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Modifications to the selectivity during partial hydrogenation of butadiene over graphite supported Pd nanoparticle catalysts may be achieved by at least three methodologies: (1) by changing the structure of the surface ensembles that constitute the active surface sites by the incorporation of another metallic component, such as Cu in the present case, (2) by self-poisoning of the surfaces by strongly adsorbed carbonaceous intermediates, or carbon deposits, which are very sensitive to the presence of excess hydrogen in the feed during reaction, and (3) by anchoring a sulfur containing compound over the Pd surfaces. A detailed analysis of the selectivity variations yielding 1-butene, cis- or trans-2-butene and undesired butanes is presented in these three cases, and the catalytic data are related to the characterization data of these materials; transmission electron microscopy was used to determine the size of the nanoparticles and X-ray photoelectron spectroscopy to obtain the surface analysis composition. The latter indicates that some electronic modifications on Pd take place., Financial support of the Spanish government by projects CTQ2011-29272-C04-01 and -03 is recognized.

N-doped and un-doped graphene samples were synthesized starting from natural graphite of different particle sizes (10, 100 and 200 mesh) by oxidation and further thermal treatment under ammonia and inert atmospheres, respectively. Samples were thoroughly characterized by TEM, XRD, Raman and XPS. The nature and quantity of nitrogen species introduced were dependent on starting materials, reduction atmosphere (NH3 or inert) and temperature. All samples were employed as basic catalysts in the dehydrogenation reaction of ethanol. Acetaldehyde was the main product obtained owing to the basicity induced by the presence of N atoms in the graphene layers. Conversion increased with higher N at.% and lower number of stacked graphene sheets. Catalysts with highest ratio between both factors gave highest conversion values., Authors acknowledge financial support from the projects CTQ 2011-29272-C04-01 and 03 and project 2011/PUNED/0001.

© 2014 The Author(s). Published by Taylor & Francis., The influence of ethylenediamine and bis(3-aminopropyl)amine insertion into graphite oxide using toluene and ethanol–water media was studied by elemental analysis, X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetry, temperature-programmed desorption and diffuse reflectance infrared Fourier transform spectroscopy. In every case, amine was incorporated between the basal planes and on the edges of the material through different interactions with epoxy, hydroxyl, carboxyl and carbonyl groups resulting in new-layered materials. Results show that incorporation was homogeneous for ethylenediamine irrespective of the solvent and that the higher level of intercalation in non-polar media was probably a consequence of the inhibition of competitive reactions with the solvent. For bis(3-aminopropyl)amine, the higher reaction times required to obtain satisfactory degrees of intercalation in the non-polar solvent suggests that with this solvent the process is kinetically controlled for longer chain amines., The authors acknowledge the MICINN of Spain (Projects CTQ-2011-29272-C04-01 and -03) for financial support.

For ex-choride Ru catalysts supported on high surface area graphite and promoted by potassium oxide, the influence of the reduction temperature on the surface properties and on the catalytic performance in the Fischer–Tropsch reaction (1 bar, H2/CO = 2/1) is investigated. The Ru metallic particle size generated on these catalysts was studied by CO chemisorption and checked by TEM. Characterization of the catalysts by XPS analysis and microcalorimetry of CO adsorption reveals the presence of residual chloride anions after reduction (hydrogen flow) at 573 and even 673 K. The chloride traces neutralize the effects of the potassium promoter in the Fischer–Tropsch reaction. When catalysts are reduced at 773 K, lower methane selectivity and higher olefin/paraffin ratio are observed for those with potassium added. Our results show the significance of the reduction treatment and the presence of residual chloride anions to achieve a ruthenium based Fischer–Tropsch catalyst with improved selectivity to light olefins., L.G.C. would like to thank to CSIC of Spain for a JAE PREDOC scholarship grant. The financial support of the Spanish Government under projects CTQ2011-29272-C04-01 and -03 is recognized.

The hydrogenation of citral has been performed over Ru–Fe catalysts supported on activated carbon and on high-surface-area graphite. It was found that selectivity to unsaturated alcohols is independent of the carbonaceous support used for ruthenium catalysts. The addition of iron enhances selectivity to unsaturated alcohols (geraniol and nerol) in a manner similar for both ruthenium catalysts, becoming maximum for the highest iron loading. Calorimetric experiments give some evidence about alloy formation in ruthenium catalysts promoted with iron. It is inferred that the surface polarity of the alloyed particles promotes the selective hydrogenation of citral toward unsaturated alcohols.

Adsorption of phenol and nonylphenol from aqueous solutions on microporous activated carbons has been studied. The phenol isotherm changes from L-shaped for surface oxygen group free carbon (I sample) to a two-stepped isotherm for oxidized carbon (IN sample, HNO(3) treated) Furthermore, the adsorbed amounts diminish in about 25% on IN carbon. It is proposed that a change in the adsorption mechanism take place; i.e., weak interaction forces between the pi electrons in phenol and the pi electron in carbon are present on the original I carbon, while a donor-acceptor complex on the oxidized IN carbon is operating between basic surface oxygen groups and phenol aromatic rings. The shape of nonylphenol isotherms is two-stepped for both carbons. The introduction of acidic oxygen surface groups on the carbon enhances the specific nonylphenol adsorption by about 40%. This may be interpreted as being due to the fact that nonylphenol is hydrogen-bonded to the oxidized carbon surface by means of acidic groups. Thermal desorption experiments indicate that phenol is mainly physisorbed. Thermal desorption further confirms that nonylphenol is possibly bonded to oxygen surface groups by hydrogen bonds. Copyright 2001 Academic Press.

