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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.

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.

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.

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 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.

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.

[EN] In the present study, the catalytic coupling of ethanol into 1-butanol through the Guerbet reaction was studied in a fixed bed reactor over different catalytic systems based on Cu and/or Ni as a hydrogenating/dehydrogenating components, and manganese oxide incorporating acid/base properties over a carbonaceous support, high surface area graphite (HSAG). The catalysts were prepared by wetness impregnation of the support with the corresponding metal nitrates and the resulting material was then reduced in-situ with hydrogen at 573 K for 1 h before reaction. The catalysts were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), specific surface area, NH temperature-programmed desorption, CO chemisorption, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). From all these techniques it can be deduced that the dimensions of the catalytic ingredients (Cu, Ni, Mn)are in the nanometric scale and homogeneously dispersed on the support. The reactions were performed in a continuous-flow fixed-bed reactor in gas phase with these bifunctional catalysts at 503 K and 50 bar using a stream of helium and ethanol. The bimetallic catalyst 2.5Cu2.5Ni-Mn/HSAG, treated in helium at 723 K prior reduction with hydrogen, exhibited the best catalytic performance in terms of 1-butanol selectivity (39%), presumably due to the synergetic effect of the weak strength acid sites and the strong base sites related to manganese oxide and the Cu-Ni nanoparticles., We acknowledge financial support from the Spanish Government (projects CTQ2017-89443-C3-2-R and CTQ2017-89443-C3-3-R). Also CLO thanks the MECD of Spain for a FPU predoctoral grant FPU16/05131.

[EN] The catalytic performance of a series of Ru-based catalysts was evaluated for the selective aerobic oxidation of benzyl alcohol to benzaldehyde under base-free mild conditions. The effect of metal precursor (RuCl, RuNO(NO) and Ru(CO)) and support on catalyst performance was investigated by comparing undoped (rGO) and N-doped (NrGO) reduced graphene oxide with commercial activated carbon and high surface area graphite supports. The surface chemistry and structure of materials were characterized by nitrogen physisorption (BET), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The average Ru nanoparticle sizes were in the range from 1.4 to 2.4 nm, with the smallest particle sizes obtained on rGO support owing to its highest surface area. Catalysts prepared from RuNO(NO) and Ru(CO) precursors exhibit the highest benzyl alcohol conversion to the corresponding aldehyde, with highest conversions observed when NrGO support is employed. Catalysts prepared from Ru(CO) on NrGO support exhibit the highest activity for benzaldehyde formation, which is over three times that of commercial activated carbon supported Ru catalysts. The differences in catalytic performance are attributed to interactions between the acidic product of the reaction and the basic surface sites of the NrGO support, and modification of the surface hydrophobicity. These factors confer a significant rate enhancement in the selective oxidation of benzyl alcohol over Ru/NrGO compared to Ru/rGO. Ru/NrGO is stable under reaction conditions, however progressive deactivation is observed owing to water accumulation at the active site. Catalysts are easily reactivated via heating, with >90% of the original activity recovered on reuse., CRB gratefully acknowledges financial support from Spanish Ministerio de Educacion, Cultura y Deporte, Grant Nº FPU15/01838. Also the financial support from the Spanish Ministerio de Economía y Competitividad under projects (CTQ2017-89443-C3-1-R and -3-R) is recognized.KW thanks the Royal Society for the award of an Industry Fellowship.

The preparation of MoxSy nanoparticles with different morphologies via a surfactant-assisted one-pot solvothermal route was reported. The concentration of surfactant was studied to evaluate its effects on the morphology and the size of the as obtained nanoparticles. The final products were comprehensively characterized using XRD, TEM, HRTEM, IR, TGA and XPS. It was found that at low surfactant concentration, MoS2 spherical shapes were obtained whereas tubular morphologies are formed at higher concentration. This issue has been discussed based on various relevant experimental data.

A particular palladium sulphide phase (Pd4S) supported on carbon nanofibers is shown to be one of the most selective alkyne hydrogenation catalysts reported to date. Propyne and ethyne (in the absence of the corresponding alkene) can be converted in the gas phase to the corresponding alkene with 96% and 83% selectivity at 100% alkyne conversion. A bulk phase PdS powder (pre-reduced at 523 K) also demonstrated excellent performance (79% ethene selectivity). Other bulk phase metal sulphides (Ni2S3 and CuS) were tested and whilst the nickel analogue was found to be active/selective the performance was poorer than observed with either supported or unsupported Pd sulphide. Exceptional alkene selectivity extends to mixed alkyne/alkene feeds using the Pd4S/CNF catalyst – 86% and 95% alkene selectivity for C3 and C2 mixes, respectively. This report opens up exciting possibilities for using metal sulphides as highly selective hydrogenation catalysts.

