Search

Reseña de: WITTGENSTEIN, Ludwig, Investigaciones filosóficas. (Traducción, introducción y notas de Jesús Padilla Gálvez). Madrid: Editorial Trotta, 2021 (2ª edición revisada), 329 págs.

In addition to the nature of the solvent, the intrinsic metal properties and degree of dispersion, the selective hydrogenation of 5-hydroxymethylfurfural (HMF) has been reported to be greatly affected by the nature of the support. In this work, four Ni catalysts were prepared starting from different carbonaceous supports ─with diverse graphitic and porous structure─ and comparatively evaluated in the hydrogenation reaction of HMF. The reaction was conducted in a batch stirred reactor under 30 bar H2 pressure at 60 °C in aqueous media. Ni supported on a commercial silica and Raney Ni were also tested for reference purposes. We found that carbon supports limit in some extent the reactivity of Ni towards C C hydrogenation, offering higher selectivity to the carbonyl hydrogenated compound, 2,5-di-hydroxymethylfuran (DHMF), in detrimental to the total hydrogenated derivative, 2,5-di-hydroxymethyl-tetrahydrofuran (DHMTHF). However, the latter was the major product over Raney Ni and Ni/SiO2. The unusual catalytic performance of our Ni/carbon catalysts was related to the composition, structural and surface properties. Among all tested Ni/carbon catalysts, Ni over the commercial high surface area graphite (HSAG) exhibited the best catalytic behaviour in terms of DHMF selectivity (90%) and intrinsic catalytic activity. Furthermore, Ni/HSAG displayed satisfactory stability after three consecutive runs.

The development of efficient, available and robust substitutes for the Pt-based electrocatalysts is very important for a sustainable energetic future. Herein, we report a series of composites based on Cu, Pd and Cu-Pd nanoparticles (NPs) supported on high surface area graphite (HSAG), as electrocatalysts for the energy-related reduction reactions – oxygen reduction (ORR) and hydrogen evolution (HER) reactions. All the composites showed interesting ORR electrocatalytic activities in alkaline medium. The Pd/HSAG and Cu-Pd/HSAG composites exhibited the most promising performances, with onset potentials of 0.84 and 0.91 V and current densities of jL, 0.3 V, 1600 rpm = −3.5 and −4.2 mA cm−2, respectively. All the composites showed selectivity for the 4-electron process and Tafel slopes in the range 48–77 mV dec−1. The metal/HSAG composites revealed a great tolerance to methanol and moderate electrochemical stability. In highly acidic medium (0.5 mol dm−3 H2SO4, pH = 0.3) only the Cu-Pd/HSAG and Pd/HSAG electrocatalysts presented electrocatalytic activity toward HER, with relative low overpotentials (η10 = 0.145 and 0.063 V, respectively), small Tafel slopes (75 and 42 mV dec−1) and similar exchange current densities (0.43 and 0.57 mA cm−2). These electrocatalysts also showed moderate electrochemical stability, in particular Cu-Pd/HSAG for which overpotential only changed between 0.033 and 0.038 V for j = 40 mA cm−2. The results showed that only small loading of Pd NPs (1 wt.% Pd) was able to improve significantly the ORR/HER electrocatalytic activity, which is a very important outcome to rationalize the design of efficient and cost-effective electrocatalysts in future.

In this paper molybdenum oxide promoted graphite supported ruthenium catalysts highly active and selective for Fischer-Tropsch synthesis (FTS) are presented. The effect of Mo loading (0–5 wt%) of promoted graphite supported Ru (2 wt%) catalysts on the syngas conversion was studied at 523 K, H2/CO = 2 and 3.5 bar. Mean diameters of Ru nanoparticles were all close to 3 nm independently of the molybdenum loading used. Microcalorimetric measurements during CO adsorption at 330 K reveal a clear interaction between Ru and Mo observing an important increase of CO adsorption heats for Mo/Ru ratios of ≤0.26. XPS analysis performed to 2Ru0.5Mo/G catalyst after in-situ reduction showed the presence of MoVI (MoO3) and MoIV (MoO2) species on the catalyst surface. It is argued that these Mo species could be located around the ruthenium nanoparticles acting as Lewis acids and therefore facilitating the CO dissociation. Mo promotion increased up to four times the activity with respect to unpromoted Ru catalyst, increased the selectivity to C5+ products and improved the olefin to paraffin ratio in the C2-C3 hydrocarbons range. These conclusions contribute to understand the Mo promotion effect in the FTS, because realistic deductions have been obtained using a proper inert support for studying the molybdenum promotion effect in ruthenium based catalysts, avoiding strong metal-support interaction effects.