Ce and Mg were used as promoters in two series of Ru based catalysts supported on alumina (Al 2 O 3 ) and activated carbon (AC). The catalysts were characterized by H 2 chemisorption and temperature-programmed reduction (TPR), and studied in the crotonaldehyde (gas phase) and the citral (liquid phase) hydrogenations. Addition of MgO and CeO 2 decreased the catalytic activity in crotonaldehyde and citral hydrogenations. With regard to the selectivity towards unsaturated alcohols, similar trends were observed for the two reactions. MgO did not influence the selectivity, but CeO 2 increased the selectivity to unsaturated alcohols, especially on carbon supported catalyst. Bulk CeO 2 and Ce/AC catalyst showed low activity but very high selectivity (93 and 100%, respectively) to the unsaturated alcohols. Based on these results and the calorimetric experiments of CO adsorption it was suggested that defect sites on the surface of the promoter are the active and highly selective sites for unsaturated aldehydes due to their influence on the CO bond activation.

Nonylphenol is a compound with estrogenic activity that is found in aquatic environments as a consequence of the biodegradation of nonylphenyl polyethoxylates discharged by many industries. The adsorption capacity for nonylphenol from aqueous solutions has been studied for four commercial microporous carbons. The texture and properties of the activated carbons were studied by means of N2 adsorption at 77 K and CO2 adsorption at 273 K, X-ray diffraction, immersion calorimetry and chemical analyses. Two-step isotherms have been determined for all carbons. The first isotherm plateau of the adsorbed nonylphenol is related to the mean pore width of the activated carbons. The second plateau seems to be related to the presence of inorganic impurities (carbonates and SiO2). Depending on the type of inorganic carbonate impurity, different behaviour was found for the nonylphenol adsorption. These differences are attributed to the type of inorganic components present in the carbon, as well as their particle sizes and locations in the porous framework. Finally, the introduction of acidic oxygen surface groups on the activated carbon surface enhances nonylphenol adsorption.

The performance of Al(2)O(3), ZrO(2) and ZrO(2) stabilized with SiO(2) (ZrO(2)-s) supported palladium catalysts for the methane combustion was studied between 473 and 873 K. The nature of the surface species of palladium catalysts under reaction conditions were detected by FT-IR and microcalorimetry of CO adsorbed. The different behavior of palladium catalysts under reaction conditions is attributed to support effects associated to differences in thermal conductivity and oxygen mobility of supports. Prereduction of the catalysts enhances their activity. Under reaction conditions, the prereduced sample becomes partially oxidized by preferential adsorption/reaction of oxygen both on Pd ( 1 1 1) planes and on the sites that can multibondedly adsorb CO. The reconstruction of the metallic particles and the formation of PdO(x) (0 1) phase were directly observed by FT-IR and microcalorimetry of adsorbed CO. Combination of different characterization techniques with reaction results suggests that a mixed phase, Pd(0)/PdO(x), is the most active phase for methane combustion, and that a redox mechanism may occur on this phase. (C) 2000 Elsevier Science B.V. All rights reserved.

The adsorption of CO on Al2O3, ZrO2, ZrO2−SiO2, and ZrO2−La2O3 supported Pd catalysts was studied by adsorption microcalorimetry and infrared (IR) spectroscopy. Some interesting and new correlations between the results of microcalorimetry and IR spectroscopy have been found. The CO is adsorbed on palladium catalysts in three different modes: multibonded (3-fold), bridged (2-fold), both on Pd (111) and (100) planes, and linear (1-fold) adsorbed species. The corresponding differential adsorption heats lie in the field of high (210−170 kJ/mol), medium (140−120 kJ/mol), and low (95−60 kJ/mol) values, respectively. The nature of the support, the reduction temperature, and the pretreatment conditions affect the surface structure of the Pd catalysts, resulting in variations in the site energy distribution, i.e., changes in the fraction of sites adsorbing CO with specific heats of adsorption. Moreover, the CeO2 promoter addition weakens the adsorption strength of CO on palladium. Based on the exposed results, a ...

A series of Mo-Mg-O catalysts with different crystalline phases (pure and mixtures) have been studied in the oxidative dehydrogenation of isobutane. X-ray diffraction, UV–Vis spectroscopy and temperature programmed reduction were applied to characterise the samples. In addition, the kinetics of the lattice oxygen exchange with labelled C18O2 was measured for all samples. It has been found that the MgMoO4 phase contains the surface active sites suitable for the adsorption of isobutane and for its dehydrogenation to isobutene with the minimum of cracking reaction. Moreover, for this reaction the migration of lattice oxygen ions is not a key parameter in the control of the catalytic properties of these materials.

