Spelling suggestions: "subject:"supports"" "subject:"upports""
341 |
Imaginaires du «roman canadien» : discours sur le genre romanesque et pratiques d’écriture au Québec (1919-1939)Loranger, Caroline 05 1900 (has links)
No description available.
|
342 |
The Importance of School Climate: How School Leaders in Inner City Middle Schools Shape ClimateRobinson, Willie 01 May 2020 (has links)
Traditional educational reform efforts have relied on standardized testing as the primary indicator of student achievement. Current research is broadening the scope as the impact of shaping positive school climates to support the needs of students is examined (Reynolds, 2016). Positive behavior interventions and supports (PBIS) is an evidence-based system of school-wide reinforcement that provides the groundwork for supportive school climates. The purpose of this study was to determine elements of PBIS programs that facilitated positive school climates.
Data collection strategies included focus individual interviews, observation, and document analysis. Triangulation was used to analyze the data. Three iterations were used to develop a process for understanding the elements that positively impact school climates. The first iteration categorized data by actions utilized by stakeholders. The second iteration grouped the actions by the school leader’s impact on school policy in relation to positive school climate. In this iteration, categories were combined from the first iteration based upon their impact on school climate. The third iteration established the role that key stakeholders must attain in order to establish a solid foundation for a positive school climate.
The results revealed that in order for a school to maintain a positive school climate, key stakeholders to include the administrator, PBIS coach, community, students and teachers, must work in concert. Study participants identified facilitating teaching and learning expectations through role playing, shaping and maintaining a safe environment and establishing productive relationships as critical elements needed to shape a positive school climate. This was achieved by solidifying consistent rituals and routines grounded in the distinct needs of each site. The consensus across all three sites acknowledges the roles of the PBIS coaches and the building level administrator. As the PBIS coach and the building administrators worked together, they assumed the lead as PBIS work is facilitated, stakeholder support was strengthened. collaborative partnerships were formed to embrace a common vision and common goals
|
343 |
A Comparative Study of Multi-Tiered Interventions on Attendance and Graduation Rates of Urban High School Students: A Whole Child-Equity in Education ApproachJeffries, Treva Elise 11 June 2020 (has links)
No description available.
|
344 |
Restructuring to a Substantial Choice-based Art CurriculumMohoric, Lauren E. 24 June 2020 (has links)
No description available.
|
345 |
Finding The Power WithinFisher, Natalie Jean 20 December 2022 (has links)
No description available.
|
346 |
Addressing Challenging Behaviours in the Classroom: Perceptions of Teachers in PolandSkura, Monika, Wheeler, John J. 24 March 2023 (has links) (PDF)
The aim of this qualitative study was to description and interpretation of experiences and perceptions of teachers working with students who have challenging behaviours in various types of school settings in Poland. Teachers’ experiences and perceptions provided insights and understandings into action strategies, in the case of the teachers who were interviewed, their assessing student difficulties and the effectiveness of various behavioural interventions. The data obtained from teacher interviews revealed their classroom management practices as well as their perceptions on the efficacy of their respective schoolwide practices for supporting students with behaviour support needs.