In this study, commercial carbon nanofibers with different graphitic structure and commercial multiwall carbon nanotubes (CNT) were used. Palladium catalysts were prepared using these supports. Subsequently, they were tested in the hydrodechloration reaction of 2,4-dichlorophenoxyacetic acid under ambient-like conditions. Thermogravimetric analyses (TGA), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and nitrogen adsorption at 77 K techniques were applied to characterize the different materials. The results have demonstrated the efficiency of a bifunctional material in an integrated process that synergically combines physical adsorption and catalytic degradation. During the process, the carbon surface provides active sites to get chlorophenoxyacetic adsorbed. After saturation of the nanocarbon, the compound was decomposed by the catalytic function of supported Palladium catalysts. The study is focused on analyzing the effects of the support surfaces and electronic state of supported palladium nanoparticles on the catalytic performances. High selectivity to dechlorinated product was obtained with the catalysts prepared over more graphitic supports, whereas no-selectivity to dechlorinated products took place over oxygen-containing support. The mechanistic aspects of this bifunctional process were postulated based on the characterisation of these catalytic materials.

Bifunctional catalysts supported over high-surface-area graphite comprising copper and a series of metallic oxides (MgO, BaO, ZnO, or MnO) that exhibit different acid/base properties were studied i...

The partial hydrogenation of but-1-yne and but-2-yne was studied with a view to probing the difference between external and internal alkynes. Catalysts with Pd and Pd4S active phases were prepared on a carbon nanofiber support. Over the simple Pd catalyst over-hydrogenation was common which restricted alkene selectivity greatly – 25–35% depending on temperature. In contrast, the Pd4S active phase offered exceptional alkene selectivity (maximum of 92–93% alkene selectivity for both the external and internal alkyne). DFT calculations were subsequently used to rationalise this difference in product selectivity – sulfur appears to change the geometry of the active site in Pd4S and create a surface which favours alkene desorption relative to over-hydrogenation. This work further emphases the potential of palladium sulfide phases as an alternative to purely metallic palladium catalysts for partial alkyne hydrogenation.

Achieving high selectivity is one of the major challenges in heterogeneous catalysis, being carbon materials universally employed as catalysts support due to their so-called “inert” nature. However, due to the complexity of its intrinsic characteristics, there are still several factors to bear in mind when selecting the appropriate carbon support. In this work we demonstrate that the remaining sulfur impurities in one type of commercial carbon nanofibers (CNFs) drastically alter the catalytic properties of palladium by triggering electro-deficient active sites. Two as-received CNFs thermally processed at different severity degrees, namely PS and HHT, were used to support Pd nanoparticles through the wet impregnation technique using palladium nitrate as precursor. The proof of principle is demonstrated through two transformation reactions of biomass platform molecules: the hydrogenation of 5-hydroxymethylfurfural, performed in a batch-type reactor, and the ethanol dehydrogenation/decarbonylation reaction, carried out in a continuous flow fixed-bed reactor. In both reactions, Pd/PS was substantially more selective than its sulfur-free counterpart Pd/HHT, and one of the most selective in comparison with the state-of-the-art Pd catalysts. This finding makes available a simple, easy and green strategy to design carbon-supported Pd catalysts for selective hydrogenation and dehydrogenation reactions.

The decomposition of formic acid to obtain hydrogen has been studied using molybdenum carbides supported on activated carbon and two high surface area graphites, H-200 (200 m(2) g(-1)) and H400 (400 m(2) g(-1)). Particular attention is paid to the effect of Mo loading. The catalysts were prepared in situ using a mixture of CH4 and H-2 at a temperature of up to 700 degrees C. Under these conditions, carburization was mostly complete. We observed that the support influenced the MoxC phase obtained so that it seems that the ratio of defective carbon influences the phase. However, for these materials the C/Mo ratio did not influence the obtained crystal phase. Characterization by XRD showed that while the beta-Mo2C phase was obtained over activated carbon and over H-200, in contrast, MoOxCy was obtained over H400. These catalysts reached 100% conversion on formic acid decomposition at temperatures in the range of 190-250 degrees C and were also highly selective under these mild conditions, with values for CO2 selectivity in the range of 85.096.5%. The best results were achieved over a 10 wt% Mo loading on activated carbon that reached 96.5% selectivity to H-2. Also, changes in the molybdenum phases were observed on the spent catalyst. Some redox transformations during reaction were responsible for the transformation of beta-Mo2C into oxycarbide MoOxCy. In summary, the results of the catalytic performance indicated that the beta-Mo2C phase was more active, selective and stable than MoOxCy under the studied conditions.

Carbon nanotubes (CNT) were prepared by a modified chemical vapor deposition (CVD) method. The synthesized carbon materials were treated with acidic and basic solutions in order to introduce certain surface functional groups, mainly containing oxygen (OCNT) or amine (ACNT) species. These modified CNTs (OCNT and ACNT) as well as the originally prepared CNT were reacted with a non-ionic Fe complex, Iron (II) Phthalocyanine, and three composites were obtained. The amount of metal complex introduced in each case and the interaction between the complex and the CNT materials were studied with the aid of various characterization techniques such as TGA, XRD, and XPS. The results obtained in these experiments all indicated that the interaction between the complex and the CNT was greatly affected by the functionalization of the latter.

