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S?ntese da mordenita a partir da Al-SBA-15 / Synthesis of mordenite from the Al-SBA-15.Valente, Tain? Dias 17 December 2015 (has links)
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Previous issue date: 2015-12-17 / In the present dissertation it was conducted the study of the synthesis of mesoporous molecular sieve Al-SBA-15 by direct synthesis in agitated reactor having the following molar ratio: 14 SiO2: 1 Al2O3: 0.235 P123: 1800 H2O. Initially, a study was done to optimize the synthesis of Al-SBA-15. Through this study, it was found that the operating conditions that resulted in the SBA-15 sample with a higher degree of ordering were gel aging time equal to 15 hours at 40 ? C and then at 100 ? C for 8 hours. These optimal conditions were used to perform scaling up to 5 gallon reactor. Samples of Al-SBA-15 were subjected to carbonization in order to fill the pores of SBA-15 with carbonaceous material and prevent the collapse of its structure. The carbonized samples were used as a source of silica for the synthesis of mordenite in dry medium using the transmission technique in the vapor phase (VPT). The purpose of this procedure was to obtain the mordenite having mesopores. For the preparation of the mordenite by VPT, several conditions were used, varying the synthesis time and form of addition of the reactants, presence or absence of an organic driver. The samples were characterized by X-ray and nitrogen adsorption. It was observed that in most of the experiments, there was no formation of mordenite phase. In the experiments in this phase was obtained, there was no significant mesoporosity training. Apparently, the presence of carbonaceous material was not sufficient to preserve the mesoporous structure of SBA-15.
Key / No presente trabalho foi realizado o estudo da s?ntese da peneira molecular mesoporosa Al-SBA-15 a partir da s?ntese direta em reator agitado apresentando a seguinte propor??o molar: 14 SiO2: 1 Al2O3: 0,235 P123: 1800 H2O. Inicialmente, foi feito um estudo visando otimizar a s?ntese da Al-SBA-15. Atrav?s deste estudo, foi verificado que as condi??es operacionais que resultaram na amostra de SBA-15 com maior grau de ordenamento foram com tempo de envelhecimento do gel de s?ntese igual a 15 horas a 40?C e depois a 100?C por 8 horas. Estas condi??es otimizadas foram utilizadas para efetuar o aumento de escala para o reator de 5 gal?es. As amostras de Al-SBA-15 foram submetidas a carboniza??o com o objetivo de preencher os poros da SBA-15 com material carbon?ceo e evitar o colapso de sua estrutura. As amostras carbonizadas foram utilizadas como fonte de s?lica para a s?ntese da mordenita em meio seco utilizando a t?cnica de transporte em fase vapor (VPT). O objetivo deste procedimento foi a obten??o de mordenita tendo mesoporos. Para o preparo da mordenita por VPT, v?rias condi??es foram utilizadas, variando o tempo de s?ntese e forma de adi??o dos reagentes, presen?a ou aus?ncia de um direcionador org?nico. As amostras obtidas foram caracterizadas por difra??o de raios X e adsor??o de nitrog?nio. Foi observado que na maioria dos experimentos n?o houve a forma??o da fase mordenita. Nos experimentos em que esta fase foi obtida, n?o foi observada forma??o de mesoporosidade significativa. Aparentemente, a presen?a de material carbon?ceo n?o foi suficiente para preservar a estrutura mesoporosa da SBA-15.
