O gênero Croton possui aproximadamente 1300 espécies amplamente distribuídas em zonas tropicais e subtropicais do novo e velho mundo e é o segundo maior gênero de Euphorbiaceae. No presente trabalho, foram analisadas a composição e a morfologia das ceras foliares cuticulares de 13 espécies de Croton. Para a maioria das espécies, foram amostrados três indivíduos. A morfologia das ceras foi analisada por microscopia eletrônica de varredura. Diversos tipos de depósitos cerosos foram observados (amorfos, plaquetas, grânulos), principalmente na face adaxial e caracterizando grupos de espécies. A observação dos padrões de depósitos cerosos de várias espécies foi prejudicada na face abaxial, devido à alta densidade de tricomas. As ceras foram extraídas por três imersões consecutivas das folhas em diclorometano e a separação das classes dos constituintes foi feita por cromatografia em camada delgada preparativa. A análise da distribuição dos constituintes foi realizada por cromatografia a gás acoplada a espectrometria de massas. n-Alcanos e álcoois primários foram detectados em todos os indivíduos analisados. Triterpenos também são muito comuns, não tendo sido detectados em apenas uma espécie. Os esteroides são constituintes raros nas espécies analisadas. Os resultados da distribuição de n-alcanos, álcoois primários e triterpenos foram utilizados para o estabelecimento de afinidades químicas por meio de análises de agrupamento pelo método UPGMA, empregando-se distâncias euclidianas (n-alcanos e álcoois) e coeficiente de DICE (triterpenos), baseando-se na distribuição de cada classe de constituinte isoladamente e combinando-se as distribuições de n-alcanos e álcoois primários. Não se notou congruência entre as topologias dos dendrogramas de afinidades químicas e a filogenia molecular do gênero. Observou-se coerência entre algumas afinidades químicas e características morfológicas, como tipos de tricomas foliares e presença de glândulas peciolares. A distribuição de n-alcanos, álcoois primários e triterpenos mostraram-se úteis como caracteres da maioria das espécies analisadas. Entre os constituintes analisados, distribuição de álcoois primários revelou-se o melhor marcador para a caracterização de espécies. A variação intraespecífica, no entanto, impede que esses caracteres sejam úteis como marcadores taxonômicos de algumas espécies de Croton / Croton comprises nearly 1300 species distributed in tropical and subtropical areas of either the New or Old Worlds, making up the largest genus of Euphorbiaceae. In the present work, the chemical composition and the morphology of the foliar cuticular waxes of 13 species of Croton were analized. Three individuals were sampled for analyses of most species. The morphology of the waxes was analyzed by scanning electron microscopy. Several types of wax deposits were observed (amorph, platlets, granules), chiefly on the adaxial side, characterizing groups of species. The observation of wax deposits on the abaxial side was hampered in several species due to the high density of trichomes. The cuticular wax was extracted by three successive immersions of the leaves in dichloromethane, and the separation of the constituent classes was achieved by preparative thin layer chromatography. The analyses of the distribution of the constituents were performed by gas chromatography coupled to mass spectrometry. n-Alkanes and primary alcohols were detected in all analyzed individuals. Triterpenes were also very common, having not been detected in only one species. Steroids are rare constituents in the analyzed species. The results of the distribution of n-alkanes, primary alcohols and triterpenes were used for the establishment of chemical affinities using cluster analysis by the UPGMA method and Euclidean distances (n-alkanes and alcohols) and DICE coefficient, based on the distribution of each constituent class alone and combining the distribution of n-alkanes and primary alcohols. No congruence was noted between the topologies of the dendrograms of chemical affinity and the molecular phylogeny of the genus. Coherence was observed between chemical affinities and morphologic characteristics, such as types of foliar trichomes and petiolar glands. The distribution of n-alkanes, primary alcohols and triterpenes were shown to be useful as characters for most analyzed species. Among the constituents analyzed, the distribution of primary alcohols was the best marker for species characterization. Intraspecific variation, however, precludes the use of these characters as taxonomic markers of some Croton species