The development of efficient electrocatalysts for the energy-related reactions, based on earth-abundant elements, is extremely important for a sustainable energetic future. Herein, we report the application of Cu nanoparticles supported on undoped and N-doped graphene—Cu/GOE and Cu/GOE-u composites, respectively—as electrocatalysts for the oxygen reduction reaction (ORR). All the materials showed ORR electrocatalytic activities in alkaline medium. The Cu/GOE-u composite exhibited the most promising performance, with an onset potential of 0.84 V and a current density of jL = − 4.4 mA cm−2 (vs. 0.84 V and − 2.8 mA cm−2 for Cu/GOE), which revealed the great influence of the created Cu–Nx/C active sites on the ORR electrocatalytic activity. The pure GOE-u support showed worse performance than the GOE, demonstrating that the N-doping advantage is not linear and also depends on the type and amount of accessible active sites created. The N-doping allowed an increase in the selectivity for the 4-electron process, resulting in a % of H2O2 produced

The physicochemical and catalytic properties of bimetallic AgCu catalysts and their monometallic counterparts supported on a high surface area graphite have been comparatively evaluated in the ethanol dehydrogenation reaction, performed in a continuous-flow reactor. While Cu was incorporated by the incipient wetness impregnation technique, for Ag catalysts two synthesis procedures were explored: incipient wetness impregnation and adsorption of Tollens’ reagent. The catalysts prepared by wetness impregnation exhibited higher metal dispersion, being improved for the bimetallic catalysts in comparison with the monometallic counterparts. The results obtained in the catalytic tests revealed that Cu catalysts is nearly two orders of magnitude more active than Ag catalyst in the dehydrogenation reaction of ethanol on either a turnover frequency or a weight basis, but at the same time both catalysts were 100% selective to acetaldehyde. Whereas selectivity was not affected by the bimetallic composition, there was a substantial decrease in the reaction rate among the bimetallic catalysts as the Cu/Ag ratio diminished, due to blockage of copper surface active sites by silver. Both silver and copper, and the bimetallic catalysts, suffered from deactivation at 523 K, caused by blocking of active sites by adsorbed hydrocarbons on the catalyst surface (fouling). Carbonaceous deposits were removed through a thermal treatment under H2 flow, which allowed the total recovery of the initial catalytic activity.

We report for the first time the selective hydrogenation of 1,3-butadiene to butene using formic acid as the hydrogen source with 1 wt% Pd/carbon in a continuous flow reactor. The catalytic results show that the selectivity is even higher when formic acid is used compared to gas hydrogen.

The carbothermal synthesis of monometallic and bimetallic molybdenum carbide and copper, supported on high surface area graphite (H), has been studied by in situ XRD, XPS, D2-TPD, TEM/STEM, TG-mass spectrometry, and N2 adsorption. The catalysts were prepared using H2 at 600 °C or 700 °C and tested in the hydrogenation of CO2 to methanol. Molybdenum carbide and oxycarbide phases were obtained, as well as hydride species, at 600 °C on both monometallic MoxC/H and bimetallic CuMoxC/H in a similar proportion. Upon increasing the temperature up to 700 °C, the formation of metallic Mo is favourable. Although this is observed on supported MoxC and CuMoxC, the bimetallic sample is less affected by the formation of the hydride, and molybdenum carbide is also observed upon treatment at 700 °C. With regards to the catalytic performance, supported monometallic copper was not active, but copper increased the activity and selectivity of the molybdenum carbide. The yield of methanol per catalyst's weight increases upon increasing the copper loading, indicating that a cooperation reaction takes place between the smallest Cu particles in contact with the molybdenum phase. The catalysts synthesized at 700 °C are less active and less selective to methanol favouring the reverse water gas shift under the studied conditions. Interestingly, the catalysts are stable under the reaction conditions, and the detected phases by XRD of the spent catalysts suggest that the hydride species favoured transformations involving MoOxCyHz ↔ β-Mo2C. A. B. Dongil acknowledges financial support from the Fundación General CSIC (Programa ComFuturo and iLink project No 20211 from CSIC (Spain)). Financial support from the Spanish Agencia Estatal de Investigación (AEI) and EU (FEDER) (projects MAT2016-80285-P, CTQ2017-89443-C3-1-R and CTQ2017-89443-C3-3-R) is also acknowledged.

Mitigation of anthropogenic CO2 emissions possess a major global challenge for modern societies. Herein, catalytic solutions are meant to play a key role. Among the different catalysts for CO2 conversion, Cu supported molybdenum carbide is receiving increasing attention. Hence, in the present communication, we show the activity, selectivity and stability of fresh-prepared β-Mo2C catalysts and compare the results with those of Cu/Mo2C, Cs/Mo2C and Cu/Cs/Mo2C in CO2 hydrogenation reactions. The results show that all the catalysts were active, and the main reaction product was methanol. Copper, cesium and molybdenum interaction is observed, and cesium promoted the formation of metallic Mo on the fresh catalyst. The incorporation of copper is positive and improves the activity and selectivity to methanol. Additionally, the addition of cesium favored the formation of Mo0 phase, which for the catalysts Cs/Mo2C seemed to be detrimental for the conversion and selectivity. Moreover, the catalysts promoted by copper and/or cesium underwent redox surface transformations during the reaction, these were more obvious for cesium doped catalysts, which diminished their catalytic performance.

