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Gold catalysis can play an important role in selective hydrogenation, transfer hydrogenation and valorization of carbon dioxide into valuable chemicals.

Flexible metal-organic frameworks that show reversible guest-induced phase transitions between closed and open pore phases have enormous potential for highly selective, energy-efficient gas separations. Here, we present the gate-opening process of DUT-8(Ni) that selectively responds to D 2 , whereas no response is observed for H 2 and HD. In situ neutron diffraction directly reveals this pressure-dependent phase transition. Low-temperature thermal desorption spectroscopy measurements indicate an outstanding D 2 -over-H 2 selectivity of 11.6 at 23.3 K, with high D 2 uptake. First-principles calculations coupled with statistical thermodynamics predict the isotope-selective gate opening, rationalized by pronounced nuclear quantum effects. Simulations suggest DUT-8(Ni) to remain closed in the presence of HT, while it also opens for DT and T 2 , demonstrating gate opening as a highly effective approach for isotopolog separation.

Gold nanoparticles (NPs) combined with Lewis bases, such as piperazine, were found to perform selective hydrogenation reactions via the heterolytic cleavage of H2. Since gold nanoparticles can be prepared by many different methodologies and using different capping ligands, in this study, we investigated the influence of capping ligands adsorbed on gold surfaces on the formation of the gold–ligand interface. Citrate (Citr), poly(vinyl alcohol) (PVA), polyvinylpyrrolidone (PVP), and oleylamine (Oley)-stabilized Au NPs were not activated by piperazine for the hydrogenation of alkynes, but the catalytic activity was greatly enhanced after removing the capping ligands from the gold surface by calcination at 400 °C and the subsequent adsorption of piperazine. Therefore, the capping ligand can limit the catalytic activity if not carefully removed, demonstrating the need of a cleaner surface for a ligand–metal cooperative effect in the activation of H2 for selective semihydrogenation of various alkynes under mild reaction conditions.

Solid acid catalysts are environmentally friendly alternatives to the use of mineral acids in a range of applications, including the esterification of carboxylic acids. Here, a phosphorus- and nitrogen-doped, carbon-modified, fully heterogeneous solid acid catalyst was prepared by pyrolysis of a mixture of melamine and tungstophosphoric acid at 250, 500, and 750 °C under a nitrogen atmosphere provided. The structure of the different catalysts was evaluated by surface area measurements, XRD, XPS, Raman spectroscopy, elemental analysis, and electron microscopies. Pyrolysis at 500 °C created complex solid materials with larger surface area and significantly higher acidity, which can be attributed to WO3 formation on a heteroatomic (N,P)-carbon structure. The 500 °C-treated heterogeneous catalysts showed remarkably better activity for esterification of palmitic acid and were thus applied in the esterification of a broad range of carboxylic acids with good overall yields. Furthermore, the solid acid catalyst c...

The epoxidation of olefin as a strategy to protect carbon–carbon double bonds is a well-known procedure in organic synthesis, however the reverse reaction, deprotection/deoxygenation of epoxides is much less developed, despite its potential utility for the synthesis of substituted olefins. Here, we disclose a clean protocol for the selective deprotection of epoxides, by combining commercially available organophosphorus ligands and gold nanoparticles (Au NP). Besides being successfully applied in the deoxygenation of epoxides, the discovered catalytic system also enables the selective reduction N-oxides and sulfoxides using molecular hydrogen as reductant. The Au NP catalyst combined with triethylphosphite P(OEt)3 is remarkably more reactive than solely Au NPs. The method is not only a complementary Au-catalyzed reductive reaction under mild conditions, but also an effective procedure for selective reductions of a wide range of valuable molecules that would be either synthetically inconvenient or even difficult to access by alternative synthetic protocols or by using classical transition metal catalysts.