Carbon dioxide reforming of methane has been studied over two ruthenium catalysts supported on silica and on γ-alumina. Catalytic activity measurements, infrared spectroscopic analysis and isotopic tracing experiments applied to the study of the surface hydroxyl groups of the supports have allowed different reaction mechanisms to be proposed on the bases of the detected surface species, their mobility, stability and reactivity. Activation of both reactants takes place on the ruthenium surface for Ru/SiO 2 catalyst. The accumulation of carbon adspecies formed from methane decomposition on the metallic particles finally impedes carbon dioxide dissociation and induces rapid deactivation of this catalyst. The alumina support provides an alternate route for CO 2 activation by producing formate intermediates on its surface that subsequently decompose releasing CO. This bifunctional mechanism, in which the hydroxyl groups of the support play a key role, induces greater stability on the Ru/Al 2 O 3 catalyst by significantly decreasing the rate of carbon deposition on the metal. The proposed reaction pathway requires continuous surface mobility of species from the metal to the support and vice versa.

A series of silica-zirconia mixed oxides were prepared by sol-gel routes wherethe zirconia content was varied from 9 to 75 mol%. The bulk and surface properties were analysed and compared with those of a sample wherezirconia was deposited as an external layer on a silica surface thereby avoiding internal mixing of the component oxides. Spin-lattice relaxation measurements made by 29 Si MAS NMR provide a useful estimation of the relative size of domains containing silica only and thus the degree of mixing. High levels of silica distribution throughout the mixed oxide prevented crystallisation of zirconia phases even at high Zr:Si ratios. The extent of mixing at the surface and throughout the bulk is discussed in relation to the generation of both Lewis and Bronsted acid sites. Increased levels of mixing and heteroatom linkages throughout the bulk did not necessarily result in an increase in the density of surface Bronsted acid sitesgenerated.

The reforming of CH{sub 4} with CO{sub 2} (dry reforming) has been studied on a series of Al{sub 2}O{sub 3}-supported Rh-Cu catalysts. The reaction has been found to proceed on these systems through a bifunctional mechanism, in which the activation on methane takes place on the rhodium phase while carbon dioxide is activated on the support surface via formate intermediates. The addition of a metal, such as copper, inactive for methane activation, has allowed the authors to evaluate the role of the interfacial Rh-Al{sub 2}O{sub 3} sites in the reaction. The presence of copper reduces the stability of the catalysts, though it does not have any effect on the initial activity per surface exposed site. It indicates that the dry reforming of methane is not a structure-sensitive reaction and that catalytic activity, largely affected by the alumina support, is dependent on the number of surface exposed rhodium centers.

Ru/C catalysts promoted, or not, by cerium were prepared by impregnation of an active carbon (961 m2 g−1) with chlorine-free precursors of Ru and Ce. They were characterized by chemisorption of H2 and of CO and by electron microscopy. TEM and H2 chemisorption gives coherent results while CO chemisorption overestimates Ru dispersion. In Ru–Ce/C, Ce is in close contact with Ru and decreases Ru accessibility. Catalytic wet air oxidation (CWAO) of phenol and of acrylic acid (160°C and 20 bar of O2) was investigated over these catalysts and their performance (activity, selectivity to intermediate compounds) compared with that of a reference Ru/CeO2 catalyst. Carbon-supported catalysts were very active for the CWAO of phenol but not for acrylic acid. Although high conversions were obtained, phenol was not totally mineralized after 3 h. It was shown that acrylic acid was more strongly adsorbed than phenol. Moreover, the number of contact points between Ru particles and CeO2 crystallites constitutes a key parameter in these reactions. A high surface area of ceria is required to insure O2 activation when the organic molecule is strongly adsorbed.

The states of surface Co and Mo sites on nitrided CoMo supported on Al2O3 were studied by adsorption of CO and NO as IR probe molecules. Three IR bands at 2200, 2060 and 2025 cm−1 were detected for adsorbed CO. These bands can be respectively attributed to the surface NCO species as a result of CO adsorbed on surface N sites, and linearly adsorbed CO on surface Co and Mo sites in low valence states. The addition of cobalt to the Mo nitride diminishes the band at 2200 cm−1. This may be due to either the change of the surface structure of the supported nitride, or the formation of a new phase, CoxMoyNz, as suggested in the literature Kim etal., Catal. Lett., 1997, 43, 91 and Logan etal., Catal. Lett., 1998, 56, 165. Comparison of CO and NO adsorption on Mo2N/Al2O3 and CoMoNx/Al2O3 indicates that the presence of cobalt can promote the reduction and nitridation of Mo.

The addition of MgO to a ruthenium catalyst dispersed on an inert activated carbon is found to improve the catalyst selectivity and stability in the dry reforming of methane to syngas. Steady-state and isotopic transient kinetic experiments carried out in a TAP reactor have revealed a cooperative interaction between the metal and the basic oxide in the CO2/CH4 reaction via a bifunctional mechanism. This specific effect is proposed to explain the discovered promoting effect.

The temperature-programmed reduction of four copper-rich, Rh−Cu/Al2O3 bimetallic catalysts was studied using X-ray absorption near-edge spectroscopy (XANES), infrared spectroscopy using CO as a probe molecule, and electron paramagnetic resonance (EPR). In the initial, fully oxidized state, copper and rhodium do not form mixed oxide phases; that is, only copper aluminates and rhodium oxide are detected. The nature of the copper aluminate is controlled by the Rh loading and pH of the preparation solution. Below 1.0 wt % of rhodium charge, there is extensive formation of a superficial copper aluminate phase, which is coreduced with rhodium oxide to yield an alloyed phase. The bimetallic particles formed have a heterogeneous composition with a Rh-rich core and a surface enriched in copper. Rh is electronically perturbed in these binary particles in relation to a metallic reference and shows a net positive charge. The analysis of the genesis mechanism of the zerovalent phases provides evidence of the critical ...

