Academic literature on the topic 'Amorphous silica-alumina'
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Journal articles on the topic "Amorphous silica-alumina"
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Sri Rahayu, Endang, Gatot Subiyanto, Arief Imanuddin, Wiranto, Sabrina Nadina, Rista Ristiani, Suhermina, and Endang Yuniarti. "Kaolin as a Source of Silica and Alumina For Synthesis of Zeolite Y and Amorphous Silica Alumina." MATEC Web of Conferences 156 (2018): 05002. http://dx.doi.org/10.1051/matecconf/201815605002.
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Kaolin is the clay mineral which containing silica (SiO2) and alumina (Al2O3) in a high percentage, that can be used as a nutrient in the synthesis of zeolites and amorphous silica alumina (ASA). The objective of this research is to convert the Belitung kaolin into silica and alumina as nutrients for the synthesis of zeolites and amorphous silica alumina, which are required in the preparation of the catalysts. Silica and alumina contained in the kaolin were separated by leaching the active kaolin called as metakaolin, using HCL solution, giving a solid phase rich silica and a liquid phase rich alumina. The solid phase rich silica was synthesized to zeolite Y by adding seed of the Y Lynde type, through the hydrothermal process with an alkaline condition. While, the liquid phase rich alumina was converted into an amorphous silica alumina through a co precipitation method. Characterization of zeolite and ASA were done using XRD, surface area and pore analyzer and SEM. The higher of alumina in liquid phase as a result of the rising molar of HCL in the leaching process was observed, but it didn’t work for its rising time. Products of ASA and zeolite Y were obtained by using liquid phase rich alumina and solid phase rich silica, respectively, which resulted through leaching metakaolin in 2.5 M HCl at temperature of 100° C for 2 hours.
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Mellowes, J. W., C. M. Chun, and I. A. Aksay. "Amorphous silica coating on α-alumina particles." Proceedings, annual meeting, Electron Microscopy Society of America 53 (August 13, 1995): 210–11. http://dx.doi.org/10.1017/s0424820100137422.
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Mullite (3Al2O32SiO2) can be fabricated by transient viscous sintering using composite particles which consist of inner cores of a-alumina and outer coatings of amorphous silica. Powder compacts prepared with these particles are sintered to almost full density at relatively low temperatures (~1300°C) and converted to dense, fine-grained mullite at higher temperatures (>1500°C) by reaction between the alumina core and the silica coating. In order to achieve complete mullitization, optimal conditions for coating alumina particles with amorphous silica must be achieved. Formation of amorphous silica can occur in solution (homogeneous nucleation) or on the surface of alumina (heterogeneous nucleation) depending on the degree of supersaturation of the solvent in which the particles are immersed. Successful coating of silica on alumina occurs when heterogeneous nucleation is promoted and homogeneous nucleation is suppressed. Therefore, one key to successful coating is an understanding of the factors such as pH and concentration that control silica nucleation in aqueous solutions. In the current work, we use TEM to determine the optimal conditions of this processing.
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Barthomeuf, D. "Amorphous silica alumina debris in zeolites and zeolitic-type clusters in amorphous silica-alumina catalysts." Zeolites 10, no. 2 (February 1990): 131–33. http://dx.doi.org/10.1016/0144-2449(90)90031-l.
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Hensen, Emiel J. M., Dilip G. Poduval, Volkan Degirmenci, D. A. J. Michel Ligthart, Wenbin Chen, Françoise Maugé, Marcello S. Rigutto, and J. A. Rob van Veen. "Acidity Characterization of Amorphous Silica–Alumina." Journal of Physical Chemistry C 116, no. 40 (October 2, 2012): 21416–29. http://dx.doi.org/10.1021/jp309182f.
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Maggard, Jeffrey G., N. David Theodore, and C. Barry Carter. "The behavior of an α-alumina twist grain-boundary in the presence of silica." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 4 (August 1990): 378–79. http://dx.doi.org/10.1017/s0424820100175028.
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Grain boundaries and polyphase boundaries can control the electrical, optical, and mechanical properties of many ceramic materials. The study of such boundaries is therefore essential for understanding these materials. Some studies of grain boundaries in alumina have reported a thin layer of amorphous intergranular material coating nearly all boundaries while others question this interpretation. The quality and structure (crystalline or amorphous) of an intentionally-added siliceous intergranular phase has been found to affect the mechanical properties of polycrystalline α-alumina and tetragonal zirconia. It is therefore of interest to examine the behavior of various α-alumina grain boundaries in the presence of controlled amounts of amorphous silica. A recent study characterized the behavior of low-angle [0001] twist boundaries in the presence of silica which had been intentionally incorporated during the course of grain boundary fabrication. The present study is aimed at characterizing the behavior of low-angle rhombohedral (102) twist boundaries under similar conditions.Single crystal wafers of α-alumina were mechanically polished parallel to the (102) plane. Silica was deposited to a thickness of 260Å on one of the wafers using plasma deposition. The silica-coated wafers were then placed face-to-face with clean, uncoated wafers and pressure-sintered at 1980°C for 3 hours. The temperature was chosen to lie above the melting point of silica and below that of alumina. A low pressure (∼50 psi) was used to hold the wafers together. The pressure and furnace heating and cooling cycles had to be carefully controlled to prevent fracture of the crystals.
