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MXenes, first discovered in 2011, are two-dimensional transition metal carbides or nitrides. Because of their interesting electrical and optical properties, they are studied for applications in batteries, supercapacitors and electrocatalysis. However, MXenes are rarely used in heterogeneous catalysis and, to our knowledge, there are no reports on the use of oxidized MXenes in catalysis. Here we used Ti3C2Tx-derived materials as supports for platinum nanoparticles and studied their effectiveness for the hydrolysis of ammonia borane, which is a promising hydrogen carrier. Hydrogen can be released from ammonia borane through catalytic hydrolysis. Most heterogeneous catalysts reported for this purpose contain a noble metal supported on a metal oxide support. The interaction between the metal and the support is important in determining the catalytic performance. Our results show that the electronic environment of platinum can be modified by oxidising the surface of MXene, thus providing a new way of developing active catalysts. Oxidising agents such as water and ozone can be used for this purpose. This electronic modification enhances the catalytic activity of platinum for ammonia borane hydrolysis, which is relevant for other reactions related to energy production/storage. T K S was supported by NWO TOP-PUNT grant 718.015.004. Z S was supported by project LTAUSA19034 from Ministry of Education Youth and Sports (MEYS). E V R F and A S E would like to thanks financial support by MINECO (Spain) through the projects MAT2017-86992-R and MAT2016-80285-P.

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.

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.

The effect of Ar plasma treatment on the catalytic performance of Pt/CeO2 has been studied. The catalyst was activated using different procedures separately or in combination: calcination, reduction under pure H2 and cold Ar plasma treatment. The resulting materials were characterized by X-ray photoelectron spectroscopy, X-ray adsorption near edge structure and temperature-programmed reduction with H2. The resulting materials were tested in the water-gas shift reaction (WGS). It has been found that the combination of calcination, plasma and hydrogen treatments leads to a very active catalyst for WGS. Furthermore, the catalyst structure–performance relationship has been assessed. The plasma treatment generated electron-enriched Pt particles which show a very strong interaction with the ceria support. This favoured CO chemisorption and increased the reducibility of the support, which takes part in the WGS the reaction by favouring water splitting. Financial support from Generalitat Valenciana (project PROMETEOII/2014/004) and MINECO (Project MAT2013-45008-P) is gratefully acknowledged. EVRF also thanks MINECO for his Ramon y Cajal fellow RYC-2012-11427 and the following project MAT2016-81732-ERC.

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.

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.

Steam reforming of glycerol to produce syngas or H2-enriched streams is a promising route that has caught the attention of many researchers around the world. This reaction is typically carried out over metal-based catalysts supported on stable materials. Herein we report a study on the effect of Sn on the catalytic properties of Pt/C in the aforementioned reaction. A series of Pt-Sn/C catalysts with different Pt:Sn ratios were prepared and characterized using ICP, H2-TPR, TEM and XPS techniques, and they were tested in the glycerol steam reforming reaction at 623 K and atmospheric pressure. The best performance was observed for the catalysts with low tin contents. It was found that Sn promoted oxidation reactions and inhibited methanation. Furthermore, the presence of Sn improved the stability of the catalysts when operating at harsher conditions of temperature and glycerol concentration. A promoter effect of Sn hindering platinum sintering and the formation of coke precursors is proposed as the origin of the observed behaviour. This work has been supported by Ministerio de Economía y Competitividad (Spain, Project MAT2010-21147). L.P.P. acknowledges her grant BES-2011-0406508.

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).

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 .

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.

This paper reports a CO adsorption study on a Pt/TiO(2) catalyst reduced at two different temperatures, 473 and 773 K, followed by in situ infrared spectroscopy and adsorption microcalorimetry. The study is complemented with XPS characterization of the reduced catalysts.

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.

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.

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.

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.