The transformation of MoO3 into γ-Mo2N during its nitridation by temperature-programmed reaction with NH3 has been investigated. The X-ray diffraction (XRD) results indicate that the conversion of the MoO3 bulk structure was significant at 673 K, although a notable increase in the surface area was observed at higher temperatures such as 773 K. For the sample synthesized at 973 K for 2 h, the achieved surface area was 140 m2·g−1 with approximately 60% pore volume within the diameter range of 20–30 A. The XRD and differential thermal analysis (DTA) results indicate that some intermediates, i.e., H0.3MoO3, MoO2, and γ-Mo2OxN1−x, were formed during the pseudomorphic transformation of MoO3 to γ-Mo2N in the temperature range of 673–973 K. Some new information about the transformation reaction was provided by X-ray photoelectron spectroscopy (XPS) and Fourier transformed infrared (FT-IR) spectroscopy. XPS results revealed that Mo2+ species was the main species exposed at the surface of passivated samples.

Three microporous commercial carbons were treated with HCl, H2F2 and HNO3. The effects of these treatments on the specific surface area and porosity, on the surface functional groups and on the adsorption behavior of phenol are studied by means of N2 adsorption at 77 K, temperature-programmed desorption (TPD) and phenol adsorption isotherms, respectively. The results show that there are carbonates and silica impurities that are occluded in all pore ranges of the activated carbons. These inorganic impurities do not have an effect on the phenol adsorption. When the carbons are oxidized (by treatment with HNO3 solution), the surface oxygen functional groups are principally placed on the micropores entrance. From TPD experiments some minor amounts of carboxylic groups on the surface of the original carbon have been found. On the oxidized carbons TPD experiments show a strong increase in the amount of carboxyl groups and the appearance of anhydride, peroxidic and phenolic groups. The adsorption of phenol on oxidized carbons remarkably diminished, in comparison with untreated carbons, as a consequence of the presence of oxygen surface groups. Also, a change from L-shaped to stepped isotherms has been detected and a shorter time is required to reach the adsorption equilibrium in comparison with the original carbons.

The catalytic production of syngas from methane was investigated over alumina- and silica-supported ruthenium catalysts. It is shown that the support is involved in reactions with reactants and products somewhat modifying the catalytic behaviour. From isotopic tracing experiments it is concluded that the syngas production reaction follows the same indirect pathway over the two catalysts, i.e. the sequence of total oxidation of methane, followed by reforming of the unconverted methane with carbon dioxide and steam to syngas. Recent literature is analysed in the light of our results.

In a study of the preparation of carbon-supported Pt and Ru catalysts, three high surface area graphites with similar textural characteristics, but differing in surface chemistry, have been used as carriers. Four series of metallic catalysts (two based on Pt and two on Ru) have been prepared by using different metal precursors and preparation methods. The catalysts were characterized by temperature-programmed reduction, H2 and CO chemisorption and microcalorimetry of CO chemisorption. The achieved metallic dispersions mainly depend on the reduction-decomposition treatments and on specific interactions between the metal particles and surface defects at the graphite. Microcalorimetry of CO adsorption evidences that the presence of oxygen surface groups diminishes the metal–support interaction.

The effect of the support (graphite, activated carbon, silica and alumina) has been investigated using the conversion of n-hexane as model reaction. The catalysts were characterized by H2 adsorption and transmission electron microscopy. Also, the CO adsorption was studied by microcalorimetry. The higher initial heat of CO adsorption observed on ruthenium/graphite indicates an enhanced electron density of the ruthenium particles caused by electron transfer from the graphite. The catalytic results show that ruthenium particles with an increased electron density have a higher activity for the n-hexane conversion accompanied by a preference for hydrogenolysis reaction, with the hydrogenolysis pattern corresponding to a multiple fragmentation. The higher resistance of ruthenium/graphite catalysts to deactivation by carbonaceous deposits was also observed.

The gas‐phase hydrogenation of crotonaldehyde has been performed over unsupported Mo2N and over Mo2N supported on two carbonaceous materials, an activated carbon (AC) and a high surface area graphite (G). These catalysts were in situ prepared by the temperature‐programmed reaction of MoO3 and carbon‐supported Mo precursors with NH3. It is found that selectivity to the unsaturated alcohol is maximum for the Mo2N/G sample, where crotylalcohol selectivities exceed the 60% during all time in reaction. Higher selectivity surface sites are associated with the (200) planes of the γ‐Mo2N crystallites.

The reduction of nitrogen oxides by propene in the presence of air under net oxidising conditions has been studied for two Cu/alumina catalysts of low (1%) and high (5%) copper loadings in a flow microreactor and by DRIFT. The reaction was studied in the range 473–773 K using mixtures of 2.5% NO, 1% C3H6 and 10% O2 with a balance of nitrogen or helium, using samples which were pretreated in air at 673 K and also over samples which had been pre-exposed to SO2 at 473 K. The surface species present under reaction conditions have been identified and the sensitivity of their adsorption sites in the two different loaded catalysts to SO2 pre-treatment has been investigated. SO2 adsorption enhanced NO adsorption at 473 K in the absence of oxygen and, in reaction, enhanced formation of NCO species leading to increased levels of adsorbed CO as a decomposition product.