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Triani, Desak Nyoman Deasi, Januarti Jaya Ekaputri, Triwulan, Setyo Hardono, and Tri Eddy Susanto. "Application of Pozzolan as Materials of Geopolymer Paste." Materials Science Forum 841 (January 2016): 111–17. http://dx.doi.org/10.4028/www.scientific.net/msf.841.111.
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This research use metakaolin and clay containing amorphous silica and alumina after calcination at 700°C. Mechanical properties and fire resistance of geopolymer paste increase as the ratio of silica to alumina. Mix design composition on this research based on the ratio of silica to alumina. The ratio of silica to alumina for metakaolin paste are 1.4 and 1.8. While for clay paste the ratio that used are 2.8 and 3.2. Na2SiO3 and NaOH with 10 M and 8 M were used as alkali activator at this research. Based on analysis the effect of increasing the ratio of silica to alumina increase fire resistance ability for both metakaolin and clay. However initial compressive strength is effected not only by ratio of silica to alumina but also the ratio of water to solid and SiO2/Na2O. The compressive strength decrease as the ratio of water to solid increases. Meanwhile compressive strength increase as the ratio of SiO2/Na2O increase.
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Beh, Gein Khai, Chang Ting Wang, Kyungduk Kim, Jiangtao Qu, Julie Cairney, Yun Hau Ng, Alicia Kyoungjin An, Ryong Ryoo, Atsushi Urakawa, and Wey Yang Teoh. "Flame-made amorphous solid acids with tunable acidity for the aqueous conversion of glucose to levulinic acid." Green Chemistry 22, no. 3 (2020): 688–98. http://dx.doi.org/10.1039/c9gc02567g.
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Composition-tunable mixed Brønsted/Lewis acids on silica-alumina and silica-alumina-phosphate prepared by the rapid flame spray pyrolysis produce exceptionally high glucose-to-levulinic acid yield, twice that of commercial ZSM-5 and Zeolite X.
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Freitas, A. A., R. L. Santos, R. Colaço, R. Bayão Horta, and J. N. Canongia Lopes. "From lime to silica and alumina: systematic modeling of cement clinkers using a general force-field." Physical Chemistry Chemical Physics 17, no. 28 (2015): 18477–94. http://dx.doi.org/10.1039/c5cp02823j.
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Wulandari, Futri, Eka Putra Ramdhani, Yatim Lailun Ni’mah, Ahmad Anwarud Dawam, and Didik Prasetyoko. "Synthesis of Amorphous Aluminosilicates from Bintan’s Red Mud as Alumina Source." Indonesian Journal of Chemistry 18, no. 4 (November 12, 2018): 580. http://dx.doi.org/10.22146/ijc.25184.
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Red mud is a generated by-product in alumina production from bauxite ore. In this study, Bintan’s red mud has been used as alumina and silica source to synthesize amorphous mesoporous aluminosilicates material. Alkali fusion method with a NaOH/red mud ratio 0.8; 1.0; 1.2; 1.4 and 1.5 followed by hydrolysis method was used to extract dissolved alumina and silica from red mud. Synthesis of amorphous aluminosilicates by hydrothermal method was conducted at 80 °C for 24 h. Cetyltrimethylammonium bromide (CTABr) was added as the structure directing agent. Aluminosilicate products were characterized using FTIR spectroscopy (Fourier Transform Infra-Red Spectroscopy), XRD (X-ray Diffraction), SEM (Scanning Electron Microscopy), and nitrogen adsorption-desorption. XRD and SEM result shows that the product was amorphous with low uniformity in terms of surface morphology and particle size. Nitrogen adsorption-desorption profile shows that all aluminosilicates products has a meso pore structure, confirmed by the highest pore distribution at 3.05–17.70 nm. The highest surface area and pore volume were obtained in ASM 0.8 (NaOH/red mud ratio = 0.8) i.e. 177.97 m2/g and 1.09 cm3/g, respectively.
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Chraska, T., J. Hostomsky, M. Klementova, and J. Dubsky. "Crystallization Kinetics of Amorphous Alumina-Zirconia-Silica Ceramics." Microscopy and Microanalysis 15, S2 (July 2009): 1000–1001. http://dx.doi.org/10.1017/s1431927609095397.
