none

Tese (doutorado)—Universidade de Brasília, Instituto de Química, 2007. / Submitted by Luis Felipe Souza (luis_felas@globo.com) on 2009-01-08T12:20:12Z No. of bitstreams: 1 Tese_2007_IvoneideBarros.pdf: 3390296 bytes, checksum: 2bd94256449111f511c6d9dad708ee99 (MD5) / Approved for entry into archive by Georgia Fernandes(georgia@bce.unb.br) on 2009-02-27T14:59:03Z (GMT) No. of bitstreams: 1 Tese_2007_IvoneideBarros.pdf: 3390296 bytes, checksum: 2bd94256449111f511c6d9dad708ee99 (MD5) / Made available in DSpace on 2009-02-27T14:59:03Z (GMT). No. of bitstreams: 1 Tese_2007_IvoneideBarros.pdf: 3390296 bytes, checksum: 2bd94256449111f511c6d9dad708ee99 (MD5) / A incorporação do metal nióbio em peneiras moleculares microporosas promove novas propriedades a esses materiais. Nesse sentido, foram preparados catalisadores suportados com 2 - 25 % em massa de óxido de nióbio(V) sobre zeólita ZSM-5 de duas fontes: Zeolyst e FCC/Petrobrás. A natureza do metal tem um papel importante na alteração da distribuição e força dos sítios ácidos na superfície do suporte. As amostras foram submetidas a um estudo térmico a fim de otimizar parâmetros e evitar uma possível redução das propriedades ácidas do catalisador por desidroxilação. Os catalisadores modificados, Nb(x)HZSM-5, foram caracterizados através da combinação de métodos térmicos (TG, DTA, DSC) e espectroscópicos (FT-IR e FT-Raman e IR-DRIFT), bem como de RMN-MAS de 29 vi Si e 27Al e CP/MAS de 29Si, DRX, ICP-AES e medidas de área superficial específica (método BET), visando a obtenção de informações estruturais e de estabilidade dos sólidos. As propriedades catalíticas foram verificadas com auxílio das reações modelo de dessulfurização do tiofeno e esterificação do ácido oléico. Para monitorar o rendimento desses processos, foram utilizadas as técnicas de FRX e RMN 1H. Resultados de RMN e DRX indicaram que a estrutura da zeólita contendo Nb não sofreu desaluminização após tratamento térmico, explicada pela presença da unidade Si-O-Nb na estrutura das zeólitas por espectroscopia de FT-IR e Raman. Análises térmicas comfirmaram que a impregnação de NbO25 reduziu a desidroxilação da zeólita ZSM-5, promovendo uma estabilização térmica. A área BET e o volume de poro diminuem gradualmente nesses sólidos com o aumento da quantidade de Nb após calcinação. Outrossim, investigou-se a natureza dos sítios ativos pelo método de pré-adsorção de uma base, utilizando piridina como molécula prova. Bandas de absorção de piridina no infravermelho referentes a sítios ácidos de Brönsted e de ligação de hidrogênio foram observadas para os sistemas derivados de ZSM-5 da Zeolyst. Nos sistemas Nb(x)HZSM-5 derivados da FCC/Petrobrás foram observados, além dos dois sítios citados, uma pequena fração de sítios ácidos de Lewis. Isto justifica a maior acidez apresentada nas zeólitas impregnadas com 2 e 5 % de NbO25, quando comparadas às suas correspondentes amostras da Zeolyst, independente da calcinação. As análises de FRX indicaram que a adsorção de tiofeno sobre os catalisadores modificados foi bem superior (quase o dobro nas amostras derivadas da Petrobrás) ao do catalisador de partida, destacando maior interação do organossulfurado quando o catalisador contém 5 % de NbO25, e observando uma queda a partir de 15 %, sendo explicado