Search

Effect of the Ni precursor and of the copper addition on the properties of Ni/KL-supported catalysts was studied by TPR, H 2 chemisorption, N 2 adsorption, CO-FTIR and CO adsorption microcalorimetry. Characterization measurements of catalysts prepared from nickel (II) nitrate hexahydrate, nickel (II) acetylacetonate and nickel (II) phthalocyanine, respectively, show different nickel species distribution in the zeolite, with electron rich metal particles inside the lattice. For NiCu/KL bimetallic catalysts, combined studies by CO-FTIR and by CO adsorption microcalorimetry, together with the TPR results, provide evidence of formation of bimetallic nanoparticles with alloy type structure. The contribution of this species to the surface composition of the catalysts depends on the respective Ni/Cu atomic ratio. Encapsulation of part of the metal components in the zeolite channels and formation of segregated copper particles were also found. Results in the hydrogenation of citral at 323 K in the liquid phase evidence a positive relationship of the catalytic activity with the population of electron rich metal species on the monometallic catalysts. Copper inhibits the hydrogenation activity of nickel and modifies the structure of the exposed nickel surface, which affects the stability of the catalysts and the selectivity for the competitive hydrogenation of conjugated C C and C O bonds of the citral molecule.

This paper presents a first approach of a simple way to obtain vertically orientated carbon nanotubes. The used catalytic system consisted of quartz or graphite plates, on which some iron solutions (of precursors such as nitrates or phthalocyanines) were deposited by simple impregnation, generating homogeneous films. After drying, the plates were submitted to reduction and reaction procedure, which consisted in acetylene decomposition at 750 °C during 1 h. Samples after reaction were studied by scanning electron microscopy and transmission electron microscopy, which confirmed the formation of homogeneous and vertically orientated structures of carbon nanotubes over the plates.

Ru catalysts supported on three types of graphite nanofiber materials, stacked-cup (PR24-HHT), platelet (CNF-P) and bamboo-like (CNF-B), have been synthesized and characterized by HRTEM and calorimetry of CO adsorption. The influence of the support nanostructure on their catalytic performance in the selective hydrogenation of paracetamol was also studied. An inverse correlation between the heats of CO adsorption and the activity and stereoselectivity to the trans-4-acetamidocyclohexanol was found. The results have been rationalized in terms of the morphology and electronic properties of the metal particles. These features are controlled by the different location of the crystallites and the metal-support interactions induced that eventually depend on the nanostructure of the support. As a consequence the supports seem to modify the Ru nanoparticles surface structures, and the shift in selectivities can be related with variations of the reactant chemisorption over such Ru surfaces.

The interactions of phenol, aniline and p-nitrophenol, adsorbed from aqueous solutions, with the surface of two activated carbons (with and without oxygen surface groups) were followed by temperature programmed desorption, thermogravimetry and analysis by mass spectrometry. The results reveal that on bare surface the three molecules can be presented as physisorbed and chemisorbed species. When oxygen surface groups are introduced on the carbon surface, there is a change in the adsorption/desorption behaviour; in such a way that the phenol chemisorption is inhibited and that decomposition of aniline and nitrophenol are originated.

The reaction of n-hexane was studied over two series of bimetallic RuCu/KL and the results were related to the surface characteristics of the catalysts. The catalysts containing 2 wt% of ruthenium and copper between 0 and 1.5%, were prepared following two different procedures: series (s) by successive wetness impregnation of KL-zeolite support with tri-ruthenium dodecacarbonyl and copper nitrate acetone solutions; series (c) by coimpregnation of the zeolite support with tri-ruthenium 2,4-pentanedionate and copper nitrate acetone solutions. The catalytic activity measurements were performed in a fixed bed flow reactor at 650 K and atmospheric pressure. For series (s) both metal dispersion and activity decrease as the copper content increases, while the TOF is not modified. For series (c) dispersion, activity and TOF decrease with the increasing of copper content. All the catalysts essentially exhibit hydrogenolysis activity with a low selectivity towards benzene that, nevertheless, increases with the copper loading more appreciably for series (c) than for series (s). The catalytic results suggest that copper and ruthenium form bimetallic particles in both series. For series (s) a covering effect of the ruthenium particles by copper without significant Ru–Cu interaction, is deduced. For series (c) important changes in the catalytic properties by effect of the copper are observed, which indicate the formation of a surface alloyed phase. In addition, copper seems to increase the fraction of active sites outside the KL-zeolite, which are more easily poisoned by coke deposition than those located inside the KL channels.

Bimetallic Ru–Cu catalysts supported on KL zeolite have been prepared by coimpregnation with ionic precursors and characterized by several methods, such as temperature-programmed reduction, CO and hydrogen chemisorption, nitrogen adsorption, infrared spectroscopy of chemisorbed CO and microcalorimetry of CO adsorption. The catalytic behavior of the samples was analyzed in the selective hydrogenation of citral in the liquid phase, at 323 K and 5 MPa. The presence of bimetallic entities as well as of segregated copper species was recognized by the TPR measurements. The CO-FTIR and microcalorimetry results evidence that the higher the Cu/Ru atomic ratio the larger the surface heterogeneity, with formation of Cuδ+ species. Bimetallic catalysts are more active than the monometallic ruthenium catalyst in the hydrogenation of citral, but this activity decreases with the increasing of copper concentration. In addition, selectivity towards citronellal decreases as the copper content increases, in opposite trend to the selectivity toward geraniol and nerol. For low copper loading (Cu/Ru ≈ 0.4) formation of a surface alloy is discussed. This surface structure is particularly active for hydrogenation of the conjugated C C double bond of citral. For Cu/Ru = 0.8 and Cu/Ru = 1.2 samples, three-dimensional islands of segregated copper seem to cover, in part, the surface alloy. This latter surface structure is less active than the preceding one for hydrogenation of the C C double bond, but more selective for hydrogenation of the C O group of citral.