Full textDissertations / Theses on the topic "Amorphous silica-alumina"
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Agulló, Pastor Javier. "1-butene isomerisation over amorphous silica-alumina." Thesis, University of Aberdeen, 2012. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=189659.
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The dehydroxylation process of pseudo-boehmite to yield acidic amorphous silica-alumina has been investigated by increasing the temperature of the sample and recording DRIFTS spectra of its surface and monitoring the water released with an on-line mass spectrometer. The Brønsted and Lewis acid sites density of amorphous silica-alumina has been determined by IR-spectrometry of adsorbed pyridine and using molar extinction coefficients specific for this system for silica-alumina samples calcined at different temperatures. The deactivation profiles of 1-butene isomerisation (double-bond migration) over amorphous silica-alumina samples calcined at different temperatures have been acquired by using a fixed bed laboratory reactor coupled to a gas chromatograph with an automated sampling valve. The initial activities of amorphous silica-alumina calcined at different temperatures correlated with the Brønsted acid site density of the samples. The deactivation profiles are consistent with a reversible rehydration deactivation mechanism involving both Brønsted and Lewis acid sites and simultaneous to an irreversible deactivation mechanism involving Lewis acid sites. Brønsted acid sites are considered to be the active sites of the reaction, whereas part of the Lewis acid sites is converted into Brønsted acid sites by rehydration.
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Brinen, Jeffrey Lawrence. "The effects of nickel on an amorphous silica-alumina cracking catalyst." Thesis, Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/12060.
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Maselosne, Molladi Andrew. "Dimerization of naphtha-range Fischer-Tropsch olefins into diesel-range products over zeolite H-ZSM-5 and amorphous silica-alumina." Master's thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/11097.
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Includes abstract.Includes bibliographical references.
In this study, the dimerization of 1-hexene and 1-octene (as model compounds for Fischer-Tropsch naphtha-range olefins) into diesel-range olefins was carried out in a tubular, continuous flow fixed-bed reactor, in the liquid phase, over zeolite H-ZSM-5 and an amorphous silica-alumina (ASA) catalyst. Both catalysts were in the form of extrudates.
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Jin, Xiaojing. "Preparation of amorphous silica-aluminas with enhanced acidic properties and spectroscopic identification of their acid sites." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066355/document.
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Des silice-alumines (SA) avec des propriétés acides améliorées et une fraction plus élevée d’aluminium acides ont été préparées en utilisant deux stratégies de synthèse. Leurs propriétés texturales ont été étudiées par physisorption de N2 et leurs propriétés acides par suivi FTIR de l’adsorption de molécules sondes (pyridine ou CO). Par ailleurs, la réaction d’isomérisation du 33DMB1 a été utilisée pour caractériser leurs performances catalytiques et leurs propriétés acides. La première stratégie de synthèse a été de désaluminer des silice-alumines commerciales avec de l’acetylacetone ou de l’acide citrique (CA). CA est plus actif et plus sélectif que Acac et permet de retirer jusqu’à 87% des Al initialement présents tout en augmentant la quantité de sites acides (jusqu’à 41%) et en multipliant par 5 la fraction d’Al acides. La seconde stratégie a été de greffé des précurseurs d’aluminium (Al(OPri)xL3-x, TIBA, DiBAH) sur des silices. Toutes les SA obtenues par greffage présentent une activité catalytique plus élevées que les SA commerciales et la zéolithe, mais seules certaines de SA obtenues par greffage de DiBAH ont des sites acides de Bronsted forts. Des SA représentatives de ces deux séries ont été caractérisées par RMN, avec comme objectif d’étudier la structure des sites acides en utilisant des séquences RMN 1D et 2D, homo- et héteronucléaires impliquant 1H et 27Al. Cette étude a mis en évidence: (i) la présence, pour la plupart des SA, de deux phases, l’une d’alumine, l’autre de silice alumine (27Al DQ-SQ NMR); (ii) une localisation des atomes d’Al près de la surface sur la base de leur flexibilité de coordination 27Al NMR (DP and 3Q MAS); (iii) l’implication possible des AlV (en plus des AlIV) dans les sites acides de Bronsted (27Al-1H D-HMQC 2D NMR); (iv) la probable différence de structure des sites acides des SA par rapport à ceux des zéolithes (1H-27Al REAPDOR)ASAs with enhanced acidity and a higher fraction of acidic Al were prepared by two experimental strategies. Their textures have been investigated by N2 adsorption–desorption and their acidic properties by FTIR of adsorbed probe molecule (pyridine or CO). Besides, isomerization of 33DMB1 was selected as model reaction to check their activity and characterize their acidity. The first strategy is based on dealumination of commercial ASAs with acetylacetone (Acac) or citric acid (CA). CA is superior to Acac for selective dealumination. It allows removing up to 87% of Al, increases total acidity up to 41%, and fraction of acidic Al by a 5 fold factor. The second strategy is based on the grafting Al precursor (Al(OPri)xL3-x, TIBA, DiBAH) on silica. All the grafted ASAs display better performance for 33DMB1 isomerization than commercial ASA and zeolite, but strong Brønsted acid sites are observed solely for some DiBAH derived samples. Representative samples of these two series were selected as model ASAs for advanced NMR characterization, with the purpose to investigate the structure of acid sites by a combination of one and two-dimensional homo- and heteronuclear 1H and 27Al NMR. On most ASAs, two separate phases are present: alumina and silica-alumina (27Al DQ-SQ NMR). Localization of most of the Al atoms was evidenced based on the flexibility of their coordination (27Al NMR DP and 3Q MAS). Brønsted acidity may be associated with both AlIV and AlV (27Al-1H D-HMQC 2D NMR) but the structure of these sites is probably different from those of zeolites (1H-27Al REAPDOR)
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Jin, Xiaojing. "Preparation of amorphous silica-aluminas with enhanced acidic properties and spectroscopic identification of their acid sites." Electronic Thesis or Diss., Paris 6, 2017. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2017PA066355.pdf.