This work reports on the investigation of the influence of the parent zeolite topology (MFI, MOR and USY) on the ammoxidation of ethylene to acetonitrile over vanadium and molybdenum oxide supported zeolite catalysts. The physico-chemical properties were investigated by several characterization techniques such as XRD, N 2 -adsorption, 27 Al MAS NMR, TEM, XPS, DR UV–vis, Raman and DRIFT spectroscopies and H 2 -TPR. From the catalytic results, V and Mo oxide species in USY and MOR zeolites led to less active catalysts when compared to MFI structure. These results suggest that the catalytic performances depend strongly on the zeolite structure and thus, the size of the formed metal oxide particles. The catalytic activity and selectivity are controlled by the porous structure and the chemical state of V and Mo species. The extent of dispersion and reducibility of supported M-O x (M V or Mo) species are governed by the chemical identity of the support as detected by TPR analysis and optical absorption spectroscopy. The good catalytic performance of MFI-type zeolite might be related to the high dispersion of metal oxide species and to the internal pore space which permits an effective accessibility of the reactants.

International audience; Hydrogen interaction with ruthenium surfaces is a complex phenomenon that can play an important role in catalytic reactions such as ammonia synthesis. In this study, H-2/D-2 isotopic homomolecular exchange has been used to characterize four different catalytic surfaces, namely Ru/AC(0), Ru/AC(1), Ru-Na/AC(0) and Ru-Na/AC(1). They are composed of 2%Ru or 2%Ru-4.5%Na supported on an active carbon with (AC(0)) and without surface groups (AC(1)). The AC(1) carbon (1162 m(2) g(-1)) is obtained by treatment of AC(0) (960 m(2) g(-1)) in N-2 at 900 degrees C. Ru/AC(0) and Ru/AC(1) catalysts are prepared by impregnation of the supports with aqueous solutions of Ru(NO)( NO3)(3). Na-promoted catalysts are then prepared by impregnation of Ru catalysts with NaOH solutions. An overall picture of the surface mobility phenomena on the four different catalytic surfaces has been described. It has been demonstrated that the presence of Na promoter in Ru-Na/AC0 and Ru-Na/AC(1) catalysts inhibits the spillover of H atoms from the Ru particles to the AC surface. However, for non Na promoted catalysts, the extension of the H spillover phenomenon depends on the amount of oxygen groups present on the AC surface. Likewise, the formation of a ruthenium hydride during the reduction treatment is suggested for catalysts promoted or not by Na. Finally, this work shows how the kinetics of the H-2/D-2 isotopic exchange reaction may be related to the surface electron density of the catalyst, which allows us to better understand the effect that both promoter and support have on the metal particles.

Dimerization of isobutene (IBE) to C8s olefins was evaluated over a range of solid acid catalysts of diverse nature, in a fixed bed reactor working in a continuous mode. All catalytic materials were studied in the title reaction performed between 50&ndash, 250 &deg, C, being the reaction feed a mixture of IBE/helium (4:1 molar ratio). In all materials, both conversion and selectivity increased with increasing reaction temperature and at 180 &deg, C the best performance was recorded. Herein, we used thermogravimetry analysis (TGA) and temperature programmed desorption of adsorbed ammonia (NH3-TPD) for catalysts characterization. We place emphasis on the nature of acid sites that affect the catalytic performance. High selectivity to C8s was achieved with all catalysts. Nicely, the catalyst with higher loading of Br&oslash, nsted sites displayed brilliant catalytic performance in the course of the reaction (high IBE conversion). However, optimum selectivity towards C8 compounds led to low catalyst stability, this being attributed to the combined effect between the nature of acidic sites and structural characteristics of the catalytic materials used. Therefore, this study would foment more research in the optimization of the activity and the selectivity for IBE dimerization reactions.

Acid hydrolysis and hydrogenation/hydrogenolysis reactions can be combined for catalytic conversion of cellulose into renewable biorefinery feedstocks by using heterogeneous bifunctional catalysts. In the present study a cooperative effect of heteropolyacids (HPA) and Ru nanoparticles supported on two carbon materials is demonstrated. The process can be suitable for the one-pot tandem reaction, yielding the conversion of cellulose into alkanediols (mainly propylene glycol and ethylene glycol). From a mechanistic point of view the differences in the distribution of polyol products, obtained from the cellulose reaction over monometallic Ru catalysts or over bifunctional Ru-HPAs materials, seem to be strongly determined by the competitive reactions of the sucrose (glucose + fructose) intermediate. HPA not only promote, as solid acids, the efficient hydrolysis of cellulose to glucose, but also catalyze the selective cleavage of the C C bonds in glucose and fructose, leading to the formation of ethylene glycol and propylene glycol. These reactions are in competition with the sugar hydrogenation to the corresponding C 6 polyols (e.g. sorbitol), which takes place on the single Ru surface sites. The strong dependence of the product distribution on both catalytic functions is clarified by the kinetic analysis of the three competitive reactions of glucose, including its hydrogenation, isomerization and C C bond cleavage. Finally, considering the applicability of this reaction, it should be raised that the ball-milling pretreatment of cellulose is compulsory. In fact, during this ball-milling the crystallinity and particle size of cellulose are reduced, which results in a much higher conversion of cellulose. Herein, mixed ball-milling of cellulose and solid catalysts together was presented, which remarkably accelerates the cellulose conversion into valuable products.

