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MXenes are a new family of 2D carbides or nitrides that have attracted attention due to their layered structure, tunable surface groups and high electrical conductivity. Here, we report for the first time that Ti 2 CT x MXene catalyses the selective oxidative dehydrogenation of n -butane to butenes and 1,3-butadiene. This catalyst showed higher intrinsic activity compared to commercial TiC and TiO 2 samples in terms of C 4 olefin formation rate. We propose that the stabilisation of structural vacancies and the change in composition (from a carbide to a mixed phase oxide) in the MXene causes its higher catalytic activity. These vacancies can lead to a higher concentration of unpaired electrons in the MXene-derived material, enhancing its nucleophilic properties and favouring the production of olefins. We thank the Netherlands Organization for Scientific Research (NWO) for the grant “Developing novel catalytic materials for converting CO2, methane and ethane to high-value chemicals in a hybrid plasma-catalytic reactor” (China.15.119). EVRF thanks the “Ministerio de Ciencia e innovación” grant (PID2020-116998RB-I00).

A mechanism for the reduction of aqueous nitrate with metal-free polypyrrole (PPy) is proposed. The activity and selectivity of the polymer has been compared to those of metal catalysts supported on polypyrrole, activated carbon or titania (TiO2). The role of formic acid (FA) and hydrogen (H2) as reductants, and carbon dioxide (CO2) as buffer of the aqueous nitrate solution is discussed and compared to the performance of PPy by itself. The ion-exchange and the redox properties of PPy are strongly affected by the oxidation state of the nitrogen moieties in the polymeric chain. This is determined by the oxidant/dopant used in the polymer synthesis (FeCl3 or K2S2O8). The degree of oxidation of PPy can also be modified by a plasma treatment of the polymer, which determines the ability of PPy to carry out the reduction of nitrate by the electrons provided by the polymeric chain and also affects the selectivity of the nitrate reduction. Financial support from Generalitat Valenciana, Spain (PROMETEOII/2014/004) and Ministry of Economy and Competitiveness (MAT2016-80285-P) is gratefully acknowledged.

We report a facile and general approach for preparing ultrafine ruthenium nanocatalysts by using a plasma-assisted synthesis at

Three different conducting polymers, polythiophene (PT), polypirrol (PPY) and polyaniline (PANI) have been synthesized via oxidative chemical polymerization in aqueous media, in such a way that the synthesis protocol did not involve any toxic solvents. They have been tested in the abatement of nitrates from an aqueous solution without the need of any metal catalyst. The N-containing polymers (PANI and PPy) were able to remove nitrates to a level that accomplishes the European legislation requirements; however, the nature of each polymer greatly influenced the process mechanism. Whereas ion exchange between Cl- and SO42- counter-ions in the polymer and NO3- from water is the main responsible for the effective nitrate removal in PANI, as assessed by FTIR and XPS analyses, the nitrate removal mechanism on PPy is based in an electron transfer from the polymer to nitrate through N sites located in the pyrrolic ring. On the other hand, PT was not able to exchange nitrate unless it was synthesized with FeCl3 as oxidant/dopant and an anionic surfactant (sodium dodecyl sulfate -SDS-) is used. In that case, the electrostatic attraction between sulfate (OSO3-) groups from the surfactant and Fe3+ ions from FeCl3 produced the anchoring of Cl- to the oxidized PT growing chain, this favoring ion exchange with nitrate in the aqueous solution, followed by a redox process. Financial support from Generalitat Valenciana, Spain (PROMETEOII/2014/004) is gratefully acknowledged.

Offsetting the impact of human activities on the biogeochemical cycle of mercury has become necessary for a sustainable planet. Herein, we report the development of a water-stable and eco-friendly metal–organic framework, which has the formula {Cu4II[(S,S)-methox]2}·5H2O (1), where methox is bis[(S)-methionine]oxalyl diamide. Its features include narrow functional channels decorated with thioalkyl chains, which are able to capture HgCl2 from aqueous media in an efficient, selective, and rapid manner. The conscious design effort in terms of size, shape, and reactivity of the channels results in extremely efficient immobilization of HgCl2 guest species in a very stable conformation, similar to that of the enzyme mercury reductase. Thus, 1 enables the highly efficient removal of toxic HgCl2 from aqueous media and reduces the [Hg2+] concentration from the dangerous level of 10 ppm to acceptable limits of below 2 ppb in drinking water. The unusual combination of a low-cost straightforward synthetic procedure and high stability under environmental conditions, together with its ability to efficiently and rapidly remove poisonous mercury ions, places 1 among the most attractive adsorbents reported to date for the purification of contaminated water. This work was supported by the MINECO (Spain) (Project CTQ2016-75671-P and Excellence Unit “Maria de Maeztu” MDM-2015-0538), the Generalitat Valenciana (Spain) (Project PROMETEOII/2014/070), and the Ministero dell'Istruzione, dell'Università e della Ricerca (Italy). M. M. and X. Q. thank the MINECO and the China Scholarship Council for grants. Thanks are also extended to the Ramón y Cajal program (E. P and E. V. R.-F.).

Platinum nanoparticles have been synthesized on polyaniline (PANI) and polypyrrole (PPy) as supports using H2PtCl6 as metal precursor and a reducing treatment with cold Ar plasma. The catalytic activity of the polymer-supported catalysts in the reduction of aqueous nitrate with H2 at room temperature was evaluated. These systems are able to considerably decrease the concentration of nitrate in water in only 5 min. The mechanism of the nitrate abatement process is determined by the nature of the conducting polymer. The nitrogen functionalities in polyaniline are external to the ring system, and favor nitrate retention at the platinum complex either by the formation of an adduct or by nitrate participating as a ligand. In contrast, polypyrrole possesses aromatic nitrogen atoms with a considerably more important steric hindrance. In this case, ion exchange between the counter ions in the doped polymer (SO42−) and nitrate from water is produced, followed by reduction of nitrate by hydrogen chemisorbed on the platinum nanoparticles. Financial support from Generalitat Valenciana, Spain (PROMETEOII/2014/004) is gratefully acknowledged.