Presently, graphenic nanomaterials are being studied as candidates for wastewater pollutant removal. In this study, two graphite oxides produced from natural graphite with different grain sizes (325 and 10 mesh), their respective reduced graphene oxides and one reduced graphene oxide with nitrogen functional groups were synthesized and tested to remove a surfactant model substrate, Triton X-100, from an aqueous solution. Kinetic experiments were carried out and adjusted to pseudo-first order equation, pseudo-second order equation, Elovich, Chain-Clayton and intra-particle diffusion models. Reduced graphene oxides displayed an instantaneous adsorption due to their accessible and hydrophobic surfaces, while graphite oxides hindered the TX100 adsorption rate due to their highly superficial oxygen content. Results from the adsorption isotherms showed that the Sips model perfectly described the TX100 adsorption behavior of these materials. Higher adsorption capacities were developed with reduced graphene oxides, being maximum for the material produced from the lower graphite grain size (qe = 3.55·10−6 mol/m2), which could be explained by a higher surface area (600 m2/g), a lower amount of superficial oxygen (O/C = 0.04) and a more defected structure (ID/IG = 0.85). Additionally, three commercial high surface area graphites in the range of 100–500 m2/g were evaluated for comparison purposes. In this case, better adsorption results were obtained with a more graphitic material, HSAG100 (qe = 1.72·10−6 mol/m2). However, the best experimental results of this study were obtained using synthesized graphenic materials.

El debate sobre el posthumanismo representa una de las cuestiones más importantes del día. También forma parte de otra controversia: la de la posmodernidad, o lo que entendemos por ella, si suponemos que esta nomenclatura no es un reflejo fiel del momento presente. Ya se ha dicho que la ausencia de una verdadera cultura posmoderna declara y advierte de la situación actual como una crisis de la modernidad. Y como tal, ha significado la generación de múltiples perspectivas y versiones de esa modernidad, que representan el único contexto posible y no algo posterior (inexistente). En este ámbito de la crisis de la modernidad, está también la crisis del sujeto. En esta diatriba se cuestiona la idea del sujeto, del ser humano, del humanismo. Estos conceptos son ahora terminológicamente débiles. Considerar que los modelos de pensamiento heredados del Renacimiento sobre el hombre ya no pueden servir para seguir el hilo del humanismo es algo tremendo: la invalidación de los modelos culturales establecidos, de sus creencias y axiomas. Pero este es, en efecto, el caso. Hay una grieta, sin duda, en la idea del hombre. The debate on post-humanism represents one of the most important issues of the day. It is also part of another controversy: that of post-modernity, or what we understand by it, if we assume that this nomenclature is not a faithful reflection of the present moment. It has already been said that the absence of a true post-modern culture declares and warns of the current situation as a crisis of modernity. And as such, it has meant the generation of multiple perspectives and versions of that modernity, which represent the only possible context and not something later (non-existent). In this sphere of the crisis of modernity, there is also the crisis of the subject. In this diatribe the idea of the subject, of the human being, of humanism, is questioned. These concepts are now terminologically weak. To consider that the models of thought inherited from the Renaissance about man can no longer serve to follow the thread of humanism is something tremendous: the invalidation of established cultural models, of their beliefs and axioms. But this is indeed the case. There is a crack, no doubt, in the idea of man.

Ni, Cu and Ni-Cu catalysts supported on high surface area graphite were synthesized by incipient wet impregnation. Also, the effect of doping the graphite support with alkali oxides (Li, Na and K) was studied. The catalysts were tested in the formic acid decomposition reaction to produce hydrogen. The bimetallic Ni-Cu catalyst doped with K showed the best catalytic performance with 100% conversion of formic acid at 130 °C and a 95% of selectivity to hydrogen. The turnover frequency (TOF) of the catalysts follows the order: Ni-Cu/K > NiCu/Na > Ni-Cu > Ni-Cu/Li. While the order for the apparent activation energy values is: Ni-Cu > Ni-Cu/Li > Ni-Cu/Na > Ni-Cu/K. The mechanism of the reaction is approached by programmed temperature surface reaction (TPSR) experiments and attenuated total reflectance (ATR). The greater catalytic activity of the Ni-Cu catalyst doped with potassium is ascribed to the lower stability of the formate, bicarbonate and carbonate species on its surface.