A catalyst comprised of SnO2 impregnated on ZnO nanowires, which presented remarkable ability to catalyze fatty acid esterification/transesterification reactions, is reported. For optimization of reaction conditions, artificially acidified soybean oil with 10 wt.% oleic acid was used as a model feed. The optimized conditions were: 150 °C, 6 h, 5 g of oil, catalyst concentration of 5%, and methanol:oil molar ratio of 15:1. The catalyst achieved 92% of total fatty acid methyl esters (FAME) content and was used five times without the necessity of catalyst washing from one reaction to the other. Then, such conditions were applied to produce biodiesel from the oil extracted from Scenedesmus sp. microalgae; the system reached 72% of FAME content, without any previous refining or degumming process of the oil. Rietveld refinement, X-ray diffraction, elemental mapping in scanning transmission electron microscopy, X-ray photoelectron spectroscopy, and pyridine-desorption Fourier-transform infrared spectroscopy were used to characterize the material.

The selective hydrogenation of alkynes to alkenes is an important synthetic process in the chemical industry. It is commonly accomplished using palladium catalysts that contain surface modifiers, such as lead and silver. Here we report that the adsorption of nitrogen-containing bases on gold nanoparticles results in a frustrated Lewis pair interface that activates H2 heterolytically, allowing an unexpectedly high hydrogenation activity. The so-formed tight-ion pair can be selectively transferred to an alkyne, leading to a cis isomer; this behavior is controlled by electrostatic interactions. Activity correlates with H2 dissociation energy, which depends on the basicity of the ligand and its reorganization on activation of hydrogen. High surface occupation and strong Au atom–ligand interactions might affect the accessibility and stability of the active site, making the activity prediction a multiparameter function. The promotional effect found for nitrogen-containing bases with two heteroatoms was mechanis...

The interaction of the organic ligands with metal nanoparticle has a very important role for applications in catalysis, as well as other processes involving ligands that can activate or poison the surface of metal nanoparticles. Very little has been studied so far on the role of organic ligands used either in the preparation of nanoparticles for applications in catalysis or addition in the reaction to activate the catalyst. In this thesis, we have studied strategies for the synthesis of metal nanoparticles, their use as components for the preparation of supported catalysts and activation and deactivation processes involving the ligands used as stabilizers or purposely added to the reaction medium or support for stimulate new reactivity and selectivity in reactions of industrial interest, such as hydrogenation. Here, the concept of frustrated Lewis pairs (FLPs) has been expanded to surface-FLP analogous formed by combining gold nanoparticles (NPs) and Lewis bases, such as amines or phosphines, creating a new channel for the heterolytic cleavage of H2, and thereby performing selective hydrogenation reactions with gold. A first approach to improve the catalytic activity of gold nanoparticles was to analyze the effect of nitrogen-containing bases. The starting inactive gold nanoparticles became highly active for the selective hydrogenation of alkyne into cis-alkenes. The hydrogenation proceeded smoothly and fully selective using H2 as the hydrogen source and under relatively mild conditions (80 °C, 6 bar H2). Our studies also have revealed that the presence of capping ligands blocks the adsorption of the amine to the gold surface, avoiding the FLPs interface and thereby leading to low catalytic activity. When the capping ligands were removed from the catalyst surface and an amine ligand was added, the FLPs interface is recovered and an enhanced catalytic activity was observed. Furthermore, we have demonstrated the successful use of simple organophosphorus ligands to boost the catalytic activity of Au NPs for a range of important reduction reactions, namely, epoxides, N-oxides, sulfoxides, and alkynes. Furthermore, the choice of phosphorus-containing ligands resulted in a decrease in the amount necessary to reach high conversion and selectivity in comparison with our previous study with N-containing ligands. The ligand-to-metal ratio decreased from 100 (amine/Au) to 1 (phosphite/Au). The synthesis of gold nanoparticles supported on N-doped carbon supports was used as an alternative method for the synthesis of a heterogeneous active gold catalyst for selective hydrogenations. The main advantage with respect to previous studies was to avoid the addition of external ligands, in large excess, for the activation of gold surfaces via FLP, making the whole process environmentally and economically attractive. A interação dos ligantes orgânicos com nanopartículas de metal certamente tem um papel muito importante para aplicações em catálise, bem como outros processos envolvendo ligantes que podem ativar ou envenenar a superfície de nanopartículas metálicas. Até agora, muito pouco foi estudado sobre o papel dos ligantes orgânicos utilizados na preparação de nanopartículas para aplicações em catálise ou adição na reação para ativar o catalisador. Nesta tese, foram estudadas estratégias para a síntese de nanopartículas metálicas, seu uso como componentes para a preparação de catalisadores suportados e processos de ativação e desativação envolvendo ligantes empregados como estabilizantes ou propositalmente adicionados ao meio de reação ou suporte para estimular novas reatividades e seletividade em reações de interesse industrial, como reações de hidrogenação. Aqui, o conceito de pares de Lewis frustrados (FLPs) foi expandido para o seu análogo de superfície formado pela combinação de nanopartículas (NPs) de ouro e bases de Lewis, como aminas ou fosfinas, criando um novo canal para a clivagem heterolítica de H2 e, assim, realizando reações seletivas de hidrogenação com ouro. Uma primeira abordagem para melhorar a atividade catalítica das nanopartículas de ouro foi analisar o efeito de bases contendo nitrogênio. As nanopartículas de ouro inicialmente inativas tornaram-se altamente ativas para a hidrogenação seletiva de alquino em cis-alquenos. A hidrogenação prosseguiu foi factível e totalmente seletiva usando H2 como fonte de hidrogênio e sob condições relativamente amenas (80 °C, 6 bar de H2). Nossos estudos também revelaram que a presença de estabilizantes pode bloquear a adsorção da base na superfície do ouro, impedindo a formação da interface FLPs e, portanto, levando a baixa atividade catalítica. Quando os estabilizantes foram removidos da superfície do catalisador e um ligante foi adicionado, o FLPs é formado sendo a atividade catalítica aprimorada. Além disso, demonstramos o uso bem-sucedido de ligantes organofosforados atuando como ativadores de Au NPs em uma série de importantes reações de redução, como, epóxidos, N-óxidos, sulfóxidos e alquinos. Além disso, a escolha do ligante fosforado resultou em uma diminuição na quantidade necessária para alcançar alta conversão mantendo a seletividade inalterada. A relação ligante/metal diminuiu de 100/1 (amina/Au) para 1/1 (fosfito/Au). A síntese de nanopartículas de ouro suportadas em carbono dopado com nitrogênio foi utilizada como método alternativo para a síntese de um catalisador heterogêneo de ouro ativo para hidrogenações seletivas. A principal vantagem em relação aos estudos anteriores foi evitar a adição de ligantes externos, em grande excesso, para a ativação de superfícies de ouro via FLP, tornando todo o processo ambiental e economicamente atraente.