Indiana University-Purdue University Indianapolis (IUPUI) / The Indian summer monsoon (ISM) is the dominant hydrometeorological phenomenon that provides the majority of precipitation to southern Asia and southeastern Tibet specifically. Reliable projections of ISM rainfall are critical for water management and hinge on our understanding of the drivers of the monsoon system and how these drivers will be impacted by climate change. Because instrumental climate records are limited in space and time, natural climate archives are required to understand how the ISM varied in the past in response to changes in climatic boundary climate conditions. Lake sediments are high-resolution natural paleoclimate archive that are widely distributed across the Tibetan Plateau, making them useful for investigating long-term precipitation trends and their response to climatic boundary conditions. To investigate changes in monsoon intensity during the Holocene, three lakes were sampled along an east-west transect in southeastern Tibet: Galang Co, Nir’Pa Co, and Cuobu. Paleoclimate records from each lake were developed using isotopic (leaf wax hydrogen isotopes; δ2H), sedimentological, and geochemical proxies of precipitation and lake levels. Sediments were sampled at high temporal frequencies, with most proxies resolved at decadal scales, to capture multi-decadal to millennial-scale variability in monsoon intensity and local hydroclimate conditions. The ISM was strongest in the early Holocene as evidenced by leaf-wax n-alkane δ2H at both Cuobu and Galang Co corresponding with Cuobu’s higher lake levels and effective moisture. Monsoon intensity declined at Cuobu and Galang Co around 6 ka which corresponds to reduced riverine sediment influxes at Cuobu and deeper lake levels at Galang Co. The antiphase relationship between lake levels and monsoon intensity at Galang Co is attributed to air temperatures and effective moisture, with a warmer and drier local hydroclimate driving early Holocene low lake levels. The late Holocene ISM was more variable with wet and dry periods, as seen in the Nir’Pa Co lake level and leaf wax n-alkane δ2H record. These records demonstrate coherent drivers of synoptic and local hydroclimate that account for Holocene ISM expression across the southeastern Tibetan Plateau, indicating possible drivers of future monsoon expression under climate change.

Surface Organometallic Chemistry (SOMC) is an excellent approach to erase the gap between homogeneous and heterogeneous catalysis by grafting the molecular organometallic complex on various oxide surfaces, forming well-defined and single-site catalysts. This strategy allows for better characterization as well as the improvement and development of existing and new catalysts. These surface species could promote a wide range of catalytic applications (i.e., metathesis of hydrocarbons, hydrogenolysis of alkanes, and olefin polymerization reactions) depending on the metal center and its coordination sphere. In particular, the grafting of alkylated organometallic complexes of groups 4, 5, and 6 metals on the surface oxide is a thermodynamically favored reaction generally leading to strongly bonded well-defined surface species, which are highly reactive catalysts. This thesis has focused on the preparation, characterization, and catalytic investigation of different supported complexes that contain methyl, alkyl, and alkylidyne ligands. The first part compares the catalytic activity of [(≡Si−O−)W(-CH3)5] and [(≡Si-O-)Mo(≡CtBu)(-CH2tBu)2] surface species experimentally and by DFT calculations in the metathesis reactions of linear classical and functionalized olefins. Both pre-catalysts perform almost equally in the α-olefin metathesis reaction. However, in the functionalized olefin metathesis reaction, W pre-catalyst provides selective metathesis products and performs much better than Mo that gives a range of isomerization products. The second part deals with the synthesis and characterization of [(THF)2Zr(-CH3)4] and its grafting on silica support for the first time. The generated surface species [(≡Si−O−)Zr(CH3)3(THF)2] and [(≡Si−O−)2Zr(CH3)2(THF)2] are used for the conversion of CO2 and propylene oxide to cyclic propylene carbonates achieving a TON of 4227. The third part describes the first synthesis and characterization of the highly unstable homoleptic [Ti(-CH3)4] without any coordinating solvent. This complex was stabilized by grafting on SiO2-700, yielding two fully characterized surface species [(≡Si-O-)TiMe3] and [(≡Si-O-Si≡)(≡Si-O-)TiMe3], which were used in the hydrogenolysis reaction of propane and n-butane, with TONs of 419 and 578, respectively. Finally, the fourth part reports the immobilization and characterization of [TiMe2Cl2], an intermediate in the synthesis of [Ti(-CH3)4], on SiO2-700 resulting in [(≡Si-O-)TiMeCl2] and [(≡Si-O-)TiMe2Cl] surface species. These complexes reacted with a demethylating Lewis acid agent (BARF), forming the corresponding cationic Ti species [(≡Si-O-)TiMeCl]+ and [(≡Si-O-)TiCl2]+. Both neutral and cationic complexes were tested in the ethylene polymerization reaction affording linear HDPE with high molecular weights of 500,367 and 486,612 g/mol.