pelo excesso da monocamada do óxido, conforme DRX e FT-Raman. A presença do cobre também exerce influência sobre a eficiência do processo de dessulfurização, otimizando-o. Finalmente, foi mostrado que entre as amostras modificadas, a melhor conversão na esterificação do ácido oléico ocorre com Nb(5)HZSM-5, corroborando com os resultados da dessulfurização, embora o catalisador sem Nb tenha apresentado maior atividade catlítica nas mesmas condições. __________________________________________________________________________________________ ABSTRACT / Incorporation of niobium into microporous molecular sieves brings up new properties for these materials. Supported catalysts containing 2 - 25 wt.% of niobium oxide were prepared over ZSM-5 from two manufacturers: Zeolyst e FCC/Petrobrás. The metal nature has a fundamental role in the changes of distribution and strength of acid sites on the original support surface. The samples were subjected to thermal studies optimizing parameters to avoid a possible reduction of acid properties by dehydroxylation. The modified catalysts, Nb(x)HZSM-5, were characterized by the combination of thermal (TG, DTA, DSC) and spectroscopic (FT-IR, FT-Raman and IR-DRIFT) methods, besides 29 viiSi and 2729Al MAS and Si CP-MAS NMR, XRD, ICP-AES and measurements of specific surface area (BET method) in order to obtain structural and stability information about the solids. Catalytic properties were verified through model reactions of thiophene desulfurization and oleic acid esterification. XRF and 1H NMR were used to monitor yields. NMR and XRD results showed that the zeolite structure containing Nb did not undergo dealumination after thermal treatment, according to the presence of Si-O-Nb units on the zeolites structure by FT-IR and Raman studies. Thermal analyses confirm that the impregnation of NbO25 reduces ZSM-5 dehydroxylation, thus promoting a thermal stabilization. BET method for Zeolyst ZSM-5 indicated that area and pore volume decreased with the increase of Nb on the calcined samples. In addition, it was investigated the nature of active sites by pre adsorption of pyridine. Infrared pyridine absorption bands related to Brönsted and hydrogen bond acid site types were observed for Zeolyst ZSM-5 systems. For the systems Nb(x)HZSM-5 using HZSM-5 from FCC/Petrobrás it was observed, besides the two abovementioned acid sites, a small faction of Lewis acid sites. This justifies the higher acidity showed by 2 and 5 wt.% NbO25 impregnated on zeolite, when compared to the Zeolyst samples, independent of calcination procedure. XRF analyses indicated that the thiophene adsorption over modified catalysts was improved in relation to the parent catalyst, emphasizing higher interaction of organosulfur compound when the catalyst has 5 wt.% of NbO25. It was observed a decrease for 15 wt.% explained by excess of oxide monolayer, according to XRD and FT-Raman results. Copper presence also affects the efficiency of desufurization process, optimizing it. Finally, it was showed that among the modified samples, the better conversion of oleic acid esterification occurs to Nb(5)HZSM-5 in agreement to desulfurization results, although the parent catalyst has showed higher catalytic activity at same conditions.

No description available.