Full textAbstract:
Des silice-alumines (SA) avec des propriétés acides améliorées et une fraction plus élevée d’aluminium acides ont été préparées en utilisant deux stratégies de synthèse. Leurs propriétés texturales ont été étudiées par physisorption de N2 et leurs propriétés acides par suivi FTIR de l’adsorption de molécules sondes (pyridine ou CO). Par ailleurs, la réaction d’isomérisation du 33DMB1 a été utilisée pour caractériser leurs performances catalytiques et leurs propriétés acides. La première stratégie de synthèse a été de désaluminer des silice-alumines commerciales avec de l’acetylacetone ou de l’acide citrique (CA). CA est plus actif et plus sélectif que Acac et permet de retirer jusqu’à 87% des Al initialement présents tout en augmentant la quantité de sites acides (jusqu’à 41%) et en multipliant par 5 la fraction d’Al acides. La seconde stratégie a été de greffé des précurseurs d’aluminium (Al(OPri)xL3-x, TIBA, DiBAH) sur des silices. Toutes les SA obtenues par greffage présentent une activité catalytique plus élevées que les SA commerciales et la zéolithe, mais seules certaines de SA obtenues par greffage de DiBAH ont des sites acides de Bronsted forts. Des SA représentatives de ces deux séries ont été caractérisées par RMN, avec comme objectif d’étudier la structure des sites acides en utilisant des séquences RMN 1D et 2D, homo- et héteronucléaires impliquant 1H et 27Al. Cette étude a mis en évidence: (i) la présence, pour la plupart des SA, de deux phases, l’une d’alumine, l’autre de silice alumine (27Al DQ-SQ NMR); (ii) une localisation des atomes d’Al près de la surface sur la base de leur flexibilité de coordination 27Al NMR (DP and 3Q MAS); (iii) l’implication possible des AlV (en plus des AlIV) dans les sites acides de Bronsted (27Al-1H D-HMQC 2D NMR); (iv) la probable différence de structure des sites acides des SA par rapport à ceux des zéolithes (1H-27Al REAPDOR)ASAs with enhanced acidity and a higher fraction of acidic Al were prepared by two experimental strategies. Their textures have been investigated by N2 adsorption–desorption and their acidic properties by FTIR of adsorbed probe molecule (pyridine or CO). Besides, isomerization of 33DMB1 was selected as model reaction to check their activity and characterize their acidity. The first strategy is based on dealumination of commercial ASAs with acetylacetone (Acac) or citric acid (CA). CA is superior to Acac for selective dealumination. It allows removing up to 87% of Al, increases total acidity up to 41%, and fraction of acidic Al by a 5 fold factor. The second strategy is based on the grafting Al precursor (Al(OPri)xL3-x, TIBA, DiBAH) on silica. All the grafted ASAs display better performance for 33DMB1 isomerization than commercial ASA and zeolite, but strong Brønsted acid sites are observed solely for some DiBAH derived samples. Representative samples of these two series were selected as model ASAs for advanced NMR characterization, with the purpose to investigate the structure of acid sites by a combination of one and two-dimensional homo- and heteronuclear 1H and 27Al NMR. On most ASAs, two separate phases are present: alumina and silica-alumina (27Al DQ-SQ NMR). Localization of most of the Al atoms was evidenced based on the flexibility of their coordination (27Al NMR DP and 3Q MAS). Brønsted acidity may be associated with both AlIV and AlV (27Al-1H D-HMQC 2D NMR) but the structure of these sites is probably different from those of zeolites (1H-27Al REAPDOR)
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Wang, Zichun. "Catalytic conversion of biomass- and petrochemical-derived model compounds over acidic catalysts." Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/13679.