Carbon nanotubes have been synthesized by catalytic chemical vapour deposition (CVD) of acetylene, over several iron–silica catalysts, in a fluidized bed reactor at 973 K. High yield and selective syntheses of carbon nanotubes was achieved with this reactor. The carbonaceous samples were submitted to acidic treatments (HF and/or HNO 3 ), which clearly produced structural changes in the nanotubes structure, as observed by transmission electron microscopy (TEM). Moreover, the formation of oxidic groups on the surface of carbon nanotubes was followed by means of temperature desorption experiments and thermo-gravimetric analyses. Adsorption of hydrogen at 300 K and relative high pressures (up to 70 bar) has been also investigated on these purified carbon nanotubes, besides on different carbon materials.

Catalytic ammonia decomposition for the generation of high purity CO x free hydrogen has been performed in a multifunctional membrane reactor with Pd membrane walls for the hydrogen separation and a high performance Ru-carbon catalyst. By adjusting the experimental conditions an enhancement of the efficiency of the system for the hydrogen production has been achieved. The chemical thermodynamic equilibrium conversion has been exceeded using an improved catalyst, at temperatures lower than those reported in the literature. In addition, both the membrane and the catalyst components were very stable. The system showed no loss of performance after having been operated for several cycles.

The behaviour of three metal–acid bifunctional catalysts, where the metal was Ru and the acid function was a heteropolyacid (HPA), was compared in the hydroconversion of n-hexane. Both the activity and the selectivity pattern depended on the used support: silica, high surface area graphite (HSAG) or zeolite KL. While Ru–HPA–SiO2 gave selectivity to isomerization products of 97%, the Ru–HPA–KL sample gave a selectivity of 96% to hydrogenolysis products. And, the performance of Ru–HPA–HSAG lied between that for Ru–HPA–SiO2 and Ru–HPA–KL, giving both isomerization and hydrogenolysis products, with selectivities of 45 and 54%, respectively. The series of techniques applied to characterize the catalysts have assisted in understanding the catalytic performance. The HPA phase has been detected over all the HPA-modified supports, but different acid sites strength distributions have been determined by calorimetry of NH3 adsorption, following the order HPA–SiO2 > HPA–HSAG > HPA–KL. Also, different Ru species have been observed on the catalysts surface due to the interaction between the Ru precursor and the HPA support. Finally, the analysis of the results has suggested that the support determines the role played by both metal and acid functions, which separately would lead to hydrogenolysis and isomerization reactions, respectively.

Aligned multiwalled carbon nanotubes (MWCNTs) of high purity, low metal content and narrow size distribution were synthesized by chemical vapour deposition of acetylene along with iron-organometallic compounds in the temperature range 650–850 °C. The obtained MWCNTs were characterized by thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy and N 2 adsorption. The effect on the carbon nanotube structure of different parameters such as, reaction temperature, nature of the iron catalyst precursor, the reaction mixture flow rate and the relative proportion of metal precursor to carbon source, has been studied. It was found that the outer and inner diameters of the carbon nanotubes were directly proportional to the iron catalyst concentration. Moreover, the wall numbers and the diameters of the carbon nanotubes were related to their apparent specific surface areas.

Ruthenium-supported catalysts modified by the addition of Mg, Na or Ce were studied in the selective hydrogenation of paracetamol (4-acetamidophenol) to cis - and trans -4-acetamidocyclohexanol. In both series, catalysts supported on carbon or on alumina, the modified catalysts were more selective to the trans isomer than the corresponding monometallic catalysts. However, the modified catalysts, particularly the supported on carbon, were less active. Moreover, there is a reduction in the hydrogenolysis reaction of the OH group on carbon-supported catalysts. The enhancement observed in the stereoselectivity for the modified catalysts may be explained by an alteration in the acid–base properties of the catalyst surface, which eventually control the mode of adsorption of the molecule of paracetamol and probably the tautomeric equilibrium of the 4-acetamidocyclohexene-1-ol intermediate. The optimum amount of promoter to improve the stereoselectivity seems to depend on the inherent acid–base characteristics of both the modifier and the support. Therefore, the proper adjustment or fine tuning of these parameters is crucial for obtaining the best results in terms of stereoselectivity.

For the first time, a glassy carbon electrode (GCE) modified with novel N-doped carbon nanotubes (CNT-N) functionalized with MnFe2O4 nanoparticles (MnFe2O4@CNT-N) has been prepared and applied for the electrochemical determination of caffeine (CF), acetaminophen (AC) and ascorbic acid (AA). The electrochemical behaviour of CF, AC and AA on the bare GCE, CNT-N/GCE and MnFe2O4@CNT-N/GCE were carefully investigated using cyclic voltammetry (CV) and square-wave voltammetry (SWV). Compared to bare GCE and CNT-N modified electrode, the MnFe2O4@CNT-N modified electrode can remarkably improve the electrocatalytic activity towards the oxidation of CF, AC and AA with an increase in the anodic peak currents of 52%, 50% and 55%, respectively. Also, the SWV anodic peaks of these molecules could be distinguished from each other at the MnFe2O4@CNT-N modified electrode with enhanced oxidation currents. The linear response ranges for the square wave voltammetric determination of CF, AC and AA were 1.0 × 10−6 to 1.1 × 10−3 mol dm−3, 1.0 × 10−6 to 1.0 × 10−3 mol dm−3 and 2.0 × 10−6 to 1.0 × 10−4 mol dm−3 with detection limit (S/N = 3) of 0.83 × 10−6, 0.83 × 10−6 and 1.8 × 10−6 mol dm−3, respectively. The sensitivity values at the MnFe2O4@CNT-N/GCE for the individual determination of AC, AA and CF and in the presence of the other molecules showed that the quantification of AA and CF show no interferences from the other molecules; however, AA and CF interfered in the determination of AC, with the latter molecule showing the strongest interference. Nevertheless, the obtained results show that MnFe2O4@CNT-N composite material acted as an efficient electrochemical sensor towards the selected biomolecules., The authors thank Fundação para a Ciência e a Tecnologia (FCT) for financial support through grants nos. PEst-C/EQB/LA0006/2013 and FCOMP-01-0124-FEDER-037285, Operation NORTE-07-0124-FEDER-000067–Nanochemistry and MICINN of Spain (Projects CTQ-2011-29272-C04-01 and -03) for financial support. DMF also thanks FCT for her PD grant SFRH/BPD/74877/2010.