Alumina-supported rhodium–copper catalysts were prepared and characterized by chemisorption of hydrogen, temperature-programmed reduction, X-ray photoelectron spectroscopy, and infrared spectroscopy of adsorbed CO. It is shown that the alumina support interacts with rhodium as well as with copper. None of the bimetallic catalysts have a single phase, but are composed of segregated phases of rhodium and copper and alloyed clusters, the latter being formed at the lowest rhodium loading. The catalytic properties of the catalysts were studied by means of then-hexane reaction. The turnover frequencies remained constant upon incorporation of copper into rhodium catalysts. However, the selectivity pattern changed; i.e., the isomerization reaction was enhanced at the expense of the hydrogenolysis reaction. The hydrogenolysis product distribution also shifted to a lower fragmentation factor. These results were explained by an ensemble effect in which the addition of copper isolates the rhodium in small clusters.

The chemical changes that occurred in two copper-based catalysts (Cu-ZSM-5 and Cu-Al2O3) during the selective reduction of NO with propene in the presence of oxygen were studied using in situ X-ray absorption near edge structure (XANES). For the quantitative analysis of the XANES spectra, a mathematical procedure based on evolving factor analysis (EFA) has been applied. Correlation with catalytic data shows that copper is fully oxidized in both systems when the conversion of propene is complete and the conversion of NO to N2 reaches its maximum value. The XANES analysis together with comparison of the catalytic behavior of Cu-ZSM-5 with Cu-Al2O3 and Cu-SiO2 systems indicates that the rate limiting step of the reaction takes place on cupic oxides (although other species may also participate). This conclusion is of general significance because it establishes the physical basis for the role of Cu in selective catalytic reduction of NO by hydrocarbons; this explains the recently recognized fact that zeolitic ...

Six different transition metals — cobalt, nickel, ruthenium, rhodium, iridium and platinum — have been supported on silica or alumina by means of the incipient wetness method. After drying and calcination at 773 K, they have been characterized by the hydrogen pulse chemisorption technique and by transmission electron microscopy. The interaction of CH4 with the catalyst surface has been studied by a temperature programmed surface reaction of methane and by examining the reactivity with hydrogen of the carbon deposits formed for three hours of reaction at 623 K in a flow of diluted methane. It has been found that the support exerts a great influence in the activity of dehydrogenation of methane and in the kind of carbonaceous species generated. It has also been proved that rhodium catalysts have a special ability to stabilize reactive carbon species (Cβ) hydrogenable between 423 K and 498 K.

Different magnesium vanadate phases, V-Mg-O phases (α- Mg2V2O7, Mg3V2O8 and β- MgV2O6), MgO and V2O5 oxides have been compared with respect to their surface properties and their oxygen exchange capacities with C18O2 in the gas phase. By temperature- programmed desorption of carbon dioxide, the absence of any basic impurities (i.e., MgO or residual oxidised K impurities resulting from the preparation) has been evidenced on the surface of magnesium vanadate phases. This demonstrates that the catalytic properties of the magnesium vanadate phases for oxidative dehydrogenation of propane as previously studied cannot be explained by synergetic effects due to the presence of any basic component impurities since they are absent in this case. While on MgO an important surface exchange process occurs with C18O2 of the gas phase, this exchange is very low on V2O5 and pure V-Mg-O phases. A comparison of the different magnesium vanadate phases in the same experimental conditions indicates that the α-Mg2V2O7 phase (which exhibited the highest selectivity for oxidative dehydrogenation of propane to propene) shows the lowest lattice oxygen exchange with C18O2 of the gas phase. This is another specificity of this phase.

The effects of the rhodium (oxidation) state on the activity and selectivity for the crotonaldehyde hydrogenation reaction over Rh/Al2O3 and Rh/SiO2 catalysts were examined using the techniques of temperature-programmed reduction, hydrogen chemisorption and X-ray absorption near-edge structure (XANES). In the alumina-supported system, the active phase-support interaction is shown to affect the chemical behavior of rhodium under the influence of a reductive atmosphere by stabilizing Rh3+ species. This behavior is not observed (as expected) for Rh/SiO2 catalysts. The structural and electronic bases of the active phase-support interaction and the effect of the latter phenomenon on the hydrogenation of crotonaldehyde are discussed.

Ruthenium catalysts supported on activated carbons, original (AC) and treated with nitric acid (AC-Ox) were prepared by incipient wetness impregnation from either chloride (Cl) or nitroxyl nitrate (n) precursors. These catalysts were characterized by TG, XPS, TEM, TPD-MS and CO adsorption microcalorimetry and evaluated in the hydrogenolysis of glycerol in the liquid phase, at 453 K and 8 MPa. Studies by TEM show that ruthenium particles supported on AC-Ox are larger than on AC, without any effect of the nature of the metal precursor. However, adsorption of CO on the ex-chloride catalysts is inhibited in comparison with that of the ex-nitroxyl nitrate catalysts. Catalysts characterization by TG, TPD-MS and XPS reveals that the nitric acid treatment and the nitroxyl nitrate precursor generate oxygenated groups on the carbon surface, which provide acid properties to the catalysts, although they are partly destroyed during the reduction treatment applied to the catalysts. The sequence of the overall TOF, Ru(Cl)/AC < Ru(n)/AC < Ru(Cl)/AC-Ox ≈ Ru(n)/AC-Ox, reasonably parallels the population increase of surface acid groups. Participation of the COOH groups in the transformation of glycerol into 1,2-propanediol is verified by using the admixture Ru(Cl)/AC+AC-Ox as catalyst. In this case, since AC-Ox was not thermally treated and no loss of oxygenated groups occurred, TOF and selectivity toward 1,2-propanediol improve in comparison with those of the more active catalysts., 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.