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Silica-aluminas (SA) as solid acids are widely used in the chemical, food, pharmaceutical and petrochemical and bio-refining industries. Their acidic properties depend on their local structure. For the first time, the presence of large amount of surface available AlV species on amorphous SA (ASA) was revealed by 27Al MQMAS NMR spectroscopy in this thesis. These AlV species can enhance the strength of neighboring SiOH groups evidenced by 1H-27Al D-HETCOR. Indeed, significantly enhancing the acidity of ASA at the same Al loading was achieved via increasing AlV concentration by applying higher combustion enthalpy solvent. In H/D exchanged with benzene-d6, ASA exhibited 4 times lower activation energy compared to zeolite H-ZSM-5, which was due to the assistance of AlV species. In the conversion of phenylglyoxal to ethyl mandelate, the performance of ASA correlated well with the enhanced Brønsted acidity, confirmed by using silica-zirconia catalyst. At the same conditions, ASA obtained a 10 times higher TOF than dealuminated zeolite HY. This was attributed to the free diffusion of molecules on ASA surface, confirmed by using [Al]MCM-41. Selective dehydration of glycerol on solid acids is important for the production of the value-added acrolein for sustainable bio-refinery. Most efforts focus on developing strong BAS to improve the acrolein production, since LAS produce by-product acetal. With Al-exchange zeolite H-ZSM-5, the significant increase of the acrolein yield was achieved via the cooperative dehydration between the BAS and LAS. In chemoselective hydrogenation of acetophenone, the selectivity was influenced by electronic properties of noble metal, indicated by FTIR investigation. Solid-state NMR spectroscopy studies revealed electronic properties depends on the strength of BAS covered by metal nanoparticles. Increasing the number of uncovered BAS on the supports can improve the performance of supported metal catalyst with similar product selectivity.
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Arancon, Rick Arneil. "Exploration of Transition Metal Sulfide Catalysts Prepared by Controlled Surface Chemistry." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEN063.
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L'hydrotraitement est un procédé catalytique important dans le raffinage du pétrole qui utilise des catalyseurs bimétalliques sulfurés NiWS ou NiMoS (ou CoMoS) supportés sur alumine. Leur mode conventionnel de préparation implique l’imprégnation d'une solution aqueuse de sels de Mo/W et de Ni/Co, puis l’activation par un agent sulfo-réducteur (H2S/H2). Pour répondre aux exigences environnementales et améliorer l'efficacité de l'hydrotraitement, des améliorations permanentes de la performance de ces systèmes catalytiques sont attendues. Ce travail se concentre sur la préparation de catalyseurs d'hydrotraitement hautement actifs par une approche de chimie de surface contrôlée (CSC) qui implique l'imprégnation successive de précurseurs moléculaires de MoV et NiII en solvant organique sur un support silice-alumine traité thermiquement. Dans la première partie de cette thèse, la genèse de la phase active du catalyseur CSC et conventionnel Mo et NiMo est étudiée par quick-XAS combinée à d’autres techniques (chimiométrie, XPS, RPE, STEM-HAADF, modélisation moléculaire). Nous proposons ainsi des structures moléculaires depuis les précurseurs oxydes de Mo et Ni supportés jusqu’aux nombreuses espèces intermédiaires (oxysulfure et sulfures) en fonction de la température. Cette analyse multi-technique permet d'abord de révéler les spécificités de la genèse des catalyseurs CSC et conventionnels qui peuvent expliquer leurs différentes activités catalytiques. Ensuite, elle révèle également de nouvelles connaissances sur les mécanismes d’insertion du Ni dans la phase NiMoS en fonction de la préparation. Dans la seconde partie, la possibilité de remplacer Co et Ni comme promoteurs est explorée. Ceci est entrepris en synthétisant des catalyseurs alternatifs de type XYMoS, où X et Y sont des métaux de transition 3d. Comme suggéré par des études de modélisation quantiques antérieures, certaines formulations XYMoS peuvent présenter un effet de synergie analogue à ceux des phases actives CoMoS et NiMoS. L’étude des formulations les plus prometteuses méritent d'être approfondies afin de mieux comprendre leur fonctionnementHydrotreating is an important catalytic process in petroleum refining which uses sulfided bimetallic catalysts NiWS or NiMoS (or CoMoS) supported on alumina. Their conventional preparation involves an incipient wetness impregnation of an aqueous solution of Mo/W and Ni/Co salts, and then activation by a sulfo-reductive agent (such as H2S/H2). To meet environmental regulations and improve the energy efficiency of hydrotreatment, permanent improvements on the performance of these catalytic systems are expected. This work is thus focused on the preparation of highly active hydrotreating catalysts through a controlled surface chemistry (CSC) approach; which involves the successive impregnation of Mo5+ and Ni2+ molecular precursors in an organic solvent on a thermally treated silica-alumina support. In the first part of this thesis, the active phase genesis of CSC and conventional Mo