Structure–activity relationships for 1 wt.% Pt catalysts were investigated for a series of TixCe(1−x)O2 (x = 1, 0.98, 0.9, 0.5, 0.2 and 0) supports prepared by the sol–gel method. The catalysts prepared by impregnation were characterized in detail by applying a wide range of techniques as N2-isotherms, XRF, XRD, Raman, XPS, H2-TPR, Drifts, UV–vis, etc. and tested in the preferential oxidation of CO in the presence of H2. Also several reaction conditions were deeply analyzed. A strong correlation between catalyst performance and the electronic properties let us to propose, based in all the experimental results, a plausible reaction mechanism where several redox cycles are involved. Financial support from Generalitat Valenciana and Ministerio de Economía y Competitividad (Spain) through projects PROME-TEOII/2014/004 and MAT2010-21147 is gratefully acknowledged. EOJ also thanks the CNPq – Brazil for her grant. EVRF gratefully acknowledge the Ministerio de Economía y Competitividad (Spain) for his Ramon y Cajal grant (RYC-2012-11427).

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).

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 reduction temperature on ceria-promoted platinum and platinum–zinc catalysts supported on silica has been studied on catalysts prepared from chlorine-free precursors and characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS). 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. Catalytic results in the selective hydrogenation of crotonaldehyde show that the presence of Zn produces a fivefold increase in catalytic activity after high-temperature reduction over that with the monometallic catalyst. This promoting effect is accompanied with an increase in the selectivity for the CO double bond hydrogenation to yield the corresponding unsaturated alcohol, crotyl alcohol (2-buten-1-ol).

Magnesia-supported bimetallic Pt–Sn catalysts with various metal contents and Pt/Sn atomic ratios were prepared using the bimetallic complex cis-[PtCl(SnCl3)(PPh3)2] or the monometallic complex cis-[PtCl2(PPh3)2] and SnCl2 as metal precursors. Catalysts were characterised by X-ray diffraction, transmission electron microscopy techniques and X-ray photoelectron spectroscopy. The bulk and surface composition of the catalysts was related to the catalytic behaviour in the vapour phase hydrogenation of crotonaldehyde (but-2-enal). It is shown that the various preparation methods produce catalysts with distinct properties and catalytic behaviour. For catalysts prepared with the bimetallic complex, the highest selectivity for the unsaturated alcohol (but-2-en-1-ol) was achieved for the catalyst containing larger bimetallic particles, which are associated with a higher surface concentration of oxidised tin species. The catalyst prepared with separate metal precursors contains a higher amount of residual chlorides, which significantly affect the catalytic activity but only slightly alter the selectivity for the hydrogenation of the carbonyl bond.

Alumina- and silica-supported bimetallic Pt–Sn catalysts with different Pt/Sn atomic ratios have been prepared by using the bimetallic complex cis-[PtCl(SnCl3)(PPh3)2], the monometallic complex cis-[PtCl2(PPh3)2] and SnCl2 as metal precursors. Catalysts have been characterised by X-ray diffraction and transmission electron microscopy techniques, including energy-dispersive X-ray microanalysis, electron diffraction experiments and lattice-fringe microanalysis. The phase composition of the different catalysts has been related to the catalytic behaviour in the vapour phase hydrogenation of crotonaldehyde (but-2-enal). Results show that catalysts containing platinum–tin alloy phases with large particles are more selective towards the hydrogenation of the carbonyl bond to yield crotyl alcohol. The presence of oxidised tin species on the surface of the large alloy particles promotes the hydrogenation of the carbonyl bond. In situ diffuse reflectance infrared spectroscopy studies of crotonaldehyde adsorption under He or H2 reveal differences between bimetallic catalysts and monometallic, and these differences have been related to the different catalytic behaviour of the catalysts.

Supported metals are traditionally prepared by impregnating a support material with the metal precursor solution, followed by reduction in hydrogen at elevated temperatures. In this study, a polymeric support has been considered. Polypyrrole (PPy) has been chemically synthesized using FeCl3 as a doping agent, and it has been impregnated with a H2PtCl6 solution to prepare a catalyst precursor. The restricted thermal stability of polypyrrole does not allow using the traditional reduction in hydrogen at elevated temperature, and chemical reduction under mild conditions using sodium borohydride implies environmental concerns. Therefore, cold RF plasma has been considered an environmentally friendly alternative. Ar plasma leads to a more effective reduction of platinum ions in the chloroplatinic complex anchored onto the polypyrrole chain after impregnation than reduction with sodium borohydride, as has been evidenced by XPS. The increase of RF power enhanced the effectiveness of the Ar plasma treatment. A homogeneous distribution of platinum nanoparticles has been observed by TEM after the reduction treatment with plasma. The Pt/polypyrrol catalyst reduced by Ar plasma at 200 watts effectively catalyzed the aqueous reduction of nitrates with H2 to yield N2, with a very low selectivity to undesired nitrites and ammonium by-products. Financial support from Generalitat Valenciana, Spain (PROMETEO2009/002 – FEDER) is gratefully acknowledged.

