No description available.

No description available.

An investigation of the cycloaddition behavior of dichloroketene with various types of olefins seemed in order to determine if dichloroketene behaved similarly to dialkylketenes. It was anticipated that a study of this type would indicate the reactivity of dichloroketene to various types of olefinic compounds and thus establish if the ease of cycloaddition with dichloroketene parallels the nucleophilicity of the olefin as it does in dialkylketenes.

No description available.

The preparation method of the catalyst highly impacts its properties and activity. Optimizing the synthesis conditions mainly targets improving the catalyst performance and overcoming the bottlenecks such as sintering of metal active sites, deactivation, short catalyst lifetime and poor selectivity. In this study, we investigated the influence of the design and preparation method of Silicalite-1 bearing Pt and Ga active species on the properties and the performance of the catalysts for propane dehydrogenation reaction aiming to increase propylene yield. Various synthesis routes, leading to different Pt and Ga location and distances were tested: (1) supporting metals on the zeolite where both Pt and Ga are randomly distributed on the surface, (2) confining of Pt and Ga within the zeolite pores following in-situ approach with no control of their relative positions, and (3) core-shell design where one metal is confined within Silicalite-1 is covered by a Silicalite-1 layer including the second metal. The influence of structure, textural properties, location of Pt and Ga nanoparticles and their synergetic interaction to form Pt-Ga alloys were studied using several characterization techniques such as XRD, BET, TEM-EDX and NMR. Catalytic performance revealed that confining metals improved the selectivity and lifetime of the catalyst. Moreover, spatial separation of Pt and Ga through the core-shell design further boosted the reaction yield with conversions hitting the equilibrium limit. Ga/Pt ratio played a crucial role in tuning the catalyst performance. 0.26%Pt(core)-2.65%Ga(shell)@S-1 catalyst with Ga/Pt of 10 exhibited superior results of 70.5% conversion and 98% selectivity.

Orientador: Gustavo Paim Valença / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-19T15:00:40Z (GMT). No. of bitstreams: 1 Anjos_WilliamLimados_M.pdf: 3114140 bytes, checksum: 2d5b6af4d6d95550df4f2b5f509c8353 (MD5) Previous issue date: 2011 / Resumo: A peneira molecular SAPO-34 foi sintetizada pelo método de cristalização hidrotérmica com razões molares de 'SiO IND. 2/Al IND. 2 O IND. 3' (SAR) de 0,3, 0,5 e 0,7. As amostras foram secas e calcinadas para serem utilizadas na reação catalítica de conversão de metanol para olefinas leves (eteno e propeno). Os sólidos foram caracterizados e foi observado através da técnica de difração de raios-X que a fase chabasita (CHA) correspondente à peneira molecular SAPO-34 foi formada. A fase AlPO-5 (AFI) também foi observada como fase contaminante deste zeólito. As medidas de área superficial (BET) obtidas através da adsorção de N2 apresentaram valores para a SAPO-34 com SAR de 0,3, 05 e 0,7 de 549, 337 e 122 m2 g-1, respectivamente, sugerindo que ocorrem reduções significativas das áreas superficiais quando o teor de Si é aumentado. Com os resultados de microscopia eletrônica de varredura foram observados estruturas uniformes cúbicas e romboédricas típicas da morfologia da SAPO-34. Os testes catalíticos foram realizados em fase gasosa em reator de leito fixo construído em quartzo nas temperaturas de 600, 625, 650, 675, 700, 725 e 750 K para a SAPO-34 com SAR de 0,3 e 700 e 750 K para SAPO-34 com SAR de 0,5 e 0,7. A massa de catalisador utilizada foi de 0,020 g com pressão de vapor de metanol de 0,04 bar e fluxo de nitrogênio de 160 mL 'min POT.-1', fornecendo um WHSV (Weight Hourly Space Velocity) de 1,47 x10-1 s-1 e um tempo de contato (razão W/F) de 0,05 g h mol-1. Os produtos identificados por cromatografia gasosa com a coluna empacotada Porapak - Q foram água, metano, eteno e propeno, quantificados a partir de curvas de calibração obtidas pela injeção de padrões de alta pureza cromatográfica. O dimetiléter foi quantificado a partir do balanço de massa obtido a partir dos coeficientes estequiométricos da reação em função da água. O catalisador que apresentou maior rendimento inicial a propeno e eteno foi a SAPO-34 com SAR de 0,3 nas temperaturas de 675, 725 e 750 K que foram superiores a 80%, enquanto os outros dois catalisadores (SAR de 0,5 e 0,7) apresentaram rendimentos inferiores a 70%. Foram realizados também estudos de atividade catalítica para determinação das constantes de desativação da equação de Voorhies e determinação da ordem de desativação catalítica / Abstract: The molecular sieve SAPO-34 was synthesized by hydrothermal crystallization with molar ratios of 'SiO IND. 2/Al IND. 2 O IND. 3' (SAR) of 0.3, 0.5 and 0.7. The samples were dried, calcined and characterized in order to be used in the catalytic conversion of methanol to light olefins (ethylene and propylene). The formation of the chabazite (CHA) phase, corresponding to SAPO-34, was proved by X-Ray diffraction analysis, as well as the contamination of the zeolite with the AlPO-5 (AFI) phase. Nitrogen adsorption showed BET surface areas for the SAPO-34 with SAR of 0.3, 0.5 and 0.7 of 549, 337 and 122 m2 g-1, respectively, suggesting that the surface area decreases significantly with a rising Si content. Uniform cubic and rhombohedral structures, typical for the SAPO-34 morphology, were observed by scanning electron microscopy. Catalytic tests were carried out in gas phase in a fixed bed quartz reactor at various temperatures between 600 and 750 K for SAPO-34 with a SAR of 0.3 and at 700 and 750 K for SAPO-34 with SARs of 0.5 and 0.7. The utilized catalyst mass was 0.020 g, the methanol vapor pressure was 0.04 bar and the total flux of methanol and nitrogen added up to 160 mL min-1, resulting in a weight hourly space velocity (WHSV) of 1,47 × 10-1 s-1 and a mass/flow ratio (W/F) of 0.05 g h mol-1. The reaction products, identified by gas chromatography employing a packed Porapak - Q column and quantified with calibration curves obtained by injection of highly pure standard samples, were water, methane, ethylene and propylene. The quantification of dimethyl ether was based on the mass balance and the reaction stoichiometry as a function of water. The catalyst exhibiting the highest initial ethylene and propylene yield was a SAPO-34 with a SAR of 0.3 at temperatures of 675, 725 and 750 K, reaching more than 80% yield, while the other catalysts (SARs of 0.5 and 0.7) showed yields of less than 70%. Studies of catalytic activity also were carried out in order to determine the deactivation constants of the Voorhies' equation and the order of catalytic deactivation / Mestrado / Desenvolvimento de Processos Químicos / Mestre em Engenharia Química

