The recently discovered mesoporous molecular sieve MCM-41 was synthesized, modified, and characterized and proposed as an alternative adsorbent for VOC control. The synthesis conditions for pure-silica and aluminosilicate MCM-41 were optimized as follows: 4.5Na2O:30SiO2:5.2C16H33(CH3)3N + :2500H2O and 7.5Na2O:30SiO2:xAl2O3:7.2C16H33(CH3)3N + :3500H2O (x < 1), respectively, and at 373 K for 4 days. Our studies showed that MCM-41 is not stable in the presence of water vapor. For example, a hydrothermal treatment of MCM-41 at 723 K for 2 hour resulted in 50 % of structure collapses. Again, when a template-free MCM-41 sample was exposed to air with a relative humidity of 60 % for three months, almost total pore structure collapses were observed. Adsorption equilibrium results showed that MCM-41 has a narrow pore size distribution and exhibits extraordinary pore volume compared to the classical microporous adsorbents, such as molecular sieves and activated carbons. Despite the impressive adsorption capacities of this material, the Type IV isotherm behavior requires the VOCs, in the gas phase, to be at high partial pressure. This is not the case with most industrial VOC streams. A real VOC stream requires an adsorbent with not only a high adsorption capacity but also a high adsorption affinity at a low VOC concentration. To overcome the above mentioned two problems, both the surface chemistry and the pore-opening sizes of MCM-41 were modified. To modify the surface chemistry, one has to better understand the surface chemistry. Our pioneering study of the surface chemistry of MCM-41 using FTIR, 29 Si CP/MAS NMR, pyridine-TPD, and TGA demonstrated that three types of silanol groups, i.e. single, (SiO)3Si-OH, hydrogen-bonded, (SiO)3Si-OH---OH-Si(SiO)3 and geminal, (SiO)2Si(OH)2 are distributed over the surface of MCM-41. The number of silanol groups per unit nm 2 , aOH, varies between 2.5 and 3.0 depending on the template-removal method. To improve the hydrothermal stability and enhance the hydrophobicity, the surface chemistry of MCM-41 was modified by silylation. Though both the free and hydrogen-bonded SiOH groups were found to be the active sites for adsorption of pyridine with desorption energies of 91.4 and 52.2 kJ mol -1 , respectively, only the free SiOH groups are highly accessible to the silylating agent, chlorotrimethylsilane. The surface coverage of the modifying agent was found to has a linear relationship with the surface free silanol groups which can be controlled by different heating temperatures. Modification by silyaltion can significantly improve hydrophobicity and stability. Rehydration/dehydration experiments demonstrate that the surface-silylated MCM-41 is highly tolerable to water vapor due to the complete replacement of surface-hydrophilic silanols. A novel modification method, namely selective tailoring (ST), was developed to tailor the pore-opening sizes of MCM-41 (rather than the entire pores). The novelty is that only the pore mouths at both ends of a cylindrical pore of MCM-41 was modified by deposition of some alkoxides. By doing so, the types of adsorption isotherms of VOCs can be changed from Type IV to Type I while the pore volume can be significantly preserved. This is of course significance in VOC removal since the adsorption affinity has been drastically enhanced. Adsorption equilibria and kinetics for VOCs in the pore-opening-modified MCM-41 materials were measured, modeled and compared to that of activated carbons and hydrophobic molecular sieves. The pore-modified MCM-41 has a much higher adsorption capacity than that of the traditional microporous adsorbents such as activated carbons and molecular sieves. The adsorption equilibrium data fit the Langmuir-Uniform distribution (Unilan) models very well. Upon the equilibrium parameters being obtained and considering the pore structure of our pore-modified MCM-41 adsorbents, the kinetic data were further modeled using the literature-existed models recently developed by Do and coworkers, i.e. the constant surface diffusivity macropore, surface and micropore diffusion (CMSMD) model and the macropore and surface diffusion (MSD) model. Results demonstrated that the CMSMD model can predict our kinetic uptake curves reasonably fine. Some key kinetic parameters including pore and surface diffusivities, apparent diffusivity, activation energy for adsorption, and pore tortuosity factor can be readily obtained. The porosity of the MCM-41 materials were primarily evaluated using the traditional methods based on nitrogen adsorption/desorption data. Results indicated that the BJH method always underestimates the true pore diameter of MCM-41. An comparison plot (t-plot or as-plot) method was suggested and improved. Plotting of