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Obtenção de materiais com estrutura hierárquica de poros através da dessilicação da Zeólita Zsm-22 / Obtaining Materials with Hierarchical Structure of Pores through Zeolite ZSM-22 DesilicationSilva, Bruno José Barros da 10 March 2017 (has links)
The present work deals with the generation of mesoporosity in ZSM-22 zeolite (TON structure). In a first part the synthesis of ZSM-22 was studied through a methodology similar to that presented by Valyocsik (1990), followed by an addition of an amphiphilic trimethoxyphenylsilane organosilane (TMPHS) in the synthesis gel, and by another substitution of 20% of the silica required for the synthesis by silanized silica beads by TMPHS. In the second part, the formation of mesoporosity by post-synthesis treatment with NaOH solution was studied, varying the concentration of 0.2, 0.4 and 0.6 mol.L-1 at a temperature of 70 °C per 1hour. The zeolites obtained were characterized by X-ray diffractometry (XRD), nitrogen adsorption at -196 °C, scanning electron microscopy (SEM), thermogravimetric analysis (ATG), absorption spectroscopy in the infrared region with Fourier transform (FT-IR) and desorption of ammonia at the programmed temperature. The catalysts that presented the best textural properties were submitted to the catalytic test with the n-hexane cracking model reaction. The diffractograms of the synthesized samples showed that they presented the main peaks referring to the TON structure, and that the desilicated samples maintained in their entirety their crystalline structure. The thermogravimetric curves presented four mass loss events, reaching values close to 10% of total loss. Infrared identified absorption bands characteristic of zeolitic materials. The micrographs of the TON-P sample showed crystal agglomerates in cylindrical form 2 μm in length. The pore diameter distribution of the desilicated samples presented a distribution in the range of 2 to 100 nm, proving one of additional mesoporosity due to the desilication process, with a higher formation of mesopores for the samples submitted to the treatments with higher OH- concentration, which caused an increase in the total acidity by the reduction of the Si/Al ratio. The desilicated samples presented a lower conversion compared to the precursor, but with higher stability in the conversion rate, with selectivity to formation of propene and isobutane. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O presente trabalho abordou a geração de mesoporosidade na zeólita ZSM-22 (estrutura TON). Numa primeira parte estudou-se a síntese da ZSM-22 via metodologia similar à apresentada por Valyocsik (1990), seguida por uma adição de um organossilano anfifílico trimetoxifenilsilano (TMPHS) no gel de síntese, e por outra via substituição de 20% da sílica requerida para a síntese por esferas de sílica nanométricas silanizadas por TMPHS. Na segunda parte estudou-se a formação de mesoporosidade por tratamento pós-síntese com solução de NaOH, variando-se a concentração de 0,2, 0,4 e 0,6 mol.L-1 à temperatura de 70°C por 1 hora. As zeólitas obtidas foram caracterizadas por difratometria de raios X (DRX), adsorção de nitrogênio à -196°C, microscopia eletrônica de varredura (MEV), análises termogravimétricas (ATG), espectroscopia de absorção na região do infravermelho com transformada de Fourier (FT-IR) e dessorção de amônia à temperatura programada. Os catalisadores que apresentaram melhores propriedades texturais foram submetidos ao teste catalítico com a reação modelo de craqueamento do n-hexano. Os difratogramas das amostras sintetizadas mostraram que estas apresentaram os principais picos referente à estrutura TON, e que as amostras dessilicadas mantiveram na sua integralidade sua estrutura cristalina. As curvas termogravimétricas apresentaram quatro eventos de perda de massa, obtendo-se valores próximos a 10% de perda total. Os infravermelhos identificaram bandas de absorção características dos materiais zeolíticos. As micrografias da amostra TON-P mostraram aglomerados de cristais em forma cilíndrica com 2 µm de comprimento. A distribuição de diâmetro de poros das amostras dessilicadas apresentaram uma distribuição na faixa de 2 a 100 nm, comprovando-se uma de mesoporosidade adicional devido ao processo de dessilicação, havendo maior formação de mesoporos para as amostras submetidas aos tratamentos com maior concentração de OH-, o que provocou um aumento na acidez total pela diminuição da razão Si/Al. As amostras dessilicadas apresentaram uma menor conversão perante a precursora, mas tendo maior estabilidade na taxa de conversão, havendo uma seletividade para formação de propeno e isobutano.