and NiMo catalysts is studied by in situ quick-XAS combined with various other techniques (chemometrics, XPS, EPR, STEM-HAADF, molecular modeling). We thus propose molecular structures from the oxide of supported Mo and Ni precursors up to the numerous intermediate sulfided species as a function of temperature. This multi-technique analysis enables first to reveal the specific features of the genesis of CSC and conventional catalysts which may explain their different catalytic activities. Then, it also reveals new insights into the mechanisms of Ni promoter incorporation into the NiMoS phase as a function of the preparation. In the second part, the feasibility of replacing Co and Ni as promoters is explored. Using the CSC method, we attempted to synthesize alternative catalysts of the form XYMoS ternary sulfides, where X and Y are 3d transition metals. As suggested by previous quantum simulations, certain XY formulations possibly reveal a synergy effect as observed in CoMoS and NiMoS active phases. The most promising formulations merit further investigations
Book chapters on the topic "Amorphous silica-alumina"
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Ishihara, Atsushi, Kohei Nakajima, Motoki Hirado, Tadanori Hashimoto, and Hiroyuki Nasu. "Pore Size Control of a Novel Amorphous Silica-Alumina with Large Mesopore by the Gel Skeletal Reinforcement and Its Catalytic Cracking Properties." In ACS Symposium Series, 51–60. Washington, DC: American Chemical Society, 2012. http://dx.doi.org/10.1021/bk-2012-1092.ch004.
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Bellussi, G., C. Perego, A. Carati, S. Peratello, E. Previde Massara, and G. Perego. "Amorphous mesoporous silica-alumina with controlled pore size as acid catalysts." In Studies in Surface Science and Catalysis, 85–92. Elsevier, 1994. http://dx.doi.org/10.1016/s0167-2991(08)64100-2.
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Jolivet, Jean-Pierre. "Nanomaterials: Specificities of Properties and Synthesis." In Metal Oxide Nanostructures Chemistry. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780190928117.003.0004.
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The concept of material concerns matter in solid state that is endowed with usable properties for practical applications. It is indeed in the solid state that matter exhibits the highest mechanical strength and chemical inertness, providing solidity and sustainability because the solid is based on an extended stiff crystalline framework. It is also in the solid state that many properties exist, including optical, electrical, and magnetic properties, providing great technological progress. A typical example is electronics which owes its enormous development to doped silicon. A material may therefore be defined as a useful solid. The properties of a solid depend directly on its chemical composition, crystalline and electronic structures, texture, as well as morphology and casting. This last point, which is often neglected, is illustrated by amorphous silica glass, which is used largely for its properties such as chemical inertness, mechanical strength, optical transparency, and low thermal and electrical conductivities. These various properties are highlighted through the many possibilities of casting and shaping: flat glass (optical transparency for glazing); hollow glass (chemical inertness and mechanical strength for bottling); short fibers (glass wool for heat insulation) and long fibers (optical fibers); massive pieces (insulators for electric power lines); and thin films (insulating layers for miniaturized electronics). Metal oxides exhibit a wide range of exploitable properties useful for innumerable applications. Silica, SiO2, as flat glass, has excellent optical properties, but other oxides such as LiNbO3 and KTiOPO4 exhibit interesting nonlinear optical properties, allowing changes in the wavelength of the transmitted light. Certain oxides are good electrical insulators (SiO2), but others are true electronic conductors (VO2, NaxWO3), ionic conductors (β-alumina NaAl11O17, NaSiCON Na3Zr2PSi2O12, yttria-stabilized cubic zirconia Zr1–xYxO2–x/ 2), and also superconductors (cuprates such as YBa2Cu3O7–x and Bi4Sr3Ca3Cu4O16+x). Compounds such as BaTiO3, PbZr1–xTixO3, and PbMg1/3Nb2/3O3 are ferroelectric solids used largely as miniaturized electronic components, whereas spinel ferrite γ-Fe2O3, barium hexaferrite BaFe12O19, and garnet Y3Fe5O12 are more or less coercive ferrimagnetic solids used in magnetic recording or as permanent magnets.
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Stumbo, A. M., P. Grange, and B. Delmon. "Discovery of a new role of spillover hydrogen emitted by sulfided catalysts: creation of acidic sites on amorphous silica-alumina." In Studies in Surface Science and Catalysis, 211–20. Elsevier, 1997. http://dx.doi.org/10.1016/s0167-2991(97)80840-3.
Full textConference papers on the topic "Amorphous silica-alumina"
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Neralla, Sudheer, Sergey Yarmolenko, Dhananjay Kumar, Devdas Pai, and Jag Sankar. "Cross-Sectional Nanoindentation of Alumina Thin Films Deposited by Pulsed Laser Deposition Process." In ASME 2006 International Mechanical Engineering Congress and Exposition. ASMEDC, 2006. http://dx.doi.org/10.1115/imece2006-14924.
