmir Institute of Technology, 2009) Kır, Serap; Selamet, YusufThis thesis work is focused on growing high purity vertically aligned Carbon nanotubes by ethylene gas thermal chemical vapor deposition method on very thin Cobalt and Iron catalyst thin films deposited on to Si/SiO2/Al2O3 substrates by DC magnetron sputtering. In this study, the effective parameters were changed to grow aligned CNTs. Hence, the vertically aligned CNTs were performed and also the ideal parameters were determined for this kind of growth mechanism. The effect of support layer was examined for three different hydrocarbon gas ratios. SiO2 and Al2O3 were used as support layers between metal catalyst thin films and Si substrate. Two kinds of samples were compared; one of them had only Al2O3 and the other one includes both Al2O3 and SiO2 layers. As a result, the sample that had both oxide layers gave better results for density of CNTs on the surface of samples. Moreover, types of catalyst material effect also were examined on growth of CNTs for three different temperatures. For this aim, the performance of Fe and Co catalyst thin films was compared. According to our results, Fe was more reactive with ethylene gas than Co catalysts and also, the density of CNTs was increased by using Fe as a catalyst material. Hydrogen pretreatment time was performed for another significant effect. Seven different time parameter which were 0, 5, 10, 15, 20, 25, 30 minutes, were examined. The density and diameters of catalysts particles were compared for these different treatment times. Finally, the electrical characterization of CNTs was performed. The resistance of CNTs was measured by using two point contact technique. Moreover, the interaction between resistance of CNTs and humidity was examined.Master Thesis Thermal and Photodehydrogenation Reactions of Terpenes Over Zeolites(Izmir Institute of Technology, 2003) Tuzcuoğlu, Esra; Artok, LeventIn this thesis study, catalytic activity of cation exchanged (Na+, Li+, Ca2+, K+, Cs+) zeolite Y, especially NaY, and various microporous and mesoporous (Na exchanged, Beta, Mordenite, and NaX, CsNaX, MCM-41, Montmorillonite KSF and amorphous Silica) catalysts was investigated in the dehydrogenation reaction of terpenes to p-cymene.The results suggested that, there are two types of acid sites are present in cation exchanged zeolites from NH4Y, which are Br Bronsted and Lewis sites. a-terpinene, disproportionated by Br Bronsted acid catalysis into 3-p-menthene and p-cymene, and pcymene was also formed by direct dehydrogenation of a-terpinene can possibly occur with the participation of Lewis acid sites in cation exchanged zeolite Y. Best conversion to p-cymene were observed in the NaHY, LiHY and CaHY exchange from NH4Y that have relatively small cations, which more acidic than the larger ones.With the catalysts that have Bronsted acid sites except ion-exchanged zeolite Y, no conversion or only acid catalyzed isomerization reactions occur that shows the Bronsted acidity was not enough to catalyze the dehydrogenation of a-terpinene. Also Lewis acidic character and the structure morphology are the most important factors affecting the conversion. Lewis acidity is influenced from the cation and zeolite type.Master Thesis Growth and Characterization of Carbon Nanotubes by Thernal Chemical Vapor Deposition Method(Izmir Institute of Technology, 2008) Aksak, Meral; Selamet, YusufThis thesis work is focused on producing carbon nanotubes (CNTs) by methane gas thermal chemical vapor deposition method on very thin Cobalt, Iron, and Nickel catalyst thin films deposited onto SiO2/Si substrates by DC magnetron sputtering. This thesis is also devoted to understanding some parameters affecting the growth of CNTs; such as catalyst material, temperature, and catalyst layer thickness effects In this study, CNT growth was performed on directly Si substrates, which was observed that the growth was too difficult and requiring very high temperatures. Hence, very thin catalyst films were deposited on SiO2/Si substrates, and the CNT growth was observed. The temperature effect was also examined. When the growth temperature was increased, the average diameters of the CNTs were decreased up to a critical temperature, but after this point the average diameter of CNTs were increased. This effect was studied systematically by utilizing Fe and Co catalyst thin films and with the help of Raman spectroscopy and Scanning Electron Microscopy results.Catalyst thickness effect was also examined. For this aim, Ni catalyst thin films with three different thicknesses; 0.7 nm, 1.4 nm, and 6 nm, were utilized. It was observed that CNTs were grown well on 0.7 and 1.4 nm thick Ni films, while there was a little growth on 6 nm thick Ni film. The roughness analysis of 0.7 nm and 1.4 nm thick Ni films were also done. Some of as-grown CNTs were also examined by X-ray diffraction method, and the results were compared one another.Master Thesis Hydrothermal Synthesis and Characterization of Single Crystalline Ceo2 Nanoparticles for Catalytic Applications(Izmir Institute