For a series of nanometric ZnO materials, the relationship between their morphological and surface functionalities and their catalytic properties in the selective decomposition of ethanol to yield acetaldehyde was explored. Six ZnO solids were prepared by a microemulsion-precipitation method and the thermal decomposition of different precursors and compared with a commercial sample. All these materials were characterized intensively by XRD and SEM to obtain their morphological specificities. Additionally, surface area determinations and IR spectroscopy were used to detect differences in the surface properties. The density of acid surface sites was determined quantitatively using an isopropanol dehydration test. Based on these characterization studies and on the results of the catalytic tests, it has been established that ZnO basal surfaces seem to be responsible for the production of ethylene as a minor product as well as for secondary reactions that yield acetyl acetate. Furthermore, one specific type of exposed hydroxyl groups appears to govern the surface catalytic properties., The financial support of the Spanish government by Projects CTQ2011‐29272‐C04‐01 and CTQ2011‐29272‐C04‐03 is recognized. M.V.M. appreciates the financial support of UNED by a predoctoral grant.

A new procedure for preparation of palladium sulfide nanoparticles, which are deposited and anchored over highly graphitized carbon nanofibers, is presented. The preparation method is based on the use of PdSO4 as metal precursor or alternatively in the previous functionalization of the carbon surfaces with sulfonic groups by treatment with fuming sulfuric acid. Using an in situ high-energy X-ray diffraction technique, in both cases it is demonstrated that during the reduction treatment, the initially present palladium hydride is transformed into a palladium sulfide (Pd4S). The catalytic properties of these materials have been tested in the gas-phase butadiene partial reduction to butenes. Although metallic palladium nanoparticles supported in the same carbon fibers produce butane as the principal product, the supported Pd4S nanocrystals mainly yield different isomers of butenes independently of the conversion level. Furthermore, applying the same X-ray diffraction method reveals that this catalytic phase is stable during reaction., We acknowledge financial support from the Spanish Ministerio de Economía y Competitividad (projects CTQ2011-29272- C04-01 and −03). The ESRF is thanked for granting beamtime at ID15.

Nickel–ceria composite catalysts prepared by a microemulsion method showed outstanding catalytic behavior in hydrogen production by glycerol steam reforming. Contrarily to usual Ni-based catalysts, the system allows long-term stability and nearly absence of by-products, particularly methane and carbon monoxide. With the help of scanning transmission electron microscopy and energy dispersive X-ray spectroscopy we confirmed the key role played by an intimate intermixing of Ni and Ceria components at reaction conditions. In addition, chemical imaging maps as well as more conventional techniques, such as Temperature Programmed Oxidation (TPO) and X-ray Photoelectron Spectroscopy (XPS) were used to identify the carbon containing (including coke) species nature and to establishing their chemical relevance. Combination of these techniques points out that the optimum interphase contact, reached for a specific 20:80 molar Ni:Ce formulation, allows; (i) to keep the Ni particle size controlled with absence of significant formation of coke and thus without deleterious effects on the long-term stability of the catalysts; and (ii) to eliminate undesirable side reactions such as methanation., Financial support of the Spanish Government by Projects ENER2013-46624-C4-1-R, CTQ2010-60480, CTQ2011-29272-C04-01 and 03 is recognized. We thank Miss María Almohalla Hernández for recording XPS spectra. Ana Kubacka thanks the Ministerio de Economía y Competitividad for a “Ramon y Cajal” Postdoctoral Fellowship.

Bimetallic nickel or cobalt molybdenum disulfide (MMoS2, M=Ni or Co) nanospheres, with a diameter ranging between 450 nm and 1 μm, have been successfully synthesized using a mild solvothermal method. The obtained nanomaterials have been comprehensively characterized using transmission electron microscopy (TEM), high resolution TEM (HRTEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry analysis (TGA), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR)., H.A. gratefully acknowledges the doctoral scholarship provided by AECID (Agencia Española de Cooperación Internacional para el Desarrollo- programa II.E-CV 2010-2011). The authors acknowledge also the financial support for the Joint Project CSIC (Spain)/CNRST (Morocco) under ref.2007MA0049 as well as the Spanish projects CTQ2011-29272-C04-01 and -03.

Two types of commercial carbon nanofibers with different graphitic structure, Pyrograph PR24-HHT (NFHHT) and PR24-PS (NFPS) were chemically modified to introduce oxygen groups or SO3H-containing species on their surface. Incorporation of these surface groups was confirmed by temperature programed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Palladium catalysts using these modified supports and PdCl2 as precursor were prepared, and subsequently tested in the partial hydrogenation of 1,3-butadiene under conditions of excess hydrogen. The effect of using a different Pd precursor (PdSO4) was also studied. All the prepared catalysts were characterized by transmission electron microscopy to determine the Pd nanoparticle sizes and by X-ray photoelectron spectroscopy to obtain the surface composition and the oxidation state characteristics of the Pd surface species. The carbon nanofiber structure seems to determine the Pd particle size and morphology, probably due to different metal–support interaction. Selectivities to butenes higher than 95% were obtained with the catalysts prepared on SO3H-modified supports or with the PdSO4 precursor, while over-hydrogenation to butane took place over the Pd on oxidized supports. Catalytic activity–structure correlations have been derived and it is proposed that the catalytic behaviour depends on the type of sulfur species, functional group or adsorbed residual sulfur. Furthermore, variations in 1-butene selectivity and 2-butene trans/cis ratio between the two series of catalysts were also detected and ultimately related to the different nanostructure of the carbon nanofiber., Financial support of the Spanish government by projects CTQ2011-29272-C04-01 and CTQ2011-29272-C04-03 is recognized.

