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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
51

Synthèses et applications de nouveaux ligands pyrroliques et méthodologies de synthèse de phosphines P-chirogéniques / Synthesis and applications of new ligands derived from pyrrole and methodologies for the synthesis of P-chirogenic phosphines

Copey, Laurent 27 November 2014 (has links)
Deux thématiques principales ont été étudiées au cours de cette thèse. La première partie porte sur la synthèse de complexes de manganèse dérivés de porphyrines et de salens. L'activité catalytique de ces complexes a été évaluée dans l'époxydation d'alcènes non-Fonctionnalisés. Suite à cette étude, les propriétés électroniques des ligands ont été étudiées, notamment par le biais de la complexation d'anions. Dans une deuxième étape, nous nous sommes intéressés à la synthèse de phosphines P-Chirogéniques. Afin de trouver un substitut à l'éphédrine, couramment utilisée dans ces synthèses, des dérivés du (1S,2S)-2-Aminocyclohexanol et de la D-Glucosamine ont été synthétisés. L'utilisation de groupements sulfonamides a permis l'obtention aisée d'oxazaphospholidines N-Tosylées. L'un ou l'autre diastéréoisomère de cet hétérocycle peut être obtenu en fonction du degré d'oxydation du réactif phosphoré utilisé. Avec cette stratégie, divers oxydes de phosphines ont été obtenus avec de bons rendements et de bonnes énantiosélectivités / This thesis is divided in two parts. The first part focuses on the synthesis of manganese complexes derived from porphyrins and salens. The catalytic activity of these complexes were evaluated toward the epoxidation of unfunctionalized alkenes. Next, the electronic properties of the ligands were evaluated using their anion binding properties. In a second part, we were interested in the synthesis of P-Chirogenic phosphines. In order to find a surrogate to ephedrine, that is commonly used in those syntheses, derivatives from (1S,2S)-2-Aminocyclohexanol and D-Glucosamine were synthesized. The use of sulfonamides allows the access to N-Tosylated oxazaphospholidines. Both diastereoisomers could be synthesized depending on the oxydation state of the phosphine precursor. Using this strategy, various phosphine oxides were obtained in good yields and enantioselectivities
52

Catalytic Reaction Of Propylene To Propylene Oxide On Various Catalysts

Kalyoncu, Sule 01 September 2012 (has links) (PDF)
Throughout this thesis work, various catalysts were investigated with combinational approach to develop highly active and selective novel catalysts for direct epoxidation of propylene to PO using molecular oxygen. The promoted and un-promoted silver (Ag), copper (Cu), ruthenium (Ru), manganese (Mn) mono and multimetallic catalytic systems over different silica supports were prepared via sol-gel method and incipient wetness method. In addition to support effect, the effects of different promoters on the catalytic performances of these catalyst candidates were investigated. The study showed that commercial silica (c-SiO2) is the most effective support when compared to silica (SiO2) and silica synthesized with templete (t-SiO2). Among bimetallic catalytic systems containing Ag, Ru, Mn and Cu metals, c-SiO2 supported Cu-Ru catalyst was determined as the most active catalytic system. In addition, the most effective v catalyst and promoter in the epoxidation reaction was determined as NaCI promoted Cu-Ru catalyst supported over c-SiO2 with 35.98% selectivity&amp / 9.55% conversion (3.44% yield) at 3000C and 0.5 feed gas ratio (C3H6/O2).. In the study, the selected catalysts showed low and high PO productivity were also investigated by characterization techniques such as XRD, XPS, BET and FTIR.It was inferred from characterization tests that bimetallic systems reveal a synergistic behavior by exposing more active sites on the silica support material with respect to their monometallic counterparts. Besides, NaCl catalytic promoter has a strong interaction particularly with the Cu sites on the Cu/Ru/SiO2 catalyst surface, altering the electronic structure of Cu sites that favors to PO production.
53

Oxyfunctionalization of alkanes, alkenes and alkynes by unspecific peroxygenase (EC 1.11.2.1) / Oxyfunktionalisierung von Alkanen, Alkenen und Alkinen durch die Unspezifische Peroxygenase (EC 1.11.2.1)

