Showing papers on "Bimetallic strip published in 1997"
TL;DR: In this paper, the preparation and structural characterization of carbon-supported Pt−Ru nanoparticles with exceptionally narrow size and compositional distributions is described. But the analysis of the structure of the nanoparticles is limited to the case of the carbon-supported PtRu5C(CO)16 with hydrogen.
Abstract: We describe the preparation and structural characterization of carbon-supported Pt−Ru nanoparticles with exceptionally narrow size and compositional distributions. The supported bimetallic particles are obtained by reduction of the neutral molecular carbonyl cluster precursor PtRu5C(CO)16 with hydrogen. A detailed structural model of the nanoparticles has been deduced on the basis of studies by in situ extended X-ray absorption fine structure spectroscopy (EXAFS), scanning transmission electron microscopy, microprobe energy-dispersive X-ray analysis, and electron microdiffraction. These experiments show that the bimetallic nanoparticles have a Pt:Ru composition of 1:5 and an average diameter of ca. 1.5 nm and adopt a face-centered cubic closest packing structure. These results demonstrate a marked sensitivity of the metal particle structure to nanoscale size effects inasmuch as the thermodynamically stable phase for bulk alloys of this composition is hexagonal close-packed. The local metal coordination en...
301 citations
TL;DR: In this paper, a sonochemical method was used to extract bimetallic nanoparticles composed of gold and palladium, which were then reduced by ultrasound irradiation in the presence of sodium dodecyl sulfate.
Abstract: Colloidal dispersions of bimetallic nanoparticles composed of gold and palladium were prepared by a sonochemical method, in which Au(III) and Pd(II) ions in an aqueous solution of sodium tetrachloroaurate(III)dihydrate and sodium tetrachloropalladate(II) were reduced by ultrasound irradiation in the presence of sodium dodecyl sulfate (SDS). In addition to the stabilizing effect, SDS remarkably enhanced the reduction rate, probably due to the thermal decomposition that occurs at the interfacial region between cavitation bubbles and bulk solution and provides reducing radicals. Transmission electron microscopy (TEM) photographs showed spherical particles whose size had a fairly narrow distribution with a geometric mean diameter about 8 nm and a geometric standard deviation of 1.1. Analyses with UV−vis spectra indicated that Au(III) ions were first reduced and after their consumption reduction of Pd(II) ions set in. A core−shell structure of the particles, a core of gold and a shell of palladium, was confirm...
288 citations
TL;DR: In this article, the Pd−Pt bimetallic colloids were characterized by transmission electron microscopy and infrared carbon monoxide (IR-CO) probe techniques and confirmed by IR-CO probe characterization.
Abstract: Polymer-protected Pd−Pt bimetallic colloids in the size range 1.5−5.5 nm with controllable core/shell structures have been successfully prepared by a so-called hydrogen-sacrificial protective strategy. The obtained bimetallic colloids were characterized by transmission electron microscopy and infrared carbon monoxide (IR-CO) probe techniques. The Pd-core/Pt-shell and Pt-core/Pd-shell structures were confirmed by IR-CO probe characterization. IR-CO probe measurements were also performed on the Pd−Pt bimetallic colloids prepared by coreduction of the corresponding metal ions in the refluxing mixture of ethanol and water.
245 citations
TL;DR: In this paper, the electrocatalytic activity of a bimetallic Pt05Ru05N(Oct4)Cl colloid toward the oxidation of CO and a CO/H2 gas mixture (simulated reformer gas) was measured.