A detailed study on the preparation of bimetallic PtSn/C catalysts using surfacecontrolled synthesis methods, and on their catalytic performance in the glycerol steam reforming reaction has been carried out. In order to obtain these well-defined bimetallic phases, techniques derived from Surface Organometallic Chemistry of Metals (SOMC/M) were used. The preparation process involved the reaction between an organometallic compound ((C4H9)4Sn) and a supported transition metal (Pt) in a H2 atmosphere. Catalysts with Sn/Pt atomic ratios of 0.2, 0.3, 0.5, and 0.7 were obtained, and characterized using several techniques: ICP, H2 chemisorption, TEM and XPS. These systems were tested in the glycerol steam reforming varying the reaction conditions (glycerol concentration and reaction temperature). The best performance was observed for the catalysts with the lowest tin contents (PtSn0.2/C and PtSn0.3/C). It was observed that the presence of tin increased the catalysts’ stability when working under more severe reaction conditions., Centro de Investigación y Desarrollo en Ciencias Aplicadas

The low temperature water–gas shift (WGS) reaction has been studied over Ni–CeO2/Graphene and Ni/Graphene. The catalysts were prepared with 5 wt.% Ni and 20 wt.% CeO2 loadings, by deposition-precipitation employing sodium hydroxide and urea as precipitating agents. The materials were characterized by TEM, powder X-ray diffraction, Raman spectroscopy, H2-temperature-programmed reduction and X-ray photoelectron spectroscopy (XPS). The characterization and the reaction results indicated that the interaction between the active species and the support is higher than with activated carbon, and this hinders the reducibility of ceria and thus the catalytic performance. On the other hand, the presence of residual sodium in samples prepared by precipitation with NaOH facilitated the reduction of ceria. The catalytic activity was highly improved in the presence of sodium, what can be explained on the basis of an associative reaction mechanism which is favored over Ni-O-Na entities. Authors thank to CONICYT (Chile, Postdoc FONDECYT 3130483) and Ministerio de Economía y Competitividad (Spain, MAT2010-21147 and MAT2013-45008-P) for financial support.

Copper-based catalysts supported on niobium-doped ceria have been prepared and tested in the preferential oxidation of CO in excess of H2 (PROX) and in total oxidation of toluene. Supports and catalysts have been characterized by several techniques: N2 adsorption, ICP-OES, XRF, XRD, Raman Spectroscopy, SEM, TEM, H2-TPR and XPS, and their catalytic performance has been measured in PROX, with an ideal gas mixture (CO, O2 and H2) with or without CO2 and H2O, and in total oxidation of toluene. The effects of the copper loading and the amount of niobium in the supports have been evaluated. Remarkably, the addition of niobia to the catalysts may improve the catalytic performance in total oxidation of toluene. It allows us to prepare cheaper catalysts (niobia it is far cheaper than ceria) with improved catalytic performance. The authors gratefully acknowledge the financial support from MINECO (Spain, Project MAT2010-21147)8/346) and Generalitat Valenciana (PROMETEOII/2014/004). EVRF thanks the MINECO for his Ramón y Cajal Fellow RYC-2012-11427. EOJ thanks the CNPq –Brazil for her grant.

Catalysts consisting in platinum supported on cerium oxide highly dispersed on activated carbon, with a Pt loading of 1 wt.% and ceria loadings of 5, 10 and 20 wt.% have been prepared by impregnation method and characterized by several techniques (N2 adsorption at 77 K, ICP, XRD, H2-TPR and XPS). Their catalytic behavior has been evaluated in the total oxidation of ethanol and toluene after reduction at 473 K. The obtained results show that the prepared catalysts have better performances than platinum supported on bulk CeO2. The best catalytic performance was obtained for 10 wt.% ceria loading, likely due to an optimum synergistic interaction between highly dispersed cerium oxide and platinum particles. Pt-10Ce/C achieves total conversion of ethanol and toluene to CO2 at 433 K and 453 K, respectively, and shows no deactivation during a test for 100 h. Under humid conditions (relative humidity, RH, of 40 and 80%), the activity was only slightly influenced due to the hydrophobic character of the activated carbon support, which prevents the adsorption of water. Financial support from Generalitat Valenciana (Spain, PROMETEO/2009/002-FEDER and PROMETEOII/2014/004) is gratefully acknowledged.

Ti–Ce mixed oxides with different Ti/Ce atomic ratios have been synthesized via a solvothermal method and used as supports for platinum nanoparticles. These catalysts were tested in the preferential oxidation of CO in excess of H2 (PROX reaction) using different feed compositions in order to simulate real conditions. Both, supports and catalysts, were characterized by a wide variety of techniques including N2 adsorption, XRF, XRD, Raman spectroscopy, XPS, H2-TPR, UV–Vis and DRIFTS. The best performance was obtained with the Pt/Ti0.9Ce0.1O2 catalyst, what was attributed to the incorporation of Ce atoms in the TiO2 lattice. 10% at. Ce is the maximum concentration we could incorporate in the TiO2 lattice by using the solvothermal method. Generalitat Valenciana and Ministerio de Economía y Competitividad (Spain) through projects PROMETEOII/2014/004 and MAT2013-45008-P, respectively, are gratefully acknowledged. EVRF gratefully acknowledge the Ministerio de Economía y Competitividad (Spain) for RYC-2012-11427 and MAT2016-81732-ERC.

In this work, we have prepared two series of layered double hydroxides (LDHs) based on three different divalent cations (Zn2+, Ni2+ and Mg2+), that were ion-exchanged by a trivalent cation (Al3+). The charge was balanced with interlayer anions, either silicate or carbonate. Thus, we have synthetized six different samples and we have studied their physicochemical properties by a wide range of techniques, in order to elucidate their properties. Finally, we have used the prepared materials as catalysts in the transesterification of ethylene carbonate with methanol to produce dimethyl carbonate and ethylene glycol. We have found that materials containing Ni as divalent cation present better catalytic activity due to their basic properties, whereas catalysts containing silicate as interlayer anion yield better selectivity, since they have a lower amount of acid sites. The authors acknowledge financial support from the MINECO projects MAT-2013-45008-P, MAT2016-81732-ERC. EVRF gratefully acknowledge support from MINECO for his Ramón y Cajal grant (RyC-2012-11427) and University of Alicante for the project GRE-13-31. Generalitat Valenciana is acknowledges for support (PROMETEOII/2014/004). JGL Fellowship for National Master Studies 2014 of the National Council of Science and Technology (CONACYT), Mexico.

Platinum nanoparticles supported on titania efficiently catalyzed the diboration of alkynes and alkenes under solvent- and ligand-free conditions in air. The cis-1,2-diborylalkenes and 1,2-diborylalkanes were obtained in moderate to excellent yields following, in most cases, a simple filtration workup protocol. The versatility of the cis-1,2-diboronvinyl compounds was demonstrated in a series of organic transformations, including the Suzuki–Miyaura cross coupling and the boron–halogen exchange. This work was generously supported by the Spanish Ministerio de Economía y Competitividad (MINECO; CTQ2007-65218 and CTQ2011-24151), the Generalitat Valenciana (GV; PROMETEO/2009/002 and PROMETEO/2009/039), and FEDER.