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Preparação de zeólitas mordenita com estrutura hierárquica de porosGrecco, Saulo de Tarso Figueiredo 08 1900 (has links)
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Tese_Doutorado_Saulo.pdf: 12043320 bytes, checksum: 9e747c238576b9219840bfcd38f02a2e (MD5) / FINEP, CNPq / As restrições difusionais aos reagentes, causadas pelos microporos, limitam o
uso das zeólitas no processamento de moléculas pesadas. Isto demanda o
desenvolvimento de materiais que combinem as propriedades de zeólitas com as de
materiais mesoporosos. Um número significativo de procedimentos experimentais,
pré ou pós síntese, vem sendo sugerido para a obtenção de zeólitas hierarquicamente
estruturadas. As metodologias de síntese mais bem sucedidas envolvem o uso de
agentes geradores de mesoporosidade (agentes orgânicos e nanopartículas) ou
nanomoldes (moldagem em nanoespaços), que geram sólidos com mesoporosidade
intracristalina com uma estreita distribuição de tamanho de poros; isto resulta em
sólidos contendo mesoporos, além dos microporos intrínsecos das zeólitas. Entretanto,
ainda não existem estudos sistemáticos, que permitam estabelecer o efeito das
variáveis de preparação sobre as características dos sólidos finais. A fim de superar
essa dificuldade, neste trabalho foi estudado o efeito do tempo e da temperatura de
cristalização do gel de síntese sobre as características de materiais baseados em
mordenita com estrutura hierárquica de poros. Na preparação das amostras,
adicionou-se um organossilano gerador de mesoporosidade (TPOAC, cloreto de [3-
(trimetoxissilil)propil]octadecildimetilamônio), ao gel de síntese da mordenita, que foi
cristalizado por diferentes períodos e em distintas temperaturas. Os sólidos obtidos
foram submetidos à troca iônica com cloreto de amônio e posterior calcinação, de
modo a obter a forma ácida do material. As amostras foram caracterizadas por
termogravimetria, espectroscopia no infravermelho com transformada de Fourier,
difração de raios X, análise textural por adsorção de nitrogênio, ressonância
magnética nuclear de 29Si e de 27Al, microscopia eletrônica de varredura e medidas de
acidez por dessorção de amônia à temperatura programada. Observou-se que a
formação da mordenita contendo mesoporos é influenciada pelo tempo e temperatura
de cristalização do gel da zeólita. O emprego de tempos relativamente curtos ou
baixas temperaturas favorece a formação de um sólido amorfo, enquanto longos
tempos ou elevadas temperaturas favorecem a formação de mesoporos intracristalinos
na mordenita. Por outro lado, tempos e temperaturas intermediárias favoreceram a
formação da mordenita com uma estrutura hierárquica de poros e mesoporos
desordenados. O aumento da cristalinidade da mordenita acarreta uma diminuição na
área e no volume de mesoporos, mas promove um acréscimo na área e no volume de
microporos. A área externa também tende a diminuir devido ao aumento do tamanho
do cristal da mordenita em função da cristalinidade. Os sólidos obtidos foram
susceptíveis à desaluminação durante a etapa de calcinação. A extensão da
desaluminação diminuiu com o aumento do tempo ou da temperatura de cristalização,
devido à inserção dos átomos de alumínio na rede da zeólita em formação. Porém, em
tempos de cristalização longos e temperaturas altas, pode ocorrer a redispersão dos
átomos de alumínio. Todos os sólidos apresentaram elevada acidez que aumentou
com a cristalinidade. Entretanto, nas amostras preparadas em tempos curtos e
temperaturas baixas, a maioria dos sítios apresentou força ácida moderada, enquanto
aquelas obtidas em tempos longos e temperaturas altas apresentaram maior
quantidade de sítios ácidos fortes. / The diffusion restrictions of the reactants caused by the micropores limit the
use of zeolites for processing heavy molecules. This demands for the development of
materials that can combine the properties of zeolites and of mesoporous materials. A
significant number of experimental procedures, pre or post synthesis, has been
suggested for obtaining hierarchically structured zeolites. The most successful
synthesis involve the use of mesoporosity generating agents (nanoparticles and
organic agents) or nanotemplates (templating in nanospaces), which generate solids
with intracristaline mesoporosity with a narrow pore size distribution. This results in
solids containing mesoporous besides the intrinsic zeolite micropores. However,
there is not any systematic study which allows to state the effect of crystallization
time and temperature of the synthesis gel on the properties of the final solid. In order
to overcome this difficulty, the effect of time and temperature of the synthesis gel on
the properties of mordenite-based materials with hierarchical pore structure was
studied in this work. In the samples preparation a mesoporosity generating
organosilane (TPOAC, [3-(trimethoxysilyl) propyl] octadecyldimethylammonium
chloride) was added to the synthesis gel of mordenite, which was crystallized for
different times and temperatures. The solids were then submitted to ion exchange
with ammonium chloride and further calcination to obtain the acidic form of the
zeolite. The samples were characterized by thermogravimetry, Fourier transformed
infrared spectroscopy, X-ray diffraction, textural analysis by nitrogen adsorption, 29Si
and 27Al NMR, scanning electron microscopy and acidity measurements by ammonia
desorption. It was observed that the formation of mordenite containing mesoporous is
affected by the time and temperature of crystallization of the zeolite gel. The use of
relatively short times and low temperatures favors the formation of an amorphous
solid, while long times or high temperatures favor the formation of intracristaline
mesoporosity in the mordenite. On the other hand, intermediate times and
temperatures favor the formation of mordenite with hierarchical pore structure and
disordered mesopores. The increase in mordenite crystallinity leads to a decrease in
mesopore area and volume but promotes an increase in micropore area and volume.
