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

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

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

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

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

Here we present a time-resolved in situ X-ray absorption spectroscopy investigation of the local chemical environment and the electronic structure of the active metal (Ru) and the promoter (Cs) present in catalysts supported over high-surface-area graphite. These catalysts were submitted to a reduction treatment under hydrogen gas and then to alternate atmospheres of Fischer–Tropsch reactants, CO/He, and H2/He atmospheres, respectively. This study reveals that Ru reduction is a complex process taking place through a two-step mechanism via an intermediate oxidation state and occurs in parallel to the Cs partial reduction. It also demonstrates a close association between Cs and Ru atoms as first neighbors. The evidence that the Ru–Cs particle morphology reverses (from flat 2D to a 3D shape with low coordination numbers) when the H2 atmosphere is changed with CO proves the strong interaction of CO with the surface of the Ru–Cs nanoparticles, a point confirmed by microcalorimetry of CO adsorption. To our know...

The catalytic properties of two noble metals, Pt and Ru, supported on KL zeolite were investigated in the selective transformation of bioethanol. In aiming to have an increased basicity of the catalyst, a KL zeolite modified by the addition of Ba was also used as support for Pt catalyst. For comparative purposes, Ru supported on hydrophobic high surface area graphite (HSAG) was also prepared. The catalytic tests were conducted in a fixed bed flow reactor, by feeding either pure ethanol vapor or a mixture of 10% water/90% ethanol in an inert gas, and working at low conversions to assure kinetic conditions. All the catalysts have relatively stable catalytic performance at up to 6 hours on stream with both reactant feedings. In general, the catalytic activities of Pt-based catalysts, given as turn-over-frequencies, were one order of magnitude higher than those obtained over Ru catalysts. It was also demonstrated that the nature of the supported metal nanoparticles (Ru vs. Pt) significantly affects the product selectivities. So when comparing Pt/KL and Ru/KL, methane and carbon monoxide by-products are mainly produced on the former, indicating that degradation of the primary product acetaldehyde by decarbonylation is higher on Pt catalysts. In the case of ruthenium nanoparticles, acetaldehyde is the predominant product. Finally, the comparison of Ru supported on KL zeolite and on HSAG revealed that, in the second case, ethylene is the principal by-product and that in some extension, this ethylene can be hydrogenated to ethane, probably spending hydrogen generated in the acetaldehyde formation. DRIFTS experiments were also conducted to identify the adsorbed intermediate species present under the reaction conditions on the different catalysts. All the selectivity differences have been rationalized using appropriate reaction pathways, and it is inferred that the variation of the chosen metal–support system is decisive to obtain a given reaction product.

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

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

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

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

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

Ruthenium catalysts supported on KL zeolite, ZrO 2 and graphite, prepared by incipient wetness impregnation, were characterized by N 2 adsorption, H 2 chemisorption, TEM and CO adsorption microcalorimetry and tested in the selective hydrogenation of citral in the liquid phase, at 5 MPa and 323 K. Characterization studies reveal that graphite promotes formation of electron-rich metal species (Ru n− ) that difficult hydrogenation of the conjugated C C double bond of citral and indirectly favor the production of geraniol and nerol. For Ru/ZrO 2 catalyst, the Ru ↔ ZrO 2 interaction at the interface, with formation of Ru 0 Zr n+ species as evidenced by the TEM and CO adsorption microcalorimetry measurements, activates the carbonyl group of citral and enhances the selectivity towards unsaturated alcohols. Characterization measurements of Ru/KL evidence that metal nanoparticles placed inside of the zeolite channels block part of ruthenium loading and hinder the free transit of citral through the channels, thus reducing the overall hydrogenation activity of the catalyst. Furthermore, this steric hindrance impedes adsorption the conjugated C C double bond of citral and forces hydrogenation of the carbonyl group in terminal position. On the other hand, the fact that active sites on occluded particles are more resistant to poisoning than those easily accessible to citral enhances the selectivity towards geraniol and nerol, as the reaction time increases. The comparative analysis of the results indicates that, in order to increase the selectivity towards unsaturated alcohols, geometrical effects derived from the size, shape and location of ruthenium particles in the KL structure are more effective than the electronic modifications induced by graphite or zirconia on the ruthenium particles.

The interaction of organic chemicals with the surface of carbon nanotubes (CNTs) has been studied by immersion calorimetry revealing new information about the unique CNT surface structures. The curvature of the graphene sheets of in the CNTs increases the adsorption strength of aromatic compounds compared to flat graphite surfaces. For a given CNT, the adsorption affinity of a non-polar aromatic molecule correlated poorly with the CNT hydrophobicity. Comparison of the immersion enthalpies that evolved when the solids were immersed in organic chemicals reveals the formation of π – π stacking interactions, H-bonds or electron–accepting interactions depending on the CNT surfaces and on the immersion substrate. The number of oxygen groups on CNTs seems to modify the electron density of their surfaces and therefore the interaction mechanism with the adsorbates.

A study of the catalytic decolourisation of one textile dye by oxidation with H 2 O 2 , using different carbon materials as catalysts, is reported. Ten carbon solids, differing both in their texture–structure features and in their surface chemistry properties, were used for this purpose. These are two activated carbons, a high surface graphite, two structured nanomaterials (carbon nanofibres and carbon nanotubes), and the derivative samples prepared by oxidation of the pristines with nitric acid solutions. All these samples were characterised by determination of the nitrogen adsorption isotherms, thermogravimetric data, transmission electron microscopy, pH at the point of zero charge and chemical composition based on the X-ray photoelectron spectra. These carbon materials were evaluated as catalysts for the catalytic wet peroxide oxidation of C.I. Reactive Red 241 dissolved in water. Carbon nanotubes (CNTs) exhibit the highest performance in terms of activity for the catalytic wet peroxide oxidation, achieving a total removal of the dye after 90 min in process. It appears that catalytic activity for this reaction is improved by the internal cylindrical mesopores of CNTs. However, when these hydrophobic CNTs are treated by incorporation of oxygen surface groups which increase their hydrophilic character, the high catalytic performance of CNTs largely disappears.