Peter, Sebastian 24 June 2013 (has links) (PDF)
Unspecific peroxygenase (EC 1.11.2.1) represents a group of secreted hemethiolate proteins that are capable of catalyzing the selective mono-oxygenation of diverse organic compounds using only H2O2 as a cosubstrate. In this study, the peroxygenase from Agrocybe aegerita (AaeUPO) was found to catalyze the hydroxylation of various linear (e.g n-hexane), branched (e.g. 2,3-dimethylbutane) and cyclic alkanes (e.g. cyclohexane). The size of n-alkane substrates converted by AaeUPO ranged from gaseous propane (C3) to n-hexadecane (C16). They were mono-hydroxylated mainly at the C2 and C3 position, rather than at the terminal carbon, and the corresponding ketones were formed as a result of overoxidation. In addition, a number of alkenes were epoxidized by AaeUPO, including linear terminal (e.g. 1-heptene), branched (2-methyl-2-butene) and cyclic alkenes (e.g. cyclopentene), as well as linear and cyclic dienes (buta-1,3-diene, cyclohexa-1,4-diene). Furthermore, the conversion of terminal alkynes (e.g. 1- octyne) gave the corresponding 1-alkyn-3-ol in low yield. Some of the reactions proceeded with complete regioselectivity and - in the case of linear alkanes, terminal linear alkenes and alkynes - with moderate to high stereoselectivity. The conversion of n-octane gave (R)-3-octanol with 99% enantiomeric excess (ee) and the preponderance of the (S)-enantiomer reached up to 72% ee of the epoxide product for the conversion of 1-heptene. Catalytic efficiencies (kcat/ Km) determined for the hydroxylation and respectively epoxidation of the model compounds cyclohexane and 2-methyl-2-butene were 2.0 × 103 M-1 s-1 and 2.5 × 105 M−1 s−1. The results obtained in the deuterium isotope effect experiment with semideuterated n-hexane and the radical clock experiment with norcarane clearly demonstrated that the hydroxylation of alkanes proceeds via hydrogen abstraction, the formation of a substrate radical and a subsequent oxygen rebound mechanism. Moreover, stopped-flow experiments and substrate kinetics proved the involvement of a porphyrin radical cation species (compound I; AaeUPO-I) as reactive intermediate in the catalytic cycle of AaeUPO, similar to other hemethiolate enzymes (e.g. cytochrome P450 monooxygenases, P450s). / Die Gruppe der Unspezifischen Peroxygenasen (EC 1.11.2.1) umfasst extrazelluläre Häm-Thiolat-Enzyme, die mittels H2O2 als Cosubstrat die selektive Monooxygenierung unterschiedlicher organischer Verbindungen katalysieren. In der vorliegenden Arbeit konnte gezeigt werden, dass die von Agrocybe aegerita sekretierte Peroxygenase (AaeUPO) verschiedene lineare (z. B. n-Hexan), verzweigte (z. B. 2,3-Dimethylbutan) und zyklische Alkane (z. B. Cyclohexan) hydroxyliert. Die Größe der von der AaeUPO umgesetzten Substrate reichte vom gasförmigen Propan (C3) bis hin zu n-Hexadekan (C16). Die Alkane wurden bevorzugt am zweiten und dritten Kohlenstoffatom (C2 und C3) hydroxyliert; eine Hydroxylierung am terminalen Kohlenstoff konnte nur vereinzelt und in geringem Umfang beobachtet werden. Die Überoxidationen der primär gebildeten, sekundären Alkohole führte außerdem zur Entstehung der entsprechenden Ketonderivate. Darüber hinaus wurde eine Vielzahl linearer terminaler (z. B. 1-Hepten), verzweigter (z. B. 2-Methyl-2-Buten) und zyklischer Alkene (z. B. Cyclopenten) sowie linearer und zyklischer Diene (1,3-Butadien, 1,4-Cyclohexadien) durch die AaeUPO epoxidiert. Die Umsetzung terminaler Alkine (z. B. 1-Octin) führte zur Entstehung der jeweiligen 1-Alkin-3-ole. Manche dieser Reaktionen verliefen ausgeprägt regioselektiv und, im Falle der linearen Alkane sowie der linearen terminalen Alkene und Alkine, mit mittlerer bis hoher Stereoselektivität. So ergab beispielsweise die Umsetzung von n-Octan einen Enantiomerenüberschuss größer 99% für (R)-3-Octanol; die Epoxidierung von 1-Hepten lieferte einen Enatiomeerenüberschuss (ee) von bis zu 72% für das (S)-Enantiomer. Die katalytischen Effizienzen, die für die Hydroxylierung bzw. Epoxidierung der Modellverbindungen Cyclohexan und 2-Methyl-2-Buten ermittelt wurden, betragen 2.0 × 103 M-1 s-1 und 2.5 × 105 M−1 s−1. Der ausgeprägte Deuterium-Isotopen-Effekt, der im Zuge der Umsetzung von semideuteriertem n-Hexan beobachtet wurde sowie die Ergebnisse des Radical-Clock-Experiments mit Norcarane als Substrat bestätigten, dass die Hydroxylierung von Alkanen über Wasserstoffabstraktion, die Bildung eines Substratradikals und anschließende direkte Sauerstoffrückbindung verläuft. Die Stopped-Flow-Experimente belegen zudem das Auftreten eines Porphyrin-Kationradikal-Intermediates (Compound I; AaeUPO-I) im katalytischen Zyklus der AaeUPO (vergleichbar mit dem reaktiven Intermediat der P450-Monooxygenasen).
54