No abstract available. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2004.

Over the past decade, advances in ethylene oligomerization have witnessed explosive growth of interest from both commercial and academic standpoint, with chromium metal invariably being the metal of preference. A common feature in this literature was the extended long debate regarding the mechanism, metal oxidation states responsible for selectivity and the role of the ligand. This thesis work embarked on the isolation and characterization of new active intermediates called “single component catalysts” (or self activating) to address two important questions: (1) how the catalyst precursors re-arrange upon activation and (2) the real oxidation state of the activated species. Four different ligands systems have been examined for this purpose. The first part is a study on the NPIIIN ligand which can be described as a dynamic and non-spectator ligand. Upon aluminum alkyl activation, a series of single component chromium catalysts for selective ethylene oligomerization and polymerization have been isolated, fully characterized and tested. New selective single component chromium(I) catalysts have also been isolated and tested positively for ethylene trimerization. The second part includes a new series of chromium complexes based on the NPVN ligand. This ligands enabled to obtain the first polymer-free extremely active catalytic system. In both NPN ligand systems, a new activation pathway was discovered by using vinyl Grignard reagent [(CH2=CH)MgCl] as activator and/or reducing agent. The third part explores new modified pyrrole-chromium complexes which were found to be highly active and selective ethylene trimerization catalysts. This part was a continuation of previous work from our lab to complete the mechanistic picture of this highly successful pyrrole-chromium catalyst independently commercialized by Phillips-Chevron and Mitsubishi. Interestingly upon aluminum alkyl treatment, the first example of a Schrock-type chromium ethylidene complex has been isolated and characterized and found to be a potent catalyst for selective ethylene trimerization. Finally, the other ligands introduced in this thesis are new systems called pyridine-SNS and Si-SNS that introduce some modification to the known commercial SNS catalyst (Sasol technology). The introduction of a pyridine ring or a silyl unit in the ligand scaffold has allowed to understand the mechanism of action of this remarkable system.

Over the past decade, advances in ethylene oligomerization have witnessed explosive growth of interest from both commercial and academic standpoint, with chromium metal invariably being the metal of preference. A common feature in this literature was the extended long debate regarding the mechanism, metal oxidation states responsible for selectivity and the role of the ligand. This thesis work embarked on the isolation and characterization of new active intermediates called “single component catalysts” (or self activating) to address two important questions: (1) how the catalyst precursors re-arrange upon activation and (2) the real oxidation state of the activated species. Four different ligands systems have been examined for this purpose. The first part is a study on the NPIIIN ligand which can be described as a dynamic and non-spectator ligand. Upon aluminum alkyl activation, a series of single component chromium catalysts for selective ethylene oligomerization and polymerization have been isolated, fully characterized and tested. New selective single component chromium(I) catalysts have also been isolated and tested positively for ethylene trimerization. The second part includes a new series of chromium complexes based on the NPVN ligand. This ligands enabled to obtain the first polymer-free extremely active catalytic system. In both NPN ligand systems, a new activation pathway was discovered by using vinyl Grignard reagent [(CH2=CH)MgCl] as activator and/or reducing agent. The third part explores new modified pyrrole-chromium complexes which were found to be highly active and selective ethylene trimerization catalysts. This part was a continuation of previous work from our lab to complete the mechanistic picture of this highly successful pyrrole-chromium catalyst independently commercialized by Phillips-Chevron and Mitsubishi. Interestingly upon aluminum alkyl treatment, the first example of a Schrock-type chromium ethylidene complex has been isolated and characterized and found to be a potent catalyst for selective ethylene trimerization. Finally, the other ligands introduced in this thesis are new systems called pyridine-SNS and Si-SNS that introduce some modification to the known commercial SNS catalyst (Sasol technology). The introduction of a pyridine ring or a silyl unit in the ligand scaffold has allowed to understand the mechanism of action of this remarkable system.

This study has shown that alkythioboranes 1,3,2-dithiaborolane and 1,3,2-dithiaborinane, disproportionated significantly during their synthesis. Their interaction with 1-octene has been investigated, and the rate constants, enthalpies and entropies of the hydroboration process, have been determined. The thermodynamic and kinetic parameters obtained have shown that the hydroboration reaction is sluggish and proceeded via an associative mechanism. / Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2008.