Abstract: The electrocatalytic activity of a bimetallic Pt05Ru05N(Oct4)Cl colloid toward the oxidation of CO and a CO/H2 gas mixture (simulated reformer gas) was measured The particle size distribution with a mean diameter of 17 ± 05 nm was determined by high-resolution transmission electron microscopy, and the formation of stoichiometrically alloyed particles was verified by point-resolved energy dispersive X-ray analysis The CO-stripping voltammetry of glassy carbon supported Pt05Ru05 clusters was found to be in excellent agreement with CO-stripping voltammetry data measured on well-characterized bulk alloy electrodes The activity of the colloid toward the continuous oxidation of 2% CO in H2 was assessed in a rotating disk electrode configuration at 25 °C in 05 M H2SO4, leading to the conclusion that PtRu colloids are a promising route toward the preparation of bimetallic high-surface-area fuel cell catalysts
207 citations
TL;DR: In this article, the authors studied the catalytic performance of Ni0.03Mg0.97O solid solution catalyst and its bimetallic derivative catalysts which contained small amounts of Pt, Pd and Rh, respectively (the atomic ratio of M/(Ni+Mg) ≈ 0.021%).
Abstract: Reforming of CH4 with CO2 to produce synthesis gas was studied over Ni0.03Mg0.97O solid solution catalyst and its bimetallic derivative catalysts which contained small amounts of Pt, Pd and Rh, respectively (the atomic ratio of M/(Ni+Mg) was varied from 0.007 to 0.032%, M=Pt, Pd or Rh). It was found that there was a significant promotion in both activity and stability due to the addition of noble metals. The optimum loadings of these noble metals were observed at the atomic ratio of M/(Ni+Mg) ≈0.021%. Temperature programmed hydrogenation (TPH) of carbonaceous species formed during the catalytic reaction indicated that the good resistance of Ni0.03Mg0.97O solid solution to carbon deposition was retained on the bimetallic catalysts. Furthermore, we obtained a clear evidence showing the formation of Pt—Ni alloy particles by means of TEM and EDS observation. The kinetic study and temperature programmed reaction (TPR) of CH4 suggest that CH4 decomposition as the rate-determining step on the Ni0.03Mg0.97O is accelerated by the alloy formation. The improved stability was attributed to the promotion in catalyst reducibility.
203 citations
TL;DR: In this article, low-density xerogel Pd-Ag/SiO2 catalysts were prepared by a cogelation of tetraethoxysilane with organically substituted alkoxides capable of forming chelates with palladium and silver ions.
133 citations
TL;DR: The structure and magnetic properties of novel hybrid molecule-basedMAGNETs formed by combination of two magnetically active sublattices, the======bimetallic oxalato-bridged honeycomb net======
125 citations
TL;DR: In this article, the plasmon absorption band is blue-shifted with increasing mercury-to-silver ratio, which is explained by an interaction of the two metal redox systems, as silver clusters are reoxidized by mercury ions.
Abstract: Silver and mercury ions are reduced in a common solution by sodium borohydride in the presence of poly(ethyleneimine). Colloidal alloy particles are formed, whose plasmon absorption band is blue-shifted with increasing mercury-to-silver ratio. The reduction mechanism is rather complex: large mercury “drops” are first formed, although silver ions are reduced simultaneously. This effect is explained by an interaction of the two metal redox systems, as silver clusters are reoxidized by mercury ions. The final particles are formed in a reaction of the mercury drops with reduced silver clusters, yielding amalgam particles smaller than the mercury drops. These processes are followed by spectrophotometric and light-scattering measurements. The alloy colloids are stable up to a mercury to silver molar ratio of 2. Upon exposure to air, part of the mercury in the alloy particles is oxidized.
102 citations
TL;DR: In this article, the authors investigated CO chemisorption on Pt catalysts supported on non-acidic alumina prepared from platinum acetylacetonate using FTIR spectroscopy.