|
347 |
<b>Influence of Metal Speciation and Support Properties for Ammonia Oxidation and Other Automotive Exhaust Catalytic Applications</b>Brandon Kyle Bolton (18116749) 07 March 2024 (has links)
<p dir="ltr">Metal speciation and structure can be influenced by the deposition method used during synthesis, interactions with the support, and by post-deposition treatments and reaction conditions experienced during its lifetime of carrying out a catalytic reaction. Supported metal particles of different size contain different surface structures and coordination environments, which may not only influence reaction rates but also the interconversion between agglomerated metallic domains and dispersed metal atom or ion sites. Here, we address the influence of post-deposition treatments and support properties on the structural interconversion of Pd and Cu on aluminosilicate chabazite (CHA) zeolites, Pt on gamma-alumina (γ-Al2O3), and Pd on amorphous oxides (γ-Al2O3, La-doped Al2O3, ΘΔ-Al2O3). The fundamental insights from these studies can be used to design catalysts used widely in automotive exhaust aftertreatment systems, including Pd-exchanged zeolites for passive NOx (x = 1,2) adsorbers (PNA), Cu-exchanged zeolites for NOx (x = 1,2) selective catalytic reduction (SCR), Pt/Al2O3 for NH3 oxidation, and Pd/oxides for three-way catalysts (TWC). Incipient wetness impregnation (IWI) and colloidal methods were used to prepare Pd nanoparticles deposited on CHA zeolites with distinct Pd nanoparticle sizes and distributions. These Pd-CHA samples were used to investigate the effects of Pd particle size distribution on structural interconversion between ion-exchanged Pd and agglomerated Pd domains under realistic operating conditions. Smaller Pd nanoparticles had larger fractions of agglomerated Pd that converted to ion-exchanged Pd2+ sites at fixed air treatment temperatures (598–973 K) and H2O pressures (2–6 kPa H2O), consistent with thermodynamic predictions from DFT calculations. Furthermore, the addition of H2O during air treatment of different Pd nanoparticles (2–14 nm) inhibited the formation of ion-exchanged Pd2+ (thermodynamics), but not the rate of redispersion (kinetics). This demonstrates that, regardless of Pd nanoparticle size, water vapor in automotive exhaust streams facilitate metal sintering in PNA applications. Aqueous-phase exchange of Cu on CHA zeolites with varying support properties (i.e., number of paired Al sites in the 6 membered ring) were used to prepare materials with distinct types and numbers of extraframework Cu species (Cu2+, CuOH+). These Cu-CHA materials were used to analyze Cu structural changes before and after exposure to hydrothermal aging conditions. In the absence of H2O, some Cu2+ sites condense to form binuclear Ox-bridged Cu species that can be reduced with H2 to form Cu-hydride sites and reject H2O, leading to a sub-stoichiometric H2 consumption (H2/Cu < 0.5). In the presence of H2O, all nominally isolated Cu2+ species convert to [CuOH]+ structures, which can subsequently be reduced by H2 to form a Cu-hydride and reject H2O, leading to stoichiometric H2 consumption (H2/Cu ~ 0.5). Furthermore, the presence of H2O led to reduction features in H2 temperature programmed reduction (TPR) profiles that were similar among Cu-CHA materials, regardless of the initial Cu2+ speciation, further supporting the proposal that all nominally isolated Cu2+ sites convert to a similar [CuOH]+ motif. This demonstrates how water influences Cu speciation on CHA materials of varying origin or treatment history, aiding in quantifying SCR-active isolated Cu ions and SCR-inactive Cu species (e.g., CuO, CuAl2O4). Pt supported on γ-Al2O3 were prepared with different average Pt particle sizes (2–13 nm) by increasing the temperature of post-deposition air treatment (523–873 K). This suite of materials was interrogated to isolate the effects of Pt particle size on NH3 oxidation rates and selectivities during conditions relevant to NH3 slip applications in diesel exhaust aftertreatment. For all Pt particle sizes, NH3 oxidation rates displayed a hysteresis with temperature, with high rates measured during temperature decreases than during temperature increases. Smaller Pt particles (2 nm) had lower rates (per surface Pt, quantified by CO chemisorption) than larger Pt particles (13 nm), signifying that NH3 oxidation is a structure-sensitive reaction. Furthermore, surfaces of Pt particles restructure under NH3 oxidation reaction conditions, influencing effective Pt oxidation states, surface structures (numbers and types of exposed Pt sites), and surface coverages of intermediates leading to the observed hysteresis in rate. These findings demonstrate that Pt particles undergo dynamic structural changes during reaction, influencing their ability to convert NH3 to environmentally benign products in NH3 slip applications. The influence of treatment conditions, support properties, and initial Pd particle size and distribution on the kinetics of nanoparticle sintering were investigated to identify which material properties allow maintaining high dispersion to maximize metal utilization for three way catalysts (TWC) during the conversion of regulated pollutants (CO, hydrocarbons, NOx). Pd was deposited by IWI methods to generate polydiserse particle size distributions, and using colloidal Pd nanoparticle solutions to generate monodisperse size distributions, onto