The catalytic performance of a series of 4 wt.% Ru-based catalysts in the aqueous-phase hydrogenation of furfural (FAL) to furfuryl alcohol (FOL) has been studied in a batch reactor under very mild conditions of 20 °C and 10 bar hydrogen. The effects induced by different commercial supports (SiO2, TiO2, Al2O3, activated carbon and high surface area graphite) and two lab synthesized graphenic materials (with and without N-doping); as well as the influence of the catalyst preparation using three metal precursors (RuCl3, RuNO(NO3)3 and Ru3(CO)12) have been assessed. Materials were characterized by mean of nitrogen physisorption (BET), transmission electron microscopy (TEM), X-ray diffraction (XRD), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). The different supports significantly modify the catalytic behavior, with the catalysts prepared using graphenic materials found to produce the highest conversion of FAL and the maximum of selectivity to FOL. On these latter supports, the highest FAL yield was achieved by using triruthenium dodecacarbonyl as ruthenium precursor. Ruthenium supported on reduced graphene oxide (rGO) shows 93.3% conversion with 98% selectivity towards FOL. This catalyst was found to exhibit excellent stability, and was reused at least 4 times without loss of activity or selectivity. Characterization data suggest that the catalytic differences can be attributed to the particle size of Ru nanocrystals as well as to their interaction with the surface of graphenic materials. Furthermore, the catalytic results are influenced by the type of metal precursor and the reduction temperature, these facts suggesting that the genesis of the Ru nanoparticles can also play a key role controlling the catalytic activities obtained with these catalysts in the hydrogenation of FAL into FOL.

The effect of alkali promotion (Li, Na, K and Cs) on the CO preferential oxidation (CO PROX) reaction has been studied over Cu-CeO2 catalyst supported on carbon nanotubes (CNT). The catalysts were prepared with 2.5 wt.% Cu and 20 wt.% CeO2 loadings, and alkali/Cu atomic ratios of 0.68. The catalytic performance and the characterization by powder X-ray diffraction (XRD), TEM-STEM, H2-temperature-programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) has been presented. TEM and XRD analyses showed that the addition of alkali reduces the size of ceria crystallites. It was found that in general the incorporation of alkali favored the conversion of CO at low temperatures, being more pronounced for the K-doped catalyst. The characterization showed that the addition of K favored the Cu-CeO2 interaction, the activity of the catalyst was enhanced and the opposite was observed for Cs-doped sample. The characterization results reveal that the observed increase in the Cu+ species proportion and in lattice oxygen are related to the better catalytic performance.

Graphenic materials have been recently applied for adsorption processes due to their high efficiency and their easy capability of surface modification. In the present study two different graphene oxides, two reduced graphene oxides under inert atmosphere and one reduced graphene oxide under ammonia atmosphere were used as adsorbents for removing two chloroaromatic compounds from water: 2,4-dichlorophenol and 2,4-dichlorophenoxyacetic acid. Hydrogen bonds and π π interactions have been detected by Attenuated Total Reflectance infrared spectroscopy in the solids with adsorbed species. Besides, two direct relationships between their adsorption capacities and graphenic surface, textural and structural properties were found. In order to obtain real adsorption information, some experiments with the presence of both pollutants at the same time were performed. From these mixture experiments, when graphene oxide was used as adsorbent some cooperative effects between pollutants were detected. Based on XRD results and an innovative comparison between different infrared techniques, the importance of interlayer spaces during adsorption was demonstrated. Otherwise, synergetic interactions between pollutants were revealed as the main adsorption forces when reduced graphene oxides were used, being their aromatic structures a decisive factor in their final adsorption capacity.

Commercial carbon nanofibers with different graphitic structure and commercial multiwall carbon nanotubes (CNT) were chemically modified in order to introduce specific alkyl ligands on their surface. Palladium catalysts have been prepared using these modified supports and subsequently tested in the partial hydrogenation of 1,3-butadiene under conditions of excess hydrogen. Herein, we used thermogravimetry (TG), temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and nitrogen adsorption at 77 K techniques in order to characterize both supports and catalysts. We focus on testing the effects of support surface functionalities either on morphology of supported palladium (Pd) nanoparticles (NPs) or on their catalytic performances. High selectivity to butenes was obtained with the catalysts prepared over supports containing alkyl chains, while over-hydrogenation to butane took place over oxygen-containing functional groups. Nicely the catalysts with modified supports minimize the secondary hydrogenation of butenes even at high conversions. Therefore, Pd NPs on modified nano-carbon catalysts may open up more opportunities to optimize the activity and the selectivity for partial hydrogenation reactions.

Au nanoparticles of different sizes were supported by the deposition–precipitation method on two metal oxides: ZnO and TiO2. The resulting catalysts were tested in the ethanol catalytic transformation reaction. Both metal oxide support materials exerted a different influence on the achieved Au particle size as well as on the behavior of the subsequent catalyst, with regard to their initial conversion values, product distribution and stability. While TiO2 favors the formation of smaller nanoparticles, ZnO offers larger Au particle sizes when prepared under similar conditions. At the same time, TiO2 produced catalysts which displayed higher initial conversions in comparison with AuZnO catalysts, even when observing catalysts of each series with similar particle sizes. At the same time, catalysts supported on ZnO exhibited higher resistance to deactivation caused by coke formation. These results were evidenced employing different characterization techniques on both used and fresh catalyst samples. The decline in deactivation was generally accompanied by an increase in the carbon content on the catalyst's surface.