nitrogen adsorption data at 77 K versus the statistical film thickness reveals three distinct stages, with a characteristic of two points of inflection. The steep intermediate stage is caused by capillary condensation occurred in the highly uniform mesopores. From the slope of the section after condensation, the external surface area can be obtained. Therefore, the true surface area of the mesopores is readily calculated. The linear portion of the last section is extrapolated to the adsorption axis of the comparison plot, and this intercept is used to obtain the volume of the mesopores. From the surface area and pore volume, average mesopore diameter is calculated, and the value thus obtained is in good agreement with the pore dimension obtained from powder X-ray diffraction measurements. The principle of pore size calculation, the thickness of adsorbed nitrogen film, and the problems associated with the BJH method were discussed in detail. It has been found that at a given relative pressure, the smaller the pore radius, the thicker the adsorbed film. Thermodynamics analysis established that the stability of the adsorbed film is determined by interface curvature and the potential of interaction between adsorbate and adsorbent. A semi-empirical equation is proposed to describe the state of stable adsorbed films in cylindrical mesopores. It is also shown to be useful in calculations of pore size distributions of mesoporous solids. The desorption of four representative volatile organic compounds (VOCs), i.e. n-hexane, cyclohexane, benzene, and methanol from MCM-41 were also investigated and compared with the hydrophobic zeolite, silicalite-1, using the technique of temperature programmed desorption (TPD). The desorption energies of these organics to MCM-41 were evaluated and compared with the adsorption isosteric heats. The affinity of organics to MCM-41 and silicalite-1, which represents surface hydrophobicity/hydrophilicity were studied and discussed. Results showed that only one desorption peak can be found for all organics from MCM-41, different from that from the microporous adsorbents (activated carbons and hydrophobic molecular sieves). The activation energies for desorption of non-polar molecules are slightly higher than their latent heats of evaporation, whereas the activation energy for desorption of methanol is well above its latent heat of evaporation. These results are consistent with those derived from the adsorption isotherm measurements. The very high activation energy for the desorption of methanol is due to the hydrogen bonds between methanol molecules and silanol groups over MCM-41 surfaces. The affinity of volatile organics to MCM-41 are in the order of methanol > n-hexane > benzene > cyclohexane.

Submitted by Haroudo Xavier Filho (haroudo.xavierfo@ufpe.br) on 2016-02-26T16:11:44Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) 5.-Tesis doutorado Yesmin 2015 UFPE Bibliot.pdf: 2813580 bytes, checksum: c994d000e414c2f79bd7b8711d5f2714 (MD5) / Made available in DSpace on 2016-02-26T16:11:44Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) 5.-Tesis doutorado Yesmin 2015 UFPE Bibliot.pdf: 2813580 bytes, checksum: c994d000e414c2f79bd7b8711d5f2714 (MD5) Previous issue date: 2015-06-05 / CAPES / CNPq / FACEPE / Neste trabalho, apresentamos a síntese e caracterização do material mesoporoso MCM-41 para o desenvolvimento de capacitores MOS. A motivação deste trabalho deve-se às propriedades interessantes que MCM-41 apresenta, tais como: área superficial e volume de poro grande e estrutura ordenada de poros. Inicialmente apresentamos a síntese do material mesoporoso MCM-41 pelo método Sol-Gel, e sua caracterização estrutural (DRX e IV), morfológica (MEV e TEM) e texturais (Análise de Adsorção e Dessorção de Nitrogênio), e fazemos uma comparação de resultados com o mesmo material produzido pela Sigma-Aldrich. Também foram obtidos filmes pelo método químico, que foram caracterizados por MEV e DRX e em seguida foram fabricados capacitores MOS. As medidas elétricas do capacitor MOS com dielétrico de MCM-41 foram comparadas com capacitores com dielétrico de SiO2 térmico. Os resultados mostraram uma clara diferença nas curvas de Corrente-Tensão. Conclui-se que a água confinada dentro do filme dielétrico é associada com os valores elevada de capacitância por unidade de área, estes valores permanecem altos depois do aquecimento, indicando que a resposta dielétrica é devida á água ligada ao material dielétrico, formando camadas paralelas á superfície do substrato. Capacitores de MCM-41 foram expostos a vários solventes polares e apolares, assim como á radiação gama e apresentaram distorção na resposta da capacitância e deslocamento nas curvas de corrente – tensão. Finalmente, capacitores