Three bimetallic PtSn/C catalysts have been prepared by successive impregnation of pregraphitized carbon black with an aqueous solutions of hexachloroplatinic acid and tin(II) chloride. One monometallic Pt/C sample was also prepared and studied for comparison. All catalysts were characterized by hydrogen and carbon monoxide chemisorption at room temperature and X-ray photoelectron spectroscopy and their behaviour in the gas phase hydrogenation of crotonaldehyde, at atmospheric pressure, determined. The amount of surface platinum is greatly reduced by the addition of tin, as deduced from chemisorption measurements and XPS. Both Pt0 and PtII are detected by XPS in the fresh bimetallic catalysts; after reduction in flowing hydrogen at 623 K platinum is completely reduced to the metallic state and, although a high proportion of tin remains in an oxidized state, a relatively important amount is reduced to Sn0, this allowing the possibility of PtSn alloys formation. The catalytic activity in the gas phase hydrogenation of crotonaldehyde is greatly improved by the presence of tin, in spite of the fact that the amount of surface platinum is reduced. Tin has also a very important effect on the selectivity towards the hydrogenation of the CO bond, increasing the production of crotyl alcohol in respect to the hydrogenation of the CC bond that would lead to the production of butyraldehyde. The observed results are explained on the basis of a promoting effect of oxidized tin species for the hydrogenation of the CO group, whereas the formation of a PtSn alloy or the dilution of surface platinum by metallic tin would hinder the hydrogenation of the olefinic CC bond.

The effect of the degree of graphitization of the support on the dispersion, sintering resistance, and catalytic activity of a series of platinum catalysts supported on heat-treated carbon blacks has been determined. The supports were prepared by heat treatment of a furnace carbon black in an inert atmosphere at temperatures up to 2473 K. The resulting samples were characterized by physical adsorption (nitrogen at 77 K and carbon dioxide at 273 K), X-ray diffraction, and surface acidity measurements. Platinum catalysts were prepared by impregnating the supports with aqueous hexachloroplatinic acid; metal dispersions were measured by hydrogen and carbon monoxide chemisorption at room temperature and by transmission electron microscopy. Benzene hydrogenation was used as a test reaction to assess the possible effect of the support on the catalytic behavior of platinum. Platinum dispersions as high as 0.99 were achieved, and they can be well correlated with the surface acidity characteristics of the supports. The only sample not following the observed trend is the catalyst prepared with the less pregraphitized support. On the other hand, the highest resistance to sintering was found for the catalyst supported on the carbon black with the highest degree of graphitization, and this is attributed to an interaction between the metal particles and the π sites on the support. However, this interaction is not strong enough to affect the catalytic behavior for benzene hydrogenation. Thus, the metallic dispersion seems to be the result of, at least, two factors: (a) an adequate metal precursor support interaction during the impregnation step and (b) a high sintering resistance under the reduction conditions which hinders the metal particle growth during this stage of the catalyst preparation.

Pt/activated carbon catalysts were prepared by using [Pt(NH3)4]Cl2 as the metal precursor, and characterized by a number of techniques. The selectivity of these catalysts towards crotyl alcohol in the gas-phase hydrogenation of crotonaldehyde was considerably increased when the activated carbon support was slightly oxidized before the metal incorporation.