In this study, performance and feasibility of a hollow fibre membrane reactor (HFMR), consisting of a packed catalyst bed around a Pd coated Al2O3 hollow fibre membrane, has been studied and compared with both conventional Pd based tubular membrane reactor (TMR) fabricated from a stainless steel substrate and traditional fixed-bed reactor (FBR). The ceramic based HFMR presents several advantages over MRs such as the deposition of ultra thin Pd membranes and the possibility to scale up the whole multifunctional process by module configuration. The results obtained at 450 °C during the methane dry reforming (MDR) reaction showed that, although CH4 conversion using the HFMR was almost the same as that of a catalytic TMR, the amount of Pd employed for the Pd layer deposition in the HFMR was fifteen times less than that in TMR. Moreover, the CH4 conversion using the HFMR was 72% higher than that in a traditional FBR and 34% higher than thermodynamic equilibrium. Also, a high purity COX-free H2 production (10.5 ml/mg h) was achieved at 525 °C using a sweep gas of 100 ml/min in the lumen side of the HFMR., The authors gratefully acknowledge the research funding provided by EPSRC in the United Kingdom (grant No. EP/G012679/1), MINECO in Spain (projects CTQ2011-29272-C04-01 and 03).

Oxygen surface groups, which are typically present on the surface of activated carbon, have a decisive effect on the achieved dispersion of active phases, which affects the electronic properties of the surface sites and stabilizes the materials against sintering phenomena. Therefore, the desorption of oxygen surface groups during the decomposition–reduction of the metal salt precursors of the fresh carbon‐based catalysts can lead to surface reconstruction of the metal nanoparticles, which can significantly affect their catalytic activity. In this work, the oxidation states of Ru atoms supported on both an activated carbon thermally treated to remove all oxygen groups and the untreated material were studied during the reduction process. The precursor to prepare these catalysts is Ru(NO)(NO3)3. The main results were obtained by using in situ X‐ray absorption near‐edge structure analysis of the Ru K‐edge under conditions comparable to the temperature‐programmed reduction experiments. The different reduction mechanism observed in each of the catalysts, of a multistep nature if oxygen surface groups are present and single‐step in the case of clean graphitic surfaces, can be regarded as a typical metal–support interaction. Moreover, differences in both the final Ru oxidation state and the subsequent interaction of the active phase with the support are the main cause of the five‐times higher catalytic activity observed in the presence of the catalyst without surface oxygen groups for the NH3 decomposition reaction., This work was supported by the Spanish Government (project CTQ2011‐29272‐C04‐01 and 03). F.R.G.‐G. gratefully acknowledges financial support from the Spanish Ministry of Science and Technology, JdC postdoc programme.

Iridium catalysts were prepared using alumina or silica as supports and two preparation methods, incipient wetness impregnation and flame spray pyrolysis. These catalysts were characterized, after reduction in hydrogen, by transmission electron microscopy, infrared spectroscopy of adsorbed CO and microcalorimetry of CO chemisorption. Aliquots of these catalysts were tested in the ethyl pyruvate hydrogenation using cinchonidine as a chiral modifier. Different enantioselectivities to (R)-ethyl lactate were obtained depending on the support material and the preparation method. Based on the structural characterization it is proposed that the different enantioselectivities are mainly due to different surface structure of the iridium nanoparticles caused by the support interaction., Authors acknowledge the MICINN of Spain (Projects CTQ-2011-29272-C04-01 and -03) for financial support.

Nitrogen-containing carbon nanotubes were prepared, characterized and used as catalysts for two reactions of interest in the biomass upgrading processes: acetone aldol and acetic acid decarboxylative condensations. N-CNT were synthesized in a fluidized bed reactor by catalytic chemical vapor decomposition of acetonitrile on iron-, cobalt- and nickel-supported catalysts. Ni-N-CNT catalyst exhibits the highest activity, attributed to the surface concentration of basic sites, particularly the pyridinic species detected by X-ray photoelectron spectra (XPS). Likewise, the selectivity toward the final products of the reaction pathway is related both to the strength of basic sites (Ni-N-CNT) and to the morphology and chemical environment of the active sites (Fe-N-CNT). Synthesized catalysts show high stability for acetone condensation, whereas for ketonic condensation the catalyst stability decreases, mainly due to acic–base interactions with the active sites., This work was financed by the Spanish Ministry for Economy and Competitiveness (projects no. CTQ2011-29272-C04-01, -02 and -03).