This work reports on the design of novel mixed valence hybrid N-doped carbon nanotubes/metal ferrite nanomaterials (MFe2O4, M(II) = Mn, Fe, Co) with tailored composition, and magnetic and electrical properties through a straightforward eco-sustainable and less time consuming one-pot in situ coprecipitation process. The potentialities of this strategy rely on the lack of oxidative treatments to the support and thermal annealing, besides the use of aqueous conditions, a chelating base (isopropanolamine) and low temperatures. The process afforded the controlled nucleation/growth of the MFe2O4 nanoparticles (NPs), with sizes of 3.2–5.4 nm and superparamagnetic properties, on the surface of the N-doped carbon nanotubes (CNT-N) and their immobilization by covalent bonding. The nitrogen-based functionalities of CNT-N allied with the use of a coprecipitation agent with coordinating properties towards M(II)/Fe(III) cations were responsible for these achievements. To unravel the potentialities of the novel nanohybrids (CNT-N@M), they were tested as electrode active nanomaterials in the fabrication of all-solid-state asymmetric paper supercapacitors (SCs). All asymmetric SCs presented significantly higher performance than the symmetric CNT-N based one, with an enhancement of the energy density to up to 6.0× and of the power density to up to 4.3× due to the occurrence of both non-faradaic and faradaic charge storage mechanisms. Moreover, they led to enhanced volumetric energy density (up to 11.1×) and power density (up to 5.2×) compared with other solid-state hybrid paper SCs based on carbon materials recently reported in the literature. These results highlight the importance of conjugating a conductive support bearing N-based functionalities with MFe2O4 NPs featuring redox properties towards synergistically enhanced energy storage.

A series of NiCu based catalysts were prepared using different carbon nanostructure as support and loading 2.5 wt% of each metal. The studied nanocarbon materials were: reduced graphene oxide (rGO), N-doped reduced graphene oxide (NrGO), high surface area graphite (HSAG), single and multiwalled carbon nanotubes (SWCNT and MWCNT), N-doped carbon nanotubes (NCNT), spheres of xerogel carbons (SXC) and N-doped SXC (NSXC). The effect of N-doping, electronic properties and morphology of the carbon nanostructures on the metallic particle size was studied as well as their capacity to produce high purity hydrogen from formic acid decomposition at low temperature. The NiCu based catalysts tested are highly selective to H2 (98−94 % at conversions above 95 %). The site time yield (STY) of the catalysts follows the order: NCNT > SXC > SWCNT∼HSAG∼rGO10>rGO325>MWCNT∼NSXC > NrGO325>NrGO10, indicating that N-doped catalysts are less active, except in the case of NCNT which is ascribed to the N-pyrrolic heteroatoms of this material.

The external surface of a commercial porous stainless steel (PSS) was modified by either oxidation in air at varying temperatures (600, 700, and 800 °C) or coating with different oxides (SiO2, Al2O3, and ZrO2). Among them, PSS-ZrO2 appears as the most suitable carrier for the synthesis of the Pd membrane. A composite Pd membrane supported on the PSS-ZrO2 substrate was prepared by the electroless plating deposition method. Supported Ru catalysts were first evaluated for the low-temperature methane dry reforming (DRM) reaction in a continuous flow reactor (CR). Ru/ZrO2-La2O3 catalyst was found to be active and stable, so it was used in a membrane reactor (MR), which enhances the methane conversions above the equilibrium values. The influence of adding H2O to the feed of DRM was investigated over a Ru/ZrO2-La2O3 catalyst in the MR. Activity results are compared with those measured in a CR. The addition of H2O into the feed favors other reactions such as Water-Gas Shift (RWGS) and Steam Reforming (SR), which occur together with DRM, resulting in a dramatic decrease of CO2 conversion and CO production, but a marked increase of H2 yield.

The Pd4S phase of palladium sulfide is known to be a highly selective alkyne hydrogenation catalyst at atmospheric pressure. Results presented here demonstrate that high selectivity can be retained at the elevated pressures required in industrial application. For example, in a mixed acetylene/ethylene feed, 100% conversion of acetylene was attained with a selectivity to ethylene in excess of 80% at 18 bar pressure. Similarly, almost 85% selectivity can be obtained with mixed C3 feeds containing methyl acetylene, propadiene, propylene and propane at 18 bar pressure. Using a low loaded sample (0.1 wt% Pd) it was possible to estimate the TOF to be 27 s−1. High selectivity was related to the crystal structure of Pd4S with the unique spatial arrangement thought to favour Pd atoms acting in isolation from one another. Based on these results, it is proposed that this catalyst could be a potential replacement for PdAg alloys currently used by industry.