Rice wine was made from broken rice (by-product of rice processing), which was hydrolyzed by amylolytic enzymes, producing syrup with high content of dextrose equivalent (51.04% DE). The must presented 164 g/L of glucose (15 oBx) and pH of 2.67 was fermented for 22 h at 25C by Saccharomyces cerevisiae. Fermented alcoholic (rice wine) reached yield value of 74.94% (Y1), 91.71% (Y2) and productivity (Pp) of 2.85 g/Lh in alcohol, with alcohol concentration of 62.8 g/L, 28.0 g/L of glucose, 2.5 °Bx and pH of 3.0. The kinetic parameters – Yp/s 27.75%, μN 0.008 h−1, gt 3.99 h, PN 0.13 logUFC/mLh – were determined. The wine contained a total of 11 volatile compounds identified by GC-FID, 7 alcohols (methanol, ethanol, n-propanol, n-butanol, iso-amylic alcohols, iso-butanol and glycerol), 2 aldehydes (acetaldehyde and acetol), 1 ester (ethyl acetate) and 1 ketone (acetone). Practical Applications The product obtained showed potential features to be employed not only as alcoholic beverage, but also as a raw material in the production of other products such as vinegar, adding value to rice processing. Considering the production outlook and the amount of generated by-product, it is a lower cost substrate for such application. The characterization of volatile flavor compounds might be made use not only for a better understanding of this new-type product, but also for the further utilization in other wine or alcohol production.