Ni-based catalysts supported on Zn-modified alumina were investigated in the ethanol steam reforming reaction. A commercial γ-alumina was impregnated with different amounts of zinc nitrate (0, 2, 5, 10, 15, 20 wt.% on Zn basis), calcined, and then impregnated with nickel nitrate aqueous solutions. The samples were characterized by a number of techniques: N(2) adsorption at 77 K, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray fluorescence (XRF), and temperature-programmed reduction (TPR). Their catalytic behavior in the ethanol steam reforming reaction was studied at 873 K, with a H(2)O/ethanol ratio of 5:1. Two effects of the presence of Zn were detected. On the one hand, zinc modifies the surface structure and the surface chemistry of the catalysts by formation of zinc aluminates, and on the other hand, zinc oxide can be reduced to metallic zinc under reaction conditions, thus modifying the catalytic properties of the active phase. The presence of Zn increases the ethanol conversion to gaseous compounds as compared with the catalyst supported on the Zn-free commercial alumina. The addition of a small amount of Pt (1 wt.%) causes a beneficial effect in the reaction. When Ni catalysts were used without a previous reduction treatment, ethylene was formed in high amounts; however, the Pt-Ni catalysts need no reduction pre-treatment to achieve high H(2) yields (close to 70%) and showed a high stability versus time on stream because of the control of the production of ethylene, a coke precursor.

Titania-supported platinum (mainly as Pt(II)) has been found to effectively catalyze the hydrosilylation of 1,3-diynes at 70 °C with low catalyst loading (0.25 mol %) under solvent-free conditions. Monohydrosilylation was achieved for diaryl-substituted diynes, whereas dialkyl-substituted diynes were transformed into the corresponding dihydrosilylated products in good yields. In every case, the process was proven to be highly stereoselective, with syn addition of the silicon–hydrogen bond, and regioselective, with the silicon moiety exclusively bonded to the most internal carbon atom of the 1,3-diyne (β-E product), as confirmed by X-ray crystallography. This work was generously supported by the Spanish Ministerio de Ciencia e Innovación (MICINN; CTQ2007-65218, CTQ2011-24151, and Consolider Ingenio 2010-CSD2007-00006), the Generalitat Valenciana (GV; PROMETEO/2009/002 and PROMETEO/2009/039), and FEDER. Y.M. thanks the ISO of the Universidad de Alicante for a grant. R.B. acknowledges the Universidad de Alicante, CAM, and Union Fenosa for his grant (UF2007-X9159987F).

The effect of the support (activated carbon or titanium dioxide) on the catalytic activity and selectivity to nitrogen of Pt-Sn catalysts in nitrate reduction was studied. The effects of the preparation conditions and the Pt:Sn atomic ratio were also evaluated. It was observed that the support plays an important role in nitrate reduction and that different preparation conditions lead to different catalytic activities and selectivities. Generally, the catalysts supported on activated carbon were less active but more selective to nitrogen than those supported on titanium dioxide. The monometallic Pt catalyst is active for nitrate reduction only when supported on titanium dioxide, which is explained by the involvement of the support in the reaction mechanism. The catalysts were characterized by different techniques, and significant changes on metal chemical states were observed for the different preparation conditions used. Only metallic Pt and oxidized Sn were observed at low calcination and reduction temperatures, but some metallic Sn was also present when high temperatures were used, being also possible the formation of Pt-Sn alloys.

Preferential oxidation of CO in excess hydrogen (PROX) was studied over Pt catalysts supported on multi-wall carbon nanotubes in the temperature range between room temperature and the temperature of the water–gas shift unit (∼473 K). Experimental results show that the Pt/CNT catalyst exhibit a superior performance in terms of catalytic activity and selectivity towards CO 2 formation compared to a Pt/AC catalyst prepared under similar conditions. Apparently, preferential CO oxidation in excess hydrogen over Pt nanoparticles supported on carbon materials is a particle size dependent reaction, i.e. larger particles exhibit higher activity and selectivity. In any case, the incorporation of oxygen functionalities to the carbon support becomes detrimental for the CO oxidation reaction independently of the carbon support used. Finally, CeO 2 addition to the Pt/CNT catalyst further improves both catalytic activity and selectivity at low temperatures (CO conversion rate of 46% at 313 K), the catalytic performance being superior to that exhibited by a traditional PROX catalyst such as Pt/CeO 2 .

Several catalysts of cerium oxide highly dispersed on activated carbon were prepared varying the cerium precursor, the solvent and the chemical surface properties of the support, and characterized by several techniques. Afterwards, these materials were investigated as ozonation catalysts for the mineralization of two organic compounds (oxalic acid and aniline). The ozonation results were compared with those obtained in the absence of catalyst and in the presence of the parent activated carbons used for the preparation of these materials. The prepared catalysts have better performances than the parent activated carbons, denoting a clear synergic effect between activated carbon and cerium oxide. The efficiency of the catalysts is mainly affected by the amount of Ce 3+ species on the surface. However, in the ozonation of oxalic acid, the specific surface area and metal oxide particle diameter also played an important role. The use of activated carbon as support favors the removal of both organic compounds studied. Highly dispersed cerium oxide on activated carbon shows better catalytic performance than a composite with the same composition.

The low temperature water gas shift reaction has been studied over carbon-supported platinum catalysts promoted by ceria. To this end, CeO2 has been dispersed over an activated carbon support at different loadings (20, 30 and 40 wt.%) in order to obtain a high ceria surface area. Then, platinum has been incorporated by impregnation with an acetone solution of [Pt(NH3)4](NO3)2. Two more catalysts have been prepared with aqueous and ethanolic solutions, respectively, to assess the effect of the solvent in the final catalysts. Pt/CeO2 and Pt/C catalysts have been used as references. Catalysts have been characterized (N2 adsorption at 77 K, TEM, H2-TPR) and tested in reaction after reduction with H2 at 473 K. The obtained results show that CO conversion increases with the amount of ceria loaded, from 20 to 40 wt.%. At this temperature, platinum supported on bulk CeO2 is less active than its carbon-based counterparts. The best results are obtained for the catalysts with 40 wt.% CeO2 prepared by aqueous impregnation of the platinum precursor, which achieves conversions higher than 70% at 573 K, and shows no deactivation under reaction at this temperature for 120 h. On the other hand, Pt/C shows a very low activity, this certifying the determinant role of ceria in this reaction. These results indicate that dispersion of ceria on activated carbon allows to obtain catalysts with superior performance than using bulk CeO2 as support, and with a lesser amount of ceria.