The highly hygroscopic MoCl 5 exhibited, under helium stream, several transformations between room temperature and 387 °C. At low temperatures (between 77 and 202 °C), the salt transforms into the stable MoO 3 oxide and the less-stable oxochloride, MoOCl 4 , which evaporates and decomposes into MoOCl 3 . The former compound evaporates at 313 °C, while the entire vanishing of MoCl 5 occurs at 387 °C. In the presence of NH 4 + –ZSM-5 zeolite, the starting salt is transformed into MoOCl 4 and then into the volatile MoO 2 (OH) 2 . The non-isothermal solid-state ion exchange of MoO 2 (OH) 2( g ) into H + –ZSM-5 zeolite occurs between 342 and 523 °C. Nonetheless, the isothermal exchange is highly recommended at a temperature below 523 °C in order to avoid the irreversible zeolite dealumination. In this study, thermodynamical calculations were used for the elucidation of the physical states of decomposition products.

The aim of this work is to understand the role of oxygen surface groups during the preparation, activation and reaction of heterogeneous ruthenium catalysts supported on activated carbon materials. Hence, non-promoted and sodium promoted ruthenium catalysts supported on two different activated carbon materials, with and without oxygen surface groups, were prepared by successive incipient wetness impregnation and tested in the ammonia decomposition reaction. The catalysts were characterised with a multi-technique approach that involves; nitrogen adsorption isotherms at −196 °C (BET and BJH methods), temperature programed oxidation (TPO), scanning electron microscope (SEM), temperature programed desorption (TPD), transmission electron microscopy (TEM), in-situ X-ray absorption near edge structure (XANES), temperature programed reduction (TPR) and microcalorimetry of hydrogen chemisorption. The performance of the different ruthenium supported catalysts during the ammonia decomposition reaction was determined in a constant flow fixed-bed reactor at 1 atm, in the temperature range from 350 °C to 450 °C. This work shows how the oxygen surface groups of the activated carbon can be used to control/influence (i) the final oxidation state of ruthenium particles, (ii) ruthenium particles size, (iii) selective deposition of the sodium promotor. We believe that such use of the presence of surface groups on the activated carbon surface could potentially be employed to improve the catalytic performance of next generation heterogeneous catalysts.

Four Ru/KL-zeolite catalysts containing 2 wt% of Ru were prepared from Ru 3 (CO) 12 , RuNO(NO 3 ) 3 , Ru(C 5 H 7 O 2 ) 3 and RuCl 3 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 523 K–573 K. 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.

International audience; The catalytic performances of Mo–ZSM-5 catalysts (6 wt% of Mo, Si/Al = 26), prepared by solid–state ion exchange from different molybdenum precursors, were evaluated in the ammoxidation of ethane and ethylene into acetonitrile in the temperature range of 425–500 °C. The catalysts were characterized by chemical analysis, N2–physisorption, XRD, FTIR, 27Al MAS NMR, DRIFT, UV/Vis DR, Raman, and XPS spectroscopies, NH3–TPD, and H2–TPR. Starting from MoCl5, Mo is stabilized in the dimeric form and only small crystallites of MoO3 were formed. However, the oxygenated precursors, i.e. MoO3, (NH4)6Mo7O24·4H2O, and MoO2(C5H7O2)2 are favorable for the agglomeration of amorphous MoO3. In the studied reaction, the required active sites are (MoO4)2–, (Mo2O7)2–, (Mo7O24)6–, and small crystallites of MoO3, while the undesired amorphous MoO3 inhibited the diffusion of reactants to the active sites and/or enhanced the hydrocarbon combustion. Upon the catalyst issued from MoCl5, UV/Vis DRS revealed the abundance of dimeric Mo at the detriment of mono and polymeric species. The former specie played a key role in the ammoxidation since the two Mo atoms in (Mo2O7)2– are spatially too separated and the steric hindrance between intermediate molecules is therefore limited.

The efficacy of three different heteropolyacids (HPAs) supported on activated carbon (AC) or on high surface area graphite (HSAG) has been comparatively evaluated in the dehydration of bio-ethanol to yield ethylene or diethyl ether. These supported heteropolyacid compounds exhibit remarkable catalytic performances for the ethanol conversion at relatively low reaction temperatures. Furthermore, taking into account the sensitivity of heteropolyacid structures to the presence of water, some catalytic tests with ethanol + water mixtures as the reactant feed have been performed, proving the stability of these composite materials under the used reaction conditions. Structural characterization of these materials has been accomplished by thermal gravimetric analysis coupled with differential thermal analysis (TGA-DTA) and by X-ray diffraction. The textural properties of the synthesized materials were determined from the nitrogen adsorption isotherms. Also, ammonia temperature programmed desorption was performed in order to evaluate the amount and strength of exposed acid surface sites. While phosphomolybdic acid is thermally unstable under the reaction conditions, supported tungstophosphoric and silicotungstic acids are stable under the reaction conditions even in the presence of water. These results are significant because these new carbon supported catalyst materials can be envisaged as highly promising candidates for the production of petrochemicals from bio-ethanol.