No description available.

Organic methods development has long dictated the molecular scaffolds available to the pharmaceutical and fine chemical synthesis industries. Photoredox catalysis has emerged as a powerful platform to enable novel reactivity with visible light irradiation through triplet sensitization and single-electron transfer. New methods involving radical intermediates are now readily accessible from countless starting materials through the application of these catalysts. Much of my work has utilized established photoredox platforms to enable both nickel catalyzed remote cross-coupling of primary amines via 1,5 hydrogen-atom transfer (HAT) and formal [3+2] synthesis of γ-lactams through triplet sensitization. My further work focuses on the application of ligand-to-metal charge transfer catalysis with cupric chloride and ferric chloride salts towards the alkylation of alkanes through the catalytic generation of chlorine radical to enable HAT. These studies expand photoredox catalysis to inner sphere mechanisms with abundant base-metal salts to enable redox chemistry at reduced electrochemical potentials.

The separation of four or more components traditionally requires the use of three or more distillation columns. Due to the associated high costs, process intensification techniques have been studied. Semicontinuous separation is one method that allows multiple separations using one column integrated with middle vessels. This thesis aims to develop a new semicontinuous separation process that can separate a mixture with four or more components into high purity products with one column and two or more middle vessels. It is an extension of the conventional ternary semicontinuous process, which has been repeatedly shown to be profitable at intermediate throughputs when compared to continuous systems. The semicontinuous process operates in a forced cycle, with three operating modes that ensure separation objectives are met. The performance of the proposed quaternary semicontinuous separation is analyzed through rigorous dynamic simulations over a range of production capacities. To determine the feasibility, operability, and applicability to non-ideal mixtures, three case studies were considered: 1. Equimolar mixture of alkanes (n-hexane; n-heptane; n-octane; n-nonane). 2. Equimolar mixture of aromatics (benzene; toluene; ethyl-benzene; and o-xylene). 3. Non-ideal mixture of mixed-alcohols (methanol, ethanol, and water; propanol; isobutanol; pentanol and hexanol) The extendibility of the quaternary semicontinuous separation process, referred to as quintenary semicontinuous separation, is then evaluated on a five-component alkane mixture (n-hexane; n-heptane; n-octane; n-nonane; n-decane), via three case studies: 1. Equimolar mixture 2. Non-equimolar mixture, rich in light and heavy components. 3. Non-equimolar mixture, rich in intermediate components. The results for both the quaternary and quintenary semicontinuous processes indicate that this new technique is successful at achieving separation objectives while staying within safe operating limits. Comparison of both equimolar mixtures of alkanes for quaternary and quintenary semicontinuous processes with continuous systems indicates that the proposed system is profitable for intermediate flow rates. / Thesis / Master of Applied Science (MASc) / Traditionally, several large distillation columns (that can be hundreds of feet tall) are required to split a mixture of liquid chemicals into its individual components. Distillation is the separation of mixtures due to differences in boiling points. When the mixture is heated, the vapour phase will contain the components with lower boiling points, which can be separated once the vapour phase is cooled and condensed. The main goal of this research is to create a new system that can carry out the same separation, but using complex techniques that require only one column and a few extra storage tanks that are much cheaper and smaller than a distillation column. Different liquid mixtures were used to show how well the new process is able to separate the liquid into its individual components, while remaining in safe operating limits.

Earth's climate is prone to natural and episodic cycles. The most recent period of climate change, the only one to be caused by humans, is significantly affecting species composition and landscapes. Northern expansion of the Boreal Forest in Canada is one of the expected outcomes, and tree line migration northward is one of the anticipated changes. Previous studies have found that many human activities like agriculture, grazing, and pastoralism can significantly affect tree line movement. Improving our ability to examine past tree line dynamics can be achieved using archival records in lake sediments. In this study, we focused on three sediment biomarkers that may be related to the presence of trees in a lake's catchment: n-alkanes, lignin-derived phenols, and stable isotopes of carbon. We examined the composition of these markers in sediment from 19 lakes in Saskatchewan spanning 4 ecoregions, from Prairie Grassland to Boreal Plain, to determine the biomarker signature for lakes in each ecoregion and relating them to land cover (trees vs herbaceous plants) in the catchments of each lake. The results showed that n-alkane composition was significantly correlated to the proportion of trees to herbaceous plants in a lake's catchment, raising the possibility that these can be used to infer the presence of trees in sediment records. The C/N ratio and δ¹³C were not effective in distinguishing ecoregions or land cover composition, likely due to algal production in the lake and agricultural activities in the surrounding farmland, while lignin-derived phenols appeared to be affected by unknown factors.