The influence of variables such as adsorption temperature, polar chain length, and nature of functional groups on the adsorption, from aqueous solutions, of various surfactants (TX-114, TX-100, TX-165, TX-305, NP1P4E, NP4P1E, NP4S, NP10S, and NP25S) has been investigated. Several nonporous solids, including various samples of quartz, QA (5.1 m2g−1), QB (5.5 m2g−1), and QC (4.0 m2g−1), kaolin (19.3 m2g−1), and dolomite (0.3 m2g−1), were studied. Conformational changes of adsorbed surfactant molecules on QC quartz, when the oxyethylenic length of Tritons increases, have been detected. For all the other solid samples the surface is not completely covered by Tritons. On quartz, the surfactants are adsorbed by hydrogen bonds between the surfactant's ether groups and the silanol groups of the solid surface. These hydroxyl groups must be free and sufficiently separated from other hydroxyls of the solid surface. When the number of propoxy groups increases (from NP1P4E to NP4P1E) the adsorbed amount of surfactant on the solid studied decreases. Anionic surfactants are adsorbed on quartz in lower amounts than the corresponding nonionic surfactants. However, the adsorbed amounts of Tritons and sulfated Tritons on kaolin are similar, probably due to the positive charges on the edges of this material.

The copper-catalysed reduction of NO with carbon has been studied over copper-loaded carbon materials (graphites and activated carbon). Characterization of the different preparations has been carried out by X-ray diffraction, temperature-programmed reduction in hydrogen and surface reaction of NO. The copper loading, the nature of the copper phase, the presence of functional groups on the surface of the carbons, the structure of the carbon (graphite or activated carbon) and the reaction temperature, have been related to the catalytic performance of the different carbon-supported copper samples. High catalytic activity may be achieved over low copper-loaded high surface area graphite with the surface covered with oxygen functional groups.

The copper-catalysed reduction of NO with CO has been investigated over copper-loaded carbon materials (graphites and activated carbon). The NO + CO reaction has been studied in the presence and in the absence of oxygen. The carbon-supported copper catalysts have a very high activity for the reduction of NO with CO; however, the presence of oxygen inhibits the reaction. Variations in catalytic activity are associated with changes in the chemical nature of the active sites. Carbonaceous materials are found to stabilize metallic copper under NO + CO reaction conditions. The presence of functional groups on the surface of the carbon and the porous structure affect the performance of the catalysts. The reduction of NO with carbon is enhanced by the presence of O2, although the activity for this reaction is very low compared with those for the NO + CO or CO + O2 reactions.

A series of copper-zinc-chromium catalysts of different compositions and calcination temperatures has been prepared, characterized by several techniques (BET specific surface area, XRD, gravimetric TPR, TPD-CO, and XPS), and tested under high alcohol synthesis (HAS) conditions. CO hydrogenation was carried out at reaction temperatures of 523-598 K and 50 bar total pressure. The influence of catalyst composition, calcination temperature, and surface characteristics on the HAS selectivity was studied. The optimum HAS yields were found in the low Cr content region, but chromium was needed. Although chromium oxide does not seem to be involved in the catalytic site, its presence in the catalyst composition is essential, owing to the larger specific surfaces and catalyst stability obtained at the highest reaction temperatures. For low Cr content composition, the temperature-programmed reduction (TPR) profiles were shifted to higher temperatures and simultaneously larger CO2 amounts were found in the temperature-programmed desorption profiles of adsorbed CO (TPD-CO). Photoelectron spectra (XPS) revealed that the oxidation state of copper is Cu2+ in the calcined catalysts and Cu0 in the reduced ones; Cu+ was only stabilized in a CuCr2O4 spinel in the Cr-rich catalysts. These features derived from catalyst characterization are discussed in the framework of the catalytic behaviour for HAS synthesis.

Carbon-supported one-component (Fe, Ru, Pt) and two-component (FeRu and FePt) catalysts were used for hydrodenitrogenation of pyridine (HDN) at 3.0 MPa and 573 K. The Fe catalyst was less active for pyridine conversion and less selective for the formation of n -pentane than the noble metal catalysts were. For the two-component catalysts, activity was closely related to that of the noble metal component, although the C 5 hydrocarbon distribution was intermediate between that for the single components. Photoelectron spectra of sulfided and used catalysts showed that iron and ruthenium monocomponent catalysts are sulfided to a large extent, but platinum preserves in part its metallic character, although the situation differs for the platinum-iron catalysts. The strong decrease in the Fe/C ratio and the significant increase in the Pt/C ratio in the two-component catalysts indicate that iron is redispersed during incorporation of platinum, the latter being deposited mainly at the outer surface.

A series of Fe-Mo catalysts with different properties was prepared by modification of the synthesis variables. Their catalytic behaviour in the oxidation reaction of methanol to formaldehyde was determined. The differences in their textural, morphological, chemical and structural properties were determined using nitrogen adsorption, SEM-energy dispersive X-ray analysis, X-ray photoelectron spectroscopy, X-ray diffraction and Fourier transform-infrared analyses. We have attempted to establish relationships between these properties and their catalytic activity in the above reaction. We have found that their catalytic behaviour principally correlated with the atomic ratio of Mo∶ Fe. This ratio was sensibly higher than that required stoichiometrically for iron(III) molybdate.