Graphene oxide and multiwall carbon nanotubes were chemically modified by treatment with an aniline derivate or by incorporating nitrogen-adatoms. These materials were used as supports for gold nanoparticles and the resulting catalytic materials have been applied as catalysts in the 1,3-butadiene hydrogenation reaction. Supports and catalysts were exhaustively characterized by chemical analysis, X-ray photoelectron spectroscopy, thermogravimetric studies, temperature programmed desorption and transmission electron microscopy. The incorporation of nitrogen groups on surfaces modifies the gold precipitation–deposition process, giving place to different nanoparticle sizes and amounts of gold. From the point of view of catalytic behaviour an unusual activity for 1,3-butadiene was obtained with the gold amine functionalized graphene catalyst. The gold nanoparticles supported on graphene modified by p-phenylenediamine are more active than when supported either in the other samples. In particular, gold supported on graphene modified with amine like groups becomes active at near ambient temperatures, which is unusual for gold catalysts. Especially interesting is the variation of the gold catalytic properties, after recycling experiments., E. C. gratefully acknowledges financial support from the UNED and Spanish Ministry of Science and Technology. This work was supported by the Spanish Government (project CTQ 2011-29272-C04-01and 03).

Two commercial metal-organic frameworks, Cu3(BTC)2 and Fe(BTC), have been selected to compare the adsorption parameters obtained on these materials by two different techniques: immersion calorimetry and inverse gas chromatography (IGC), in order to find a relationship between thermodynamic parameters obtained by so different techniques. From comparison between the enthalpy of adsorption obtained from IGC and the enthalpy of immersion, three molecules of the same number of carbon atoms have been selected: n-heptane, methylcyclohexane and toluene. Both by IGC and immersion calorimetry, the interaction is stronger in Fe(BTC), being the aromaticity of TOL determinant in the strength of the interaction. However, splitting of the enthalpy of adsorption into the dispersive and specific components allows to deduce that both parameters are more important on the Cu3(BTC)2, due to the higher available surface area in the case of the dispersive interaction; and for the specific interaction, due to the high potential of interaction into the micropores., This work was supported by the Spanish Government (contracts CTQ2011-29272-C04-01, -02 and -03) and the Research Fund for Coal and Steel of the European Union (contract UE-10-RFCR-CT-2010-00004). I. Gutiérrez thanks the Government of the Principality of Asturias for a Ph. D. fellowship (Severo Ochoa Program).

Supported ruthenium catalysts were prepared by incipient wetness impregnation of three different carbon materials: activated carbon (AC), high surface area graphite (HSAG) and multiwalled carbon nanotubes (CNT). Another catalyst was prepared by treating KL zeolite with RuCl3·xH2O in aqueous solution. All these samples were characterized by temperature programmed reduction (TPR), CO chemisorption coupled with microcalorimetry and transmission electron microscopy (TEM). The reduced catalysts were tested in the hydrogenolysis of glycerol in the liquid phase, under a reaction pressure of 8 MPa and isothermally at the reaction temperature of 453 K. The CO microcalorimetry measurements evidenced that electron donor properties of graphite and carbon nanotubes promote formation of electron-rich metal species (Ruδ−) in Ru/HSAG and Ru/CNT catalysts, which not only favors formation of 1,2-propanediol from glycerol but also enhances the successive CC cleavage, with formation of undesired products, mainly methane. For Ru/KL the occurrence of Brönsted acid sites, resulting of the reduction of the chlorinated ruthenium species bonded to the zeolite framework, was verified by temperature programmed desorption (TPD) of NH3. Furthermore, observations by TEM of the Ru/KL catalyst showed an important population of metal nanoparticles lower than 1 nm, part of which exhibits electron deficient character as indicated by the CO microcalorimetry. As a consequence, the transformation of glycerol into 1,2-PDO over Ru/KL seems to be promoted through formation of the intermediate acetol on acid sites, while for the scarcely acid Ru-carbon catalyst conversion of glycerol occurs mainly on metal sites, ethylene glycol being the preferred hydrogenolysis product., E.G.S. would like to thank to UNED of Spain for a scholarship grant. The financial support of the Spanish Government under projects CTQ2011-29272-C04-01 and -03 is recognized.

Four 2 wt% Ru/KL catalysts, doped with copper, were prepared by successive impregnation of a KL zeolite with Ru 3 (CO) 12 and Cu(NO 3 ) 2 · 3H 2 O aqueous solutions in an adequate concentration to obtain 0, 0.5, 1 and 1.5 wt% of copper. The samples Ru / KL , RuCu0.5 / KL , RuCu1.0 / KL and RuCu1.5 / KL were characterized by X-ray diffraction, temperature-programmed reduction, chemisorption of CO and H 2 , BET surface area, infrared spectroscopy of adsorbed CO and microcalorimetry of CO adsorption. Catalytic activity measurements in the selective hydrogenation of citral, at 323 K and 5 MPa in the liquid phase, showed that copper inhibits the overall hydrogenation activity of Ru/KL catalysts, the higher the copper concentration the larger the activity reduction, without significant modification of the hydrogenation turnover frequencies. Selectivity toward unsaturated alcohols decreases as the copper content increases in favor of that of citronellal. The presence of bimetallic entities on the doped catalysts was suggested by the TPR measurements and the occurrence of hydrogen spillover phenomenon evidenced by the results of the chemisorption measurements of hydrogen and CO. The catalyst behavior is consistent with both, decoration/encapsulation of ruthenium by copper particles and occlusion of Ru inside the zeolite pores. This is suggested by the strong decrease of CO chemisorption capacity of the catalysts in the order Ru / KL > RuCu0.5 / KL > RuCu1.0 / KL > RuCu1.5 / KL and strengthened by the CO-FTIR and microcalorimetry results.