No description available.

In many catalytic systems, the activity and selectivity of supported metal catalysts or extended metal surface catalysts would be affected by the metal surface structure, and this phenomenon is called structure sensitivity. Generally, structure sensitivity is led by the change of geometric and electronic properties of the metal on the surface. The variation of metal nuclearity and metal-support interactions are effective ways to change the geometric and electronic properties of the supported metal catalyst, leading to different types of the active sites exposing on the support that would take effect on catalyzing the reaction. In this work, a series of supported Ir catalysts (on MgAl2O4 and SiO2) with different particle sizes less than 3 nm were utilized for hydrogenolysis of n-butane and ethane to study the structure sensitivity as well as the potential reaction pathways. The results indicate that the activity of n-butane hydrogenolysis increases as Ir particle size increases in the small particle size range (0.7–1.4 nm) and then drops when the Ir particle size further increases and the Ir single atoms might be inactive for hydrogenolysis after the post-reaction analysis. The selectivity of n-butane hydrogenolysis is dominated by central and one terminal C–C bond cleavage on the n-butane molecules at low temperature range. The selectivity to central C–C bond cleavage is highly dependent on the size of Ir and increases with a decrease in particle size down to ~1.4 nm but remains constant with further decrease in size. The hydrogenolysis of ethane shows a similar trend in the small size range but the activity is much lower than n-butane, which supports the low level of series reaction pathway in the case of n-butane hydrogenolysis. In addition to Ir nuclearity, the effect of electronic properties was also studied on another series of Ir catalysts supported on ZnAl2O4, in which zinc replace the magnesium within the same spinel structure. The characterization results including HAADF-STEM and volumetric CO chemisorption show the difference of Ir nuclearity in the subnanometer regime and nanoparticles (~1.4 nm), while XPS and DRIFTS indicate the difference of electronic properties from metal-support interaction on the two Ir catalysts with the same nuclearity but reduced at different temperatures. Acetylene hydrogenation is structure sensitive on Ir/ZnAl2O4 catalysts and the activity and selectivity are mainly determined by Ir nuclearity instead of the difference in electronic properties. The Ir single atoms and subnanometer clusters are more selective to the target product of C2H4 but less active than large Ir nanoparticles as there might be more π-bonded adsorption than di-σ bonded adsorption for C2H2 on the Ir single atoms and subnanometer clusters. / Doctor of Philosophy / The supported metal catalyst is a kind of effective substance that could help increase the reaction rate when being properly utilized in the reaction. From the industry point of view, the best thing is to maximize the catalyst productivity and minimize the expense so that the economic benefit could be magnified. The catalyst effectiveness in a certain reaction might be different when the surface structure of the catalyst varies. Usually, only the fraction of the surface metals could take effect. As the particle size of the catalyst decreases, the fraction of the surface atoms that contain active sites drastically changes, leading to a different catalytic performance and probably lower cost with improved efficiency for metal utilization. Therefore, it is very significant for the researchers to study the reaction structure sensitivity on the same series of catalysts with different particle sizes. Also, by understanding the reaction mechanism and fundamentals of the catalytic system, it would be possible for the researchers to rationally design the catalysts aiming at higher efficiency and lower cost. In this work, the reaction of hydrogenolysis that cleaves the C–C bonds within the alkanes molecules was studied on the supported Ir catalysts (Ir/MgAl2O4 and Ir/SiO2) with different particle sizes ranging from mostly single atoms, subnanometer clusters to nanoparticles. For n-butane hydrogenolysis, it is found that the selectivity to the target product of ethane is weakly dependent on particle size when smaller than 1.4 nm but decreases as the size further increases. Meantime, the activity is highest on the catalyst with surface-average particle size of 1.4 nm. Therefore, Ir size of ~1.4 nm is optimum for activity and selectivity to ethane. The series of Ir/ZnAl2O4 catalysts was tested for structure sensitivity by another probe reaction, semi-hydrogenation of acetylene. The adsorbed acetylene molecules could be hydrogenated by adding two hydrogen to form the adsorbed ethylene before desorption or further hydrogenation to form ethane. Our results show the Ir single atoms and subnanometer clusters are more selective to the target product of ethylene but less active than the large nanoparticles. With the understanding of structure sensitivity, researchers are able to rationally design the catalysts based on their necessity for certain reactions.