various supports (γ-Al2O3, La-doped Al2O3, ΘΔ-Al2O3) and subjected to aging under oxidative and reductive conditions relevant for TWC operation. The average Pd particle size for all materials increased with treatment time under both reductive and oxidative environments. For samples prepared with IWI (i.e., log normal distribution of Pd particle sizes), reductive aging treatments led to higher sintering rates than oxidative treatments. In contrast, for samples prepared using colloidal Pd solutions (i.e., normal distribution of Pd particle sizes), oxidative aging treatments led to higher sintering rates than reduction treatments. Furthermore, after the same treatment condition and time, samples prepared with IWI resulted in higher average Pd particle sizes. These results indicate that more monodisperse initial Pd particle size distributions lead to lower sintering rates, providing guidance to design of supported metal TWCs with improved metal utilization during their lifetimes. Here, the combination of synthesis approaches to prepare a suite of model (e.g., powder) supported metal catalysts of varying structure and composition, interrogated using site and structural characterizations and steady-state and transient kinetic measurements, along with predictions from theoretical calculations, enabled unraveling the influence of material properties and gas environments that affect metal speciation, structure, and oxidation state in real-world aftertreatment systems that use more complex catalytic architectures (e.g., layered washcoats) and reactor designs (e.g., monoliths). This approach provides insights into the fundamental thermodynamic and kinetic factors influencing metal restructuring and interconversion under realistic conditions encountered in automotive exhaust aftertreatment applications, and the kinetic and mechanistic factors that underlie complex phenomena (e.g., reaction rate hysteresis) from data measured in the absence of hydrodynamic artifacts. The overall approach used in this work enabled development of synthesis-structure-function relationships on various metal supported catalysts for automotive exhaust aftertreatment applications, which can provide guidance for material design and treatment strategies to form and retain desired metal structures throughout the material lifetime, including synthesis, reaction, and regeneration treatments.</p>
|
348 |
En jämförelsestudie mellan KL-träbjälklag och prefabricerade armerade betongbjälklag : Utifrån kostnad, miljö, antalet upplag och aktörers inställningAxelsson, William, Tudt, Isabella January 2024 (has links)
In order to maintain a sustainable construction industry, it is important to consider sustainability aspects in buildings. Material selection and optimizations are a fundamental part of this process. The purpose of this degree project is to contrast cross laminated timber slabs with prefabricated concrete slabs based on cost, carbon dioxide emissions, number of supports and the attitude of the construction industry. This is to see if one of the slabs can be considered more advantageous than the other and if it can be optimized. In order to achieve the aim and purpose of the study, a literature review, theoretical calculations and interviews with actors in the construction industry have been carried out. The study has resulted in a comparative analysis that shows that cross laminated timber slabs have a significantly lower carbon dioxide emission than prefabricated concrete slabs, but are less economically profitable. The result further shows that continuity can optimize both slabs through thinner thicknesses and thus be cost- and environmental-saving. The actors, in turn, have a tendency to prefer the materials that they are used to and feel safe working with, as there are risks involved in trying something newer. However, the actors show a great openness towards cross laminated timber and feel that its development will increase in connection with the knowledge about the material being established. The most central thing is to apply the right material in the right place. / För att upprätthålla en hållbar byggindustri är det viktigt att beakta hållbarhetsaspekter i byggnationer. Materialval och optimeringar är en grundläggande del av denna process. Syftet med det här examensarbetet är att ställa KL-träbjälklag mot prefabricerade betongbjälklag med utgångspunkt i kostnad, koldioxidutsläpp, antal upplag och byggbranschens inställning. Detta för att se om något av bjälklagen kan anses vara mer fördelaktigt än det andra och om det går att optimeras. För att uppnå studiens mål och syfte har en litteraturöversikt, teoretiska beräkningar och intervjuer med aktörer inom byggbranschen genomförts. Studien har utmynnat i en jämförande analys som visar att KL-träbjälklag har ett betydligt mindre koldioxidutsläpp än prefabricerade betongbjälklag, men blir mindre ekonomiskt lönsamt. Resultatet visar ytterligare att kontinuitet kan optimera båda bjälklagen genom tunnare tjocklekar och på så vis vara kostnads- och miljöbesparande. Aktörerna i sin tur har en benägenhet att preferera de material som de är vana och trygga att arbeta med då det medför risker att bepröva något nyare. Aktörerna visar dock en stor öppenhet mot KL-trä och upplever att dess utveckling kommer att öka i samband med att kunskapen kring materialet etableras. Det mest centrala är att man tillämpar rätt material på rätt plats.