Chemistry of dawsonites and application in catalysis

Stoica, Georgiana 18 February 2010 (has links)
La dawsonita es un mineral cristalino hallado generalmente en la naturaleza en forma de hidróxicarbonato de sodio y aluminio, NaAlCO3(OH)2. Además del mineral, se han sintetizado diferentes tipos de dawsonitas variando su composición, es decir, cambiando el sodio y/o aluminio por cationes de similar naturaleza. El trabajo descrito en esta tesis se centra en estudiar la química de este tipo de compuestos incluyendo: la estabilidad en medios acuosos de las dawsonitas en condiciones moderadas, la obtención de compuestos nanoestructurados dawsonita-hidrotalcita a partir de hidrotalcita, y el efecto memoria de las alúminas derivadas de dawsonita. El objetivo final es la evaluación de los materiales sintetizados y sus derivados, en catálisis. Estos materiales han resultado ser eficientes o en algunos casos más activos que los catalizadores reportados en la literatura para reacciones básicas (la transesterificación de carbonato de etileno para producir carbonato de dimetilo) y redox (epoxidación de alquenos). Teniendo en cuenta los resultados obtenidos, estos materiales podrían ser utilizados como catalizadores, adsorbentes, y aditivos abriendo así una nueva vía de investigación. / Dawsonites are crystalline minerals generally present in nature as sodium aluminum carbonate hydroxide, NaAlCO3(OH)2. Besides the mineral, a variety of compositions with dawsonite-type structure have been synthesized by changing the nature of sodium or aluminum cations. The work described in this thesis focuses on the chemistry of dawsonite-type compounds including: the stability of dawsonites in aqueous media at mild conditions; the achievement of dawsonite-hydrotalcite nanostructured composites starting from the hydrotalcite; and the memory property of dawsonite-derived aluminas. The final goal is to evaluate the as-synthesized or derived dawsonite-materials in selected catalytic reactions. These materials were efficient or even more active than catalysts in the state-of-the-art in basic (dimethyl carbonate production by transesterification of ethylene carbonate with methanol) and redox (alkene epoxidation of cyclooctene with hydrogen peroxide) reactions. The above findings could have further practical implications as activated dawsonites open a new window of research with potential applications as catalysts, adsorbents, and additives.
55

Development Of Sol-gel Catalysts By Use Of Fast Combinatorial Synthesis And High Throughput Testing Techniques For Catalytic Oxidation Of Propylene To Propylene Oxide