Made available in DSpace on 2016-06-02T19:56:55Z (GMT). No. of bitstreams: 1 DissJEF.pdf: 1826030 bytes, checksum: a3043074648b14bbec76bd05d3190200 (MD5) Previous issue date: 2005-03-04 / Universidade Federal de Sao Carlos / The minimization of the emissions of nitrogen oxides (NOx) in the atmosphere has been one of the great goals in the area of environmental protection. Among the possible processes to treat the NOx, the selective catalytic reduction of NO with hydrocarbons (SCR-HC) has presented important expectations. For this process, the metal/ZSM-5 type catalysts have appropriate levels of conversion in oxidative conditions. In this context, the aim of this work was to prepare Cu, Co and FeZSM-5 catalysts. The samples were characterized by XRD, DRS-UVVIS, FTIR, H2-TPR, SEM and tested in the reduction of NO to N2 with propane or methane in oxidative atmosphere in the presence or absence of water steam. The H2-TPR data showed that the cationic species present in the prepared Cu, Co and FeZSM-5 catalysts, after thermal activation, were mainly Cu2+ (Cuα 2+ e Cuβ 2+), Co2+ and Fe3+ cations located in charge compensation sites in the zeolite, respectively. From FTIR and DRS-UVVIS it was also possible identify oxide species, which were present in a lower content. In the reduction of NO to N2 in the absence of water steam, the CuZSM-5 catalysts showed higher levels of conversion of NO than those based in Co and Fe. However, the FeZSM-5 catalysts showed, in this condition, activity at lower temperatures. This behavior makes them potentially interesting to be applied for practical purposes. On the other hand, in the presence of water steam, it was verified a higher loss of activity of the CuZSM-5 catalyst, which was totally restored removing the water in the feed. For the Co and FeZSM-5 catalysts, the activity loss in the presence of water steam was partially recovered during time on stream. / A minimização das emissões de óxidos de nitrogênio (NOx) na atmosfera tem sido um dos grandes desafios da área de proteção ambiental. Dentre os processos para o tratamento dos NOx possíveis, a redução catalítica seletiva do NO com hidrocarbonetos (RCS-HC) vem apresentando excelentes perspectivas. Para este processo os catalisadores metal/zeólita ZSM-5 possuem adequados níveis de conversão em condições oxidantes. Dentro deste contexto, este trabalho teve como objetivo preparar catalisadores Cu, Co e FeZSM-5. As amostras foram caracterizadas por DRX, DRS-UVVIS, FTIR, RTP-H2, MEV e sua atividade verificada através da redução de NO a N2 com propano ou metano em atmosfera oxidante, na presença ou ausência de vapor de água. Os resultados de RTP-H2 mostraram que as espécies presentes nos catalisadores Cu, Co e FeZSM-5, após ativação térmica, foram principalmente os cátions Cu2+ (Cuα 2+ e Cuβ 2+), Co2+ e Fe3+ compensando carga na zeólita, respectivamente. A partir de FTIR e DRS-UVVIS foi possível, também, identificar espécies oxidas, as quais estavam presentes em teores menores. Na redução de NO a N2 na ausência de vapor de água os catalisadores CuZSM-5 apresentaram maiores conversões de NO que os contendo Fe ou Co. Entretanto, os catalisadores FeZSM-5 apresentaram, nessa condição, atividade em temperaturas menores, o que mostra uma vantagem para o seu uso prático. Na presença de vapor de água, verificou-se uma maior queda da atividade no catalisador CuZSM-5, somente recuperada com a retirada desse composto na alimentação, sendo que para os catalisadores CoZSM-5 e FeZSM-5 a perda de atividade foi parcialmente recuperada ao longo do tempo.

Thesis (Ph.D. (Physics)) --University of Limpopo, 2003 / Refer to the document / National Research Foundation, and the Standard Bank

The study of the aromatisation of methane was conducted at 750oC over metalimpregnated H-ZSM-5 catalysts with a feed flow rate of 13 ml/min and the composition of the feed was 90% methane balance argon. Typical products that were detected from the outlet stream were ethene, ethane, benzene and toluene. The amount of coke produced was determined by using 10% argon as an internal standard. The effects of different parameters such as the type of the support material, the molybdenum content, the %XRD crystallinity and SiO2/Al2O3 ratio of H-ZSM-5, the reaction temperature, the feed flow rate, the type of the molybdenum precursor, the catalysts preparation method, the addition of dopants, silanation and the regenerability of the catalysts were investigated. The results obtained showed that H-ZSM-5 was a better support for the preparation of catalysts used for the aromatisation of methane. Mo/H-ZSM-5 catalysts were more active when the molybdenum loading was between 2 and 4 wt% and loadings higher than 4% led to lower activities. The lower activities observed at higher molybdenum loadings was related to the poor dispersion and decrease in the pore volumes and surface areas observed due to the formation of MoO3 crystallites. Furthermore, the zeolite structure collapsed under the reaction conditions when the molybdenum