[EN] The effect of using two different promoter precursors on the Fischer-Tropsch synthesis was studied over cesium promoted ruthenium catalysts supported on a high surface area graphite support. In this work we reveal significant modifications in the selectivity values for Fischer-Tropsch reaction depending on the Cs promoter precursor (CsCl vs CsNO3). Specifically the bimetallic catalyst (4Ru-4Cs), prepared from nitrates both for metal and promoter precursors, showed a high selectivity to CO2 during reaction. By modifying the cesium precursor, it was possible to inhibit the water gas shift reaction, decreasing significantly the selectivity to CO2. In order to understand the chemical origin of these modifications a careful characterization of the materials was performed including: X-ray absorption near edge spectroscopy, transmission electron microscopy measurements, temperature programmed reduction studies, determination of the CO uptakes on the catalysts and the evolution of the CO adsorption heats as a function of surface coverages. It was found that upon reduction and under reaction atmosphere the promoter in the ex-nitrate catalyst appears as Cs2O which is considered responsible of the CO2 production, while in the catalysts prepared with Cs chloride the promoter remains as CsCl suffering a slight partial reduction., We acknowledge financial support from the Spanish Government (projects CTQ2014-52956-C3-2-R and CTQ2014-52956-C3-3-R) and thanks CSIC for PIM-2014-201480I012 project. The ESRF and ALBA synchrotron are thanked for granting beamtime at ID24 and BL22-CLAESS, respectively.

Adsorption of three representative emerging pollutants - 1,8-dichlorooctane, nalidixic acid and 2-(4-methylphenoxy)ethanol- on different carbon nanotubes was studied in order to determine the influence of the morphological and chemical properties of the materials on their adsorption properties. As adsorbents, multiwall carbon nanotubes (MWCNTs) without functionalization and with oxygen or nitrogen surface groups, as well as carbon nanotubes doped with nitrogen were used. The adsorption was studied in aqueous phase using batch adsorption experiments, results being fitted to both Langmuir and Freundlich models. The adsorption capacity is strongly dependent on both the hydrophobicity of the adsorbates and the morphology of the adsorbents. Thermodynamic parameters were determined observing strong interactions between the aromatic rings of the emerging pollutant and the nitrogen modified adsorbents., This work was supported by the Spanish Government (contract CTQ2011-29272-C04-01, -02 and -03). Y. Patiño thanks the Government of the Principality of Asturias for a Ph.D. fellowship (Severo Ochoa Program).

Graphene oxide and multiwall carbon nanotubes (CNTs) were chemically modified by treatment with urea and subsequent annealing at different temperatures. These materials were used as supports for gold nanoparticles and the resulting samples have been applied as catalysts in the 1,3-butadiene partial hydrogenation reaction. The supports and catalysts were exhaustively characterized. It was shown that urea treatments modified the graphene surfaces and the morphology of CNTs, in both cases with incorporation of significant amounts of different nitrogen surface groups. The presence of these groups on few layered graphene or on CNT surfaces modifies the gold precipitation–deposition process during catalyst preparation, giving place to different amounts of incorporated gold on the various supports. The obtained catalytic results suggested that the partial hydrogenation requires limited availability of hydrogen, and for this the migration through adsorbed species between the metal and support to initiate the hydrogenation, probably by a spillover mechanism, seems to be a required step. In general intramolecular selectivity is structure-sensitive meanwhile catalytic activity is not structure-sensitive, as evidenced when the gold nanoparticle sizes are decreased., E C gratefully acknowledges nancial support from the Spanish Ministry of Science and Technology and from the UNED postdoc programme. This work was supported by the Spanish Government (project CTQ 2011-29272-C04-01and 03).