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Alumina is a widely used ceramic material due to its high hardness, wear resistance and dielectric properties. The study of phase transformation and its correlation to the mechanical properties of alumina is essential. In this study, interfacial adhesion properties of alumina thin films are studied using cross-sectional nanoindentation (CSN) technique. Alumina thin films are deposited at 200 and 700 °C, on Si (100) substrates with a weak Silica interface, using pulsed laser deposition (PLD) process. Effect of annealing on the surface morphology of the thin films is studied using atomic force microscopy. Xray diffraction studies revealed that alumina thin films are amorphous in nature at 200 °C and polycrystalline with predominant gamma alumina phase at 700 °C.
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Khor, K. A., and Y. Li. "Novel ZrO2-Mullite Composites Produced by Plasma Spraying." In ITSC 1998, edited by Christian Coddet. ASM International, 1998. http://dx.doi.org/10.31399/asm.cp.itsc1998p1233.
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Abstract Zirconia can induce enhanced fracture toughness to a number of ceramics when introduced as a reinforcement either in the form of particulates, dispersed phase or whiskers because of its unique tetragonal-monoclinic transformation. This paper presents the preparation of ZrO2 reinforced mullite by plasma spraying a mixture of zircon and alumina. The dissociation of zircon into zirconia and silica in a plasma flame is well-known. Pre-mixed powders of zircon and alumina are injected into a dc plasma jet. The plasma sprayed particles are collected in distilled water and analyzed. The results indicate that the plasma sprayed powders consist of zirconia, zircon and alumina. It was found that fine, mostly amorphous and chemically homogeneous composite powders can be obtained by ball milling and plasma spraying. Recrystallization of amorphous phases and formation of mullite occurred at about 1000 °C in plasma sprayed powders. This value is more than 500 °C lower than the formation of mullite in as-milled powders. Uniform coatings with good structural integrity were obtained by plasma spraying. The amount of amorphous phases was much higher in plasma sprayed coatings than in spheroidized powders, and the relative quantity of mullite in coatings after heat treatment is about 4 times as much as that obtained in the spheroidized powders.
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Chraska, T., K. Neufuss, J. Dubsky, P. Ctibor, and M. Klementova. "Fabrication of Bulk Nanocrystalline Ceramic Materials." In ITSC2008, edited by B. R. Marple, M. M. Hyland, Y. C. Lau, C. J. Li, R. S. Lima, and G. Montavon. Verlag für Schweißen und verwandte Verfahren DVS-Verlag GmbH, 2008. http://dx.doi.org/10.31399/asm.cp.itsc2008p0435.
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Abstract An alternative method to produce bulk nanocrystalline materials and avoid the powder compaction step is to produce amorphous material by rapid solidification followed by controlled heat treatment to introduce nanocrystalline structure. The extremely high cooling rates in plasma sprayed particles give rise to formation of nonequilibrium phases, which may become amorphous for certain materials. Five different materials studied in this work are based on near-eutectic mixtures of alumina, zirconia and silica. The powder feedstock materials have been plasma sprayed using water stabilized plasma torch (WSP) and subsequently heat-treated to prepare nanocomposite materials with varying nanocrystallite size. The as-sprayed materials have very low open porosity and are mostly amorphous. The as-sprayed amorphous materials crystallize at temperatures around 950°C with an associated volume shrinkage of 1-2%. The resulting structure is best described as nanocomposite with very small crystallites (12 nm on average) embedded in inter-crystallite network. Role of the silica compound on phase composition, microstructure, and mechanical properties of the as-sprayed and annealed materials is discussed. Elastic properties were measured for the nanocrystalline materials. The as-sprayed amorphous materials exhibit high hardness and high abrasion resistance. Both properties are significantly improved in the heat treated nanocrystalline samples.
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Dubsky, J., K. Neufuss, and B. Kolman. "Phase Composition Changes in Annealed Plasma-Sprayed Zircon-Alumina Coatings." In ITSC 1997, edited by C. C. Berndt. ASM International, 1997. http://dx.doi.org/10.31399/asm.cp.itsc1997p0473.
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Abstract Phase transformations and/or decomposition of deposited compounds have an indisputable influence on materials properties of plasma sprayed deposits. Using water stabilized plasma, free-standing parts were manufactured from a mechanical mixture of zircon and alumina powders and annealed. The phase composition was determined by X-ray diffraction and the chemical composition was checked by x-ray microanalysis. ZrSiO4 during plasma spraying decomposes into ZrO2 and SiO2. In the as-sprayed condition, after a relatively fast quenching, the following phases can be found: a very fine eutectic mixture of tetragonal and monoclinic ZrO2, amorphous SiO2 and a spinel phase of Al2O3. On annealing for 2 hours at 1300 and 1500 °C the spinel Al2O3 transformed to corundum. At the same time, amorphous silica crystallized. Tetragonal ZrO2 transformed to the monoclinic modification and together with SiO2 formed again ZrSiO4. At the highest annealing temperature Al2O3 and SiO2 partialy reacted to form a small amount of mullite (3Al2O3.2SiO2).