The textural characterization of a series of activated carbons prepared from olive stones, by carbonization at different temperatures (400, 550, 700 and 850 °C) and thermal activation with CO2, has been investigated using N2 adsorption at −196 °C and CO2 adsorption at 0 °C. The effect of pre-oxidation of the carbonized precursor has also been studied, using temperature-programmed decomposition (TPD), to evaluate the effect of oxygen content of the chars in the performance of the obtained activated carbons for mercury removal. The adsorption of Hg(II) cations from aqueous solutions at room temperature by the prepared activated carbons was studied. Experimental results show that all samples exhibit a large microporosity (pore diameter below 0.56 nm). The amount of surface oxygen groups increased after pre-oxidation treatment, this enhancing the Hg(II) uptake (up to 72%). It can be concluded that these groups make the support more hydrophilic, thus providing a more efficient adsorption of Hg(II). The formation of a great amount of surface oxide groups such as carboxyl, phenol and lactone alters the surface charge properties of the carbon, this enhancing the surface-Hg(II) interaction.

The influence of calcination and reduction temperatures on the catalytic properties of Pd–Cu and Pt–Cu bimetallic catalysts supported on activated carbon for the reduction of nitrates was studied. The catalysts were prepared using different calcination and reduction temperatures, and the respective activities and selectivities for the reduction of nitrates in water with hydrogen were assessed. It was found that the different preparation conditions lead to different catalytic performances. For both catalysts, the activity decreases by increasing calcination and reduction temperatures, whereas the effect on the selectivity is not uniform. For the 1%Pd–0.3%Cu (wt.%) catalyst, the nitrate conversion after 5 h of reaction varies from 93% (sample calcined at 200 °C and not reduced) to 25% (sample calcined and reduced at 400 °C). The formation of alloys during the preparation of the catalysts is prejudicial for nitrate reduction. In all the preparation conditions tested the Pd–Cu pair is more selective for the transformation of nitrate into nitrogen. All the samples have been characterized by nitrogen adsorption at −196 °C, CO adsorption microcalorimetry, TPR, XRD, XPS and TEM.

The effect of the ruthenium precursor (chlorinated or chlorine-free) on the properties and the catalytic behaviour of Ru/ZnO catalysts in the vapour phase hydrogenation of crotonaldehyde (2-butenal) has been studied. Two catalysts were prepared, using ruthenium (III) chloride (Ru(Cl)/ZnO) and ruthenium (III) acetylacetonate (Ru(A)/ZnO) as the metal precursors. The catalysts have been characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), H 2 temperature-programmed desorption (H 2 -TPD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM), and their catalytic behaviour has been evaluated in the title reaction after reduction at low (473 K) and high (623 K) temperatures. Ru(Cl)/ZnO showed better catalytic behaviour after both reduction treatments, what has been explained on the basis of a well controlled metal-support interaction. For Ru(A)/ZnO this interaction is too high, resulting in a dramatic lost of active sites that yields worse catalytic behaviour. It is important to remark that both catalysts were very active and selective to the desired product, the unsaturated alcohol (crotyl alcohol, 2-buten-1-ol).

Two series of activated carbons have been prepared from date pits; series C, using carbon dioxide as activating agent, and series S, prepared by activation with steam under the same experimental conditions. The obtained samples were oxidized with nitric acid in order to introduce more oxygen surface groups. The surface area and porosity of the parent and oxidized activated carbons were studied by N2 adsorption at 77 K and CO2 adsorption at 273 K. The oxygen surface complexes were characterized by temperature-programmed decomposition (TPD). The results show that carbon dioxide and steam activations produce microporous carbons with an increasing amount of CO evolving groups when increasing the burn-off. On the other hand, oxidation with nitric acid increases the amount of CO and CO2 evolved by the decomposition of surface oxygen groups, this increase being related to the development of porosity in the carbon with the degree of activation and to the activating agent used (CO2 versus steam).

The alkylation of imidazole (C 3 H 4 N 2 ) with different alkyl halides, such as 1-Br-butane, 2-Br-butane and 1-Br-hexane, has been carried out in the absence of solvent using basic zeolites as catalysts. Catalysts were prepared by cation exchange of a commercial NaX zeolite with different alkaline-earth cations (Ca, Sr and Ba). The resulting zeolites were characterised by N 2 (77 K) and CO 2 (273 K) adsorption, immersion calorimetry, CO 2 adsorption calorimetry and CO 2 temperature-programmed desorption experiments. The influence of the irradiation time and power and the alkaline-earth exchanged cation on the catalytic activity has been studied. Conversion values as high as 95% and selectivity values of 100% were obtained at 700 W in only 5 min in most of the cases when 1-Br-butane and 2-Br-butane were used as alkylating agents. In general, NaX is the best catalyst in most of the reaction conditions studied.

The effect of Zn location and reduction temperature have been studied on pure and Zn-modified MCM-41 supported Pt catalysts. Experimental results show that incorporation of Zn into the siliceous framework of the MCM-41 material introduces structural oxidized Zn centres with a high stability towards a reduction treatment even at high temperatures. XP spectra confirm the high stability of these Zn species although, at the highest reduction temperature (723 K), a high mobility of the doping cations from structural positions to the inner wall of the mesopores is observed. Catalytic studies in the chemoselective hydrogenation of crotonaldehyde show that the presence of Zn produces an important decrease in the catalytic activity of the Pt nanoparticles, in accordance with Pt dispersion measurements. However, the presence of Zn improves the selectivity towards the formation of crotyl alcohol. Compared with a conventional impregnated PtZn/MCM-41 catalyst, structural Zn centres in the doped Pt/ZnMCM-41 catalysts exhibit a higher polarizing/activation of the carbonyl double bond giving rise to a higher yield to crotyl alcohol, the product of interest. Additionally, these Zn-modified MCM-41-based Pt catalysts show an excellent behaviour in an important industrial reaction such as the dehydrogenation of iso-butane to iso-butene, with a selectivity of 100%, which remains stable with time on stream.

Platinum(0) nanoparticles supported on titania have been prepared by impregnation of a commercial TiO 2 support with an aqueous solution of H 2 PtCl 6 and further reduction under flowing H 2 at 473 or 773 K. These materials, with a low platinum loading, have been found to effectively catalyze the reduction of acetophenone by hydrogen transfer, using isopropanol as the hydrogen donor, in the presence of potassium hydroxide at 349 K. To the best of our knowledge, this is the first time that a supported platinum catalyst has been successfully used in the transfer hydrogenation of carbonyl compounds with isopropanol. Both catalysts could be reused several times, with the one reduced at 773 K exhibiting better catalytic performance than that reduced at 473 K.

