6 research outputs found
NanopartĂcules metĂ l•liques i de magnetita: suports i materials catalĂtics
[cat] En aquesta tesi doctoral es descriu la sĂntesi i la caracteritzaciĂł de nanopartĂcules homo- i heterometĂ l•liques, aixĂ com la dels seus lligands estabilitzadors. A mĂ©s, s’estudia el comportament catalĂtic de les nanopartĂcules quan s’utilitzen com a materials catalĂtics en sĂ, i quan s’utilitzen com a suport d’altres entitats catalĂtiques. En una primera fase, s’ha detallat la sĂntesi i la caracteritzaciĂł de dendrons tipus carbosilĂ funcionalitzats al punt focal amb un grup tiol. Posteriorment, aquestes molècules s’han utilitzat com a agents estabilitzadors en la formaciĂł de nanopartĂcules d’or (AuNPs). Mitjançant el mètode bifĂ sic de Brust, s’obtenen les AuNPs estabilitzades amb els dendrons de generaciĂł zero i primera generaciĂł amb diĂ metres de 2,5 i 2,6 nm, respectivament. Les AuNPs formades tenen una distribuciĂł uniforme i una estabilitat remarcable. D’altra banda, s’ha sintetitzat un compost model amb el que s’han estabilitzat AuNPs amb un diĂ metre d’uns 2,7 nm. Fent Ăşs d’un micromonòlit funcionalitzat amb nanopartĂcules d’or estabilitzades amb el dendrĂł de primera generaciĂł (MFAu), s’ha assajat l’oxidaciĂł selectiva de CO en presència d’hidrogen, i s’ha comparat amb l’activitat de monòlits convencionals (MC). L’activitat del MFAu Ă©s mĂ©s de dos ordres de magnitud superior a la del MC. En una segona fase, s’ha sintetitzat un lligand estabilitzador compost per una cadena tipus alcĂ funcionalitzada amb un grup tiol a un extrem i amb una piridina a l’altre. Mitjançant processos d’intercanvi a partir de nanopartĂcules d’or estabilitzades amb 1-hexantiol s’ha incorporat una quantitat controlada del lligand. La reacciĂł entre les nanopartĂcules i els dĂmers [RhCl(cod)]2 i [RuCl2(p-cimè)]2 ha permès la incorporaciĂł de fragments metĂ l•lics a la perifèria. S’han estudiat les reaccions catalĂtiques d’isomeritzaciĂł del geraniol i hidrogenaciĂł de l’1-octè amb les AuNPs que contenien ruteni i rodi, respectivament. Es creu que els processos de degradaciĂł i aglomeraciĂł de les nanopartĂcules observats sĂłn els causants de les baixes conversions obtingudes. En una tercera fase, s’ha descrit la formaciĂł de nanopartĂcules de magnetita funcionalitzades amb lligands que contenen unitats fosfina (d’uns 13 nm de diĂ metre), i s’ha analitzat la seva capacitat per carregar diferents complexos metĂ l•lics, aixĂ com la possibilitat dipositar-hi les nanopartĂcules metĂ l•liques corresponents. D’aquesta manera, s’ha aconseguit obtenir nanopartĂcules de magnetita amb nanopartĂcules de fins a tres metalls de transiciĂł diferents (Pd, Au i Rh) dipositades a la seva superfĂcie. A mĂ©s, la comparaciĂł de la cĂ rrega de Pd obtinguda separadament sobre de les nanopartĂcules de magnetita funcionalitzada i de nanopartĂcules de magnetita nues, aixĂ com d’unes noves nanopartĂcules dissenyades expressament (nanopartĂcules de magnetita funcionalitzades amb unitats catecol), ha permès establir les vies d’incorporaciĂł del metall a les nanopartĂcules de magnetita. Altrament, s’ha demostrat en diversos processos catalĂtics el bon comportament catalĂtic dels nous catalitzadors magnètics. TambĂ© s’ha estudiat per primera vegada una reacciĂł seqĂĽencial one-pot, que implica en primer lloc la reacciĂł d’acoblament creuat C-C Suzuki-Miyaura, entre el 1-bromo-4-nitrofenol i l’à cid fenilborònic, seguit de la reducciĂł del grup nitro corresponent a amina. Per Ăşltim, s’ha intentat funcionalitzar AuNPs amb un lligand que contĂ© un grup ditiocarbamat a un extrem i dos grups difenilfosfina a l’atre. Tot i que es creia que en un principi l’ús d’un grup ditiocarbamat enlloc d’un grup tiol solucionaria els problemes de degradaciĂł de les nanopartĂcules, vistos AuNPs estabilitzades amb lligands tiol-fosfina, s’ha comprovat que no Ă©s aixĂ: s’observa el desancoratge dels lligands i la precipitaciĂł d’or metĂ l•lic. La sĂntesi de complexos moleculars anĂ legs ha permès corroborar que en l’estabilitzaciĂł de AuNPs amb aquest tipus de lligands, els grups fosfina es coordinen als Ă toms d’or superficials i els arrenquen de les nanopartĂcules. Amb la idea d’obtenir un lligand versĂ til, capaç d’estabilitzar AuNPs i coordinar fragments metĂ l•lics, s’ha sintetitzat un lligand que contĂ© en un extrem un grup tiol i a l’altre un grup carboxilat. L’ús d’aquests lligands ha permès obtenir nanopartĂcules d’or i pal•ladi que contenen fragments metĂ l•lics de ruteni a la perifèria.[eng] In this thesis the synthesis and characterization of homo- and heterometallic nanoparticles, as well as the synthesis and characterization of their stabilizing agents, are described. Furthermore, the catalytic behavior of nanoparticles is studied when the nanoparticles are used as catalytic materials, and when they are used as a support for other catalytic entities. In a first step, the synthesis and characterization of carbosilane dendrons functionalized with a thiol group at the focal point have been detailed. Subsequently, these molecules have been used as stabilizing agents for the formation of gold nanoparticles (AuNPs). Using the Brust’s method, AuNPs stabilized with zero and first generation dendrons with diameters around 2.5 and 2.6 nm respectively, are obtained. Furthermore, a model compound has been synthesized and also used as a stabilizing agent for the formation of AuNPs (with an average diameter of 2.7 nm). The use functionalized micromonolith with gold nanoparticles stabilized with the first generation dendron (MFAu) was tested for the