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Salimi Jazi, H., M. Hosseini, A. Shafyei, H. Samadi, L. Pershin, T. W. Coyle, and J. Mostaghimi. "Study of Plasma Sprayed Mullite Coating Using Mullite and a Mixture of Alumina and Silica Powder Particles." In ITSC2011, edited by B. R. Marple, A. Agarwal, M. M. Hyland, Y. C. Lau, C. J. Li, R. S. Lima, and A. McDonald. DVS Media GmbH, 2011. http://dx.doi.org/10.31399/asm.cp.itsc2011p0960.
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Abstract Plasma sprayed ceramic coatings are widely used for thermal barrier coating applications. Commercially available mullite powder particles and a mixture of mechanically alloyed alumina and silica powder particles were used to deposit mullite ceramic coatings by plasma spraying. Microstructure and morphology of both powder particles as well as coatings were investigated by using scanning electron microscopy (SEM). Phase formation and degree of crystallization of coatings were analyzed and estimated by using X-ray diffraction technique. Differential thermal analysis (DTA) method was used to study the phase transformation of coatings. Results indicated that the porosity level in the coating deposited using mullite as initial powder particles was lower than that deposited using the mixed powder particles. The crystallization degree of the coating deposited using the mixed powder particles are higher than that deposited using mullite powder particles. DTA curves of coatings deposited using the mixed powders have showed some phase transformation due to the crystallization of the retained amorphous phases such as mullite and alumina in the coatings. The degree of crystallization of both as sprayed coatings was significantly increased after post deposition heat treatments.
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Castillo, Eduardo, Sadia Choudhury, Hyun Woo Shim, Jaron Kuppers, Hanchen Huang, and Diana-Andra Borca-Tasciuc. "Thermal Characterization of Silicon Carbide Nanowire Films." In ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-67321.
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This paper reports on thermal characterization of SiC nanowire films on alumina substrate. The SiC nanowires films were synthesized via carbothermal reduction by thermal evaporation of silica and graphite powders using a high temperature alumina tube furnace. Structural characterization showed that nanowires have a core-shell structure, with a core of single crystal SiC of ∼50 nm in diameter and an amorphous shell of silicon oxide of ∼10 nm in thickness. Prior thermal measurements as-deposited SiC nanowires were compacted into more dense films via capillary coalescence. The effective thermal conductivity in the direction perpendicular to the film was determined employing a steady-state experimental method in conjunction with one-dimensional heat transfer modeling. Preliminary results suggest that these films have a very low thermal conductivity, in the range of 0.1W/mK. The low thermal conductivity may be due to intrinsic structure of the nanowire film such as porosity and large number of interfaces between the SiC nanowire core and its outer oxide layer as well as thermal contact resistance at nanowires junctions.
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Milanova, Denitsa, Ranganathan Kumar, Satyanarayana Kuchibhatla, and Sudipta Seal. "Heat Transfer Behavior of Oxide Nanoparticles in Pool Boiling Experiment." In ASME 4th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2006. http://dx.doi.org/10.1115/icnmm2006-96197.
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The heat transfer characteristics of silica (SiO2), ceria (CeO2), and alumina (Al2O3) nanofluids at 0.5% concentration and particle size of 10nm and 20 nm in pool boiling have been analyzed. The influence of acidity on heat transfer has been studied. The pH value of the nanosuspensions is important from the point of view that it determines the stability of the particles, their mutual interactions towards the wire. When there is no particle deposition on the wire, the nanofluid with any oxide suspension increases CHF by about 50% within uncertainty limits regardless of the type of the oxide particle and its size. The extent of oxidation on the wire impacts CHF, and is influenced by the chemical composition of nanofluids in buffer solutions. Amorphous oxides (SiO2) are generally more disordered and less closely packed compared to the crystalline oxides such as CeO2 and Al2O3. The arrangement of the atoms within the unit cell and the layer of water molecules at the surface possibly influence the natural convection as well as the CHF. The boiling regime is further extended to higher heat flux when there is agglomeration on the wire. This agglomeration allows high heat transfer through interagglomerate pores, resulting in a nearly 3-fold increase in CHF. This deposition occurs for the charged 10 nm silica particle, and was not seen for other oxide particles. The chemical composition, oxidation and packing of the particles within the deposition on the wire are shown to be the reasons for the extension of the boiling regime and the net enhancement of the Critical Heat Flux.