The external area also tends to decrease due to the increased crystal size as a function
of mordenite crystallinity. The solids obtained were susceptible to dealumination
during the calcination step. The degree of dealumination decreased with the
increasing crystallization time or temperature due to the insertion of aluminum atoms
in the zeolite lattice. However, at long crystallization times and high crystallization
temperatures the redispersion of aluminum atoms can occur. All solids showed high
acidity which increased as a function of crystallinity. However, the samples prepared
at short times and low temperatures showed the majority of moderate acid sites of
medium strength, whereas those obtained at long times and high temperatures have
more strong acid sites. Thus, intermediate times and temperatures favor the formation
of solids having zeolitic characteristics and high mesoporosity.
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Revalorización catalítica de glicerina para una obtención más respetuosa con el medio ambiente de aditivos para combustiblesGonzález Candela, Mª Dolores 14 October 2011 (has links)
Durante la fabricación del biodiesel se obtiene glicerina (o glicerol) como subproducto (10 % en peso del producto total) dando lugar a importantes excedentes. Por tanto, es necesario buscar nuevas vías de transformación de glicerina en productos de alto valor añadido. Una de las reacciones a estudiar es la eterificación de glicerol, en presencia de tert-butanol o isobuteno, para la obtención de los di- y tri-tert-butil éteres de glicerol (h-GTBE), que se pueden utilizar como aditivos oxigenados en combustibles. Por ello, en esta tesis se han preparado, modificado y caracterizado tres zeolitas, una zeolita con porosidad jerarquizada, un aerogel y un liogel de sílice, además de materiales mesoporosos ordenados para su uso como nuevos catalizadores heterogéneos ácidos activos y selectivos hacia la formación de di- y tri-tert-butil éteres de glicerol (h-GTBEs) en la reacción de eterificación de glicerol con tert-butanol o isobuteno. Otro de los objetivos importantes de esta tesis ha sido el estudio del efecto de la radiación microondas (autoclave y reflujo) en la desaluminación de tres zeolitas comerciales. La radiación microondas se ha empleado también en la sulfonación de zeolitas, materiales mesoporosos ordenados, montmorillonita K-10, aerogel y liogel sílice. La incorporación de grupos sulfónicos en estos materiales nos ha permitido obtener elevadas conversiones (100 %) y selectividades hacia los productos de interés (91 %). / There is an increasing interest in searching new processes to transform glycerol (surplus in the biodiesel manufacture) into high-added value products. In addition, the use of microwaves for the synthesis and modification of materials is becoming an important tool to reduce the synthesis time (energy saving). In this thesis, we prepared, modified and characterized three zeolites, a zeolite with hierarchical porosity, an aerogel and a liogel of silica and ordered mesoporous materials to be tested as new heterogeneous catalysts for the glycerol etherification with tert-butanol or isobutene to obtain selectively di- and tri-ethers of glycerol (h-GTBE), which can be used as fuel additives. Other important objective of this thesis was to study the effect of using microwaves during dealumination of three zeolites on their resulting surface and acidic properties and during sulfonation of zeolites, montmorillonite K-10, aerogel, and liogel of silica and ordered mesoporous materials. The incorporation of sulfonic groups into these materials resulted in higher conversion (100 %) and higher selectivity (91 %) to desired products than non-functionalized materials.