Selective hydrogenation of alkynes to alkenes and reductive amination are industrially important reactions to synthesize a variety of fine and bulk chemicals. We report herein on a green and convenient approach for Z-alkenes and secondary amines using gold catalyst and formic acid (FA) as a green reductant. Furthermore, we highlight that the key to successfully obtain high reaction rates is to use an appropriate amine, which acts cooperatively with the gold surface, to activate formic acid. Studies with deuterium-labeled hydrogen donors gave insights that the decomposition of Au-formate species is involved in the rate-determining step. Moreover, various valuable secondary amines could be synthetized from readily available nitro and carbonyl compounds. This new strategy provides a cleaner, safer, more efficient and selective way to catalyze the synthesis of Z-alkenes and valuable amines.

Gold catalysts are best known for their selectivity in oxidation reactions, however, there is a promising future for gold in selective hydrogenations. Herein, the hydrogenation of several aldehydes and important bio-based chemical building blocks, namely 5-hydroxymethylfurfural (5-HMF), furfural and vanillin, was performed throughout the combination of Au nanoparticles with Lewis bases. The Au-amine ligand (e.g., 2,4,6-trimethylpyridine) catalytic system could reduce the aldehyde carbonyl group selectively, without reducing alkene moieties or opening the furanic ring that occur on most traditional catalysts. Otherwise, the reduction of nitro group is preferential and the catalytic system was used for the synthesis of furfurylamines, important intermediates in the synthesis of different pharmaceuticals (e.g., furosemide), through the selective reductive amination of furfural starting from nitro-compounds. Moreover, a fully heterogeneous gold catalyst embedded in N-doped carbon (Au@N-doped carbon / TiO2) was able to perform these reactions in successive recycles without the addition of ligands, with impact in the development of a continuous flow process for biomass valorization.

Metal nanoparticles have received intense scientific attention in the field of catalysis. Precise engineering of nanomaterials’ size, shape and surface composition, including adsorbed capping ligands, is of utmost importance to control activity and selectivity, and distinguish colloidally prepared metal nanoparticle catalysts from traditional heterogeneous catalysts. The interface between the material and the reaction medium is where the key interactions occur; therefore, catalysis occurs under the influence of capping ligands. In this Perspective review, we focus on the choice of capping ligands (or stabilizing agents), and their role and fate in different steps from preparation to catalysis. Evaluating the influence of the ligands on the catalytic response is not trivial, but the literature provides examples where the ligands adsorbed on the nanoparticle surface dramatically change the activity and selectivity for a particular reaction, while acting either as a dynamic shell or a passivation coating. Steric and electronic effects resulting from the presence of adsorbed ligands have been proposed to influence the catalytic properties. Attempts to remove the capping ligands are discussed, even though they are not always successful or even necessary. Finally, we outline our personal understanding and perspectives on the use of ligands or functionalized supports to tune the activity and selectivity of supported metal nanoparticles.

Considering the limited availability of technology for the production of rice vinegar and also due to the potential consumer product market, this study aimed to use alcoholic fermented rice (rice wine (Oryza sativa L.)) for vinegar production. An alcoholic solution with 6.28% (w/v) ethanol was oxidized by a submerged fermentation process to produce vinegar. The process of acetic acid fermentation occurred at 30 ± 0.3°C in a FRINGS® Acetator (Germany) for the production of vinegar and was followed through 10 cycles. The vinegar had a total acidity of 6.85% (w/v), 0.17% alcohol (w/v), 1.26% (w/v) minerals and 1.78% (w/v) dry extract. The composition of organic acids present in rice vinegar was: cis-aconitic acid (6 mg/L), maleic acid (3 mg/L), trans-aconitic acid (3 mg/L), shikimic + succinic acid (4 mg/L), lactic acid (300 mg/L), formic acid (180 mg/L), oxalic acid (3 mg/L), fumaric acid (3 mg/L) and itaconic acid (1 mg/L).