Modifications of texture and surface properties of a commercial activated carbon (Norit GF-40) were performed by several treatments in order to study their effects on the selective adsorption of nitromethane from nitromethane/water vapor mixtures. Characterisation of the samples by nitrogen adsorption and thermal analysis showed that HNO3 treatments produce important losses of porosity and surface area, accompanied of an increase of oxygenated functional groups on the surface of carbon, which are progressively removed by heating at temperatures between 573 and 1073 K. All this leads to a drastic decrease of the adsorption capacity per gram of adsorbent with respect to the raw carbon, which offers, on the other hand, the best adsorptive performance. Oxidation by H2O2 does not practically affect its textural properties and introduces an important amount of oxygen functional groups at the surface, but changes in the adsorptive properties of carbon are insignificant. Sample oxidised by H2O2 and subsequently treated by diethylentriamine shows a decrease in adsorption capacity, without any relevant loss of surface area. The raw carbon treated at high temperature that exhibits the highest surface area and where surface functional groups are absent, showed the greatest adsorption capacity for nitromethane, being much more selective for nitromethane than for water, in nitromethane-water mixtures. Adsorption capacity values for nitromethane on the different samples are related to the extent of the surface area, while water vapour adsorption seems to depend on the population of functional groups at the surface, which may work as adsorption sites.

This study illustrates the effect of the adsorbent porosity (activated carbon and high surface area graphite) on the phenol adsorption kinetics. We have developed an experimental system where on line analysis of the solution is carried out by an optic fiber probe introduced in the water solution and directly connected with the UV spectrometer. This experimental setup permits to be more precise in determining kinetic parameters, considering that measurements are taken each 20 seconds. Our results show that the choice of the particle diameter of the adsorbent is critical in the control of the adsorption process kinetic, while the porosity of the carbon materials appears to be less relevant.

The adsorption from aqueous solutions of a series of non-ionic surfactants (TX-114, TX-100, TX-165 and TX-305, where the ethoxylation degree is increasing in the series) on a non-microporous carbon surface, that is a high surface area graphite (GT), and on a mainly microporous activated carbon (NT) has been comparatively studied. Also the initially hydrophobic GT and NT surfaces have been modified by oxidation treatments in order to achieve partially hydrophilic carbon materials (GTox and NTox samples). The adsorption results reveal that for GT sample below the critical micellar concentrations (cmc) of surfactants practically the whole surface is covered by monomers. For NT there are steric hindrance limitations, so the surfactant molecules are adsorbed only on micropores of sizes larger than 8 A. When oxygen surface groups are introduced on the carbonaceous surfaces, the adsorption behaviour is again different for both materials. Thus, for GTox the adsorbed amounts below the cmc decrease probably due to withdrawal effect of the oxygen surface groups. On the contrary, the adsorbed amounts above the cmc slightly increase with regard to bare graphite, possibly due to an improved formation of micelles. In the case of NTox the adsorbed uptakes below and above cmc increase remarkably in comparison with NT sample, which can be explained by some specific interactions of the surfactants molecules with oxygen surface groups inside the micropores.

Several 2 wt.% Ru/KL supported catalysts were prepared by various methods with different ruthenium precursors and characterized by CO and H2 chemisorption, N2 adsorption, TPD of NH3, TEM and XPS. Furthermore, CO chemisorbed species have been studied by FT-IR and microcalorimetry. Characterization measurements of catalyst IWI-Ru, prepared by incipient wetness impregnation from ruthenium acetylacetonate, evidence metal nanoparticles of 1 nm placed inside the zeolite channels, thus blocking the accessibility to part of ruthenium loading inside the micropores. Catalyst prepared by treating the KL zeolite with RuCl3·xH2O aqueous solution (I-Ru) exhibits nanoparticles in the range 6–8 nm at the external surface and clusters smaller that 1 nm, inside the micropores. These latter do not significantly affect the diffusion of probe molecules through the channels. Catalytic performances in the selective hydrogenation of citral in the liquid phase, at 323 K and 5 MPa, show that IWI-Ru is less active than I-Ru, but more selective towards unsaturated alcohols. Furthermore, for IWI-Ru, selectivity increases with the increasing conversion. On the other hand, removal of acid sites of the I-Ru catalyst enhances the hydrogenation activity and increases the selectivity towards citronellal. All these results are analyzed and discussed in terms of the size, shape and location of ruthenium particles in the catalysts, as well as of the metal–support interaction.

Catalytic wet air oxidation (CWAO) reactions of aniline and phenol were conducted over supported ruthenium catalysts. Three support materials were employed: ZrO 2 and graphite, which exhibit medium adsorption capacities for pollutants and present mesopores in their texture, and an activated carbon. This latter has higher adsorption capacity for pollutants because of the large capability of the micropores for contaminant retention from water. The Ru catalysts supported on the activated carbon material showed the higher values of conversion in the oxidation of aniline and of conversion and mineralization in the reaction of phenol. Under our experimental conditions the role of micropores present on the support material seems to be relevant for improving catalytic performances. The incorporation of Ru nanoparticles from different precursors has been also evaluated. Even if the final Ru particle size is a key parameter for the catalytic mineralization, a cooperative effect with the activated carbon support has been established.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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 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.

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).

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

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.

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.

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.

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.