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

Addition of barium (from 2 to 16 wt.-%) to alumina was performed by impregnation of the support with barium nitrate and by a sol-gel procedure using alkoxide precursors. After calcination at 1073 K and for high barium loading, the formation of barium monoaluminate was shown by X-ray measurements. The barium hexaaluminate phase was observed after calcination at 1473 K. The solids prepared by the sol-gel method showed a very high specific area which was not preserved for a calcination temperature exceeding 1473 K. Platinum was introduced onto the barium-modified alumina using hexachloroplatinic acid. The properties of the metallic phase were strongly dependent on the nature of the solvent used for H2PtCl6 (water or ethanol). In the case of an aqueous solution, the BaAl2O4 phase disappeared during the impregnation procedure because of an acidic attack and the metallic area accessible to gases was low. On the other hand, when H2PtCl6 dissolved in ethanol was used, the barium monoaluminate phase was still present and the chemisorptive properties of platinum were less affected by comparison with impregnation with aqueous solutions. A Fourier transform IR study of carbon monoxide adsorption showed that the surface properties of the platinum particles were strongly modified by the presence of barium additive; the changes in surface properties were less marked when platinum was introduced by ethanolic solutions. It was postulated that the dissolution of barium aluminate in aqueous medium led to the formation of barium containing compounds onto the metal particles or close to the platinum crystallites. The influence of the medium used for the impregnation by the platinum precursor was also shown in cyclohexane dehydrogenation: the catalytic activity was less affected by barium addition when platinum was introduced by using ethanolic solutions.

It allows efficient, regio- and stereoselective formation of a wide range of vinyl silanes.

Pt/activated carbon catalysts were prepared by using [Pt(NH3)4]Cl2 as the metal precursor, and characterized by a number of techniques. The selectivity of these catalysts towards crotyl alcohol in the gas-phase hydrogenation of crotonaldehyde was considerably increased when the activated carbon support was slightly oxidized before the metal incorporation.

Publisher Summary This chapter examines the effect of the zinc (Zn) content and the reduction temperature on the characteristics and catalytic properties of bimetallic platinum (Pt)–Zn catalysts supported on zeolite NaX. Catalysts have been characterized by temperature-programmed reduction (TPR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Their catalytic behavior in the vapor phase hydrogenation of crotonaldehyde (2-butenal) is studied after reduction a 632 and 773 K. The presence of zinc causes a drastic decrease in catalytic activity, although the selectivity toward the hydrogenation of the C=O bond is improved. Higher reduction temperature also improves the catalytic selectivity. The formation of Pt–Zn alloyed phases upon reduction can explain this catalytic behavior, although the contribution of a steric effect due to constraints creation in the pores of the zeolite support cannot be discarded.

The effect of the tin content and the reduction temperature on the ability of bimetallic platinum-tin catalysts supported on activated carbon cloth (ACC) to retain hydrogen after the reduction treatments has been analysed by temperature-programmed desorption of hydrogen (H2-TPD). A series of Sn/ACC samples with different tin contents has been prepared by impregnation of ACC with a solution of tin (II) oxalate in diluted HNO3 and subsequent heat-treatment at 623 K under flowing helium. Platinum (1 wt.%) was then introduced by impregnation of the Sn/ACC samples with aqueous solutions of H2PtCl6. Catalysts have been characterised by temperature-programmed reduction under diluted hydrogen and X-Ray Photoelectron Spectroscopy (XPS). The extent of hydrogen spillover from the metallic particles to the support has been determined by H2-TPD, the products being analysed by online mass spectrometry. The presence of tin oxide provides anchoring sites for hydrogen atoms spilt-over from platinum, although the ability of the latter to dissociate H2 molecules seems to be influenced by the presence of tin, both in an oxidised state after reduction at low temperature (523 K) and in the metallic state (possibility of alloy formation) after reduction at higher temperatures (623 and 723 K).

Activated carbon-supported cerium dioxide (CeO2/C) has been prepared by impregnation of the support with a solution of cerium (III) nitrate and further decomposition in helium. Then, platinum has been deposited on CeO2/C by impregnation with solutions containing H2PtC16 or [Pt(NH3)4](NO3)2. Sample characterisation has been carried out by thermogravimetry (TG), temperature-programmed decomposition (TPD) and reduction (TPR), X-Ray diffraction and temperature-programmed desorption of adsorbed hydrogen (H2-TPD). The interaction between cerium oxide and platinum after different reduction treatments has been checked in two test reactions carried out in the gas phase: hydrogenation of benzene and hydrogenation of crotonaldehyde (2-butenal). Results show that ceria is very well dispersed on the carbon support, this enhancing its interaction with the active metal after high temperature reduction treatments (773 K).

