archives@tulane.edu / 1 / Ross Stephen Ransom

Zeolites are crystalline, microporous aluminosilicates that have been extensively used in heterogeneous catalysis, separations, and ion-exchange operations. It has long been understood that particle size and morphology play a central role in the successful application of zeolites. This dissertation reports on controlling the morphology of all-silica zeolite, silicalite-1, made in nonionic/ionic microemulsions under conventional synthesis conditions. Silicalite-1 materials formed in microemulsion-mediated syntheses possess different morphological properties as compared to samples grown using the same synthesis mixture in the absence of the microemulsion. The work presented here is a systematic study showing how parameters such as synthesis temperature, microemulsion composition, silica precursor, alkali content, presence of salt, and the surfactant identity impact the material properties, most notably crystal morphology. In the nonionic microemulsion mediated synthesis, the work demonstrates the possibility of using microemulsions to manipulate the shape and size of silicalite-1 materials, growing both spheres and high-aspect ratio platelets. In both cases these large particles are robust aggregates of small submicron particles. Based on the results presented, a mechanism is proposed illustrating the role of both the confined space presented by the microemulsion as well as the importance of the surfactant-silicate interactions leading to the formation of the large aggregates. In the cationic microemulsion mediated synthesis, it is concluded that the surfactant??silicate interactions are primarily responsible for the modulation of crystal morphology observed. The results indicate that surfactant adsorption on the growing crystal surface, not the confined space afforded by the microemulsion, is essential. The results suggest that this may be a versatile and useful approach to controlling zeolite crystal morphology and growth of crystals obtained from conventional high-silica zeolite synthesis procedures.

Zeolites are crystalline, microporous aluminosilicates that have been extensively used in heterogeneous catalysis, separations, and ion-exchange operations. It has long been understood that particle size and morphology play a central role in the successful application of zeolites. This dissertation reports on controlling the morphology of all-silica zeolite, silicalite-1, made in nonionic/ionic microemulsions under conventional synthesis conditions. Silicalite-1 materials formed in microemulsion-mediated syntheses possess different morphological properties as compared to samples grown using the same synthesis mixture in the absence of the microemulsion. The work presented here is a systematic study showing how parameters such as synthesis temperature, microemulsion composition, silica precursor, alkali content, presence of salt, and the surfactant identity impact the material properties, most notably crystal morphology. In the nonionic microemulsion mediated synthesis, the work demonstrates the possibility of using microemulsions to manipulate the shape and size of silicalite-1 materials, growing both spheres and high-aspect ratio platelets. In both cases these large particles are robust aggregates of small submicron particles. Based on the results presented, a mechanism is proposed illustrating the role of both the confined space presented by the microemulsion as well as the importance of the surfactant-silicate interactions leading to the formation of the large aggregates. In the cationic microemulsion mediated synthesis, it is concluded that the surfactant??silicate interactions are primarily responsible for the modulation of crystal morphology observed. The results indicate that surfactant adsorption on the growing crystal surface, not the confined space afforded by the microemulsion, is essential. The results suggest that this may be a versatile and useful approach to controlling zeolite crystal morphology and growth of crystals obtained from conventional high-silica zeolite synthesis procedures.

Melanoidin is responsible for the dark brown color of distillery wastewater. Discharge of colored wastewater has a major environmental impact on the biota of the receiving water body. Consequently, this study explores the removal of melanodin from aqueous solution. The equilibrium, kinetics and thermodynamics of melanoidin sorption are studied by varying initial solution pH, initial concentration, adsorbent dose and temperature. Kinetically, the melanoidin removal from solution by a surfactant modified zeolite is rapid and the amount adsorbed is dependent on pH, initial concentration, adsorbent dose and temperature. The equilibrium sorption data are fitted to the Freundlich and Langmuir models while the sorption kinetics are described by the Ho pseudo-second order and Elovich models. The thermodynamic analysis indicates that the sorption is spontaneous and endothermic in nature. The FTIR spectra analyses show no new peaks or shift in peaks after sorption indicating that the melanoidin sorption may have occurred by a physical process. The results from desorption studies showed that melanoidin eluted back easily to the solution using distilled water which corroborates the physical sorption mechanism.