loading was more than 4 wt%. The study showed that the conversion of methane increased linearly with increasing reaction temperature and the apparent activation energy of the reaction was found to be 64.5 kJ/mol. The results of the effect of the %XRD crystallinity of H-ZSM-5 on the performance of H-ZSM-5 catalysts showed that 2%Mo/H-ZSM-5 catalysts were more active when the crystallinity of the zeolite was between 50 and 70%. The conversion of methane decreased with an increase in the SiO2/Al2O3 ratio of H-ZSM-5. Higher aromatisation activities were observed when the SiO2/Al2O3 ratio of H-ZSM-5 was iii 60. The type of the molybdenum precursor used in the preparation of 2%Mo/HZSM- 5 catalysts did not have a significant influence on the conversion of the catalysts, but higher selectivities for aromatics were observed when ammonium heptamolybdate was used as a source of molybdenum. The catalysts prepared by physical mixing of MoO3 and H-ZSM-5 catalysts were more active than those prepared by impregnation with solutions of ammonium heptamolybdate. The presence of dopants such as boron, silver and alkali metal ions (Li+, Na+ and K+) in 2%Mo/H-ZSM-5 catalysts was also investigated. Boron (0.05-0.2 wt%) did not affect the conversion level of the catalysts but changed their selectivity properties. The selectivity for C2 hydrocarbons increased with boron content, while the selectivity for aromatics decreased. The addition of silver ions (0.5 wt%) significantly improved the conversion of the catalysts. This was attributed to the enhancement of the acvidity of the catalysts upon addition of silver ions which was observed by temperature programmed desorption of ammonia and pyridine adsorption studies of the infrared spectra of the catalysts. The addition of alkali metal ions in the Mo:Metal ratio of 0.5 led to decreased catalytic activities, due to the lowered acidities of the catalysts. The silanation of H-ZSM-5 improved the conversion of methane but lowered the selectivity for aromatics. A comparative study of the W-based and Mo-based catalyst at equivalent molar contents showed that molybdenum-based catalysts were more active than tungsten based catalysts. The study also showed that the catalytic performance of 2%Mo/H-ZSM-5 catalysts could be regenerated to appreciable levels by treatment of the catalysts in air at 600oC. The possibility of using Mo/H-ZSM-5 catalysts for the aromatisation of propane was also evaluated at 530oC, with consideration of three variables, namely, the molybdenum loading, the reaction temperature and %XRD crystallinity. The results indicated that impregnation H-ZSM-5 catalysts with molybdenum led to lower iv propane aromatisation activities. This lower activity was attributed to the lower Brønsted acid sites in the Mo/H-ZSM-5. The activities of the catalysts could be improved by operation at higher temperatures, but the rate of deactivation was also improved at higher temperatures. In line with the observations from the conversion of methane, higher activities were observed when the %XRD crystallinity of the catalyst was 61%.

Saudi Aramco is investigating the potential use of oxidized disulfide oil (ODSO), a refinery waste, as a solvent to replace water in zeolite preparation for the implication in industrial processes such as Fluidized Catalytic Cracking (FCC) aiming to increase propylene production. Utilizing ODSO helps Saudi Aramco reduces its processing costs, creates a value for this solvent and reduces the zeolite synthesis cost. One major concern is the effect ODSO may have on the catalytic performance of the prepared zeolites. This study investigates the catalytic cracking of 1-hexene and 2-methyl-2-butene (2M2B) at various WHSV and temperatures over ZSM-5 catalysts prepared from gels with SiO$_2$/Al$_2$O$_3$ ratios (SAR) of 50 and 25 and various ODSO/water substitutions. Six ODSO-based ZSM-5 catalysts were prepared and characterized in terms of acidity, morphology, and textural properties. The impact of catalyst composition and properties on conversion and selectivity is examined and compared to commercial ZSM-5 catalysts with similar SAR (CBV2314 and CBV5524G). At 477 h$^{-1}$ WHSV, ODSO-based catalysts achieved 80% 1-hexene conversion with 53-60% propylene selectivity, outperforming commercial catalysts (52%). However, 2M2B cracking exhibits slower reaction rates and more oligomerization cracking, resulting in lower conversion (46-61%) and propylene selectivity (22-29%). Notably, MAR- 2-3 (30% ODSO, 50 SAR gel) shows the best performance among the ODSO catalysts in terms of stability and selectivity, with results comparable to the commercial catalysts. We noticed, on the other hand, that ODSO-based catalysts possess larger crystals and higher acid site density compared to the commercial catalysts leading, generally, to a decreased stability. These findings enhance understanding of waste-based zeolites in catalytic cracking processes and guide the development of improved ODSO-based catalysts for petrochemical applications.