Several high surface area graphite-supported Ni catalysts were prepared and reduced by different methods. Samples were prepared by impregnation of the support and then submitted to traditional H 2 flow reduction at high temperature or to reduction with aqueous hydrazine at low temperature, and compared with a sample prepared by the deposition–precipitation method by means of the reduction of the dissolved Ni precursor by hydrazine at low temperature. The surface of these catalysts was characterised by means of CO adsorption microcalorimetry and by X-ray photoelectron spectroscopy (XPS), and a correlation of the results obtained with those on the selective hydrogenation of citral can be done. In this sense, only Ni 0 sites were detected at the surface of the Ni catalysts prepared by reduction with hydrogen leading to high catalytic activities and selectivity towards citronellal formation, while Ni oxidised species are also present (and are major) for catalysts prepared by reduction with hydrazine, what leads to an enhanced selectivity towards the formation of the unsaturated alcohols, geraniol and nerol. The oxidation of these latter catalysts seems to be only superficial, as suggested by the absence of H 2 consumption peaks in the TPR experiments. The presence of Ni 0 sites over these latter catalysts was not detected by XPS, thus our study proves that CO adsorption microcalorimetry is a very powerful tool for surface characterisation of heterogeneous catalysts.

A new infiltrated microporous membrane without defects has been obtained. For that, a microporous glassy carbon (GC) membrane was infiltrated inside the mesoporous structure of a γ-Al2O3 support with 70% of porosity. GC material was formed after carbonisation of a phenolic resin which is deposited on the inner face of a tubular ceramic multilayer system. This consists of a cordierite support, an intermediate layer of α-Al2O3 and a γ-Al2O3 top layer. Textural properties of the unsupported GC membrane were determined by CO2 adsorption at 273 K and inmersion calorimetry employing organic solvents with different molecular dimensions. The sequence of the GC deposition in γ-Al2O3 support was studied by scanning electron microscopy (SEM). The final infiltrated membrane system was studied by N2 adsorption–desorption isotherms at 77 K and gas permeation measurements.

This study extends and amplifies earlier work carried out over two series of bimetallic catalysts, Ru–Cu and Ni–Cu, supported on a high surface area graphite. The n -hexane hydroconversion, and the selective hydrogenation of paracetamol to cis and trans -4-acetamidocyclohexanol were studied on both catalyst series. The activity in the hydroconversion of n -hexane was reduced for the bimetallic catalysts in comparison with the monometallic counterpart (Ni or Ru), and it decreased as the Cu content increased. On the other hand, while the selectivity to the hydrogenolysis products followed the trend Ni > 4Ni1Cu > 4Ni2Cu > 4Ni3Cu in the Ni–Cu series, the catalyst 2Ru0.3Cu points up among its series, leading to lower selectivities to the fragmentation products than the Ru monometallic catalyst and the rest of the Ru–Cu bimetallic catalysts. On the other hand, no clear variation of the activity was observed for the Ni–Cu series in the hydrogenation of paracetamol. Also, the selectivity patterns were similar for all the catalysts among the series, i.e. the selectivity to the cis and trans -4-acetamidocyclohexanol higher than 90% and stereoselectivities to the trans isomer of ca. 60%. However, a reduction of the catalytic activity was again observed for the Ru–Cu catalysts, particularly for the two catalysts with highest Cu content. Furthermore, modifications on the product distribution were detected. While the 4-acetamidocyclohexanols were the main products formed on 2Ru and 2Ru0.3Cu catalysts with selectivities higher than 97%, higher amounts of secondary products were detected for 2Ru0.6Cu and 2Ru0.9Cu, where selectivities to the 4-acetamidocyclohexanols of only 22 and 14% were reached. The correlation of the data obtained in these two reactions with those reported previously provide information concerning the influence of the addition of different amounts of Cu on the structure and reactivity of the final bimetallic catalyst depending on the base metal, Ru or Ni.

Temperature-programmed reduction (TPR) and CO adsorption microcalorimetry along with the catalytic behaviour in the n-butane/H2 test reaction were performed in order to determine the specific interactions of Ru nanoparticles supported on different carbon materials. Aspects such as the porous structure and surface chemistry (presence and elimination of surface oxygen functional groups) of the carbon material, or the effect of the metal precursor (e.g. presence of residual chlorine) on the final metal dispersion and on the surface structure of the Ru nanoparticles have been studied. The results obtained confirm that surface oxidation of the support along with the nature of the Ru precursor affects the distribution of the metal precursor over the support (and, consequently, the final ruthenium dispersion) and also the surface site distribution. Besides, elimination of the surface oxygen functional groups of the carbon material, during the reduction treatments of the fresh catalyst samples, leads to surface reconstructions on the Ru nanoparticles that seem to expose different crystallographic planes. The presence of residual chlorine leads to electron deficient Ru sites, and this modifies the CO chemisorption heats and affects the catalytic properties in the n-butane/hydrogen test.

Three Ru/KL-zeolite catalysts containing 2 wt% of Ru were prepared from Ru 3 (CO) 12 , RuNO(NO 3 ) 3 and Ru(C 5 H 7 O 2 ) 3 precursors. The samples named Ru(c)/KL, Ru(n)/KL and Ru(a)/KL were studied by temperature-programmed reduction (TPR), by microcalorimetry of CO adsorption, by volumetric hydrogen chemisorption, by X-ray diffraction (XRD) and also by infrared spectroscopy of the CO adsorbed species (CO-FTIR). The catalytic activities and selectivities were evaluated in the hydrogenation of citral at 323 K and 5 MPa, in a stirred batch reactor. Metal dispersion follows the order Ru(c)/KL > Ru(n)/KL > Ru(a)/KL. The CO-FTIR spectra show a set of different ruthenium species on the support, suggesting the presence of large metal particle outside the zeolite and small crystallites inside the channels, the latter being majority in the Ru(c)/KL sample. Hydrogenation activity per surface metal atom (TOF) was found to be independent on the metal dispersion and, consequently, on the precursor used. The selectivity towards unsaturated alcohols (geraniol + nerol) is in the order Ru(c)/ KL < Ru(a)/KL = Ru(n)/KL, while the citronellal selectivity is maximum over the Ru(c)/KL catalyst. This latter effect can be correlated to the special catalytic properties of the smaller Ru particles located inside the zeolite cavities.