This paper reports a study on the effect of the support composition in Pt/Ta 2 O 5 –ZrO 2 catalysts in regard to their catalytic behaviour in the vapour phase selective hydrogenation of crotonaldehyde (2-butenol). Two Ta 2 O 5 –ZrO 2 supports with different Ta/Zr ratios and a pure Ta 2 O 5 were prepared by a sol–gel route. The platinum catalysts were characterized by CO chemisorption, infrared spectroscopy of adsorbed CO and X-ray photoelectron spectroscopy (XPS). The best catalyst in terms of activity and selectivity to crotyl alcohol (2-butenol) was Pt/Ta 2 O 5 , and this behaviour is tentatively related to the metal–support interaction. On the other hand, under the experimental conditions used, the acidic properties of the supports could not be correlated to the catalytic behaviour of these materials.

Catalytic adsorption of SO2 on activated carbon materials provides an appropriate alternative for the control of low concentration emissions of this air pollutant. The surface complexes formed upon SO2 adsorption at 30 °C were studied by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD). The effect of the addition of O2 and the presence of copper as catalyst were studied. Copper assisted the oxygen transfer to the carbon matrix. For the Cu-impregnated carbon sample, the presence of O2 favored SO2 adsorption by increasing the breakthrough time, the adsorption capacity and the formation of sulfur and oxygen complexes of higher thermal stabilities, which mainly desorb as SO2 and CO2.

An enhancement of the catalytic performance of platinum in the liquid phase hydrogenation of cinnamaldehyde has been achieved by modifying a ZnO support by addition of Cr(III) cations. The addition of chromium improves the structural properties of the support (larger surface area) and increases its reducibility, and resulted in a better Pt dispersion. The presence of chromium in the support enhanced the overall catalytic activity, and improved the high selectivity towards the unsaturated alcohol. The increase of the reduction temperature from 473 K to 623 K produces an impressive decrease in the turnover frequency for Pt/ZnO, whereas this value remains practically unmodified for Pt/Cr–Zn. The higher reduction temperature reduces the overall activity in both catalysts, but improves selectivity towards the unsaturated alcohol. The present 5 wt% Pt/Cr–ZnO catalyst showed the best results (in terms of selectivity) published until now without use of reaction promoters. The improved performance of this catalyst is ascribed to an adequate metal–support interaction and to the higher reducibility of the support that opens the possibility of alloy formation.

A series of pure siliceous and Zn-modified MCM-41 spheres were synthesized at room temperature, atmospheric pressure and at short reaction times. Mesoporous molecular sieves were characterized by a number of techniques: XRD, N2 adsorption, TEM, XPS and NH3–TPD. Pure siliceous MCM-41 exhibits the typical hexagonal array of well-defined pores with a mean pore diameter of 3.0 nm. Addition of a small percentage of Zn (Zn/Si ratio 0.02) into the synthesis gel produces a material with increased lattice parameter (ao), pore diameter and total adsorption capacity. These results suggest the incorporation of zinc, with a larger ionic radius, into the silica framework. Unfortunately, higher zinc contents (Zn/Si ratio 0.04) produce a deterioration of the long-range order of the material, together with a decrease in the surface area and total pore volume. In this sample, the presence of small ZnO nanoparticles embedded into the silica matrix can be envisaged. From a catalytic point of view, these Zn-modified MCM-41 mesoporous molecular sieves appear as quite interesting materials to be used as a catalyst by themselves or as a support for noble metal catalysts.

A new material constituted by cerium dioxide highly dispersed on activated carbon (CeO 2 /AC) was prepared by an impregnation method using cerium(III) nitrate as CeO 2 precursor. In order to evaluate the degree of ceria dispersion on the carbon support, CeO 2 /AC was characterized by a number of techniques: thermogravimetry coupled with a mass spectrometer (TG-MS), N 2 adsorption at 77 K, temperature-programmed desorption (TPD), temperature-programmed reduction (TPR) and transmission electron microscopy (TEM). The analysis of the decomposition process under inert atmosphere indicated that cerium nitrate decomposes at 440–460 K, with the evolution of NO. Furthermore, this process produces an additional oxidation of the carbon surface (with evolution of N 2 O) and the subsequent onset of new oxygen surface groups, detected by means of temperature-programmed desorption. The ceria deposition process takes place with a decrease in the N 2 adsorption capacity of the starting carbon support, and the analysis of the pore size distribution showed that the majority of ceria particles are situated at the most internal part of the carbon porosity. The temperature-programmed reduction profile of CeO 2 /AC was very different to that shown by unsupported CeO 2 , with only one continuous reduction process at low temperatures (800–900 K). Finally, TEM pictures gave direct evidence that ceria is highly dispersed on the carbon surface, with a narrow CeO 2 particle distribution centred around 3 nm.

This paper reports a study of PtSn/TiO2 catalysts reduced at two different temperatures (473 and 773 K) by infrared spectroscopy of CO adsorbed at 298 K and XPS, as well as their behaviour in the vapour phase selective hydrogenation of crotonaldehyde at 333 K. Catalysts with 2 wt% Pt and different Pt:Sn atomic ratios were prepared by co-impregnation of a commercial TiO2 (P25, from Degussa) with aqueous solutions of H2PtCl6 and SnCl2·2H2O. XPS results show that tin is in oxidized state when the catalysts are reduced at 473 K, whereas a proportion is in the metallic state after reduction at 773 K. The amount of surface platinum decreases when the tin loading and the reduction temperature increase. The presence of Pt-Sn alloy in the catalysts after reduction at high temperature has been assessed by in situ IR spectroscopy of adsorbed CO, although a proportion of platinum remains in a non-alloyed state. The catalytic activity in the vapour-phase hydrogenation of crotonaldehyde increases after high temperature reduction, and the same behaviour is obtained with selectivity towards the hydrogenation of the carbonyl bond to yield the unsaturated alcohol, the best selectivity being obtained for the catalyst with the lowest Pt/Sn ratio.

An impressive enhancement of the catalytic performance of platinum in the vapour phase selective hydrogenation of crotonaldehyde (2-butenal) has been achieved by modifying a ZnO support by addition of Cr(III) cations. The addition of chromium enhances the structural properties of the support (larger surface area) and increases its reducibility. The presence of chromium in the support enhanced the catalytic activity and the selectivity towards the unsaturated aldehyde in such a way that the Pt/Cr–ZnO catalyst showed the best results (in terms of yield and stability) published until now. The improved behaviour of this catalyst has been explained on the basis of the high support reducibility and a proper metal-support interaction.