de MCM-41 foram hidrolisados com o objetivo de aumentar a concentração dos grupos silanol na superfície do MCM-41 e como consequência alterar a capacitância do dispositivo. / In this work, we report the synthesis and characterization of MCM-41 mesoporous material for the development of devices types MOS capacitors. The motivation of this work is due to the MCM-41 interesting properties such as: surface area and pore volume large and pore ordered structure. Initially, we present a synthesis of MCM-41 mesoporous material by sol-gel method and their structural characterization (XRD and IR), morphological (SEM and TEM) and texture (Nitrogen Desorption and Adsorption Analysis) and make a comparison with the same material produced by Sigma. Also, films were obtained by chemical method, which were characterized by SEM and XRD, and then MOS capacitors were fabricated. The electrical characteristics MCM-4 MOS capacitors were compared with thermal SiO2, the results showing a clear difference in the voltage-current curves. It concludes that water confined within the dielectric film is associated with high values of capacitance per unit area these values remain high even after heating, indicating a dielectric response due to water strongly bonded to the dielectric material forming layers parallel to the substrate surface. The MCM-41 capacitors were exposed to various polar and nonpolar solvents and gamma radiation and showed good results were due to variations in the response to capacitance and the voltage-current curves showed displacement and distortion. Finally, the MCM-41 capacitors were hydrolyzed in order to be able to increase the concentration of silanol groups on the surface of MCM-41; as a consequence the material is more sensitive to moisture and therefore, the capacitance of the device response.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / The significant increase of carbon dioxide emissions in the atmosphere comes intensifying the global warming. The search for energetic source that turn emission down is of great importance, as well as the use of complementary actions like dioxide carbon capture process of the main emissions sources. From among some processes already very well-known industrially highlights chemical absorption with alkanolamine, which shows some disadvantages in being costly and generate waste derived from recovery. The use gas-solid selective in carbon dioxide adsorption has very advantages over absorption liquid amine such as easy handling without risks to the environment and recovering of adsorbent material, being possible to use industries plants with continuous flux. In this context were synthesized through hydrothermal method two materials of family M41S of type MCM-41 and MCM-48. Then the materials were impregnated with ethylenediamine by wet impregnation method. These materials were used for the carbon dioxide adsorption process and were characterized by several physic-chemical techniques. The powder X-ray diffraction patterns of the samples showed all peaks characteristics of MCM-41 and MCM-48 before and after impregnation with amines. The absorption spectrum in the infrared region showed bands due to Si-O and O-Si-O bonds in all materials and N-H bonds due to presence of amine in the supports after impregnation process. The thermogravimetric curves showed that stability of material containing amines is up to 100 °C. The materials showed N2 adsorption isotherms type IV, some with hysteresis type H1 and high surfaces areas (over 1000 m2 g-1). Carbon dioxide capture tests in flux system and atmosphere pressure showed significant drawbacks in the capture capacities of carbon dioxide for the materials impregnated with ethylenediamine in comparison to the values obtained with the MCM-41 and MCM-48 supports alone. Tests with closed system and pressure variation in the range of 0.5 to 30 bar allowed the construction of the isotherms to prepared materials of which were fitted using the Langmuir model. The results showed that the samples of MCM-41 and MCM-48 without impregnation are favorable for applications where high pressures are required. / O aumento significativo das emissões de dióxido de carbono na atmosfera vem acentuando o efeito do aquecimento global. A busca por fontes energéticas que minimizem as emissões é de grande importância, como também o uso de ações complementares como processos para captura deste gás das principais fontes emissoras. Dentre alguns processos já bem conhecidos industrialmente, destaca-se a absorção química com alcanolaminas, a qual apresenta algumas desvantagens por ser dispendiosa e gerar rejeitos da sua recuperação. O uso da adsorção gás-sólido seletiva de dióxido de carbono tem muitas vantagens sobre a absorção com aminas