selective oxidation of CO in the presence of hydrogen, and compared with conventional monoliths’ activity (MC). MFAu activity proves to be two orders of magnitude higher than the MC. In a second step, it has been synthesized a stabilizing ligand with a chain alkane functionalized with a thiol and a pyridine group. The ligand was bonded to previous AuNPs stabilized with 1-hexanethiol. The reaction between the nanoparticles formed and the dimers [RhCl(cod)]2 and [RuCl2(p-cymene)]2 allows the incorporation of metal fragments in the periphery of the nanoparticle. The catalytic isomerization of geraniol and the hydrogenation of 1-octene have been studied using AuNPs containing ruthenium and rhodium, respectively. In a third step, it has been described the formation of magnetite nanoparticles functionalized with ligands containing phosphine units (with an averga diameter of 13 nm), and it has been analyzed firstly, their ability to coordinate with different metal complexes, and secondly, the possibility of depositing the corresponding metal nanoparticles. Thus, we have synthesized nanoparticle magnetite nanoparticles with up to three different transition metals (Pd, Au and Rh) deposited on its surface. The good catalytic activity of the new magnetic catalysts has been demonstrated in various catalytic processes. Finally, the possibility of obtaining AuNPs functionalized with a dithiocarbamate ligand bearing diphenylphosphine (DTC) groups has been tested. However, the AuNPs were not stable: the detachment of DTC ligands and precipitation of metallic gold were observed. With the idea of obtaining a versatile ligand, capable of stabilizing AuNPs and coordinating metal fragments, it has been synthesized a ligand containing a thiol and a carboxylate group. Using these ligands it has been possible to synthesize gold and palladium nanoparticles containing ruthenium metal fragments in the periphery
A general approach to fabricate fe3O4 nanoparticles decorated with Pd, Au, and Rh: Magnetically recoverable and reusable catalysts for Suzuki C-C cross-coupling reactions, hydrogenation, and sequential reactions
A facile strategy has been explored for loading noble metals onto the surface of ferrite nanoparticles with the assistance of phosphine-functionalized linkers. Palladium loading is shown to occur with participation of both the phosphine function and the surface hydroxyl groups. Hybrid nanoparticles containing simultaneously Pd and Au (or Rh) are obtained by successive loading of metals. Similarly, ferrite nanoparticles decorated with Pd, Au, and Rh have also been formed by using the same strategy. The catalytic properties of the new nanoparticles are evidenced in processes such as reduction of 4-nitrophenol or hydrogenation of styrene. Besides, the sequential process involving a cross-coupling reaction followed by reduction of 1-nitrobiphenyl has been successfully achieved by employing Pd/Au decorated nanoferrite particles. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Postprint (published version
Bifunctional Chalcogen Linkers for the Stepwise Generation of Multimetallic Assemblies and Functionalized Nanoparticles
Macroporous silicon microreactor for the preferential oxidation of CO
A macroporous silicon micromonolith containing ca.
40,000 regular channels of 3.3 Âżm in diameter per square millimeter has been successfully functionalized with an Au/TiO2 catalyst for CO preferential oxidation (CO-PrOx) in the presence of hydrogen. The functionalization of the silicon microchannels
has been accomplished by growing a SiO2 layer on the channel walls, followed by exchange with a titanium alkoxyde precursor and decomposition into TiO2 and, finally, by anchoring carbosilanethiol dendron protected pre-formed Au nanoparticles.
Catalytically active centers at the Au-TiO2 interface have been obtained by thermal activation. With this method, an excellent homogeneity and adherence of the catalytic layer over the microchannels of the macroporous silicon micromonolith has
been obtained, which has been tested for CO-PrOx at 363-433 K and Âż=2 under H2/CO=0-20 (molar). The macroporous silicon micromonolith converts ca. 3 NmL of CO per minute and mL of microreactor at 433 K under H2/CO=20, suggesting that it could
be particularly effective for hydrogen purification in lowtemperature microfuel cells for portable applications
Macroporous silicon microreactor for the preferential oxidation of CO
A macroporous silicon micromonolith containing ca.
40,000 regular channels of 3.3 Âżm in diameter per square millimeter has been successfully functionalized with an Au/TiO2 catalyst for CO preferential oxidation (CO-PrOx) in the presence of hydrogen. The functionalization of the silicon microchannels
has been accomplished by growing a SiO2 layer on the channel walls, followed by exchange with a titanium alkoxyde precursor and decomposition into TiO2 and, finally, by anchoring carbosilanethiol dendron protected pre-formed Au nanoparticles.
Catalytically active centers at the Au-TiO2 interface have been obtained by thermal activation. With this method, an excellent homogeneity and adherence of the catalytic layer over the microchannels of the macroporous silicon micromonolith has
been obtained, which has been tested for CO-PrOx at 363-433 K and Âż=2 under H2/CO=0-20 (molar). The macroporous silicon micromonolith converts ca. 3 NmL of CO per minute and mL of microreactor at 433 K under H2/CO=20, suggesting that it could
be particularly effective for hydrogen purification in lowtemperature microfuel cells for portable applications