This article describes the synthesis of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) by the catalytic decomposition of acetylene at 973 K over several Fe/silica catalysts (sol–gel method ...prepared) in a fluidized bed reactor. Characterization of the catalysts and the products was performed by chemical analyses, N
2 adsorption isotherms (BET surface area), temperature-programmed reduction (TPR), CO volumetric chemisorption, X-ray diffraction (XRD), temperature-programmed oxidation (TPO), and transmission electron microscopy (TEM). An apparent relationship was found to exist between the metallic iron content of the catalysts, metal particle size distribution on the surface of the silica support, and final characteristics of the carbon products obtained. High-purity CNTs and CNFs were achieved after acid treatment of the catalytically produced carbon deposits. Difficulties in exact quantitative characterization of pure CNTs in the presence of other carbon species (CNFs, capsules of carbon, amorphous carbon, etc.) are also reported and discussed.
Conversion of 1-butene was studied over Mo carbides and Ni, Co and Mo phosphides, under continuous gas phase operating conditions at atmospheric pressure and 100 °C, using 1-butene/helium mixture in ...a molar ratio of 4:1. The conversion was in the range 30–44% and the values were quite stable except for (1:2)CoP, (1:2)NiP, (1:2)MoP-and MoxC supported catalysts. The main reaction was isomerization of 1-butene, and the selectivity to dimerization was observed in a higher ratio on (1:2)MoP and MoxC supported on high surface area graphite. In situ XRD, XPS, NH3-TPD and thermogravimetry (TG) have been used to assess for the formed species on the surface.
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•Conversion of 1-butene over Mo phosphides and carbides on carbon-based catalysts.•Stable catalysts on isomerization reaction.•MoP enhanced the selectivity to dimerization.
Despite more than three decades of intense effort, no anti‐Ras therapies have reached clinical application. Contributing to this failure has been an underestimation of Ras complexity and a dearth of ...structural information. In this regard, recent studies have revealed the highly dynamic character of the Ras surface and the existence of transient pockets suitable for small‐molecule binding, opening up new possibilities for the development of Ras modulators. Herein, a novel Ras inhibitor (compound 12) is described that selectively impairs mutated Ras activity in a reversible manner without significantly affecting wild‐type Ras, reduces the Ras–guanosine triphosphate (GTP) levels, inhibits the activation of the mitogen‐activated protein kinase (MAPK) pathway, and exhibits remarkable cytotoxic activity in Ras‐driven cellular models. The use of molecular dynamics simulations and NMR spectroscopy experiments has enabled the molecular bases responsible for the interactions between compound 12 and Ras protein to be explored. The new Ras inhibitor binds partially to the GTP‐binding region and extends into the adjacent hydrophobic pocket delimited by switch II. Hence, Ras inhibitor 12 could represent a new compound for the development of more efficacious drugs to target Ras‐driven cancers; a currently unmet clinical need.
All bound up: The oncogenic activity of mutated Ras is impaired by a new inhibitor, which reduces the Ras–guanosine triphosphate (GTP) levels, inhibits the mitogen‐activated protein kinase (MAPK) pathway, and is cytotoxic in Ras‐driven cellular models (see figure). This new inhibitor adds to the scarce number of compounds available to fight Ras‐driven cancers; a currently unmet clinical need.
•Carbon nanofiber supported Pd catalysts were studied in selective hydrogenation of 1,3-butadiene.•Catalytic performance depends on Pd size, morphology and electron density induced by nanofiber ...structure.•Improvement in selectivity to butenes for catalysts with sulfur species.•Performance depending on type of sulfur, SO3H-groups or residual adsorbed sulfur.•Electronic and geometric effects are invoked to explain different catalytic performances.
Two types of commercial carbon nanofibers with different graphitic structure, Pyrograph PR24-HHT (NFHHT) and PR24-PS (NFPS) were chemically modified to introduce oxygen groups or SO3H-containing species on their surface. Incorporation of these surface groups was confirmed by temperature programed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Palladium catalysts using these modified supports and PdCl2 as precursor were prepared, and subsequently tested in the partial hydrogenation of 1,3-butadiene under conditions of excess hydrogen. The effect of using a different Pd precursor (PdSO4) was also studied. All the prepared catalysts were characterized by transmission electron microscopy to determine the Pd nanoparticle sizes and by X-ray photoelectron spectroscopy to obtain the surface composition and the oxidation state characteristics of the Pd surface species. The carbon nanofiber structure seems to determine the Pd particle size and morphology, probably due to different metal–support interaction. Selectivities to butenes higher than 95% were obtained with the catalysts prepared on SO3H-modified supports or with the PdSO4 precursor, while over-hydrogenation to butane took place over the Pd on oxidized supports. Catalytic activity–structure correlations have been derived and it is proposed that the catalytic behaviour depends on the type of sulfur species, functional group or adsorbed residual sulfur. Furthermore, variations in 1-butene selectivity and 2-butene trans/cis ratio between the two series of catalysts were also detected and ultimately related to the different nanostructure of the carbon nanofiber.