líquidas, tais como: fácil manipulação sem riscos ao ambiente, e recuperação do material adsorvente, podendo-se utilizar plantas industriais com fluxo contínuo. Neste contexto, foram sintetizados através do método hidrotérmico dois materiais da família M41S do tipo MCM-41 e MCM-48. Em seguida os materiais foram impregnados com etilenodiamina, através do método de impregnação por via úmida. Estes materiais foram utilizados para o processo de adsorção de dióxido de carbono e foram caracterizados por diversas técnicas físico-químicas. Os difratogramas de raios-X das amostras sintetizadas apresentaram os picos característicos do MCM-41 e do MCM-48 antes e após a impregnação com aminas. Os espectros de absorção na região do infravermelho mostraram bandas devido às ligações Si-O e O-Si-O em todos os materiais e de ligações N-H devido à presença da amina nos suportes após a impregnação. As curvas termogravimétricas mostraram que a estabilidade do material contendo aminas é de até 100 °C. Todos os materiais apresentaram isotermas de adsorção de N2 do tipo IV, alguns com histerese do tipo H1 e elevadas áreas superficiais (acima de 1000 m2 g-1). Os testes de captura de dióxido de carbono em sistema com fluxo e pressão atmosférica mostraram significativas reduções nas capacidades de captura para os materiais impregnados em comparação com os valores obtidos com os suportes MCM-41 e MCM-48. Testes com sistema fechado e variação de pressão na faixa de 0,5-30 bar permitiram o levantamento de isotermas de equilíbrio para os materiais preparados as quais foram ajustadas através do modelo de Langmuir. Os resultados mostraram que as amostras de MCM-41 e MCM-48 são favoráveis para aplicações onde altas pressões são requeridas.

La incorporación de titanio en la estructura de tamices moleculares ha dado lugar a la obtención de catalizadores altamente efectivos en procesos de oxidación selectiva. En particular, la síntesis de la zeolita de poro grande Ti-Beta y del material mesoporoso Ti-MCM-41, ha permitido ampliar el campo de aplicación de estos materiales en procesos de Química Fina ya que el mayor diámetro de poro de estas estructuras permite la oxidación de sustratos muy voluminosos para los que la Ti-Siliclita-1, único material disponible hasta el momento, era prácticamente inactiva. En el presente trabajo se ha llevado a cabo un estudio sobre la actividad catalítica de la Ti-Beta y la Ti-MCM-41 para, a partir del mismo, diseñar los procedimientos de síntesis de estos tamices moleculares de poro grande y ultragrande más adecuados para la oxidación de diferentes sustratos orgánicos tales como olefinas, alcoholes y alcanos empleando peróxidos como oxidantes. Durante el estudio se ha puesto de manifiesto la influencia de parámetros concernientes tanto al propio catalizador (composición química, carácter hidrófilo/hidrófobo) como a la propia reacción química (estructura del sustrato, tipo de oxidante, naturaleza del disolvente, ...) sobre la actividad catalítica de la zeolita Ti-Beta. Por último, se estudió la aplicación de la Ti-Beta y la Ti-MCM-41 en procesos de oxidación con un claro interés comercial como son la epoxidación de ácidos y ésteres de ácidos grasos y la epoxidación de terpenos y donde se ha observado la viabilidad de estos catalizadores como alternativas reales a los catalizadores actuales que se emplean en estos procesos / Esteve Ciudad, P. (1998). Oxidación selectiva de hidrocarburos sobre tamices moleculares de poro grande conteniendo titanio [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/5763 / Palancia

Development of Power Electronic Building Block (PEBB) modules, initiated through the Office of Naval Research (ONR), is a promising enabling technology which will promote future electrical power systems. Key in this development is the thermal design of a PEBB packaging scheme that will manage the module's high heat dissipation levels. As temperatures in electronics are closely associated with operating efficiency and failure rates, management of thermal loads is necessary to ensure proper and reliable device performance. The current work investigates the thermal design requirements for a preliminary PEBB module developed by the NSF Center for Power Electronics Systems (CPES) at Virginia Tech. This module locates four primary heat-generating devices onto a copper bonded substrate in a multi-chip module format. The thermal impact of several design variables (including heat sink quality, substrate material, device spacing, and substrate and metallization thickness) are modeled within the multi-layer thermal analysis software TAMSä. Model results are in the form of metal layer surface temperatures that closely represent the device junction temperatures. Other design constraints such