The platinum-ceria interaction, induced after high temperature reduction of platinum based catalysts, has been used to improve the selectivity towards crotyl alcohol in the gas phase hydrogenation of crotonaldehyde. Three catalysts have been used in this study, Pt/SiO2, Pt/CeO2, and Pt/CeO2/SiO2. They have been characterized by X-ray diffraction and temperature-programmed reduction, and their catalytic behavior in the gas phase benzene hydrogenation and crotonaldehyde hydrogenation reactions have been determined after reduction treatments in flowing hydrogen at 473 and 773 K. Results obtained in the gas phase hydrogenation of crotonaldehyde show that the presence of ceria clearly promotes the hydrogenation of the carbonyl bond when the sample is reduced at high temperature, this being attributed to the presence of oxygen vacancies or Ce3+cations in the neighbourhood of platinum particles, induced by the thermal treatment under hydrogen. The promoting effect is more important for Pt/CeO2; crotonaldehyde hydrogenation on this catalyst yields up to 80% crotyl alcohol after reduction at 773 K, whereas it produces 100% butanal after reduction at only 473 K.

Three activated carbons were prepared with different content of oxygen surface complexes and impregnated with aqueous solutions of [Pt(NH34]Cl2. The catalysts were characterized by H2 and CO chemisorption at room temperature, temperature-programmed decomposition (TPD) and X-ray photoelectron spectroscopy, and their catalytic behavior in the vapor phase hydrogenations of benzene and crotonaldehyde (trans-2-butenal) was determined. Metal dispersion is highly dependent on the degree of support oxidation, being lower for the catalyst support containing the highest amount of surface acidic complexes. This is attributed to the decomposition of the surface complexes, which act as anchoring centers for the platinum precursor, upon the reduction treatments at which the catalysts are subjected. The specific catalytic activity in the gas phase hydrogenation of crotonaldehyde is higher as the starting support is more oxidized, and the activity per gram of platinum increases with reduction temperature. The selectivity for the hydrogenation of the carbonilic CO bond instead of the olefinic CC bond is also improved when an oxidized support is used, and the production of the unsaturated alcohol, crotyl alcohol, is enhanced when catalysts are reduced at higher temperature, especially those prepared with oxidized supports.

Two heat-treated carbon blacks, one of them subjected to an oxidizing treatment with hydrogen peroxide, have been used as supports for platinum, which has been introduced using both H 2 PtCl 6 in acid media and [Pt(NH 3 ) 4 ]Cl 2 in basic media. The catalysts have been characterized by H 2 chemisorption at room temperature (after different pre-treatments), temperature-programmed reduction (TPR) and temperature-programmed desorption of adsorbed hydrogen (H 2 -TPD), and their catalytic behavior in the gas-phase hydrogenation of benzene has been determined under differential conditions. TPD profiles of oxygen surface groups in fresh catalysts evidenced the support oxidation by H 2 PtCl 6 , with the occurrence of a CO evolution peak at low temperature (630 K). The presence of oxygen surface groups in the support favors the anchoring of [Pt(NH 3 ) 4 ] 2+ , but does not affect the amount of platinum retained by the support when H 2 PtCl 6 is used as metal precursor. TPR experiments have evidenced that the oxidized support hinders the reduction of the platinum precursor. The catalytic activities in the benzene hydrogenation reaction do not show a direct correlation with dispersion values obtained from hydrogen chemisorption, and it has been related to storage and mobility of hydrogen which is spilt over the support during the reduction treatments.

The effect of a previous oxidation treatment of the carbonaceous support on the catalytic behavior of platinum in the gas phase hydrogenation of crotonaldehyde (trans-2-butenal) over Pt/carbon black catalysts has been analyzed. Two heat-treated carbon blacks, one of them subjected to an oxidizing treatment with hydrogen peroxide, have been used as supports for platinum, which was introduced using H2PtCl6 as metal precursor. The catalysts were characterized by H2 chemisorption at room temperature and temperature-programmed desorption, and their catalytic behavior in the gas phase hydrogenation of crotonaldehyde was determined under differential conditions. Both the specific catalytic activity and the selectivity towards the formation of the unsaturated alcohol (crotyl alcohol) in the title reaction have been found to be higher for the catalyst with the oxidized support, and they are enhanced after reduction at increasing temperatures.