|
349 |
Remoistenable temporary supports for facing of canvas paintingsAlba, Paola 30 March 2021 (has links)
[ES] Aunque el empapelado es una técnica ampliamente utilizada en restauración con diversos propósitos, todavía no se dispone de mucha información técnica sobre la misma. A primera vista, acarrea consecuencias complejas, incluyendo cambios en lascapas pictoricas, pudiendo tener también potenciales repercusiones en la propia conservación de la obra. En la mayoría de casos, sería más adecuado recurrir a otras técnicas alternativas y menos intrusivas. Por este motivo, a lo largo de esta tesis doctoral se ha desarrollado un protocolo de investigación orientado al diseño de soportes temporales rehumectables (remoistenable temporary supports: RTS) para la protección de pinturas sobre lienzos, un método alternativo que permite un mayor control de la penetración de adhesivo en el sustrato, y por tanto una remoción de residuos más sencilla y eficaz. Durante este estudio se prestó especial atención a las necesidades de los restauradores, no solo en términos de disponibilidad y eficiencia económica, sino también en lo concerniente a la salud de los operadores y el cuidado del medio ambiente. En la primera sección de esta tesis se ha realizado una revisión histórica, comenzando por las primeras fuentes indirectas del Siglo XVIII hasta la actualidad. A continuación, se analizan los mecanismos adhesivos y de penetración del empapelado, focalizándose en aspectos relacionados con la conservación, relacionados con los materiales empleados y metodologías de aplicación. En la segunda sección se describe el estudio de la metodología innovadora de los RTS, ensayada de acuerdo a un meticuloso proyecto de investigación adaptando tecnologías analíticas avanzadas a las necesidades específicas del estudio realizado. Durante la primera etapa experimental, se realizaron análisis químicos, físicos y mecánicos de las diferentes clases de materiales (adhesivos y soportes temporales) y su compatibilidad para la preparación de tejidos rehumectables. La segunda etapa de la investigación se centró en la evaluación de la aplicación de soportes temporales rehumectables en maquetas simuladoras de pinturas en lienzo, con el fin de ensayar aquellos factores considerados más relevantes. Se realizaron observaciones con Microscopía Óptica empleando luz visible y UV, Microscopía electrónica de barrido de emisión de campo (FESEM) para evaluar la permanencia de residuos y el estudio de posibles modificaciones que podrían darse en la superficie de la pintura. Se empleó micro-espectroscopía Raman asociada a un microscopio de alta resolución para determinar la penetración del adhesivo en las grietas de las maquetas. Finalmente, se realizaron pruebas de desprendimiento (peeling test) en diferentes condiciones ambientales para estudiar la fuerza adhesiva de los RTS seleccionados. / [CA] Tot i que la protecció del color és una tècnica àmpliament utilitzada en
restauració amb diversos propòsits, encara no s'hi disposa de molta informació
tècnica. A primera vista, implica conseqüències complexes, incloent-hi canvis
en les capes pictòriques, que poden tenir també potencials repercussions en la
mateixa conservació de l'obra. En la majoria de casos, seria més adequat
recórrer a altres tècniques alternatives i menys intrusives.
Per aquest motiu, al llarg d'aquesta tesi doctoral s'ha desenvolupat un
protocol d'investigació orientat al disseny de suports temporals rehumectables
(Remoistenable Temporary Supports: RTS) per a la protecció de pintures sobre
llenç, un mètode alternatiu que permet un major control de la penetració
d'adhesiu en el substrat i, per tant, una eliminació de residus més senzilla i eficaç.
Durant aquest estudi es va prestar especial atenció a les necessitats dels
restauradors, no solament en termes de disponibilitat i eficiència econòmica,
sinó també pel que fa a la salut dels operadors i la cura del medi ambient.
En la primera secció d'aquesta tesi s'ha realitzat una revisió històrica,
començant per les primeres fonts indirectes del segle XVIII fins a l'actualitat. A
continuació, s'analitzen els mecanismes adhesius i de penetració de
l'empaperat, i es focalitza en aspectes relacionats amb la conservació futura
dels materials emprats i metodologies d'aplicació.
En la segona secció es descriu l'estudi de la metodologia innovadora dels RTS,
assajada d'acord amb un meticulós projecte d'investigació que adapta
tecnologies analítiques avançades a les necessitats específiques de l'estudi
realitzat. Durant la primera etapa experimental, es realitzaren anàlisis químiques,
físiques i mecàniques de les diferents classes de materials (adhesius i suports
temporals) i la seua compatibilitat per a la preparació de teixits rehumectables.