The hybrid material graphite oxide (GO) intercalated with an iron(III) porphyrin was obtained upon a silylation reaction of GO with 3-bromotrimethoxypropylsilane (BrTMS) followed by metalloporphyrin immobilization. Diverse reaction conditions and microwave versus conventional heating were tested. The materials were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), thermogravimetry (TGA) and temperature programmed desorption (TPD). Microwave-assisted synthesis allowed functionalization reactions of 1 h instead of 24 h (conventional heating) with equivalent or improved yields on both silylation and metalloporphyrin immobilization reactions. The immobilizations performed in anhydrous solvent and absence of other exfoliation agents led to an increase on the GO interlayer distance of 0.14 nm, in a total space of 7 Å that match the metalloporphyrin thickness., The authors thank the Fundação para a Ciência e a Tecnologia (FCT, Portugal), the European Union, QREN, FEDER, COMPETE, for funding REQUIMTE through projects PEst-C/EQB/LA0006/2013, NORTE-07-0124-FEDER-000067-nanochemistry and PTDC/EQU-ERQ/110825/2009. Authors acknowledge the MICINN of Spain (Projects CTQ-2011-29272-C04-01 and -03) for financial support. Thanks are also due to Joint Project “Acções Luso-Espanholas” E20/11 Acciones Integradas AIB2010PT-00104. Monika E. Lipińka also thanks FCT for a PhD grant SFRH/BD/66297/2009.

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.

The interaction of organic chemicals with the surface of carbon nanotubes has been studied by immersion calorimetry revealing significant differences in the properties when these materials are modified thermally or chemically. Therefore, multiwall carbon nanotubes have been synthesized using a chemical vapour deposition procedure and subsequently aliquots were treated with HNO3 at reflux, maintaining the reaction during different times, in order to incorporate oxygen surface groups, or were treated at 2873 K under inert atmosphere. The aim of this thermal treatment is to eliminate structural defects of the carbon nanostructures and to graphitize the amorphous carbon phases. These features were confirmed by high-resolution transmission electron microscopy. The immersion in organic compounds, including toluene, methanol and methylcyclohexane, of all these carbon nanotubes samples reveals that the surface properties are remarkably modified. Thus, the formation of different types of interaction, depending on the surface, gives place to changes in the immersion enthalpies., E.C. gratefully acknowledges financial support from the Spanish Ministry of Science and Technology and from the CSIC, JAE postdoc programme. To J.M.D. Tascon of INCAR-CSIC, for having kindly provided the Raman spectra and the SEM micrographs, as well as for his valuable discussion of these data. This work was supported by the Spanish Government (project CTQ2011-29272-C04-01 and -03).

Chemisorption of CO combined with microcalorimetry has been applied to study the nature, number and adsorption strength distribution of surface sites exposed by carbon-supported Ru catalysts. A comparative analysis of the CO chemisorption on different Ru catalysts, prepared using two different metal precursors, RuCl3·xH2O and Ru(NO)(NO3)3, has been carried out. An activated carbon and the corresponding derivative where oxygen surface groups were incorporated, as well as carbon nanotubes and a high surface area graphite, were used as catalytic supports. Based on previous temperature programmed reduction studies, all the catalysts were reduced under hydrogen flow at 523 K or at 573 K. The CO adsorption differential enthalpy profiles show that Ru(NO)(NO3)3 precursor produces more homogeneous surface site distribution in the Ru nanocrystals, in comparison with those prepared from RuCl3, as well as higher values of enthalpies in the medium range of coverage. As a possible explanation for this effect, residual chloride species remaining after reduction treatment in the ex-chloride catalysts, that can be anchored to the Ru nanoparticles weakening the CO adsorption, have been considered. This behavior occurs for the three studied carbon supports. On the other hand, the oxygen surface groups incorporated on the activated carbon seem not to modify the CO adsorption properties of the catalysts, independently of the precursor employed., EGS would like to thank to UNED in Spain for a scholarship grant and LGC to the CSIC for a JAE predoct-grant. The financial support of the Spanish government under projects CTQ2011-29272-C04-01 and -03 is recognized.

The low temperature reforming of methane by carbon dioxide is studied over a calcium oxide promoted Ni catalyst supported on a tetragonal zirconia stabilized by lanthana, which presents an improved stability compared to the non-promoted catalyst. Steady-state catalytic activity measurements, diffuse reflectance infrared Fourier transform spectroscopic analysis and isotopic temporal analysis of products experiments reveal the occurrence of a bifunctional mechanism on the promoted catalyst: methane is activated on the Ni particles, carbon dioxide interacts with the calcium oxide to form carbonates which scavenge carbon from nickel at the Ni-O-Ca interphase, thus restoring Ni particles to the original state. This is assumed to hinder the formation of deactivating coke, which explains the improved catalytic stability of the promoted catalyst. The main route for the carbon deposit formation is found to be the methane cracking in spite of the low temperature reaction., Financial support by the MICINN of Spain (project CTQ2008-03068-E/PPQ) and the German Ministry of Education and Research (BMBF, contract no. 03X216) are gratefully acknowledged.