In this work we report a simple procedure for synthesis of Cu and Pd catalysts supported on high surface area graphite (HSAG) by wetness impregnation technique, and further generation of metal nanoparticles using NaBH 4 as reducing agent. The catalysts have been tested in the reduction of 4-nitrophenol to 4-aminophenol, at room temperature, in presence of NaBH 4 as hydrogen source. Both Cu and Pd catalysts exhibited exceptionally high catalytic activity with the total degradation of 4-nitrophenol in less than 45 s. Taking into account that Cu is cheaper than Pd, we focused our investigation on studying the catalytic properties of Cu nanoparticles supported over two lab prepared graphene-materials (one N-doped and other undoped) and the commercial HSAG. The maximum catalytic activity was obtained with Cu supported on undoped graphene due to the combination of two parameters: small metal particle size and the unique properties of graphene generated by its electron transference ability. However, recyclability of both Cu/graphene-materials fell after 5 consecutive runs, while Cu/HSAG displayed high stability even after 10 cycles. In order to rationalize these findings, it is postulated that copper nanoparticles in Cu/HSAG are located at the edges of the graphite layers, where a stronger metal-support interaction takes place.

A number of inorganic carbonaceous materials (activated carbon, high surface area graphite and graphenic materials) have been used as supports of Ru nanoparticles in order to determine their catalytic properties in the base-free aqueous-phase oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). In particular, we have studied in detail reduced graphene oxide (rGO) and nitrogen doped reduced graphene oxide (NrGO), which are the support materials that produce more selective ruthenium catalysts. Also the effects of different metal precursors used in the preparation of the Ru nanocrystallites have been evaluated. Both support materials and Ru catalysts were characterized by elemental analysis, nitrogen physisorption (BET), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The point of zero charge (PZC) for the graphenic materials was also determined. Interestingly the different supports significantly modify the catalytic performances, the graphenic materials being those that under our experimental reaction conditions produce the highest selectivity to FDCA. On these supports (rGO and NrGO) the highest HMF conversion was achieved by using triruthenium dodecacarbonyl as the ruthenium precursor. For the improved catalyst, Ru supported on NrGO, the yield of FDCA becomes close to 80%. This catalyst has been reused several times with neither loss of activity nor modification in selectivity values. Characterization data indicate these catalytic results can be correlated to the basic properties of the NrGO support as well as to the surface properties of Ru nanoparticles. These findings indicated that the metal precursor and the surface functional groups exposed on the support can modulate the catalytic properties, in particular amending the selectivity towards FDCA production.

© 2019 by the authors., N-doped (NrGO) and non-doped (rGO) graphenic materials are prepared by oxidation and further thermal treatment under ammonia and inert atmospheres, respectively, of natural graphites of different particle sizes. An extensive characterization of graphene materials points out that the physical properties of synthesized materials, as well as the nitrogen species introduced, depend on the particle size of the starting graphite, the reduction atmospheres, and the temperature conditions used during the exfoliation treatment. These findings indicate that it is possible to tailor properties of non-doped and N-doped reduced graphene oxide, such as the number of layers, surface area, and nitrogen content, by using a simple strategy based on selecting adequate graphite sizes and convenient experimental conditions during thermal exfoliation. Additionally, the graphenic materials are successfully applied as electrocatalysts for the demanding oxygen reduction reaction (ORR). Nitrogen doping together with the starting graphite of smaller particle size (NrGO325-4) resulted in a more efficient ORR electrocatalyst with more positive onset potentials (Eonset = 0.82 V versus RHE), superior diffusion-limiting current density (jL, 0.26V, 1600rpm = −4.05 mA cm−2), and selectivity to the direct four-electron pathway. Moreover, all NrGOm-4 show high tolerance to methanol poisoning in comparison with the state-of-the-art ORR electrocatalyst Pt/C and good stability., This research was supported by the Spanish Agencia Estatal de Investigación (AEI) under projects CTQ-2017-89443-C3-1-R and CTQ-2017-89443-C3-3-R. C.S.R.B. gratefully acknowledges financial support from Spanish Ministerio de Educacion, Cultura y Deporte, Grant Nº FPU15/01838. D.M.F. also thanks Project UNIRCELL - POCI-01-0145-FEDER-016422 funded by European Structural and Investment Funds (FEEI) through - Programa operacional Competitividade e Internacionalização - COMPETE2020 and by national funds through FCT - Fundação para a Ciência e a Tecnologia, I.P.

[EN] 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., We acknowledge the financial support from the Spanish Government (projects CTQ2017-89443-C3-1-R and CTQ2017-89443-C3-3-R). Juan M. Zamaro thanks CONICET of Argentina for the support given to carry out a research stay at ICP-CSIC, Spain.

Correction for 'Multifunctional mixed valence N-doped CNT@MFe2O4 hybrid nanomaterials: from engineered one-pot coprecipitation to application in energy storage paper supercapacitors' by Clara Pereira et al., Nanoscale, 2018, 10, 12820-12840.