Alumina-supported tungsten and molybdenum oxide catalysts with a wide range of MO3 loadings were studied in the metathesis of propene. The catalysts were activated by several procedures in order to correlate the oxidation state of Mo or W, as characterized by XPS, and the acidic character, as determined by IR of adsorbed pyridine, with the main metathesis reaction and side olefin reactions. The catalytic activity of the samples under standard conditions was found to be invariant with the pretreatment (air or He). This leads to the conclusion that the activation of catalysts takes place under the propene atmosphere during the first minutes of reaction. XPS studies of fresh and spent catalysts showed that the active sites for metathesis seem to be W(VI) or Mo(VI) species. Both MoO 3 Al 2 O 3 and WO 3 Al 2 O 3 catalysts are active in parallel reactions such as polymerization, isomerization and cracking. The product distribution for the metathesis reaction differed greatly from that expected. Thus, for all catalysts the ethene/butene ratio is lower than 1 and isobutene was the main component of the C4 fraction, its proportion increasing with the metal oxide content. Studies by IR of adsorbed pyridine showed the Bronsted acid sites generated on MoO3 or WO3 in samples with high metal oxide content to be responsible for the lateral acid-catalyzed reactions.

International audience; Gold nanoparticles have been deposited on zinc oxide by deposition–precipitation methods. The selection of the support characteristics is critical to control gold nanoparticle sizes and surface properties. Two ZnO supports have been studied, one is commercially obtained and the second is lab prepared by chemical vapor deposition resulting in tetrapod morphologies. In the latter two gold loadings were incorporated. These catalysts were mainly characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Also the three samples were tested for the selective hydrogenation of cinnamaldehyde. We have shown that the use of AuZnO as catalyst permits higher selectivity in desired products than that observed using alternative catalysts. The selectivity values which vary among 58% and 99% depending on the surface structure of the gold nanoparticles induce steric constraints between the phenyl group of the substrate and the metal surface of large particles. These catalysts show also good stability without detectable sintering.

Treatments of wastewater decontamination are a major technological issue in the last decades. Depending on the pollutants' nature and on their concentration, different strategies can be applied in order to remove such contamination. Adsorption and catalysis are recognized as some of the most widespread treatments for polluted waters, carbon materials being a key in many of the recent and future technologies. The potentiality of using carbon materials in the fields of the wastewater treatments has already been investigated and documented in different scientific studies. To date, most of these researches have focused on activated carbons, while novel carbon materials have received much less attention even if recently these are under evaluation in various fields. In this review, the different methods of removing organic pollutants, particularly aromatic compounds, from aqueous phases are considered, emphasizing on the potential use of new carbon structures, for example, carbon nanotubes, nanofibers, or graphenes.

The promoting effects of magnesium, vanadium and cerium oxides on cobalt and ruthenium/carbon catalysts in the hydrogenation of carbon monoxide have been compared. The reducibility of the promoted and unpromoted catalysts was investigated by temperature-programmed reduction. In all cases the added oxide promoter enhanced the specific activity and the selectivity for alkenes and long chain hydrocarbons. These results are discussed on the basis of a general mechanism of promotion.

The reforming of CH4 with CO2 over activated carbon- or silica-supported cobalt catalysts with and without added MgO as promoter has been studied over a range of temperatures (500–700°C). A significant effect of the MgO on catalyst efficiency was observed. The presence of MgO markedly reduces the carbon deposition on the surface of the catalyst and therefore, contributes to the stability of the catalyst. Based on temperature-programmed surface reaction experiments of chemisorbed CO2, the role of MgO may be ascribed to the formation of strongly adsorbed CO2 species over its surface. These CO2 species can easily react with the surface carbon deposits under CO2-reforming reaction conditions, preventing in this way catalyst deactivation.

A series of carbon-supported platinum catalysts with different metallic dispersions (from 0.05 to 0.68) was tested for the n-heptane aromatization reaction. The influence of a basic function (MgO) on the catalytic behaviour was also examined. It is found that, as the metal particle size decreases, the turnover frequency for hydrogenolysis increases, while those for isomerization and aromatization remain unchanged. Moreover, the selectivities for isomerization and hydrogenolysis change with the metal dispersion while that for aromatization remains constant. In addition, no modification in catalytic properties is observed by adding base sites to a Pt/carbon catalyst. These results suggest that aromatization is a structure-insensitive reaction and that it is independent of the other reactions.

The interaction of NO with copper in Cu-ZSM-5 and Cu-Y catalysts has been studied by IR techniques and TPSR. The adsorption of CO was followed by DRIFTS. Adsorption of CO on Cu-ZSM-5 and Cu-Y at room temperature gives bands corresponding to chemisorption on Cu+ in both cases, with those formed on Cu-ZSM-5 being the more stable in the temperature range up to 473 K. Upon adsorption of NO on Cu-ZSM-5 at room temperature bands corresponding to chemisorption on both Cu+, including those for the dinitrosyl species, and Cu2+ appear. On Cu-Y only bands belonging to species bound to Cu2+ are detected. This suggests that the Cu+ sites in Cu-Y are rapidly oxidized to Cu2+ by contact with NO, whereas Cu-ZSM-5 stabilizes Cu+ ions. Above 373 K, no NO species were detected on the Cu-Y sample, however with Cu-ZSM-5, bands for the mononitrosyls on both Cu+ and Cu2+ appear at higher temperatures (