Duzenli, Derya 01 August 2003 (has links) (PDF)
Propylene oxide (PO) is an important raw material for the chemical industry, which is produced commercially by the chlorohydrin process and hydroperoxide process. However the deficiencies in these processes have given rise to considerable interest in the development of a direct route to PO that does not produce by-products or coproducts. The development of novel, active and selective catalysts for gas phase oxidation of propylene using molecular oxygen were studied via testing a large number of catalysts by high-throughput screening method over combinatorially prepared different catalytic system in this study. v The promoted and un-promoted silver (Ag), copper (Cu), manganese (Mn) mono and bimetallic catalytic system over high and low surface area silica, alumina, titanium oxide and titanium-silicate supports were prepared by single step sol-gel method and by incipient wetness method. The study to determine the most effective catalyst and promoter in the epoxidation reaction with different reaction conditions, showed that potassium (K)- promoted Cu metal supported over high surface area silica favored the PO production at a high reaction temperature (350 &deg / C) and oxygen rich atmosphere (C3H6/O2=1.0). The catalyst showed high and low propylene oxide productivity was investigated by some of the characterization techniques. The highlydispersed copper particle over silica support was determined by XRD, TEM and XPS techniques. The only change between promoted and un-promoted catalyst was found out in the temperature dependence of propylene consumption and PO production rate. It was inferred that potassium (K) only neutralizes the acid sites of silica.
56

Cyanide-catalyzed C-C bond formation: synthesis of novel compounds, materials and ligands for homogeneous catalysis

Reich, Blair Jesse Ellyn 25 April 2007 (has links)
Cyanide-catalyzed aldimine coupling was employed to synthesize compounds with 1,2-ene-diamine and α-imine-amine structural motifs: 1,2,N,N'- tetraphenyletheylene-1,2-diamine (13) and (+/-)-2,3-di-(2-hydroxyphenyl)-1,2- dihydroquinoxaline (17), respectively. Single crystal X-ray diffraction provided solidstate structures and density functional theory calculations were used to probe isomeric preferences within this and the related hydroxy-ketone/ene-diol system. The enediamine and imine-amine core structures were calculated to be essentially identical in energy. However, additional effects-such as π conjugation-in 13 render an enediamine structure that is slightly more stable than the imine-amine tautomer (14). In contrast, the intramolecular hydrogen bonding present in 17 significantly favors the imine-amine isomer over the ene-diamine tautomer (18). Aldimine coupling (AIC) is the nitrogen analogue of the benzoin condensation and has been applied to dialdimines, providing the first examples of cyclizations effected by cyanide-catalyzed AIC. Sodium cyanide promoted the facile, intramolecular cyclization of several dialdimines in N,N-dimethylformamide, methanol, or dichloromethane/water (phase-transfer conditions) yielding a variety of six-membered heterocycles. Under aerobic conditions, an oxidative cyclization occurs to provide the diimine heterocycle. Cyanide-catalyzed aldimine coupling was employed as a new synthetic method for oligomerization. Nine rigidly spaced dialdimines were oxidatively coupled under aerobic conditions to yield conjugated oligoketimines and polyketimines with unprecedented structure and molecular weight (DP = 2 - 23, ~700 -8200 g/mol). The α- diimine linkage was established based on IR spectroscopy, NMR spectroscopy, size exclusion chromatography, and X-ray crystallographic characterization of the model oxidized dimer of N-benzylidene-(p-phenoxy)-aniline. Cyclic voltammetry indicates ptype electrical conductivity, suggesting they are promising candidates for plastic electronic devices. The cyanide-catalyzed benzoin condensation reaction of 4-substituted benzaldehydes followed by oxidation to the diketone, and the Schiff Base condensation of two equivalents of o-aminophenol provides 2,3-(4-X-phenyl)2-1,4-(2- hydroxyphenyl)2-1,4-diazabutadiene. The ligand is given the moniker X-dabphol. These ligands are readily metallated to form M-X-dabphol complexes. The copper complexes catalytically fix CO2 with propylene oxide to yield propylene carbonate. DFT studies along with a comparison with Hammet parameters help validate and elaborate on the catalytic cycle and the catalytic results obtained. The nickel complex is competent for olefin epoxidation. Synthesis, characterization, X-ray structure, DFT analysis, and catalytic activity of the parent nickel dabphol complex are reported.
57