The adsorption of CO on carbon-supported metal (Ru, Co and Ni) catalysts was studied by microcalorimetry. A correlation of the results thus obtained with those reported for monocrystals or with other studies available in the scientific literature for supported metal catalysts, including infrared spectroscopy data, enables the determination of the type of exposed crystalline planes and/or of the different types of CO adsorbed species. The results obtained suggest that the energetic distribution of the surface sites depends on the carbon support material and on the applied reduction treatment. In this way, the use of a high surface area graphite (clean of surface oxygen groups) leads to an electron density enrichment on the small metal particles (Ru) and, in general, to a higher heterogeneity of the active surface sites. The elimination of surface oxygen functional groups (with the reduction treatment at the higher temperature) of the carbon molecular sieve support leads to changes in the surface structure of the metal particles and, consequently, to higher CO adsorption heats, particularly for Ru and Co.

The adsorption of CO on graphite-supported monometallic catalysts (Ni and Ru) and bimetallic catalysts (Ru–Cu and Ni–Cu) reduced at different temperatures was studied by microcalorimetry. The calorimetric profiles obtained over these two bimetallic systems provides information about the different types of interaction (bridged, linear or subcarbonyl species) that could exist in the bimetallic system when Cu was introduced in the Ru and Ni monometallic catalysts.

Several alumina-supported Ru catalysts prepared from different metal precursors were comparatively studied by H 2 and CO adsorption microcalorimetry and by Fourier transformed-infrared spectroscopy (FT-IR) of the chemisorbed CO molecule. The correlation of the results thus obtained from these techniques with those on the n -butane/H 2 reaction test, provides useful information about the type and distribution of the surface active sites on the supported metal crystallites. Also, the comparison of the results obtained from these complementary techniques with those reported for monocrystals or from other studies available in the scientific literature for supported Ru catalysts, enables the tentative attribution of the type of exposed crystalline planes. In this way, the energetic distribution of surface sites has been shown to depend on the mean metal particle size as well as on the Ru precursor involved in the preparation.

The influence of the support, the metal precursor, and the solvent on the selective hydrogenation of paracetamol (4-acetamidophenol) was studied over supported ruthenium catalysts. The catalysts supported on the oxidic supports Al2O3 and SiO2 gave the best results in terms of activity, selectivity for the acetamidocyclohexanols (99%), and stereoselectivity for the trans isomer (53 and 46%, respectively). Carbon-supported catalysts produced larger amounts of secondary compounds, mainly N-cyclohexylacetamide, which was derived from the hydrogenolysis reaction of the OH group. The use of a chloride precursor resulted in the enhancement of the formation of N-cyclohexylacetamide and partially hydrogenated products; the stereoselectivity also increased. Moreover, because of the acidity caused by residual Cl, condensation led to oligomers of paracetamol. In spite of the decrease in the selectivity for cyclohexanol derivatives when the more polar solvent ethanol was used instead of isopropanol or tetrahydrofuran the stereoselectivity for the trans isomer increased from 30 to 38%. The results confirm that the factors studied affect the mode of adsorption of the molecule of paracetamol on the catalyst in different ways. These effects determine the product distribution and the selectivity of the reaction.

The Sn(0.3 or 0.5 wt.%) addition to Pt(0.3 wt.%)/ZnAl2O4 and Pt(0.3 wt.%)/MgAl2O4 catalysts leads to an increase of the activity and selectivity to olefins in the n-butane dehydrogenation reaction. Slight differences in the catalytic behaviour were found between 0.3 and 0.5 wt.% of Sn added to Pt in both catalyst series. Besides, the bimetallic catalysts also show a good stability through the five successive reaction-regeneration cycles, mainly the PtSn/MgAl2O4 one. The mono- and bimetallic catalysts were characterized by using different techniques: tests reactions of the metallic phase (cyclohexane dehydrogenation and cyclopentane hydrogenolysis), temperature programmed reduction, X-ray photoelectron spectroscopy, H2 chemisorption, microcalorimetric measurements of the propylene adsorption and XRD. Results show that the nature of the metallic phase in monometallic samples appears to be different for the two supports. Thus, metallic particles with a very low concentration of hydrogenolytic sites (steps, corners and edges) would exist in the Pt/ZnAl2O4 catalyst in contrast with the structure of the metallic phase of the Pt/MgAl2O4 one, where the existence of an important concentration of hydrogenolytic sites is clearly observed (according to the cyclopentane hydrogenolysis results). The modification of Pt by the Sn addition clearly improves the catalytic behaviour in n-butane dehydrogenation due to important changes in the structure of the metallic phase. Thus, when Sn is added to Pt/ZnAl2O4 and Pt/MgAl2O4 catalysts the metallic surface structure seems to be more complex. In fact, results would indicate not only a partial formation of PtSn alloys or intermetallic compounds between Pt0 and a fraction of Sn(0), but also a surface enrichment in Sn, dilution effects as well as the presence of tin stabilized on the support, probably as Sn(II/IV) oxides and SnCl2 species. Fil: Bocanegra, Sonia Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina Fil: Guerrero-Ruiz, A.. Universidad Nacional de Educación a Distancia; España Fil: de Miguel, Sergio Ruben. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina Fil: Scelza, Osvaldo Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina

Several graphite-supported Ru–Co and Ru–Ni bimetallic catalysts were comparatively studied by X-ray diffraction (XRD) and CO adsorption microcalorimetry. The correlation of the results thus obtained from these techniques with those on the n -butane hydrogenolysis reaction test, provides useful information about the type and distribution of the surface active sites. The CO adsorption microcalorimetry technique provides, in some cases, information that allows identification and quantification of the surface sites of the metallic nanoparticles. Thus, these data may be used to identify specific catalytic properties (activity and selectivity) in the n -butane/hydrogen test, and how such properties are modified on the different surface sites. Also, comparison with the parent monometallic catalysts allows to envisage the contribution of each individual metal to the total surface composition or else of the formation of alloys or bimetallic surface clusters. The results so obtained suggest the formation of surface Ru–Co and Ru–Ni alloys on these bimetallic catalysts, their contribution to the surface composition depending on the relative atomic ratio (Ru/M) and on the pre-treatment (reduction) conditions.