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Zéolitas ZSM-12 mesoporosas textura, cristalinidade e atividade ácida para o craqueamento de cicloexanoCarvalho, Kele Tatiane Gomes 12 September 2013 (has links)
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Previous issue date: 2013-09-12 / Universidade Federal de Sao Carlos / The research addressed the generation of mesoporosity in the zeolite ZSM-12 (MTW). In the first part we studied the synthesis of ZSM-12 via conventional methodology and in the presence of a mesopore directing agent, organosilane [3-(Trimethoxy-silyl)propyl] octadecyldimethylammonium chloride (TPOAC). It was verified to influence the TPOAC/SiO2 and H2O/SiO2 ratios and, also the aging of the reaction mixture, temperature and time of the hydrothermal treatment. In the second part we studied the formation of mesoporosity by post-synthesis treatment with alkaline solution (NaOH). For optimization of such treatment the concentration of the NaOH solution and the temperature were varied. The zeolites were characterized by X-ray diffraction, chemical analysis by energy-dispersive X-ray spectroscopy, N2 adsorption/desorption, scanning electron microscopy, nuclear magnetic resonance of 27Al, and temperature-programmed desorption of ammonia. By the analyses of X-ray diffraction and Rietveld refinement, we verified a decrease in crystallization kinetics with increasing TPOAC/SiO2 ratio and a tendency for simultaneous crystallization of MFI and MTW phases with increasing H2O/SiO2 ratio, temperature and aging time. It was possible to obtain mesoporous ZSM-12 with high purity and crystallinity with only small quantities of TPOAC and relatively long crystallization times. For ZSM-12 zeolites treated in basic medium, there was the formation of mesopores in the range from 2.9 to 23 nm due to the silicon extraction from the crystalline framework, which caused a decrease in the volume of micropores and an increase in the total acidity, assigned to the decrease in Si/Al ratio. In the cracking of cyclohexane at 400 °C, although the presence of mesoporosity had caused a decrease in the total acidity, the zeolites synthesized with TPOAC showed similar conversions to conventional zeolite with minimal catalytic deactivation, which was attributed to the better mass transfer and less coke formation. The ZSM-12 zeolites treated with NaOH exhibited activity and stability similar to those obtained in the presence of TPOAC. By its higher proportion of strong acid sites, the conventional ZSM-12 zeolite showed higher hydrocarbon yields in the range from C2 to C4 in comparison with the mesoporous zeolites, with the latter showing a higher yield for C6 hydrocarbons. / A pesquisa abordou a geração de mesoporosidade na zeólita ZSM-12 (MTW). Numa primeira parte estudou-se a síntese da ZSM-12 via metodologia convencional (hidrotérmica) e na presença de um agente direcionador de mesoporos, o organossilano cloreto de 3-(trimetoxi-silil)propil-octadecildimetil amônio (TPOAC). Verificou-se a influência das razões TPOAC/SiO2 e H2O/SiO2 e, também, da temperatura, tempo de envelhecimento da mistura reacional e tempo de tratamento hidrotérmico. Na segunda parte estudou-se a formação de mesoporosidade por tratamento pós-síntese com solução alcalina (NaOH). Para a otimização desse tratamento, variou-se a concentração da solução de NaOH e a temperatura. As zeólitas obtidas foram caracterizadas por difratometria de raios X, análise química por espectroscopia de energia dispersiva de raios X, fisissorção de N2, microscopia eletrônica de varredura, ressonância magnética nuclear do 27Al e dessorção de amônia à temperatura programada. Pelas análises de difratometria de raios X e refinamento de Rietveld, verificou-se um decréscimo da cinética de cristalização com o aumento da razão TPOAC/SiO2 e uma tendência à cristalização simultânea das fases MTW e MFI com o aumento da razão H2O/SiO2, da temperatura e do tempo de envelhecimento. Foi possível obter ZSM-12 mesoporosa com alta pureza e cristalinidade somente com pequenas quantidades de TPOAC e tempos de cristalização relativamente longos. Para as zeólitas ZSM-12 tratadas em meio básico, houve a formação de mesoporos na faixa de 2,9 a 23 nm devido à extração de silício da rede cristalina, o que provocou uma diminuição do volume de microporos e um aumento da acidez total pela diminuição da razão Si/Al. No craqueamento de cicloexano em fase gasosa a 400 °C, as zeólitas sintetizadas com TPAOC, embora a presença de mesoporosidade tenha provocado uma diminuição na acidez total, apresentaram conversões semelhantes às da zeólita convencional com mínima desativação catalítica, o que foi atribuído à boa transferência de massa e menor formação de coque. As zeólitas ZSM-12 tratadas com NaOH exibiram atividade e estabilidade similares às obtidas na presença de TPOAC. Pela sua maior proporção de sítios ácidos fortes, a zeólita ZSM-12 convencional apresentou rendimentos maiores a hidrocarbonetos C2 a C4 do que as zeólitas contendo mesoporos, com estas últimas apresentando maior rendimento a hidrocarbonetos C6.