Partial Oxidation of Ethene to Ethylene Oxide in Microchannel Reactors

Kursawe, Ansgar 03 September 2010 (has links) (PDF)
In der vorliegenden Arbeit wurde die heterogen katalysierte Oxidation von Ethen zu Ethylenoxid an Silberkatalysatoren untersucht. Ziel dieser Arbeit war es, Mikrostrukturreaktoren für schnelle und stark exotherme Oxidationsreaktionen zu erproben und diese Epoxidation diente als Modellreaktion. Gleichzeitig wurden explosions- und flammhemmende Eigenschaften des Mikrostrukturreaktors ausgenutzt, um die partielle Oxidation von Ethen zu Ethyenoxid im Explosionsbereich (> 9% Sauerstoff) ohne Sicherheitsprobleme zu ermöglichen. Um die gesteckten Ziele zu erreichen wurden zwei parallele Lösungswege beschritten. Zunächst wurden modulare Mikrostrukturreaktoren und geeignete mikrostrukturierte Katalysatorträger entwickelt, um Untersuchungen verschiedener katalytischer Beschichtungen in dieser neuen und nicht allgemein verfügbaren Reaktorbauweise zu ermöglichen. Zur katalytische Erprobungen dieser Konstruktion war es notwendig, geeignete Beschichtungstechniken zur Immobilisierung katalytisch aktiver Spezies zu entwickeln. Durch die Bauweise dieser Reaktoren als Wandreaktor erschien es anfänglich nicht möglich, kommerziell verfügbare pellet-artige Katalysatoren zu verwenden. Daher wurden, parallel zur Konstruktion der modularen Mikroreaktoren, verschiedene auf Silber basierende Beschichtungstechniken hinsichtlich ihrer Eignung für diese Reaktion erprobt. Zur Erprobung kamen u.a. Silberimmobilisierung in einem durch anodischen Oxidation erzeugen Porensystem bzw. einer durch Sol-Gel Beschichtung erzeugten a-Aluminiumoxid Schicht und die Abscheidung von metallischem Silber per Vakuumbeschichtung auf einem Trägermaterial. Zuletzt wurde die Immobilisierung eines gemahlenen, kommerziellen Katalysators per elektrostatischer Pulverabscheidung auf einem entsprechend präparierten Trägermaterial vorgenommen und erfolgreich erprobt. Die wichtigste Erkenntnis dieser Arbeit aus chemisch-katalytischer Sicht ist der enorm positive Einfluss hoher Sauerstoffkonzentrationen auf die Selektivität und gleichzeitig den Umsatz des umzusetzenden Ethylens. Wird die Sauerstoffkonzentration von unter 10% auf bis zu 80% erhöht, so steigt die Selektivität zu Ethylenoxid um ca. 10% an und simultan kann der Umsatzgrad abhängig vom Katalysator und der Reaktortemperatur um den Faktor 2 bis 10 gesteigert werden. Diese Beobachtung wurde für jeden funktionierenden Katalysator gemacht, unabhängig von dessen Herstellung. Mittels Promotoren wie Cs-Salzen und Stickoxiden konnte die Selektivität in Abwesenheit gängiger Moderatoren wie Chlorkomponenten auf 70% (Cs-Salze) bzw. 75% (NOx) gesteigert werden. Verfahrenstechnisch ist festzuhalten, dass Mikrostrukturreaktoren gleich welcher Bauweise unter allen Reaktionsbedingungen thermisch stabil und beherrschbar blieben. Es wurden Umsatzgrade bis 99% bezüglich Ethen erzielt bzw. Reaktionstemperaturen von über 630 K bei einem binären Ethylen-Sauerstoff Gemisch (20%/80%) angewendet. Angesichts adiabater Temperaturerhöhungen von mehr als 3000 K konnte dennoch ein stabiler Betrieb des Reaktors festgestellt werden. Diese thermische Stabilität war bei Katalysatoren in Festbettreaktoren nicht gegeben.
58

Corrole Synthesis and Catalytic Applications Toward Cobalt(III)-Catalyzed Epoxidation, N-H Insertion, and Cyclopropanation