In this thesis I present my most relevant research work I performed as a main author from 2002 until these days in the field of Catalysis by Oxides by grouping it on a thematic basis. Consequently, each chapter in Section A presents a research direction which corresponds to several papers. I tried to avoid technical details in the text and illustrate the main ideas using results and their discussion. It is worth noting that the results presented here were mainly obtained in the Laboratory of Chemical Technology and Catalysis from the University of Bucharest but also in laboratories abroad where I worked or we are collaborating with. Chapter I presents the most relevant of my results on the subject of the oxidative dehydrogenation (ODH) of light alkanes following two main directions: i) enhancing the ODH selectivity of highly active catalysts and ii) developing new effective catalysts for ODH of light alkanes. Thus, we have shown that the ODH reaction of n-butane over highly active and selective TiP2O7 catalysts can be further improved by addition of CO2 in the feed and that phosphating ceria produces an increase in ODH selectivity mainly at the expense of total oxidation products. We studied new rare earth and transition metal-containing mixed-oxides obtained from layered double hydroxides (LDH) precursors as ODH catalysts. We have shown first that the use of the LDH-derived Mg-containing mixed oxides as catalysts in the ODH reaction favored the desorption of alkenes, and, consequently, improved the ODH selectivity. Among them the Co-containing system was the most active and selective for propane ODH. In this case we have shown that the well-dispersed cobalt species with tetrahedral coordination played a main role in the ODH reaction of propane into propene, the highest propene yields being obtained with the catalysts containing 7.5-9 at % Co with respect to cations. Chapter II is dedicated to the study of total oxidation of short-chain alkanes over different novel oxide-based catalysts with the aim of finding highly active catalysts for volatile organic compounds (VOCs) destruction, capable to replace the precious metal catalysts presently used. Thus, we have studied Pb and Ba titanates, LDH-derived transition metal-containing mixed oxides and Ni and Co ferrospinels. The most active and stable catalyst in the total oxidation of methane was the LDH-derived Cu-containing system. In this case we have shown that the active sites were the highly reducible copper species, their optimum dispersion being observed for the catalyst containing ~ 12 at % Cu with respect to cations. We have also shown for the first time that Co ferrite was highly active and stable in the total oxidation of propane as a VOC model. Chapter III is focussed on the study of oxidation catalysts by electrical conductivity measurements, a powerful technique for catalysts characterization that can provide information on the nature of surface oxidizing species, of structure defects and of the oxidic phase involved in the catalytic reaction which allows us to explain the catalytic behavior of the catalysts studied and to propose a reaction mechanism. Thus, we studied by electrical conductivity measurements ceria and phosphated ceria, catalysts for isobutane ODH, Pb and Ba titanates, catalysts for methane total oxidation, and vanadium antimonate and mixed vanadium and iron antimonate, catalysts for propane ammoxidation, the relationship existing between their redox and catalytic properties being evidenced and their catalytic behavior explained. Chapter IV is devoted to the study of catalytic processes involving the acid-base properties of the catalyst, such as conversion of ethanol into higher added value products over LDH-derived mixed oxides, cyanoethylation of methanol over transition-metal containing Mg-Al hydrotalcites and their corresponding mixed oxides and esterification of n-butanol with acetic acid over almina-supported molibdena and vanadia catalysts. Thus, we have shown that the Pd-containing LDH-derived mixed oxide was active for ethanol conversion into n-butanol while the Cu-based catalyst oriented the transformation towards n-butanol or 1,1-diethoxyethane depending on the reaction conditions and on the copper content. In the cyanoethylation reaction of methanol MgAlO system showed the best catalytic performances which diminished after introduction of the transition metal cations, the equilibrium between basic and acid sites being a key factor. Finally, we have shown that molybdena supported on γ-alumina acts as an efficient stable solid acid catalyst for the esterification of acetic acid with n-butanol, while vanadia supported on γ-alumina loose its activity because of the leaching of the active component. In Section B a plan for my research and academic career development is emphasized, different research topics in the field of Catalysis by Oxides that I intend to tackle in the future being described and justified based on a literature survey.