Carbon materials with different textural and surface chemistry properties have been studied to analyze their behavior in removing aromatic compounds (phenol, o-chlorophenol, p-nitrophenol, aniline, and phenol compound mixtures) from water. A mesoporous high surface area graphite and a microporous activated carbon with (HSAGox and ACox) and without (HSAGT and ACT) oxygen surface groups, were used as adsorbents. Apparent surface areas, surface oxygen groups, and zero points of charge have been determined. The adsorption behavior of single compounds on ACT depends on the relation between the molecular and the pore sizes. The aniline, the nitrophenol, and the chlorophenol interact with the oxygen surface groups of oxidized graphite, while there is no evidence of any type of interaction of the phenol with these groups. The adsorption of the organic compound mixtures on the thermally treated samples is determined by the acid-base character of the adsorbate-adsorbent, whereas on the oxidized carbons, the controlling forces are the specific interactions between organic molecules and the oxygenated groups. Selectivity coefficients for the different mixtures are presented over the entire range of adsorption.

Two rhodium catalysts supported on alumina (metal loading 1 and 3 wt.%) were comparatively studied by H2 and CO adsorption microcalorimetry and by infrared spectroscopy of the chemisorbed CO. The correlation of the results obtained from these two techniques with the n-butane hydrogenolysis reaction test provides useful information about the type and distribution of the surface active sites. The energetic distribution of surface sites has been shown to depend slightly on the metal loading and it can be modified by the pretreatment conditions. The obtained results also reveal the presence of partially reduced Rh atoms stabilized by Cl ions remaining from the precursor. On the other hand, the increased density on Rh (1 1 1) planes on the sample with 3 wt.% Rh treated with water, detected from CO adsorption experiments, can be related with enhanced both activity for the hydrogenolysis reaction and selectivity towards ethane.

This paper describes the results obtained on the catalytic hydrogenation of Paracetamol (4-acetamidophenol), carried out at 393 K, over carbon-supported Ru, Co and Ni based monometallic catalysts, and over graphite-supported RuM (M = Co, Ni) bimetallic catalysts. A comparative study of the effect of the different supported-metal catalysts and of the applied reduction temperature has been carried out. Two selectivity parameters have been controlled: the production of by-products and the trans – cis composition of 4-acetamidocyclohexanol (stereoselectivity). Characterisation of the catalysts was performed by temperature-programmed reduction (TPR) and CO volumetric chemisorption. It was found that the hydrogenation reaction of Paracetamol is structure sensitive, since intrinsic activity and selectivity values are modified with variations in the metallic particle sizes. Generally, the catalytic activity, under our experimental conditions, follow the trend: Pt N -cyclohexylacetamide) and/or of partial hydrogenation reactions (4-acetamidocyclohexanone), depends on the active metal: Ni trans to cis ratio), among the monometallic catalysts Co exhibited the highest T/C ratio, with the overall sequence: Co > Ni > Ru. Finally, the bimetallic catalysts, particularly those of RuNi, show an improved stereoselectivity (T/C ratio) in comparison with the corresponding counterparts.

This paper describes the synthesis of carbon nanotubes by the catalytic decomposition of acetylene at 700 °C over several Fe/silica catalysts in a thermobalance. Characterization of the catalysts was performed by chemical analyses, N 2 adsorption isotherms, X-ray diffraction, temperature-programmed reduction and CO volumetric chemisorption. The carbon products were mainly characterized by transmission electron microscopy. It was found a high influence of the iron precursor used in the synthesis of the catalysts on the final reaction yield and on the characteristics of the carbon products obtained.

A kinetic study of the synthesis of carbon nanotubes (CNTs) by catalytic decomposition of acetylene over an iron-supported catalyst was carried out using a thermobalance. The CNTs were mainly characterized by transmission electron microscopy (TEM and HRTEM). It was found that there is a high influence of the reaction conditions (feed mixture, reaction temperature, etc.) on the final reaction yield and on the structural and morphological characteristics of the carbon products obtained. A complete discussion of the results by comparison of the carbon deposition curves with the TEM images is given. Finally, a kinetic model for explaining the growing mechanism of carbon nanotubes is developed and the displayed conclusions are clearly shown.

The adsorption behavior of phenol, aniline and phenol–aniline mixtures in water over carbonaceous material surfaces has been studied. The adsorbents used were: a mesoporous high surface area graphite (HSAG) and a microporous activated carbon (AC). Aliquots of AC were treated with HCl and H 2 F 2 to remove inorganic surface impurities. Furthermore, samples of HSAG and AC were subjected at 1173 K, to inert He flow, in order to eliminate surface oxygen groups. Apparent surface areas, surface oxygen groups and, zero point of charge of the adsorbent surfaces have been determined. All the adsorption isotherms of phenol and aniline on HSAGs are adequately fitted by Freundlich type isotherms, while on ACs, the extended Langmuir equation provides a better description of the experimental results. This fact reveals the importance of the textural characteristics (i.e., pore sizes) on the adsorption behavior. The presence of oxygen surface groups affects the adsorption behavior. Their effect depends on the amount of these groups that are present on the adsorbent surface and on the nature of the adsorbate molecule. In the case of HSAG, aniline is adsorbed to a larger extent than phenol for all the studied phenol–aniline mixtures. The opposite trend was found for ACs. Elimination of oxygen groups, originally present in larger amounts on the HSAG surface than on AC, produces an inversion in the selectivity adsorption of the mixtures. That is, more phenol than aniline is adsorbed on the surface of heat-treated HSAG (HSAGT).

The structural/morphological and oxygen handling properties of two high-surface-area Ce−Tb mixed oxides prepared by a microemulsion method with Ce/Tb atomic ratios of ca. 4 and 1 have been analyzed...