as electrical and material characteristics are also considered in the thermal design. Design results indicate for the device heat dissipation levels that a low resistance heat sink coupled with a high conductivity substrate, such as aluminum nitride, are required for acceptable device junction temperatures. Substrate performance, in the form of a spreading resistance component, will be negatively affected by a lower quality heat sink. Both forced air and cold plate cooling methods were found acceptable; factors such as environment, cost and integration will determine which solution is most feasible. Maximum surface temperatures can be lowered somewhat through adjustment of device spacing. However, this reduction was small compared to the impact on parasitic capacitance. Additionally, there is some thermal benefit to thicker high-conductivity substrates, whereas lower conductivity substrates will increase the maximum surface temperature. Thicker copper layers will prove beneficial though this benefit is not as great for higher conductivity substrates. Also discussed are the on-going and future development efforts that are expected to require thermal consideration. These consist of a top-level thermal bus for additional heat removal, the use of metal matrix composites and concepts for multi-module integration. / Master of Science

[pt] A zeólita MCM-22 foi desenvolvida por pesquisadores da Mobil em 1990. É um aluminossilicato com características de peneira molecular e com amplas aplicações em processos catalíticos devido a sua estrutura de dois sistemas de canais independentes. Neste trabalho, as condições reacionais de preparação desta zeólita utilizando tratamento hidrotérmico estático e sob agitação foram estudadas. A composição molar das amostras foi mantida enquanto a temperatura e o tempo de tratamento hidrotérmico ao qual o gel foi submetido foram variados. Os materiais obtidos foram caracterizados usando técnicas analíticas de difração de raios-X com refinamento de Rietveld, adsorção física de nitrogênio (BET), espectroscopia no infravermelho, análise química (espectrometria de absorção atômica), ressonância magnética nuclear (RMN), microscopia eletrônica de varredura e de transmissão. A zeólita MCM-22 característica foi obtida apenas com tratamento hidrotérmico sob agitação. As amostras obtidas a partir do tratamento hidrotérmico estático apresentaram fases como ferrierita, ZSM-5 e quartzo. A morfologia das amostras, observada por microscopia eletrônica de varredura, varia dependendo do tratamento adotado, estático ou sob agitação. Estas diferenças refletem diretamente nas áreas específicas dos materiais. Porém, não se observou diferenças relevantes no volume de poros dos materiais sintetizados sob sistema estático, exceto a amostra obtida com 5 dias de síntese, a qual possui fase amorfa presente. Apesar das fases contaminantes presentes, a microscopia eletrônica de transmissão permite ver o crescimento dos cristais nas três direções. Através dos espectros de infravermelho pode ser observada a eliminação do direcionador orgânico e o caráter hidrofílico da zeólita após o processo de calcinação. / [en] MCM-22 zeolite was first synthesized by Mobil researchers in 1990. It is an aluminosilicate with molecular sieve characteristics and several applications in catalytic processes because of its two independent pore systems. In this work, the MCM-22 zeolite synthesis conditions were studied using both static as stirred hydrothermal treatment. Molar composition of synthesis gel was fixed while the temperature and the gel aging time were varied. The products obtained were characterized using analytical techniques of X-ray diffraction with Rietveld refining, nitrogen adsorption (BET), infrared spectroscopy, atomic emission spectrometry, nuclear magnetic ressonance spectroscopy (NMR), scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM). Typical MCM-22 zeolite was only obtained from hydrothermal treatment in stirring conditions. Samples obtained by static conditions showed contamination with ferrierita and ZSM-5 zeolites and quartz. The morphology of the samples, as showed by scanning electron micrographs, changed according the conditions of hydrothermal treatment, static or stirring. These differences affected the BET surface areas of obtained samples. However, no differences were observed in pore volume in samples obtained by static system, except the sample synthesized in 5 days, which presented an amorphous phase. Although, there were contaminant phases, transmission electron micrographs permitted to observe the crystal growing in the three directions. Trough infrared spectra it could be observed the template elimination and the zeolite hydrophilic nature after process calcination.