Activated carbon-supported cerium dioxide (CeO2/C) was prepared by impregnation of a commercial support (Norit R2030) with aqueous solutions of two different cerium precursors, [(NH4)2Ce(NO3)6] and Ce(NO3)3·6H2O. The effect of carbon surface chemistry on the dispersion of ceria was studied by using two different carbon supports, the R2030 and the same material after an oxidation treatment with H2O2. Thus, four samples were obtained by combining the precursors and the supports. The prepared materials were characterized by thermogravimetry, nitrogen adsorption isotherms (77 K), X-ray diffraction, temperature-programmed desorption, temperature-programmed reduction and transmission electron microscopy, in order to study the degree of ceria dispersion over the supports. It was found that the best results in terms of ceria dispersion were obtained for the material prepared with the oxidized carbon and ammonium cerium nitrate as cerium precursor.

The influence of the shape/surface structure of Pt nanoparticles on the selective hydrogenation of crotonaldehyde and cinnamaldehyde has been studied. (111) and (100) preferentially oriented Pt nanoparticles (10 nm) as well as polyoriented Pt nanoparticles (3 nm) were synthesized, characterized (by TEM, cyclic voltammetry and adsorption microcalorimetry) and their catalytic properties evaluated. TEM analysis provided information about the size and shape of the Pt nanoparticles, whereas cyclic voltammetry allowed gaining qualitative and quantitative information about their surface structure. Thus, small Pt nanoparticles ( ≈ 3 nm ) were revealed to have a polyoriented surface, containing high ratio of corner and edges atoms to terrace atoms, whereas large Pt nanoparticles ( ≈ 10 nm ) were shown to have larger Pt domains with (100) and (111) surface structures. Microcalorimetric results for CO adsorption showed higher values of initial heat for polyoriented Pt/C compared to preferentially oriented samples, thus accounting for a higher amount of highly unsaturated surface platinum atoms for Pt/C, in agreement with cyclic voltammetry. The catalytic performances of the samples showed a strong structure-sensitive character for both reactions, with TOF values following the trend Pt(100)/C > Pt(111)/C > Pt/C. Moreover, Pt(111)/C showed higher selectivities to unsaturated alcohol than Pt(100)/C and Pt/C samples.

PtSn/TiO 2 catalysts containing 2 wt% Pt and a Pt:Sn atomic ratio of 2:1 and 1:1 were prepared by coimpregnation or successive impregnation method with aqueous solutions of SnCl 2 ·2H 2 O and H 2 PtCl 6 ·6H 2 O of a commercial TiO 2 (P25, from Degussa). Both catalyst series, independent of the preparation method, were reduced at 473 and 773 K. XPS results show that tin was in an oxidized state after reduction at 473 K, and that a fraction was in the metallic state after reduction at 773 K. By use of in situ FTIR spectroscopy of adsorbed CO, the presence of bimetallic Pt–Sn phases was assessed after reduction at 773 K. Microcalorimetric analysis of CO adsorption enthalpy indicates that reduction at 773 K causes the appearance of a more heterogeneous distribution of active sites, as well as a loss in the amount of sites. The catalytic activity for the gas phase hydrogenation of crotonaldehyde was greatly improved when the catalysts were prepared by coimpregnation, at both reduction temperatures. The selectivity toward crotyl alcohol was higher after reduction at 773 K and independent of the preparation method, although it increased with the amount of tin, suggesting a promoting effect of tin on this reaction.

A novel kind of bimetallic Pt–Sn catalysts supported on carbon and promoted with highly-dispersed ceria were prepared by a co-impregnation method and tested in the liquid phase hydrogenation of citral after reduction at low (473 K) and high (773 K) temperatures. They were characterized by N 2 adsorption at 77 K, X-ray diffraction, temperature-programmed reduction (TPR), transmission electron microscopy (TEM) and CO chemisorption at room temperature. Results from N 2 adsorption, XRD and TEM indicated that impregnation method used here led to a highly-dispersed ceria on carbon. Conversely to massive CeO 2 , TPR profile of CeO 2 /C showed two broad overlapped peaks at low temperatures (803 and 903 K), which are indicative of the easier reduction of the supported promoter. Addition of platinum partially promotes the reduction of surface ceria, this indicating a close metal–promoter interaction. Ceria reducibility was increased with tin addition. The reduction treatment at 773 K produced a strong decrease in the CO adsorption capacity in all cases, although this loss was more relevant for the monometallic catalyst. After reduction at low temperature (473 K), the monometallic Pt/CeO 2 /C was the most active catalyst, while the presence of tin reduced the catalytic activity. Reduction at high temperature (773 K) produced the decrease of activity in the case of monometallic sample while bimetallic catalysts, specially the one with Sn/Pt = 0.25, increased the citral conversion values. Reduction treatment at 773 K also increased selectivity to unsaturated alcohols (geraniol and nerol) of bimetallic samples, which presented in all cases higher values than their monometallic counterpart. The onset of new Pt–CeO x and Pt–SnO x sites after the reduction process is proposed to explain the increase in activity and selectivity of bimetallic catalysts.

A series of bimetallic platinum–tin catalysts supported on CeO 2 /C were prepared and tested in the nonoxidative catalytic dehydrogenation of isobutane. Pt–Sn/CeO 2 /C catalysts with varying Sn content (Sn/Pt = 0, 0.25, 0.5, and 0.75) were prepared using a co-impregnation method and chlorinated metal precursors. They were characterized by XPS and by CO and ethylene adsorption microcalorimetry at room temperature after in situ reduction treatments. It was found that the presence of cerium in bimetallic catalysts inhibited reduction of tin species, whereas tin facilitated reduction of cerium(IV) to cerium(III). Reduction at 773 K caused a strong decrease in CO saturation coverage for all catalysts studied. For the bimetallic catalysts, a strong interaction between tin and platinum produced significant changes in the initial heat of CO adsorption. The presence of cerium caused a strong decrease in the heat of ethylene adsorption on platinum in catalysts reduced at high temperature. The monometallic Pt catalyst undergoes a fast deactivation with time on stream in the isobutane dehydrogenation reaction. The addition of tin strongly suppresses the deactivation process. It was found that cerium-containing catalysts showed higher isobutene yields compared with their corresponding cerium-free counterparts. The bimetallic catalyst with Sn/Pt = 0.5 showed the best isobutene yield, and it was studied further. This optimized catalyst demonstrated good deactivation behaviour (comparable with the best catalysts reported in the literature). Furthermore, oxidation treatment at a mild temperature (573 K) allowed recovery of nearly all of its catalytic properties.