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Nanostructured Porous High Surface Area Ceramics for Catalytic ApplicationsKrawiec, Piotr 30 January 2007 (has links) (PDF)
In the present work new methods were developed for preparation of novel nanosized and nanostructured ceramic materials. Ordered mesoporous silica SBA-15 was found to be useful as a hard template for the nanocasting of silicon carbide and allowed the preparation of high temperature stable mesoporous silicon carbide ceramics. Chemical vapor infiltration of SBA-15 with dimethyldichlorosilane at elevated temperatures yields SiC/SBA-15 nanocomposites. The subsequent HF treatment of those composites resulted in silica removal and preparation of mesoporous silicon carbide with surface areas between 410 and 830 m2g-1 and high mesopore volume (up to 0.9 cm3g-1). The pore size (between 3 and 7nm in diameter) and surface area of mesoporous silicon carbide were controlled by adjusting the infiltration conditions (time, atmosphere). The mesoporous silicon carbide prepared via this method showed high structural thermal stability at 1300 oC, exceeding that of the SBA-15 template. However, the ordering on the mesoscopic scale was low. Nevertheless, highly ordered mesoporous silicon carbide materials were obtained via polymer melt infiltration in SBA-15. The low molecular weight polycarbosilane used as a preceramic precursor was converted at 1300 oC to silicon carbide inside the SBA-15, and after subsequent silica removal by HF, a highly ordered mesoporous material was obtained. Ordered mesoporous silicon carbide prepared by the methods reported here, may be an interesting material as a support due to its high temperature stability, chemical inertness, high thermal conductivity and semiconductor properties. In contrast to the nanocasting approach, based on the complete pore filling, also a new in-situ procedure for the preparation of finely dispersed metal and metal oxide particles inside ordered mesoporous silica was developed. A swelling agent (toluene) was used to deliver a hydrophobic platinum precursor into the surfactant micelles before addition of silica source. Such an in-situ method resulted in very high platinum incorporation (80-100%), not achieved for any other in-situ preparation procedures. Additionally, the presence of platinum allowed to decrease the template removal temperatures. Moreover, the method was also extended to other metal or metal oxide/ordered mesoporous silica systems. This may be especially interesting for the preparation of ordered mesoporous materials with low melting points, where typically the structure collapses during the high temperature calcinations process. The in-situ synthesized V2O5/MCM-41 materials were used to prepare VN/MCM-41 composites via nitridation in ammonia at 800oC. This method allowed to prepare highly dispersed, X-ray amorphous vanadium nitride species, with high activity in the propane dehydrogenation. Compared to nitridation of supported vanadium oxide prepared via the ex-situ procedure, in-situ synthesized materials showed similar catalytic activity, in spite of having significantly lower vanadium loading. As an alternative for the preparation of supported nitride materials, a novel preparation procedure of bulk not supported nanocrystalline vanadium nitride with high surface area was presented. Instead of pure oxide powder (which was typically used in the preparation of high surface area vanadium nitride catalysts), a macroporous amine intercalated V2O5 was used as the starting material. The obtained nitride consisted of small crystallites and had a surface area up to 198 m2g-1. Moreover, this foam-derived VN showed significantly improved activity as a catalyst in propane dehydrogenation. This novel preparation method could also be extended to other systems such as ternary VMoxNy nitrides.