Les sites actifs de l’époxydation des alcènes dans les catalyseurs au titane supporté sur silice sont des ions Ti(IV) isolés. La stratégie d’isolation de site adoptée ici consiste à greffer l’isopropoxyde de titane par réaction avec les groupements silanol de surface dont la densité est diminuée par « capping » chimique remplaçant le traitement thermique usuel, très énergivore. La technique du pochoir moléculaire à motifs périodiques (PMP) a été appliquée pour forcer l’isolation de site. Dans les silices poreuses mesostructurées par un tensio-actif, c’est ce dernier, partiellement extrait, qui génère l’effet PMP lors du capping. Son élimination à l’étape suivante libère des îlots de groupements silanol sur lesquels sont greffés les ions Ti(IV). Une étude spectroscopique quantitative menée en parallèle par FT-IR et par RMN du solide du 29Si démontre que le pochoir organique inverse formé de groupement organosilyls greffés est conservé à toutes les étapes de synthèse. La spectroscopie UV en corrélation avec l’activité catalytique en époxydation du cyclohexene montent que ces surfaces originales favorisent un nombre beaucoup plus grand de sites mononucléaires isolés que les surfaces de silice non modifiées. La démonstration est faite avec une fonction de capping dipodale, 1-2-ethanebis(dimethylsilyl) (EBDMS), beaucoup plus stable que le monopodal classique, trimethylsilyl (TMS). Par ailleurs, le pochoir organique inverse issu du TMS ou de EBDMS voit sa stabilité augmentée par traitement thermique tout en préservant son effet dispersant pour le titane. Pour ce faire, un suivi quantitatif de la décomposition des organosilanes greffés a été réalisé par RMN du solide du 29Si. Finalement, une description affinée et quantitative du mode de greffage du titane a été réalisée par simulation des spectres UV sur une série de catalyseurs supposant 5 types d’espèces comprenant les sites isolés et les clusters, les derniers se différenciant par leur gamme de taille. / The active sites for epoxydation of alkenes in silica supported titanium catalysts are isolated Ti(IV) ions. The strategy for site isolation consists here to graft titanium isopropoxyde by reaction with surface silanol groups, the density of which is decreased by chemical capping instead of the energy consuming thermal treatment. The molecular stencil patterning technique (MSP) is applied to enforce site isolation. In mesostructured porous silicas, the partly extracted templating surfactant plays the role of a MSP mask during capping. Then, the elimination of the remaining surfactant liberates silanol islands for the grafting of Ti(IV) ions. Quantitative FT-IR and 29Si MAS-NMR studies reveal that the inverse organic stencil made of grafted organosilyls groups is maintained at each synthesis steps. Diffuse reflectance UV spectroscopy in correlation with the catalytic activity in epoxidation of cyclohexene show that these original surfaces favor the formation of a much larger number of isolated mononuclear sites than the unmodified silica surfaces. The demonstration is obtained using a dipodal organosilyl function, 1-2-ethanebis (dimethylsilyl) (EBDMS) that is much more stable than the classic and monopodal, trimethylsilyl (TMS). Besides, it is shown that the inverse organic stencil (from EBDMS or TMS) is stabilized further by thermal treatment while its dispersive effect on titanium can be preserved. The proof relies on a quantitative 29Si solid State NMR study. Finally, a refined description of the grafting mode of titanium was realized by simulation of the UV spectra of a large series of catalysts assuming only 5 different types of species including isolated species and clusters differentiated by the range of sizes.