La segona etapa de la investigació es va centrar en l'avaluació de l'aplicació
de suports temporals rehumectables en maquetes simuladores de pintures en
llenç, amb la finalitat d'assajar aquells factors considerats més rellevants. Es
realitzaren observacions amb microscòpia òptica emprant llum visible i UV,
Microscòpia electrònica d'escaneig d'emissió de camp (FESEM) per a avaluar la
permanència de residus i l'estudi de possibles modificacions que podrien donarse
en la superfície de la pintura. S'empraren microespectroscòpia Raman
associada a un microscopi d'alta resolució per a determinar la penetració de
l'adhesiu en les clivelles de les provetes. Finalment, es realitzaren proves de
despreniment (peeling test) en diferents condicions ambientals per a estudiar la
força adhesiva dels RTS seleccionats. / [EN] Although facing is widely used for multiple purposes, there is still little
information about it. At first glance, facing seems to be an almost neutral and
simple intervention. Its application, however, entails complex consequences
including changes to a painting's strata, and it can have potential repercussions
on the conservation of the paint itself. In most cases, it would be better to recur
to alternative and less intrusive methods, but sometimes the use of facing is strictly
necessary.
For this reason, during this PhD a research protocol addressed the design of
remoistenable temporary supports (RTS) for the facing of canvas paintings, an
alternative method that enables a higher control of the adhesive penetration
into the substrate, and thus the easier removal of residues. Great attention was
given in this assessment to the needs of restorers, in terms of not only availability
and the cost-effectiveness of materials, but also for the concerns of the safety of
the operator as well as the environment.
In the first section of this dissertation, a historical review is made starting from
the first indirect sources of the 18th century up to the present day. Then facing's
adhesive and penetrative mechanisms are analysed, focusing on conservative
issues related to the used materials and application methodologies.
The second section describes the assessment of the innovative RTS
methodology, tested according to a meticulous research project adapting
advanced analytical technologies to the specific needs. During the first
experimental stage, chemical, physical and mechanical analyses of the
different classes of materials (adhesives and temporary supports) and their
compatibility for the preparation of remoistenable tissues were carried out. The
second step of the investigation focused on the evaluation of the application of
remoistenable temporary supports on mock-ups reproducing a canvas painting,
in order to test those considered the most relevant factors. Observations with
optical microscope in visible and ultraviolet (UV) light and analyses with fieldemission
scanning electron microscopy (FESEM) were carried out to evaluate the
permanence of residues and the assessment of the possible modifications that
may have occurred on the painted surface. Micro-Raman spectroscopy
associated with a high-resolution microscope was used to determine the
penetration of the adhesive into the cracks of the mock-ups. Finally, peeling tests
at different environmental conditions were carried out to assess the adhesion
strength of the selected RTS. / An acknowledgment to the financial support from the Spanish “I+D+I” project CTQ2017-85317-C2-1-P, which is supported by the Ministerio de Ciencia, Innovación y Universidades, Fondo Europeo de Desarrollo Regional (ERDF) funds and Agencia Estatal de Investigación(AEI). / Alba, P. (2021). Remoistenable temporary supports for facing of canvas paintings [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/164901
|
350 |
Síntesis y caracterización avanzada de materiales zeolíticos mediante el empleo de nuevos agentes orgánicos directores de estructuraSala Gascón, Andrés 03 October 2022 (has links)
[ES] Las zeolitas han destacado por sus aplicaciones en procesos catalíticos y de adsorción/separación de gases de alto impacto industrial. Esto es debido a que presentan propiedades de tamiz molecular como consecuencia de sus estructuras microporosas y, además es posible ajustar sus propiedades catalíticas variando su composición química, presencia de defectos estructurales, tamaño promedio de cristal, etc. Hasta el momento se han reconocido 255 estructuras zeolíticas diferentes, pero la obtención de zeolitas con nuevas estructuras es un aspecto muy relevante dentro de la ciencia de materiales ya que permite ampliar el rango de aplicaciones de estos materiales.
Por ello, el objetivo fundamental de esta tesis doctoral es la obtención de nuevos materiales zeolíticos, empleándose para ello, cationes orgánicos que actuarán como agentes directores de estructura (ADEs) en la cristalización de zeolitas.