of Technology, 2012) Meşin, Taylan; Eanes, MehtapSingle crystalline cerium oxide nanoparticles were synthesized with hydrothermal method by mixing cerium nitrate[Ce(NO3)3.6H2O] aqueous solution with alkali bases CsOH and RbOH. SEM, TEM and XRD characterization methods were used in order to identify morphology. First part of the study includes the work on effect of hydrothermal parameters, such as reaction temperature, reaction time, alkali base type and concentration on particle size and morphology. It was prooved that the size of ceria nanoparticles is directly proportional with the reaction time. The reaction temperature is also an important parameter that effect the morphology of nanoparticles. At 120 oC nanoparticles form rod like structure and as time goes they start to form cubic crystals. When the alkali base and concentration was changed the results showed that higher base concentration favors the particles to form bigger structures than that of lower concentrations. In addition, optical properties of CeO2 nanoparticles were studied by using the UV-Vis and Fluorescence Spectrometry. UV-Vis Spectroscopy results show that particle size of CeO2 nanoparticles synthesized in the presence of 8M RbOH are larger than that of synthesized in presence of 8M CsOH. When the reaction time decreases the Ce3+ defect increases based on the results of Fluorescence Spectrometry results. Second part of the study includes catalytic property of CeO2 nanoparticles. Ceria nanoparticles were used as catalyst in the synthesis of flavone from 2’-hydroxychalcone. Several reaction parameters were studied in order to achieve the flavone synthesis. TLC, GC, GC-MS and NMR were used in order to monitor the results of the reactios.Master Thesis Suzuki Reactions Over Palladium Loaded Y Zeolite(Izmir Institute of Technology, 2002) Bulut Güllübağ, Hatice; Artok, LeventIn this study, the use of Pd(II) loaded NaY type zeolite as a catalyst in the Suzukiinvestigated.For this aim, Pd(OAc)2, and [Pd(NH3)4]Cl2 complexes were loaded into NaY zeolite in order to form an appropriate catalyst system. Pd(NH3)42+ loaded Y type zeolite was calcined to obtain Pd(II) form Pd(OAc)2 loaded Y type zeolite showed high activity in the reactions of 4-iodoanisole and 4-bromoanisole with arylboronic acid. However the reusability which is an important property of heterogeneous catalyst could not be provided, the following studies were continued with Pd(II) loaded Y type zeolite.When, 4-iodo and 4-bromoanisole reactives were used in the presence of Pd(II) loaded Y type zeolite, 60-100% biaryl products were obtained. The amount and type of the base and DMF:H2O ratio have high effects on the yield. In order to prove that the reaction took place in heterogeneous phase, at the end of the reaction Pd analysis of the solution was performed by AAS technique. It was found that the Pd amount in solution was trace.Master Thesis Growth and Characterization of Carbon Nanotubes Over Co-mo/Mgo Catalysts(Izmir Institute of Technology, 2010) İnce Yardımcı, Atike; Selamet, YusufThis thesis work is focused on synthesis of high quality and high yield Carbon nanotubes by methane decomposition catalytic chemical vapor deposition method on Co-Mo/MgO catalyst prepared by gel-combustion method. Catalyst contained weight %1.06 Co and weight %0.86 Mo having a molar ratio of Co:Mo:MgO;0.5:0.25:10. CNTs were grown in a quartz tube. In this study, three different growth conditions were examined. Argon, hydrogen or mixture of two gases were added to methane during growth. And for all of the three growth conditions, four different pretreatment processes were investigated. Pretreatment lasted for one hour at 850 oC. Firstly hydrogen effect was examined with 200 sccm flow rate, then argon effect was examined with again 200 sccm flow rate. And the third pretreatment included both argon and hydrogen gases flow together. For these three pretreatment conditions cooling and heating processes also took place with the same gas rates. However, the last pretreatment condition was carried out with hydrogen gas at 850 oC for just one hour, and for heating and cooling processes argon was used. The highest quality CNTs were sythesized under pure hydrogen atmosphere for both pretreatment and growth processes. Then, three different H2 flow rates were investigated; 100, 150 and 200 sccm. High hydrogen flow rate during growth was better for CNT growth in terms of quality. Growth temperature was performed as another important parameter. Four different temperatures were investigeted; 850 oC, 900 oC, 950 oC and 1000 oC. With increasing growth temperatures, structural quality increased and tangled CNTs formation decreased. It was found that 950 oC was the optimum growth tempertaure to obtain high yield of CNT. Finally, the growth time effect on CNT growth was examined for four different growth times; 10, 20, 30 and 40 minutes and the results showed that amount of CNTs increased with increasing time and CNTs became longer and graphitization was higher at longer growth times. Disorder also decreases with increasing time.