ABSTRACT COMPARISON OF SORPTION CAPACITIES OF HYDROCARBONS ON DIFFERENT SAMPLES OF MCM-41 AYDOGDU, Birsu M. Sc., Department of Chemical Engineering Supervisor: Prof. Dr. Hayrettin Y&Uuml / CEL Co-Supervisor: Prof. Dr. G&uuml / rkan KARAKAS January 2013, 69 pages MCM-41(Mobil Composition Matter-41) is one of the three members of M41S family and has a highly ordered hexagonal honeycomb like structure with a narrow pore size distribution in mesopore range, high surface area, high pore volume and high thermal stability. These features make MCM-41 proper to use for adsorption, catalysis, ion exchange and separation processes. . In this study sorption capacities of C8 aromatics (o-, m-, p-xylene and ethylbenzene at 30 &deg / C, 50 &deg / C and 65 &deg / C) on a MCM-41 sample synthesized in our laboratory were determined gravimetrically by using a commercial automated electro balance system and compared with results obtained in a previous and similar MSc thesis study with a sample of different origin and characteristics / specifically low BET surface area (492 m2/g). MCM-41 sample was synthesized by hydrothermal synthesis method with cetyltrimethylammoniumbromide (CTAMBr as surfactant) and tetraethyl ortosilicate (TEOS as silica source) in basic conditions. This MCM-41 sample was calcined at 540 oC for 8 h and characterized by XRD, nitrogen adsorption at 77 K, TGA, TEM, SEM and SEM-EDX. According to XRD data, main characteristic peak for synthesized MCM-41 was obtained at 2&theta / =2.28&deg / . Three small reflection peaks can be seen at 2&theta / values of 2.59, 4.27&deg / and 4.5&deg / . XRD pattern of the MCM-41, indicated that the desired structure of MCM-41 was successfully synthesized. Surface area, pore volume and average pore diameter were obtained from the nitrogen adsorption data at 77 K as 1154 m2/g, 1.306 cm3/g and 2.75 nm respectively. TGA analysis showed that the 540 oC is proper for the calcination. SEM -EDX analysis gave an oxygen atomic concentration 66.40% and silicon atomic concentration 33.60%. These results showed that the chemical composition of the synthesize material was in almost pure SiO2 form. The adsorbed amount for all isomers at the same pressure decreased as the temperature of the adsorption isotherms increases as expected for physical adsorption. Nitrogen adsorption of MCM-41 in this study showed type IV isotherm with H2 type hysteresis loop according the IUPAC classification. However, for o-,m-, and p-xylene an approximately linear increase in the adsorbed amount as a function of relative pressure was observed from the adsorption isotherms. Except for adsorption isotherms of m-xylene and p-xylene at 65 oC all isotherms of xylenes showed hysteresis loops. Hysteresis loops narrowed down with increasing temperature. p-xylene and m-xylene adsorption isotherms at 65 oC were reversible and did not show any hysteresis loop. Ethylbenzene adsorption isotherms at 30 oC, 50 &deg / C and 65 oC also showed a linear increase in the adsorption amount as a function of relative pressure like xylenes. At 50 &deg / C and 65 oC adsorption isotherms of ethylbenzene were reversible without a hysteresis loop. For all adsorbates volume of adsorbed amounts were calculated on the assumption that they exist as saturated liquids at the isotherm temperature and found to be significantly lower than pore volume obtained from nitrogen adsorption isotherm at 77K. Sorption capacities of these hydrocarbons on MCM-41 were also very low when compared to values found in a previous study which involved a MCM-41 sample of significantly lower surface area ( 492 m2/g ). This may be attributed to structure degradation which requires further investigation.