Pyrolysis of Au(OAc)3 in the presence of 1,10- phenanthroline over TiO2 furnishes a highly active and selective Au nanoparticle (NP) catalyst embedded in a nitrogen-doped carbon support, Au@N-doped carbon/TiO2 catalyst. Parameters such as pyrolysis temperature, type of support, and nitrogen ligands as well as Au/ligand molar ratios were systematically investigated. Highly selective hydrogenation of numerous structurally diverse alkynes proceeded in moderate to excellent yield under mild conditions. The high selectivity toward the industrially important alkene substrates, functional group tolerance, and the high recyclability makes the catalytic system unique. Both high activity and selectivity are correlated with a frustrated Lewis pairs interface formed by the combination of gold and nitrogen atoms of N-doped carbon that, according to density functional theory calculations, can serve as a basic site to promote the heterolytic activation of H2 under very mild conditions. This “fully heterogeneous” and recyclable gold catalyst makes the selective hydrogenation process environmentally and economically attractive.

The design of palladium-based catalysts with improved selectivity, while maintaining high activity in hydrogenation reactions and avoiding the use of lead or ligands is still a major concern in heterogeneous catalysis. Here, a novel protocol has been proposed to prepare colloidal PdCuy nanoparticles with tailored metal composition, enabling a remarkable improvement in the semihydrogenation of alkynes when compared to pure Pd or a physical mixture of Cu and Pd catalysts. The PdCuy bimetallic catalyst with 1:4 Pd/Cu atom ratio showed the best performance. The synergistic effect between the closely contacting Pd and Cu species resulted in full conversion of alkyne and high alkene selectivity for a broad range of multifunctionalized substrates under very mild conditions (30 °C and 1 bar of H2).

The localized surface plasmon resonance (LSPR) excitation in plasmonic nanoparticles can enhance or mediate chemical transformations. Increased reaction rates for several reactions have been reported due to this phenomenon; however, the fundamental understanding of mechanisms and factors that affect activities remains limited. Here, by investigating hydrogenation reactions as a model transformation and employing different reducing agents, H2 and NaBH4 , which led to different hydrogenation reaction pathways, we observed that plasmonic excitation of Au nanoparticle catalysts can lead to negative effects over the activities. The underlying physical reason was explored using density functional theory calculations. We observed that positive versus negative effects on the plasmonic catalytic activity is reaction-pathway dependent. These results shed important insights on our current understanding of plasmonic catalysis, demonstrating reaction pathways must be taken into account for the design of plasmonic nanocatalysts.

The extraction of essential oils obtained by the hydrodistillation of needles/twigs waste of Pinus taeda L. was optimized by applying response surface methodology (RSM), with 24 full factorial design, in order to improve oil essential production, and aggregate value to the production chain of pine wood. Through the model it was possible to ascertain the influence of the variables in the average amount of essential oil (0.1032 mL), being the variables analyzed: biomass - Bm (x1), extraction time - ET (x2), Bm:ET (x1x2) and sample size - SS: drying times - DT (x3x4). Only linear terms (biomass and extraction time) and your interaction demonstrated significant positive values (0.0344, 0.0206 and 0.0131). The major components of the essential oil identified by GC-MS were: β-phellandrene: (30.39 and 22.44%), tricyclene (26.14 and 20.46%), β-myrcene (14.32 and 11.50%), β-pinene (22.49 and 1.43%) and α-pinene (0.25 and 11.26%) in the years 2011 and 2012, respectively. Our results show that the essential oil obtained from P. taeda represents a way of using some of the waste generated by the timber industry. The process of obtaining doesn't require treatments such as controlled drying or size reduction of the sample, indicating that it can be used in an industrial scale.

In a hydrothermal process for the gelatinization of the rice starch, it was studied the rate of hydration, temperature and time. An incomplete 3 3 factorial design was used to evaluate the effects of temperature, enzyme/substrate relation and liquefaction time, with dextrose equivalent (DE) as the response variable. The maximum value obtained was 14.69% DE at 89oC, with 0.21% (w/w) of enzyme to substrate in 22 minutes. For saccharification, it was studied enzyme/substrate ratios (0.6, 2.4, 4.2 and 6.0% (w/w)) at 60oC at a pH of 4.30, yielding 49.23, 69.65, 65.12 and 74.67% DE, respectively, after 72 hours. The syrup had a content of 12.78, 16.87, 15.96 and 17.87% of glucose (w/v), pH 2.60 - 2.71. The starch content converted into glucose after liquefaction was 61.80% and after saccharification ranged from 75.16 to 77.05% for the relation enzymes substrate tested.