Así, se ha estudiado el empleo cationes derivados de biciclopirrolidina como ADEs sintetizados mediante reacciones orgánicas de cicloadición [3+2]. Estos ADEs han sido efectivos en la síntesis de zeolitas, obteniéndose diversos sólidos microporosos cuya preparación había sido descrita anteriormente con otros cationes orgánicos. Sin embargo, uno de los cationes empleados ha dado lugar a la cristalización de una nueva zeolita, denominada ITQ-69, que presenta un sistema tridireccional de canales rectos, de poro pequeño (8 x 8 x 8 R) y ausencia de cavidades. Este material ha sido efectivo en la separación selectiva de propileno de propano en su forma de germanosilicato.
La síntesis de zeolitas quirales, es sin duda el objetivo más ambicioso propuesto. En esta tesis se ha explorado el empleo de derivados de azúcares como parte fundamental en la síntesis de ADEs. En concreto, se ha explorado la isomanida como unidad sintética quiral en la preparación de dicationes quirales. Cuando la isomanida se combina con la presencia de imidazolios (altamente selectivos hacía la estructura STW) se ha obtenido un material STW en forma de germanosilicato. Este sólido cristaliza formando cristales de tamaño suficientemente grande como para realizar estudios de difracción de Rayos X en monocristal, y determinar el exceso enantiomérico de distintas preparaciones. En todos los casos, se obtiene cristales S-STW homoquirales enantimórficamente puros, constituyendo el primer ejemplo de obtención selectiva quiral de una zeolita reportado hasta la fecha.
En esta parte de la tesis, también se obtuvieron zeolitas con topología STW empleando ADEs no quirales. Algunos de estos sólidos, se evaluaron en la separación de hidrocarburos con diferentes grados de ramificación (zeolita STW puramente silícea) y en la reducción selectiva de NO con propano (zeolita Al-STW intercambiadas con Cu).
Finalmente, se han estudiado diferentes cationes organofosforados como ADEs. La elevada estabilidad de estos cationes en el medio de síntesis, ha permitido la obtención de una nueva zeolita, ITQ-70, que presenta un elevado grado de defectos de conectividad y una muy baja densidad de red. La estructura de la zeolita ITQ-70 presenta un sistema de supercavidades con ventanas interconectadas de acceso a las mismas (20 x 20 x 18 R) y cristaliza con un grupo de simetría proquiral. / [CAT] Zeolites are well-known for their industrial applications. The presence of pores of molecular dimensions forming a structured channels system confers them the property of performing as a molecular sieve. This characteristic of zeolites, combined with the possibility of modifying their chemical composition, structural defects, average crystal size, etc., provides them with exceptional properties for catalytic and separation processes. Up to now, 255 different zeolitic structures have been compiled. However, obtaining zeolites with new structures remains an important challenge in materials science and broadening their applications.
Therefore, the main objective of this doctoral thesis is the obtention of new zeolitic materials using organic cations as structure-directing agents (SDAs) in the crystallization process.
Thus, the use of bicyclopyrrolidine-derived cations as ADEs, synthesized by organic cycloaddition reactions [3+2], has been studied. Several microporous solids whose preparation had been previously described using other organic cations have been obtained by utilizing these bicyclopyrrolidine-derived cations as ADEs. In addition, the crystallization of a new zeolite, ITQ-69, has been reached. This structure presents a tridirectional system of straight small pore size channels (8 x 8 x 8 R) and the absence of cavities. ITQ-69, in its germanosilicate form, has been proved to be significantly effective for the separation of propylene from propane.
Obtaining chiral zeolite is undoubtedly one of the most ambitious objectives proposed in the field of zeolite synthesis. In this thesis, sugar derivatives have been specifically considered as starting molecules for the synthesis of chiral ADEs. Particularly, the synthesis of dicationic ADEs starting from isomannide as a chiral synthetic unit has been explored. When isomannide was combined with imidazole (highly selective towards the STW structure), a STW-structure material in the form of germanosilicate was obtained. This solid crystallizes forming sufficiently large crystals to perform single-crystal X-ray diffraction studies and determine the enantiomeric excess of different preparations. In all cases, enantiomorphically pure homochiral S-STW crystals are obtained, constituting the first reported example of chiral selective synthesis of a zeolite.
Zeolites with STW structure were also obtained using non-chiral ADEs. The properties of these microporous solids were evaluated in the separation of hydrocarbons with different branching, in the form of purely siliceous STW, and in the selective reduction of NO with propane using Cu-exchanged Al-STW zeolites.