Abstract: CO chemisorption on Pt catalysts supported on non-acidic alumina prepared from platinum acetylacetonate has been studied by FTIR spectroscopy. The stretching frequency for isolated CO species is observed at 2032 cm−1 for highly dispersed Pt samples (dispersion 0.99) and at 2067 cm−1 for poorly dispersed samples (dispersion 0.09). This frequency shift is in agreement with single-crystal and on supported Pt catalyst data, and may be ascribed to the change of coordination at the Pt chemisorption site. Large shifts, reaching 180 cm−1 can be observed upon coadsorption of ammonia suggesting the possibility of long-range interactions involving the collective electronic properties. CO adsorption has also been studied on well dispersed bimetallic samples obtained by modifying the well dispersed Pt/Al2O3 catalyst with Sn or Ge. Quite different effects of the two additives were observed: whereas Ge decreased the dipole–dipole coupling in the adsorbed layer, Sn did not. This suggests that Sn segregates at sites of low coordination at the surface of the Pt particles, while Ge is more homogeneously distributed. The coadsorption of ammonia and CO on the bimetallic particles also shows that the electronic properties of Pt were dramatically modified by Ge and unaffected by Sn.
102 citations
TL;DR: In this article, an oxide known to give special metal-support interaction, namely TiO2, was chosen as a support for cinnamyl alcohol in liquid phase hydrogenation.
Abstract: The ethylenic unsaturation of α-β ethylenic aldehydes is much more reactive to catalytic hydrogen addition than the carbon-oxygen double bond, giving saturated aldehydes in a first step. Fortunately, in a liquid phase hydrogenation, the selectivity to the unsaturated alcohols may be improved by the choice of appropriate solvents and bimetallic catalysts. In this work much attention has been brought to the factors that allow to achieve the best possible selectivity to cinnamyl alcohol. An oxide known to give special metal-support interaction, namely TiO2, was chosen as our support. A careful study of the precursor reduction by TPR was a valuable guide to establish the final preparation for the active phase. The catalyst precursor was dried and reduced in an electric furnace under a flow of gas at atmospheric pressure. Compared to Pt, Pt-Sn and Pt-Fe on carbon, a monometallic Pt/TiO2 catalyst gives an excellent selectivity but a rather poor activity. Finally a selectivity to cinnamyl alcohol as high as 97% and a high activity are reached by using a bimetallic Pt-Fe/TiO2. This good selectivity has been attributed to the metal support interaction.
101 citations
TL;DR: In this article, the preparation and catalytic properties of bimetallic colloids consisting of a ligand-stabilized Pt shell on Au or Pd cores supported by alumina are described.
Abstract: The preparation and catalytic properties of bimetallic colloids consisting of a ligand-stabilized Pt shell on Au or Pd cores supported by alumina are described. The aim of this work is to study the influence of the electronegativity of the colloidal core metals on the activity and selectivity of the surface Pt in hydrosilation reactions. Au is more electronegative and Pd is more electropositive than Pt. Results are compared to controls in which the hydrosilation reaction is catalyzed by colloids made of pure Pt which are also stabilized with the same ligands and supported by alumina. The reaction of HMTS with 1-octene to form bis(trimethylsiloxy)octamethylsilane (BTOMS) was selected to serve as an example of a typical hydrosilation reaction. The synthesis of the bimetallic colloids was accomplished by the seed-growth mechanism. The inner core consisting of Au (diameter = 18 nm) or Pd (diameter = 20 nm) was generated by the reduction of HAuCl4 or H2PdCl4, respectively, by sodium citrate. The Pt outer shell...
TL;DR: In this article, a polymer-anchored bimetallic palladium-ruthenium catalyst, PVP-PdCl2-RuCl3, was used for the hydrogenation of p-chloronitrobenzene (CNB) to aniline (AN).
Abstract: Polymer-achored monometallic palladium catalyst PVP-PdCl2 (PVP = poly(N-vinyl-2-pyrrolidone)) exhibits very high activity for the hydrogenation of p-chloronitrobenzene (CNB) to aniline (AN) in the presence of base at 65°C and atmospheric pressure. In this case, the substrate is rapidly hydrodechlorinated to nitrobenzene (NB) which is then reduced to AN. Using the polymer-anchored bimetallic palladium-ruthenium catalyst, PVP-PdCl2-RuCl3, and in the presence of 1.0 mol% of sodium acetate, a strong synergic effect gives rise to a remarkable increase of the selectivity for p-chloroaniline (CAN) and the maximum selectivity of CAN is up to 94%. For the hydrogenation of the non-halo-substituted nitroaromatics to the corresponding aromatic amines, the monometallic PVP-PdCl2 catalyst only shows mild or poor activity, but the colloidal polymer-anchored bimetallic palladium-platinum catalyst, PVP-Pd-1 4Pt , exhibits very high activity and selectivity.