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•Activated carbon, graphite, carbon nanotubes and KL-zeolite as Ru-catalyst supports for hydrogenolysis of glycerol.•Ruthenium supported on activated carbon produces mainly ethylene ...glycol.•Reduction of ruthenium generates Brönsted acid sites in the KL-zeolite which enhance the selectivity toward 1,2-PDO.•Graphite and carbon nanotubes promote formation of Ruδ− species and favor largely production of methane and 1,2-propanediol.
Supported ruthenium catalysts were prepared by incipient wetness impregnation of three different carbon materials: activated carbon (AC), high surface area graphite (HSAG) and multiwalled carbon nanotubes (CNT). Another catalyst was prepared by treating KL zeolite with RuCl3·xH2O in aqueous solution. All these samples were characterized by temperature programmed reduction (TPR), CO chemisorption coupled with microcalorimetry and transmission electron microscopy (TEM). The reduced catalysts were tested in the hydrogenolysis of glycerol in the liquid phase, under a reaction pressure of 8MPa and isothermally at the reaction temperature of 453K. The CO microcalorimetry measurements evidenced that electron donor properties of graphite and carbon nanotubes promote formation of electron-rich metal species (Ruδ−) in Ru/HSAG and Ru/CNT catalysts, which not only favors formation of 1,2-propanediol from glycerol but also enhances the successive CC cleavage, with formation of undesired products, mainly methane. For Ru/KL the occurrence of Brönsted acid sites, resulting of the reduction of the chlorinated ruthenium species bonded to the zeolite framework, was verified by temperature programmed desorption (TPD) of NH3. Furthermore, observations by TEM of the Ru/KL catalyst showed an important population of metal nanoparticles lower than 1nm, part of which exhibits electron deficient character as indicated by the CO microcalorimetry. As a consequence, the transformation of glycerol into 1,2-PDO over Ru/KL seems to be promoted through formation of the intermediate acetol on acid sites, while for the scarcely acid Ru-carbon catalyst conversion of glycerol occurs mainly on metal sites, ethylene glycol being the preferred hydrogenolysis product.
•The nitric acid treatment creates oxygen groups on the activated carbon surface.•Nitroxyl nitrate precursor generates oxygenated groups at the surface of Ru/C catalysts.•Carboxyl groups promote ...formation of 1,2-propanediol from glycerol.•Oxygenated groups enhance the CC and the CO cleavage of glycerol.•Formation of ethylene glycol is inhibited by effect of carboxyl acid sites.
Ruthenium catalysts supported on activated carbons, original (AC) and treated with nitric acid (AC-Ox) were prepared by incipient wetness impregnation from either chloride (Cl) or nitroxyl nitrate (n) precursors. These catalysts were characterized by TG, XPS, TEM, TPD-MS and CO adsorption microcalorimetry and evaluated in the hydrogenolysis of glycerol in the liquid phase, at 453K and 8MPa. Studies by TEM show that ruthenium particles supported on AC-Ox are larger than on AC, without any effect of the nature of the metal precursor. However, adsorption of CO on the ex-chloride catalysts is inhibited in comparison with that of the ex-nitroxyl nitrate catalysts. Catalysts characterization by TG, TPD-MS and XPS reveals that the nitric acid treatment and the nitroxyl nitrate precursor generate oxygenated groups on the carbon surface, which provide acid properties to the catalysts, although they are partly destroyed during the reduction treatment applied to the catalysts. The sequence of the overall TOF, Ru(Cl)/AC<Ru(n)/AC<Ru(Cl)/AC-Ox≈Ru(n)/AC-Ox, reasonably parallels the population increase of surface acid groups. Participation of the COOH groups in the transformation of glycerol into 1,2-propanediol is verified by using the admixture Ru(Cl)/AC+AC-Ox as catalyst. In this case, since AC-Ox was not thermally treated and no loss of oxygenated groups occurred, TOF and selectivity toward 1,2-propanediol improve in comparison with those of the more active catalysts.