Finally, different organophosphorus cations have been studied as ADEs. The high stability of these cations in the zeolites crystallization medium has allowed the isolation of a new zeolite, ITQ-70, which presents a high number of connectivity defects and a very low lattice density. The structure of the ITQ-70 zeolite possesses a super-cavity system with interconnected access windows (20 x 20 x 18) and crystallized with a prochiral symmetry group. / [EN] Les zeolites han destacat per les seues aplicacions en processos catalítics i processos d'adsorció/separació de gasos d'alt impacte industrial. Açò és degut al fet que presenten propietats de tamís molecular a conseqüència de les seues estructures microporoses i, a més és possible ajustar les seues propietats catalítiques variant la seua composició química, presència de defectes estructutals, grandària del cristall, etc. Fins al moment es reconeixen 255 estructures zeolítiques diferents, però l'obtenció de zeolites amb noves estructures és un aspecte molt rellevant dins de la ciència de materials, ja que permet ampliar el rang d'aplicacions d'aquests materials.
Per tant, l'aspecte fonamental d'aquesta tesi doctoral és l'obtenció de nous materials zeolítics empleant cations orgànics que actuaran com a agents directors d'estructura (ADEs) en la cristal·lització de zeolites.
Així, s'ha explorat l'us de cations derivats de biciclopirrolidina com ADEs sintetitzats mitjançant reaccions orgàniques de cicloadició [3+2]. Aquests ADEs han sigut efectius en la síntesis de zeolites, obtenint-se diversos sòlids microporosos, la preparació dels quals havia sigut descrita anteriorment amb altres cations orgànics. No obstant, un dels cations empleats ha donat lloc a la cristal·lització d'una nova zeolita, denominada ITQ-69, que presenta un sistema tridireccional de canals rectes, porus xicotets (8 x 8 x 8 R) i absència de cavitats. Aquest material ha sigut efectiu en la separació selectiva de propilé de propà en la seua forma de germanosilicat.
Dins de la síntesi de zeolites, la síntesi de zeolites quirals, és sens dubte un dels objectius més ambiciosos proposats. En aquesta tesi s'ha explorat l'ús de derivats de sucres com a part fonamental en la síntesi de ADEs. En concret, s'ha explorat la isomanida com a unitat sintètica quiral en la preparació de dications quirals. Quan la isomanida es combina amb la presència de imidazolios (altament selectius feia l'estructura STW) s'ha obtingut un material STW en forma de germanosilicato. Aquest sòlid cristal·litza formant cristalls de grandària prou gran com per a realitzar estudis de difracció de Raigs X en monocristall, i determinar l'excés enantioméric de diferents preparacions. En tots els casos, s'obté cristalls S-STW homoquirals enantimórficament purs, constituint el primer exemple d'obtenció selectiva quiral d'una zeolita reportat fins a la data.
En aquesta part de la tesi, també es van obtindre zeolites amb topologia STW empleant ADEs no quirals. Alguns dels materials STW es van avaluar les propietats d'aquests sòlids microporosos en la separació d'hidrocarburs amb diferents graus de ramificació amb STW purament silici i en la reducció selectiva de NO amb propà empleant zeolites Al-STW intercanviades amb Cu.
Finalment, s'han estudiat diferents cations organofosforats com ADEs. L'elevada estabilitat d'aquests cations en el mitjà de cristal·lització de zeolites ha permés aïllar una nova zeolita, ITQ-70, que presenta un elevat grau de defectes de connectivitat i una molt baixa densitat de xarxa. L'estructura de la zeolita ITQ-70 té un sistema compost per supercavitats amb finestres interconnectades d'accés a les mateixes (20 x 20 x 18) i cristal·litza amb un grup de simetria proquiral. / Al Ministerio de Economía, Industria y Competitividad por concederme la Beca BES-2016-078684 que ha permitido la realización de esta tesis doctoral, junto a la ayuda económica proporcionada en los proyectos MAT2015-71842 y RTI2018-101784-B-100. A la Generalitat
Valenciana su financiación a través del proyecto PROMETEO/2021/07 y por
último a la Universidad Politécnica de Valencia (UPV), al Consejo Superior de
Investigaciones Científicas (CSIC) y al Instituto de Tecnología Química (ITQ) por
proporcionar las instalaciones y equipamiento necesarios para llevar a cabo el
trabajo de investigación. / Sala Gascón, A. (2022). Síntesis y caracterización avanzada de materiales zeolíticos mediante el empleo de nuevos agentes orgánicos directores de estructura [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/186873
|
Page generated in 0.0492 seconds