This article describes the synthesis of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) by the catalytic decomposition of acetylene at 973 K over several Fe/silica catalysts (sol–gel method prepared) in a fluidized bed reactor. Characterization of the catalysts and the products was performed by chemical analyses, N 2 adsorption isotherms (BET surface area), temperature-programmed reduction (TPR), CO volumetric chemisorption, X-ray diffraction (XRD), temperature-programmed oxidation (TPO), and transmission electron microscopy (TEM). An apparent relationship was found to exist between the metallic iron content of the catalysts, metal particle size distribution on the surface of the silica support, and final characteristics of the carbon products obtained. High-purity CNTs and CNFs were achieved after acid treatment of the catalytically produced carbon deposits. Difficulties in exact quantitative characterization of pure CNTs in the presence of other carbon species (CNFs, capsules of carbon, amorphous carbon, etc.) are also reported and discussed.

The adsorption of CO on both nitrided and reduced passivated Mo2N catalysts in either alumina supported or unsupported forms was studied by adsorption microcalorimetry and infrared (IR) spectroscopy. The CO is adsorbed on nitrided Mo2N catalysts on three different surface sites: 4-fold vacancies, Moδ+ (0

The application of a novel Ce0.5Zr0.5O2 mixed oxide prepared by the microemulsion method as a support of Ru catalysts for the reforming of CH4 with CO2 originates a high-activity catalytic system with excellent stability under reaction conditions. The support characteristics clearly determine the catalytic stability of Ru catalysts under CH4 + CO2 reaction conditions. The introduction of cerium as a promoter in the ZrO2 structure is shown to improve the catalyst performance by increasing the oxygen mobility in the support and consequently reducing deactivation by carbon deposition during reaction.

Some parameters influencing methylcyclohexane dehydrogenation over a Pt/Al2O3 catalyst using a porous Vycor membrane reactor are evaluated. For the Vycor membrane H2 separation factors with respect to methylcyclohexane (MCH) and toluene (TOL) have been found to be above the values predicted by the Knudsen diffusion model. By adjusting the experimental conditions to equilibrate the H2 production and the extraction rates, an enhancement of the net performance of the system is achieved. For an adequate ratio between the reactant fed flow and the membrane surface area, the extraction conditions used can improve the yield. Thus, the increase in the purge gas flow rate and the countercurrent operation mode favour the equilibrium shift by increasing the H2 and TOL partial pressures difference between both sides of the membrane and decreasing that of MCH. The distribution of the catalytic zone is also important. The membrane efficiency can be optimised if the reactant mixture reaches the catalyst in the porous zone under the equilibrium conditions achieved in a conventional fixed-bed reactor.

The coupling of a catalytic reactor and a separator in the same unit is an attractive concept which still entails complex technological problems caused by the generally severe conditions at which a large part of heterogeneous catalytic reactions take place. The application of this technology to the conversion enhancement in reversible chemical reactions with high reaction enthalpies can provide interesting advances in the methane conversion processes. This paper analyses the applicability of mesoporous ceramic filters in a membrane reactor to carry out the reforming of methane with carbon dioxide. The effect of the variation of the sweep gas flow rate as compared to the feed rate of reactants has been studied. It has been observed that, even for membranes in which the main mechanism for the gas transport is the Knudsen diffusion, high sweep gas flows rates induce large changes in the distribution of species at both sides of the membrane. This change is dependent on the membrane permeance and gives place not only to a moderate conversion enhancement but also to maximise selectivity to hydrogen by hindering the progress of the secondary reverse water gas shift reaction.

Recent results achieved by microcalorimetry of CO adsorption over supported metal catalysts will be reviewed by considering some parameters that control the surface properties of the supported metallic particles. In particular, the effects induced by the nature and the particle size of supported metallic clusters, the conditions of pretreatment, the support materials, the addition of promoters and the presence of a second metal will be shown.

Different MoS2 nanostructures have been obtained following an innovative one-step solvothermal method by changing the concentration and type of the electrolyte while avoiding the use of surfactant. It was found that the chemical nature of the studied electrolyte ((NH4)2CO3 or KCl) do not significantly affect the morphology and structure of the obtained MoS2 nanomaterials. Nevertheless, increasing the electrolyte concentration yields to a remarkable modification of the morphology of the resulting MoS2 from nanospheres to worm-shaped then finally to nanotubes. All the obtained nanomaterials were characterized by X-ray diffraction, (XRD), transmission electron microscopy (TEM, HRTEM), Fourier transformation infra-red spectroscopy (FTIR), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS)., H. Akram thanks the AECID (Agencia Española de Cooperación Internacional para el Desarrollo- programa II.E-CV 2010-2011) for the doctoral scholarship. The financial support under projects CTQ2011-29272-C04-01 and -03 is recognized.

A new modified electrode based on N-doped carbon nanotubes functionalized with Fe3O4 nanoparticles (Fe3O4@CNT-N) has been prepared and applied on the simultaneous electrochemical determination of small biomolecules such as dopamine (DA), uric acid (UA) and ascorbic acid (AA) using voltammetric methods. The unique properties of CNT-N and Fe3O4 nanoparticles individually and the synergetic effect between them led to an improved electrocatalytic activity toward the oxidation of AA, DA and UA. The overlapping anodic peaks of these three biomolecules could be resolved from each other due to their lower oxidation potentials and enhanced oxidation currents when using the Fe3O4@CNT-N modified electrode. The linear response ranges for the square wave voltammetric determination of AA, DA and UA were 5–235, 2.5–65 and 2.5–85 μmol dm−3 with detection limit (S/N = 3) of 0.24, 0.050 and 0.047 μmol dm−3, respectively. These results show that Fe3O4@CNT-N nanocomposite is a promising candidate of cutting-edge electrode materials for electrocatalytic applications., The authors thank Fundação para a Ciência e a Tecnologia (FCT) for financial support through Grant Nos. PEst-C/EQB/LA0006/2013 and PTDC/CTM-POL/0813/2012, to Operation NORTE-07-0124-FEDER-000067–Nanochemistry and MICINN of Spain (Projects CTQ-2011-29272-C04-01 and -03) for financial support. DMF also thanks FCT for her PD Grant SFRH/BPD/74877/2010.