[pt] Neste trabalho, as zeólitas mordenita, ferrierita e ZSM-5 foram preparadas através de síntese hidrotérmica com a variação dos parâmetros fontes de alumínio e silício, quantidade de água, utilização de sementes, temperatura e tempo de cristalização com a finalidade de obter zeólitas nanocristalinas. As amostras preparadas foram caracterizadas por espectrofotometria de absorção atômica, difração de raios-X com refinamento através do método de Rietveld, adsorção física de N2, microscopia de força atômica, microscopia eletrônica de varredura, microscopia eletrônica de transmissão e ressonância magnética nuclear no estado sólido de 27Al e 29Si. Para se obter um controle do tamanho de cristal foi importante encontrar um equilíbrio entre temperatura e tempo de síntese. A fonte de alumínio mais adequada seria o aluminato de sódio enquanto que a de silício variou de acordo com tipo de zeólita. Foram obtidas amostras de mordenita de tamanho médio de cristalito entre 56 e 292 nm com diferentes percentuais de cristalinidades. As amostras de ferrierita preparadas possuíam tamanho médio de cristalito entre 61 e 82 nm. Já em relação à ZSM-5, foram obtidas uma amostra de tamanho médio de cristalito de 46 nm e uma de 58 nm. Este estudo mostrou a necessidade do conhecimento aprofundado da influência dos diversos parâmetros, individualmente, no processo de cristalização de cada uma zeólitas para se obter um controle eficaz do tamanho da zeólita. Finalmente, foi possível propor um mecanismo de cristalização para cada zeólita estudada. / [en] In this work, the mordenite, ferrierite and ZSM-5 zeolites were prepared by hydrothermal synthesis, modifying the parameters aluminium and silicium sources, water content, seeding, crystallization time and temperature. The objective was to obtain nanocrystalline zeolites. The prepared samples were characterized by atomic absorption spectrophotometry, X-ray diffraction with Rietveld refinement, N2 physical adsorption, atomic force microscopy, scanning electronic microscopy, transmission electronic microscopy and 27Al and 29Si solid state nuclear magnetic resonance. To achieve crystal size control it was important to find the equilibrium between synthesis time and temperature. Sodium aluminate was found to be the most suitable aluminium source. As for the silicium source, each zeolite type had a more suitable source. Mordenite samples with crystallite size between 56 and 292 nm and different crystallinity percentages were obtained. Ferrierite samples with crystallite size between 61 and 82 nm were obtained. Two ZSM-5 samples with crystallite size of 46 nm and 58 nm were prepared. This study showed that to obtain an efficient crystal size control, it is necessary to have a deep knowledge of the influence of all individual parameters in each zeolite`s crystallization process. Finally, it was possible to propose a crystallization mechanism to each zeolite studied.