The efficacy of the claycop system in the nitration and the dinitration of toluene has been investigated.Comparison of regioselectivity and of rate constant with homogeneous nitric acid nitration was made. The use of ion-exchanged montmorillonite clay as a catalyst for acetyl nitrate nitration was studied. The system was found to enhance Para selectivity in the nitration of toluene and to catalyse the reaction. Additionally, the catalyst was shown to be recyclable. The reaction of toluene was too fast to allow kinetic study. However, kinetic study was possible,using chlorobenzene as substrate.Again, the system was found to decrease both the reaction time and the o-/ p- ratio. It was possible to demonstrate a dependence of rate constant upon mass of clay. The effect of the counter ion was investigated and the use of trifluoroacetyl anhydride was studied. A new system for aromatic nitration has been developed in this work using zeolite with dinitrogenp entoxide.A series of zeolites were screened in the nitration of onitrotoluene, with the H-faujasites showing the quickest reaction times and highest degree of regioselectivity. The silica/ alumina ratio of the faujasite used was varied and this was shown to have an effect on regioselectivity. However, reactions were too fast for kinetic study. The faujasite/ dinitrogen pentoxide system was used in the nitration of some deactivated benzenes using these substrates allowed kinetic studies to be made and the order in each component to be determined. It was found that nitration was zeroth order in dinitrogen pentoxide, that the reaction obeyed a first order rate law, and that the first order rate constant was proportional to the mass of zeolite used. Comparison of the relative rates of nitration of 1-chloro-2-nitrobenzene1, -chloro-4-nitrobenzene and nitrobenzeneb y this system to the relative rate constants of nitronium ion nitration was made. The similarity suggested that the mechanism of nitration by faujasite/d initrogen pentoxide might involve nitronium ion transfer.Amongst the H-faujasites of different silica/ alumina ratio, the rate constant was shown to increase with the aluminium content. A mechanism is proposed in which zeolite protons (present in proportion to the aluminium atoms) are first replaced by nitronium ions. The latter are transferred to the aromatic in the rate-determining step. The use of non-chlorinated solvents and the recycling of zeolite were both studied, and the nitration of 2,6-dinitrotoluene was attempted. The use of the faujasite/ dinitrogen pentoxide system was extended to the nitration of nitrogen containing aromatic heterocycles direct C-nitration of quinolone was not possible, only N-nitration. However, pyrazole was converted to 1,4-dinitropyrazole quickly and cleanly under mild conditions. It was shown that the N-nitration occurred instantly, followed by slower C-nitration. The kinetics of the second nitration were studied and comparison with deactivated benzenes was made.

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Thesis (Master)--İzmir Institute of Technology, İzmir, 2002. / Includes bibliographical references (leaves. 92-96).

This diploma thesis covers the tracking of final quality parameters of polyether polyol – Slovaprop G-160, which are: amount of sodium and potassium, color, acidity and amount of water. The most important parameter was the amount of sodium and potassium, because the aim this thesis was to achieve satisfactory amount of sodium and potassium after the purification process with use of zeolite (ZeoCem Micro 200) and to improve the effectivity of the purification and filtration process in the production of polyether polyol – Slovaprop G-160. In theoretical part, Diploma thesis deals with the method of production and characteristics of polyether polyols for the production of polyurethane foams. Practical part consists of nine series of experiments in order to get addictions of amount of sodium and potassium to temperature, weight of Pyrofos and amount of zeolite. Based on laboratory test a new way of purification process of polyether polyols was developed. With this new purification process the production time of Slovaprop G-160 will be shorten thanks to removal of hydrolysis from the reaction process and in the end of the process the time needed for drainage is reduced in half.

The preparation method of the catalyst highly impacts its properties and activity. Optimizing the synthesis conditions mainly targets improving the catalyst performance and overcoming the bottlenecks such as sintering of metal active sites, deactivation, short catalyst lifetime and poor selectivity. In this study, we investigated the influence of the design and preparation method of Silicalite-1 bearing Pt and Ga active species on the properties and the performance of the catalysts for propane dehydrogenation reaction aiming to increase propylene yield. Various synthesis routes, leading to different Pt and Ga location and distances were tested: (1) supporting metals on the zeolite where both Pt and Ga are randomly distributed on the surface, (2) confining of Pt and Ga within the zeolite pores following in-situ approach with no control of their relative positions, and (3) core-shell design where one metal is confined within Silicalite-1 is covered by a Silicalite-1 layer including the second metal. The influence of structure, textural properties, location of Pt and Ga nanoparticles and their synergetic interaction to form Pt-Ga alloys were studied using several characterization techniques such as XRD, BET, TEM-EDX and NMR. Catalytic performance revealed that confining metals improved the selectivity and lifetime of the catalyst. Moreover, spatial separation of Pt and Ga through the core-shell design further boosted the reaction yield with conversions hitting the equilibrium limit. Ga/Pt ratio played a crucial role in tuning the catalyst performance. 0.26%Pt(core)-2.65%Ga(shell)@S-1 catalyst with Ga/Pt of 10 exhibited superior results of 70.5% conversion and 98% selectivity.