Kim, Chung Sik 31 December 2010 (has links)
A variety of bromocorroles, useful precusors for Pd-based cross coupling, were sucessfully synthesized in moderate to good yields. Chiral corroles were also synthesized through use of chiral amides in the aforementioned cross coupling reactions. Cobalt complexes bearing π-acceptor (CNtBu) and σ-donor (PPh3) ligands were also prepared in excellent yields. In this dissertation, cobalt (III) corrole complexes were applied to three different reaction areas: epoxidation, N-H insertion, and cyclopropanation. Cobalt(III) corroles were found to be efficient catalysts for epoxidation reactions. The epoxidation reactions can be carried out using ethyl phenyldiazoacetate, an acceptor/donor diazo compound, as a carbenoid precusor.The reaction provided highly diastereoselective epoxides. In addition to epoxidation, N-H insertion reactions using cobalt(III) corroles as catalysts smoothly produced the desired products with diverse diazo reagents. The reactions were screened using ethyl phenyldiazoacetate with a selection of anilines and amides. In order to investigate non-ylide intermediate based metal-mediated catalytic reactions, cyclopropanation was conducted using cobalt (III) corroles as catalysts, producing the desired cyclopropyl nitroesters in high yields and with excellent diastereoselectivity under a concerted mechanism. Asymmetric cyclopropanation reactions were carried out using chiral cobalt(III) corrole complexes to generate the enatiomerically pure desired cyclopropanes in moderate yields.
59

SELECTIVE TRIPODAL TITANIUM SILSESQUIOXANE CATALYSTS FOR THE EPOXIDATION OF UNACTIVATED OLEFINS

Peak, Sarah M. 01 January 2015 (has links)
Regiomeric mixture of HMe2Si(CH2)3(i-Bu)6Si7O9(OH)3 (6), containing a Si-H group in one of the ligands of the silsesquioxane, was tethered onto a vinyl terminated hyperbranched poly(siloxysilane) polymer via a hydrosilation reaction to generate extremely active catalysts, P1-8 and c-P1-8. The synthesis of 6, in good yield, was accomplished via hydrosilation of CH2=CHCH2(i-Bu)7Si8O12 (1) to generate ClMe2Si(CH2)3(i-Bu)7Si8O12 (3) followed by the reduction of 3 with LiAlH4 to afford HMe2Si(CH2)3(i-Bu)7Si8O12 (4) where the base-catalyzed excision of one framework silicon was employed to generate a regiomeric mixture of 6. [Ti(NMe2){Et3Si(CH2)3(i-Bu)6Si7O12}] (7), [Ti(NMe2){HMe2Si(CH2)3(i-Bu)6Si7O12}] (8), [Ti(NMe2){(i-C4H9)7Si7O12}] (9) and [Ti(NMe2){(c-C6H11)7Si7O12}] (10) were synthesized via protonolysis of Ti(NMe2)4 with one equivalent of the trisilanol precursor in order to determine if the presence of isomers would be intrinsically different as compared to the uniformly substituted catalysts. Isomers 8 and 9, demonstrated lower activity as compared to the uniformly substituted catalysts 9 and 10, however the isomers still exhibited extremely high catalytic activity for the epoxidation of 1-octene using tert-butyl hydroperoxide (TBHP) relative to titanium catalysts used in industry. Additionally, 9, 10, P1-8 and c-P1-8 were very selective catalysts for the epoxidation of various olefins such as terminal (1-octene), cyclic (cyclohexene or 1-methylcyclohexene), and more demanding olefins (limonene or α-pinene) employing TBHP as the oxidant. Furthermore, P1-8 and c-P1-8 were recyclable with minimal loss of titanium however the catalysts could also be repaired if a loss in activity was observed. Preliminary epoxidation reactions employing P1-8 and c-P1-8 along with hydrogen peroxide (H2O2) as the oxidant were also explored using different solvents. P1-8 degraded quickly due to the hydrolysis of the titanium from the large amount of water present in the reaction mixture however c-P1-8 showed activity for the epoxidation of cyclohexene. Finally, regiomeric mixture of Ti(NMe2)(HS(CH2)3)(i-C4H9)6Si7O12) (13), was tethered onto gold nanoparticles for the conversion of propene to propylene oxide using molecular hydrogen and oxygen. While the catalysts showed low activity under our reaction conditions, numerous improvements can be investigated in order to improve upon the catalysts.
60

Surface Engineering of Mesoporous Silica for Ti-Based Epoxidation Catalysts

Fang, Lin, Fang, Lin 13 November 2012 (has links) (PDF)
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.

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