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Nanostructured Porous High Surface Area Ceramics for Catalytic ApplicationsKrawiec, Piotr 20 December 2006 (has links)
In the present work new methods were developed for preparation of novel nanosized and nanostructured ceramic materials. Ordered mesoporous silica SBA-15 was found to be useful as a hard template for the nanocasting of silicon carbide and allowed the preparation of high temperature stable mesoporous silicon carbide ceramics. Chemical vapor infiltration of SBA-15 with dimethyldichlorosilane at elevated temperatures yields SiC/SBA-15 nanocomposites. The subsequent HF treatment of those composites resulted in silica removal and preparation of mesoporous silicon carbide with surface areas between 410 and 830 m2g-1 and high mesopore volume (up to 0.9 cm3g-1). The pore size (between 3 and 7nm in diameter) and surface area of mesoporous silicon carbide were controlled by adjusting the infiltration conditions (time, atmosphere). The mesoporous silicon carbide prepared via this method showed high structural thermal stability at 1300 oC, exceeding that of the SBA-15 template. However, the ordering on the mesoscopic scale was low. Nevertheless, highly ordered mesoporous silicon carbide materials were obtained via polymer melt infiltration in SBA-15. The low molecular weight polycarbosilane used as a preceramic precursor was converted at 1300 oC to silicon carbide inside the SBA-15, and after subsequent silica removal by HF, a highly ordered mesoporous material was obtained. Ordered mesoporous silicon carbide prepared by the methods reported here, may be an interesting material as a support due to its high temperature stability, chemical inertness, high thermal conductivity and semiconductor properties. In contrast to the nanocasting approach, based on the complete pore filling, also a new in-situ procedure for the preparation of finely dispersed metal and metal oxide particles inside ordered mesoporous silica was developed. A swelling agent (toluene) was used to deliver a hydrophobic platinum precursor into the surfactant micelles before addition of silica source. Such an in-situ method resulted in very high platinum incorporation (80-100%), not achieved for any other in-situ preparation procedures. Additionally, the presence of platinum allowed to decrease the template removal temperatures. Moreover, the method was also extended to other metal or metal oxide/ordered mesoporous silica systems. This may be especially interesting for the preparation of ordered mesoporous materials with low melting points, where typically the structure collapses during the high temperature calcinations process. The in-situ synthesized V2O5/MCM-41 materials were used to prepare VN/MCM-41 composites via nitridation in ammonia at 800oC. This method allowed to prepare highly dispersed, X-ray amorphous vanadium nitride species, with high activity in the propane dehydrogenation. Compared to nitridation of supported vanadium oxide prepared via the ex-situ procedure, in-situ synthesized materials showed similar catalytic activity, in spite of having significantly lower vanadium loading. As an alternative for the preparation of supported nitride materials, a novel preparation procedure of bulk not supported nanocrystalline vanadium nitride with high surface area was presented. Instead of pure oxide powder (which was typically used in the preparation of high surface area vanadium nitride catalysts), a macroporous amine intercalated V2O5 was used as the starting material. The obtained nitride consisted of small crystallites and had a surface area up to 198 m2g-1. Moreover, this foam-derived VN showed significantly improved activity as a catalyst in propane dehydrogenation. This novel preparation method could also be extended to other systems such as ternary VMoxNy nitrides.
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SOFT-TEMPLATING SYNTHESIS OF MESOPOROUS SILICA-BASED MATERIALS FOR ENVIRONMENTAL APPLICATIONSGunathilake, Chamila Asanka 19 April 2017 (has links)
No description available.
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