The application of Metal-Organic Frameworks (MOFs) in gas phase heterogeneous catalysis is still not widely spread because of their limited stability under reaction conditions. Obtaining stable ...acidic MOFs to be used in reactions that demand strong acid sites remains a challenge up to the present time. In this work, it is shown that nanocrystals of Zirconium MOF UiO-66 can be conveniently and easily functionalized through a simple one-pot synthetic approach, i.e. the direct treatment of UiO-66 with ammonium sulfate followed by an adequate thermal treatment, giving rise to a highly acidic and thermally stable material (named as S-UiO-66). This material can act as catalyst in the gas phase isobutene dimerization demonstrating high catalytic activity at moderate temperatures while maintaining the structural integrity of the MOF after several catalytic evaluations and/or after reuse cycles. The S-UiO-66 material represents a novel alternative in the search of robust MOF-based catalysts to be applied in gas phase heterogeneous catalytic reactions that demand strong acid sites.
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•A green post-synthetic sulfation of the Metal-Organic Framework UiO-66 is reported.•An acidic and thermally stable S-UiO-66 derived material was obtained.•S-UiO-66 is a highly active catalyst in the gas phase isobutene dimerization.•The novel MOF-based catalyst is useful for reactions with strong acid demand.
Whole mitochondrial genomes are often used in phylogenetic reconstruction. However, discordant patterns in species relationships between mitochondrial and nuclear phylogenies are commonly observed. ...Within Anthozoa (Phylum Cnidaria), mitochondrial (mt)-nuclear discordance has not yet been examined using a large and comparable dataset. Here, we used data obtained from target-capture enrichment sequencing to assemble and annotate mt genomes and reconstruct phylogenies for comparisons to phylogenies inferred from hundreds of nuclear loci obtained from the same samples. The datasets comprised 108 hexacorals and 94 octocorals representing all orders and > 50% of extant families. Results indicated rampant discordance between datasets at every taxonomic level. This discordance is not attributable to substitution saturation, but rather likely caused by introgressive hybridization and unique properties of mt genomes, including slow rates of evolution driven by strong purifying selection and substitution rate variation. Strong purifying selection across the mt genomes caution their use in analyses that rely on assumptions of neutrality. Furthermore, unique properties of the mt genomes were noted, including genome rearrangements and the presence of nad5 introns. Specifically, we note the presence of the homing endonuclease in ceriantharians. This large dataset of mitochondrial genomes further demonstrates the utility of off-target reads generated from target-capture data for mt genome assembly and adds to the growing knowledge of anthozoan evolution.
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•New catalysts for controlling the selectivity in the ethanol transformation into acetaldehyde.•Interaction of Ru metallic precursors with KL zeolite.•Molecular designing of ...catalytically active surfaces sites.•Modifications of the KL acid-base surface properties during the incorporation of Ru nanoparticles.
Four Ru/KL-zeolite catalysts containing 2wt% of Ru were prepared from Ru3(CO)12, RuNO(NO3)3, Ru(C5H7O2)3 and RuCl3 precursors. The evolution of electronic structure and local chemical environment of ruthenium in the samples named Ru(c)/KL, Ru(n)/KL, Ru(acac)/KL and Ru(Cl)/KL was studied by in-situ XANES during temperature-programmed reduction. Also by CO chemisorption and transmission electron microscopy (TEM) the sizes of the Ru nanoparticles were determined. Activity and selectivity of the catalysts were evaluated in the transformation of ethanol, under kinetic conditions, in a fixed bed flow reactor, at 523K–573K. Characterization of the samples shows that metal dispersion values follow the trend Ru(c)/KL≥Ru(n)/KL > Ru(Cl)/KL≥Ru(acac)/KL. Activity of the catalysts is in the order Ru(acac)/KL≥Ru(c)/KL>Ru(n)/KL≥Ru(Cl)/KL. The TOF values, however, are in the same order of magnitude for all the samples, nonetheless the Ru(Cl)/KL catalyst has slightly lower TOF at all the reaction temperatures. Selectivity towards the dehydrogenation product, acetaldehyde, follows the trend Ru(c)/KL>Ru(n)/KL=Ru(acac)/KL>>Ru(Cl)/KL, this being 100% for Ru(c)/KL. Selectivity towards acetaldehyde is highly diminished for Ru(Cl)/KL in favor of the dehydration products, diethyl ether and ethylene, the higher the decrease the higher the temperature. The catalytic results are related to the properties of the surface metal species and their location in the zeolite framework, as well as to their surroundings, as evidenced from the results of the characterization measurements, which are in turn influenced by the different nature of the metal precursor.
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