Cette thèse s'articule autour des zéolithes, plus particulièrement leur synthèse, leur caractérisation et leur application comme catalyseurs hétérogènes. Dans certains cas, la compréhension des phénomènes encontrés au cours de ce processus nécessitait un travail de rationalisation. Ce dernier ingrédient permet une réelle amélioration continue, ou une conception sur mesure d'un catalyseur pour une réaction. Les zéolithes sont des aluminosilicates, microporeux et cristallins, qui se définissent et se différencient de part leur arrangement 3D de tétraèdres (SiO4 et AlO4) . Il a été essayé d'utiliser des zéolithes conçues sur mesures en tant que catalyseurs pour des réactions faisant partie d'une chimie renouvelable. Ainsi, ces travaux s'inscrivent dans le cadre des concepts de la chimie verte et de l'addition graduelle de complexité moléculaire. Au cours de cette thèse, la boucle itéative de l'amélioration continue a mené à deux reprises à un catalyseur très adapté au processus catalytique en question: d'une part l'halogènation d'aromatiques a été effectuée en phase liquide, il s'agit d'un procédé liquide-solide pour lequel le meilleur catalyseur résulte en une zéolithe béta (H-*BEA) avec une porosité hiérarchisée. Au contraire, la réaction de la conversion du méthanol en oléfines (MTO) une réaction gas-solide semble avoir comme catalyse uroptimal des zéolithes de type ZSM-5 sans porosité hierarchisée, mais ayant des tailles cristallines élevées, une qualité cristalline proche de la perfection (sans défauts) et une densité de sites acides très disperses. / This work revolved around the synthesis, characterisation and application of zeolites in heterogeneous catalysis. In some cases, counterintuitive observations and results needed a thorough rationalisation, which allowed a truly continuous improvement, or rational design of a catalyst for a given reaction. Zeolites are crystalline and microporous aluminosilicates, which are defined and differ one from another through their 3D arrangement of tetrahedra (SiO4 and AlO4).It has been aimed to design heterogeneous catalysts for reactions that fit in the concepts of a sustainable chemistry. Thus, this works describes and tried to respect the concepts of green chemistry and carbon upgrading. Remarkably, during this thesis the feedback looped continuous improvement approach has led twice to adapted catalysts for a catalytic chemical transformation: the liquid-solid continuous flow halogenation of aromatics was best performed with nanosized H-*BEA zeolites exhibiting a hierarchical porosity. In contrast, the gas-solid Methanol-to-Olefins (MTO) process needed an unusual catalyst. Indeed based on our study, large and perfectly crystalline H-ZSM-5 crystals with a disperse Brønsted acidity were the optimum catalyst.

This research explored different catalytic cracking zeolite additives to improve propylene selectivity and minimize dry gas yield. A comprehensive study of the effect of zeolite structure, pore system and crystal size on maximizing propylene production in FCC unit and the effect of post synthetic modifications on the physicochemical properties and cracking activity of ZSM-5 was investigated using X-ray diffraction (XRD), pyridine adsorption fourier transform infra-red (FTIR), 27Al and 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR) and the catalytic cracking using n-heptane, as a model compound for heavy naphtha. The catalytic performances of these additives were evaluated in a fixed-bed reactor unit using n-heptane as a model compound for naphtha at temperatures 450 - 500 oC and W/F 38 - 92 gcat.h/mol. A range of zeolites were tested with ZSM-5 showing the optimum results at high feed conversion. Further studies on ZSM-5 crystal size illustrated that nano ZSM-5 (300 nm) was superior compared to the regular ZSM-5 (2000 - 4000 nm) in achieved conversion level and propylene selectivity. These improvements were attributed to the shorter path lengths for the reactant reducing diffusion constraints significantly. Modifying nano ZSM-5 acidity using steaming, acid leaching and silanation showed significant improvement over nano ZSM-5 parent. Mild steaming of nano ZSM-5 improved both n-heptane conversion and propylene selectivity whilst severe steaming only improved propylene selectivity. This work attempted to address the often discussed catalytic activity enhancement from mild steaming and identified newly created moderate acid sites as the source of increased activity. Dealumination by acid leaching decreased the total aluminium content of nano ZSM-5 and changed the Brønsted/Lewis ratio. Increasing the B/L ratio, increased the conversion and propylene selectivity. In addition, this research focussed for the first time on the silanation of nano ZSM-5 and its effect on n-heptane cracking, in particular, propylene and dry gas selectivity. Silica was deposited on the external surface of nano ZSM-5 neutralising the acidic sites and as a result, dry gas yield was significantly decreased due to the elimination of non-selective cracking. However, the trade off with conversion was high.