The world&rsquo / s being alerted to the global warming danger and the depletion of fossil fuel resources, has increased the importance of the clean and renewable hydrogen energy. Bioethanol has high potential to be used as a resource of hydrogen since it is a non-petroleum feedstock and it is able to produce hydrogen rich mixture by steam reforming reactions. Discovery of mesoporous MCM-41 type high surface area silicate-structured materials with narrow pore size distributions (20-100 &Aring / ) and high surface areas (up to 1500 m2/g) opened a new avenue in catalysis research. Catalytic activity of such mesoporous materials are enhanced by the incorporation of active metals or metal oxides into their structure. Nickel and copper are among the most active metals to be used in steam reforming of ethanol to produce hydrogen. In this study, copper and nickel incorporated MCM-41 type catalytic materials were tested in the steam reforming of ethanol. Two Ni-MCM-41 samples having different Ni/Si ratios were prepared by high temperature direct synthesis method and two Cu-MCM-41 samples having same Cu/Si ratios were synthesized by two different methods namely, high temperature direct synthesis method and impregnation method. The synthesized materials characterized by XRD, EDS, SEM, N2 physisorption and TPR techniques. XRD results showed that Ni-MCM-41 and Cu-MCM-41 catalysts had typical MCM-41 structure. The d100 and lattice parameter values of Ni-HT (I) (Ni-MCM-41 sample having 0.036 Ni/Si atomic ratio) was obtained as 3.96 and 4.57 nm., respectively. In addition Ni-HT (I) was found to have a surface area of 860.5 m2/g and 2.7 nm pore diameter. The d100 and lattice parameter values for a typical Cu-MCM-41 prepared by impregnation method having Cu/Si atomic ratio of 0.19 were obtained as 3.6 and 4.2 nm., respectively. This sample also has a 631 m2/g surface area and 2.5 nm pore diameter. Steam reforming of ethanol was investigated in the vapor phase by using Ni-MCM-41 and Cu-MCM-41 catalysts between 300&deg / C and 550&deg / C. Results proved that Ni incorporated MCM-41 type catalytic materials were highly active in hydrogen production by steam reforming of ethanol and actualized almost complete ethanol conversion for Ni-MCM-41 having Ni/Si atomic ratio of 0.15 over 500&deg / C . The side products obtained during reforming are methane and formaldehyde. Although the Cu-MCM-41 samples were not as active as Ni-MCM-41, it was observed that Cu-MCM-41 catalyst synthesized by the impregnation method showed an ethanol conversion of 0.83. However, the main product was ethylene with the copper incorporated catalysts. Effects of space time, the operating conditions (reaction temperature), metal/Si ratio of the catalyst and the preparation method on the product distributions were also investigated and best reaction conditions were searched.

Noble metal incorporated MCM-41 based nanostructured mesoporous materials have attracted the attention of material researchers in recent years. Sorption characteristics of MCM materials can be improved by surface modification techniques. Besides surface modification, metal nanoparticles can also be produced within the pores of mesoporous materials. MCM-41 can act as host for several metal nanoparticles such as palladium. The present study is focused on the synthesis of Pd-MCM-41 nanocomposite catalytic materials by using different direct synthesis procedures, as well as an impregnation method. Impregnated samples were used to synthesize Pd nanoparticles inside the pores of MCM-41. In the direct hydrothermal synthesis of Pd-MCM-41, incorporation of the Pd metal was achieved by adding PdCl2, K2PdCl4 and Pd(NH3)4(NO2)3 solutions into the synthesis mixture. Syntheses were performed in acidic and basic routes. Hydrothermal synthesis was carried out in an autoclave at 120 oC. The solid product was filtered, washed, dried, calcined at 550 oC in a stream of dry air and reduced in a stream of hydrogen at 200 oC. In the case of impregnation, PdCl2 solution was added to a suspension of MCM-41. The product was evaporated to dryness, dried under vacuum and reduced with H2 gas at 200 oC. Physical and chemical properties and surface morphology of Pd-MCM-41 nanomaterials were characterized by using XRD, XPS, EDS, BET, SEM, TEM and TPR techniques. Very high Pd/Si ratios, as high as 0.45 and 0.18 were obtained in the mesoporous materials produced by the basic and acidic direct synthesis routes, respectively. The BET surface areas of these materials were found as 999 m2/g and 694 m2/g, respectively. These results showed that the basic direct synthesis procedure was highly successful for the incorporation of Pd into the mesoporous Si structure. In addition, EDS analysis of the Pd-MCM-41 materials prepared by the impregnation technique showed that Pd/Si ratios were 0.24 and 0.12 in the two samples having surface areas of 527 m2/g and 883 m2/g, respectively. In conclusion, high surface area of the material synthesized by the basic route together with a higher Pd/Si ratio makes this material more attractive for catalytic and hydrogen storage applications.