Pt and Pt/Sn catalysts supported on polypyrrole (PPy) have been prepared using Ar plasma to reduce the metal precursors dispersed on the polymer. The PPy support was synthesized by chemical polymerization of pyrrole with FeCl3·6H2O, this leading to the conducting form of the polymer (conductimetric measurements). The Ar plasma treatment produced a partial reduction of platinum ions, anchored as platinum chloro-complexes to the PPy chain, into metallic platinum. A homogeneous distribution of Pt and Sn nanoparticles was observed by TEM. Activity of the PPy-supported catalysts was evaluated in the reduction of aqueous nitrate with H2 at room temperature. Nitrate concentration in water below the maximum acceptable level of 50 mg L−1 was achieved with all catalysts. However, considering not only efficiency in nitrate reduction, but also minimized concentrations of undesired nitrite and ammonium, the monometallic Pt catalyst seems to be the most promising one. Financial support from Generalitat Valenciana, Spain (PROMETEO/2009/002 – FEDER and PROMETEOII/2014/004) is gratefully acknowledged. Support by PEst-C/EQB/LA0020/2013, financed by FEDER through COMPETE – Programa Operacional Factores de Competitividade, and by FCT – Fundação para a Ciência e a Tecnologia; NORTE-07-0162-FEDER-000050, financed by QREN, ON2 and FEDER is acknowledged by LCM group. O. S. G. P. Soares acknowledges the grant received from FCT (SFRH/BPD/97689/2013).

Simultaneous adsorption of NO and SO2 on activated carbon provides an adequate alternative to control the low concentration emissions of these air pollutants. The surface complexes formed during the NO and SO2 adsorptions at 30 °C were studied by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD). The effects of the addition of copper supported on the carbon and O2 on the gas stream were studied. The presence of copper enhanced the chemical adsorption of both NO and SO2. In the simultaneous adsorption of NO and SO2, SO2 inhibited the adsorption of NO, while SO2 adsorption was notably improved. The reaction carried out under a NO/SO2/O2 gas mixture showed a synergic effect increasing the formation of surface complexes. The addition of copper assisted the oxygen transfer to the carbon matrix.

Vapor-phase hydrogenation of toluene and selective hydrogenation of crotonaldehyde (2-butenal) have been performed at 333 K over Cl-free Pt/ZrO 2 and Pt/Ce x Zr 1− x O 2 catalysts ( 0.2 ⩽ x ⩽ 0.8 ) after reduction under H 2 at low (473 K) and high (773 K) temperatures. The catalysts were characterized by X-ray diffraction, Raman spectroscopy, temperature-programmed reduction, and X-ray photoelectron spectroscopy after each reduction treatment. An important effect of the support composition on the catalytic activity was observed for both reactions. The catalytic behavior of Pt in the two test reactions studied was strongly dependent on the support composition and on the reduction temperature. For toluene hydrogenation, after reduction at 473 K, catalytic activity was higher for catalysts with no or low ceria content. Furthermore, whereas the increase in the reduction temperature hardly modified the activity of Pt/ZrO 2 , it strongly deactivated the catalysts with high cerium content in the support. For crotonaldehyde hydrogenation, on the other hand, increased reduction temperature produced a general increase in activity (except for the catalyst with the highest cerium content), along with an increase in selectivity toward the hydrogenation of the carbonyl bond to yield crotyl alcohol. The results are explained on the basis of the effect of partial reduction of Ce(IV) in the support.

The effect of the reduction temperature has been studied on ceria-supported bimetallic platinum–zinc catalysts prepared from H2PtCl6 and Pt(NH3)4(NO3)2 as the platinum precursors and Zn(NO3)2 as the zinc precursor. The catalysts have been characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS), and their catalytic behavior has been evaluated in the vapor-phase hydrogenation of toluene and of crotonaldehyde (2-butenal) after reduction at low (473 K) and high (773 K) temperatures. The increase in the reduction temperature produces a strong decrease in the catalytic activity for toluene hydrogenation in both systems, but an important increase of activity for crotonaldehyde hydrogenation, which is more evident for the chlorine-free catalyst. The selectivity towards the hydrogenation of the carbonyl bond to yield the unsaturated alcohol (crotyl alcohol, 2-buten-1-ol) also increases after reduction at high temperature, being somewhat higher for the Cl-containing catalyst. The results are discussed in terms of differences in surface composition of the catalysts. C.I.C.Y.T. (Project BQU 2000-0467).

The effect of the presence of zinc on the catalytic behaviour of platinum in the vapour phase hydrogenation of crotonaldehyde (2-butenal) and in iso -butane dehydrogenation has been determined in activated carbon-supported catalysts prepared using H 2 PtCl 6 and Zn(NO 3 ) 2 as the metal precursors. The catalysts have been characterised by temperature-programmed reduction (TPR), adsorption microcalorimetry of CO at room temperature and X-ray photoelectron spectroscopy after in situ reduction at 773 K. The bimetallic catalyst, with a bulk Zn/Pt atomic ratio of 13.7, showed a much higher initial activity in crotonaldehyde hydrogenation, although it deactivated more strongly with time on stream. Lower activation energy for this reaction was also obtained, as well as a higher selectivity towards the unsaturated alcohol. On the other hand, the catalytic behaviour for iso -butane dehydrogenation was greatly improved by the presence of zinc, the bimetallic catalyst being more active than its monometallic counterpart and showing 100% selectivity to iso -butene.

The effect of different preparation parameters (pyrolysis temperature, process time, benzene concentration and residence time) on the properties of carbon molecular sieves obtained by pyrolytic carbon deposition from benzene on a microporous activated carbon, has been studied. For a fixed process time of 2 h, the increase of the pyrolysis temperature from 525 to 700∘C produced a strong increase of the CO2/CH4 selectivity, reaching a maximum value of 13 for pyrolysis at 700∘C. Selectivity also increased with process time (up to 5 h, with the pyrolysis temperature fixed at 650 and 675∘C), yielding values as high as 28. The obtained results have allowed to find the optimal preparation parameters for the preparation of CMS with high selectivity.

Vapor-phase hydrogenation of toluene and selective hydrogenation of crotonaldehyde have been performed over Pt/TiO2 and PtZn/TiO2 after low (473 K) and high (773 K) temperature reduction. The catalysts were characterized by H2 chemisorption, X-ray photoelectron spectroscopy (XPS), and Auger spectroscopy (AES) after each reduction treatment. Infrared spectra of CO alone and followed by the introduction of crotonaldehyde have been recorded for both catalysts after reduction at 473, 673, and 773 K. The presence of zinc and an increase in the reduction temperature strongly decreased the catalytic activity for toluene hydrogenation, but a different effect was observed for crotonaldehyde hydrogenation. After reduction at low temperature, the bimetallic catalyst was somewhat less active than the monometallic catalyst, but the initial activity of the former was greatly increased after reduction at 773 K, whereas the Pt/TiO2 catalyst reduced at this high temperature was almost inactive. The selectivity toward the hydrogenation of the carbonyl bond exhibited a strong dependence on the presence of zinc and on the reduction temperature. Monometallic Pt/TiO2 reduced at low temperature showed the maximum selectivity (up to 75%), although with a continuous decrease with time on stream. The bimetallic PtZn/TiO2 catalyst, reduced at 773 K, showed a more stable selectivity to crotyl alcohol, centered at about 30%.

Infrared spectra of CO alone and CO followed by the introduction of 2-butenal (crotonaldehyde) have been recorded for Pt/CeO2–SiO2 and Zn doped Pt/CeO2–SiO2 catalysts which had been pre-reduced at 473, 623 and 773 K. Samples treated at the highest reduction temperature showed the greatest selectivity toward the unsaturated alcohol although no clear spectroscopic evidence for the formation of an SMSI state was obtained. Although 773 K reduced Zn containing catalysts showed the greatest yield, there was no IR spectroscopic evidence to support the formation of significant quantities of a Pt–Zn alloyed phase or that the addition of Zn enhanced Pt-support interactions beyond increasing the amount of surface reduced ceria. Results show that, contrary to popular opinion, the development of an SMSI state which enhances the density of support-metal interface sites is not essential in order to increase the yield of unsaturated alcohol and the presence of reduced cationic sites at the interface zone may be the crucial factor. Although IR spectra in the νCO region were dominated by dipole coupling effects, enhanced intensity of carbonyl bands in the 2030–1950 cm−1 region for 773 K reduced samples and for Zn containing samples reduced at lower temperatures suggests that sites responsible for these carbonyl bands may be the active sites in the selective hydrogenation reaction.

The effect of the metal precursor (presence or absence of chlorine) on the preferential oxidation of CO in the presence of H2 over Pt/CeO2 catalysts has been studied. The catalysts are prepared using (Pt(NH3)4)(NO3)2 and H2PtCl6, as precursors, in order to ascertain the effect of the chlorine species on the chemical properties of the support and on the catalytic behavior of these systems in the PROX reaction. The results show that chloride species exert an important effect on the redox properties of the oxide support due to surface chlorination. Consequently, the chlorinated catalyst exhibits a poorer catalytic activity at low temperatures compared with the chlorine-free catalyst, and this is accompanied by a higher selectivity to CO2 even at high reaction temperatures. It is proposed that the CO oxidation mechanism follows different pathways on each catalyst. The authors gratefully acknowledge financial support from Ministerio de Ciencia e Innovación (Project MAT2010-21147) and Generalitat Valenciana (PROMETEO/2009/002 – FEDER and PROMETEOII/2014/004) (Spain). EOJ thanks the CNPq – Brazil for her grant.

In the present work we have studied the effect of carbon supports with different graphitic character (carbon nanotubes, mesoporous graphite and activated carbon) on the catalytic performance of iridium nanoparticles on the liquid phase chemoselective hydrogenation of para-chloronitrobenzene at room temperature. The effect of the oxygen groups was also evaluated by oxidizing a portion of the carbon nanotubes. The Raman and XRD spectra showed that the mesoporous graphite displayed the strongest graphitic character. The characterization of the catalysts by HR-TEM, XPS and TPR-H2, showed that the catalysts had similar particle size and that the catalysts prepared over the previously oxidized support, Ir/CNTox, was not fully reduced. The activity and selectivity achieved with the catalyst Ir/CNT was the best among the samples and the presence of irdium oxide on Ir/CNTox diminished the yield to p-chloroaniline, being the worse catalyst. The reactivity of different isomers was also studied over Ir/CNT and it followed the order m > o > p. Authors thank to CONICYT (Chile, FONDECYT 3130483) and Generalitar Valenciana (Spain, PROMETEOII/2014/004–FEDER) for financial support.

This study reports experimental data of water adsorption at 303 K on single-wall carbon nanohorns (SWNHs). The analysis of the water adsorption isotherms supports a cluster-mediated model for filling the interstitial and intratube nanospaces in contrast to the monolayer formation observed for simple nonpolar molecules. The enthalpies of water immersion of SWNHs with closed and open nanohorns show a very week interaction between the water molecules and the hydrophobic carbon nanotubular structure; the observed specific enthalpy of immersion expressed per unit surface area is lower than the reported values for graphite.

Vapor-phase hydrogenation of toluene and selective hydrogenation of crotonaldehyde have been performed after reduction at low (523 K) and high (773 K) temperatures over Pt/TiO2 and PtSn/TiO2 catalysts prepared from the metal precursors tin(II) oxalate and H2PtCl6. A sequential impregnation method was used to prepare the bimetallic catalyst, wherein the tin precursor was loaded first. The surface characteristics of both catalysts were evaluated with X-ray photoelectron spectroscopy (XPS) after the reduction treatments. It was shown in this analysis that tin was mainly in an oxidized state in the bimetallic catalyst (about 80%) even after reduction at 773 K. The presence of tin and the increase in the reduction temperature strongly decreased the catalytic activity for toluene hydrogenation, but the opposite effect was observed for crotonaldehyde hydrogenation. After reduction at low temperature, the bimetallic catalyst was more active than the monometallic catalyst, but it was less selective toward hydrogenation of the carbonyl bond to yield the unsaturated alcohol. However, reduction at 773 K yielded a bimetallic catalyst that showed an initial activity five times higher than that of the Pt/TiO2 catalyst reduced at the same temperature and a high selectivity (around 50%) toward the unsaturated alcohol, which was stable with time on reaction. Furthermore, the catalytic behavior of the bimetallic catalysts was also evaluated after reduction at even higher temperatures. Reduction at 873 K increased the catalytic activity in crotonaldehyde hydrogenation while the selectivity to crotyl alcohol remained at about 50% molar fraction; however, reduction at 973 and 1023 K caused a loss of catalytic performance in terms of both activity and selectivity.