TL;DR: In this article, the authors investigated the influence of reaction temperature and reactant pressure on the activity and selectivity of the catalysts and the role of deactivation in gas and liquid phase hydrogenation of crotonaldehyde.
Abstract: Gas and liquid phase hydrogenation of crotonaldehyde was studied over silica supported promoted Pt catalysts The influence of reaction temperature and reactant pressure on the activity and selectivity of the catalysts and the role of deactivation was investigated Addition of Ni, Co and Fe to Pt/SiO2 increased the activity and the selectivity in gas phase hydrogenation This is attributed to the existence of polar sites in a bimetallic phase favoring the interaction with the carbonyl group and, thus, increasing the rate for the hydrogenation to crotylalcohol Addition of Ga, Sn and Ge improved the selectivity to crotylalcohol, but decreased the activity of the catalysts These promoters form catalytically inactive oxides that decorate part of the Pt surface The electron pair donor?acceptor interaction of the oxygen of the carbonyl group with the Lewis sites present in such oxide clusters is concluded to cause the enhanced selectivity to crotylalcohol The addition of La, Bi, Pb and Sb to Pt decreased the activity and the selectivity of the parent catalyst by blocking a part of the active surface With respect to selectivity, catalyst behavior is independent of the reaction medium In contrast, the highest activities in gas phase were found for catalysts forming a bimetallic phase, while these catalysts showed the lowest activity in liquid phase due to a fast deactivation
TL;DR: In this paper, the structure and morphology of the metal clusters in polyamide imide (PAI) polymers were investigated by means of X-ray absorption spectroscopy (XAFS), XRD, and transmission electron microscopy (TEM) measurements consistently show a homogeneous distribution of metallic nanoclusters of 1−3 nm size.
Abstract: Noble metal clusters were generated and stabilized in poly(amide imide) (PAI) polymers in high dispersion and high concentration of typically 15 wt %. The loaded polymers were prepared as pore-free, mechanically stable membranes, which have been successfully tested for catalytic activity in membrane reactors. Pure Pd- and Ag-loaded as well as bimetallic Pd/Ag, Pd/Cu, Pd/Co, and Pd/Pb PAI films were investigated by means of X-ray absorption spectroscopy (XAFS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) to characterize the structure and morphology of the metal clusters in the protective polymer. The measurements consistently show a homogeneous distribution of metallic nanoclusters of 1−3 nm size with a smaller amount of larger aggregates up to 30 nm in some of the films. The precise cluster size and distribution critically depend on the solvents used (N-methyl-2-pyrrolidone, tetrahydrofuran) as well as on other preparation parameters such as the stirring time of the metal precursor...
TL;DR: In this paper, the authors presented extended X-ray absorption fine structure (EXAFS) and transmission electron microscopy (TEM) measurements on three zeolite-supported bimetallic Pt−Pd catalysts prepared by wet impregnation.
Abstract: We present extended X-ray absorption fine structure (EXAFS) and transmission electron microscopy (TEM) measurements on three zeolite-supported bimetallic Pt−Pd catalysts prepared by wet impregnation. Alloy formation and segregation of Pd to the surface of the small bimetallic particles is clearly identified. Ab initio LMTO calculations are used to predict segregation profiles of low-index single-crystal Pt−Pd alloy surfaces. Pd is found to be enriched at the surface. EMT potentials for Pt and Pd are adjusted in order to give the same segregation profiles at low-index single-crystal surfaces as linear muffin tin orbital (LMTO) calculations. Monte Carlo simulations based on the adjusted EMT potentials are then used to calculate the equilibrium structure of small bimetallic Pt−Pd particles. Coordination numbers derived from these equilibrium structures are compared with those derived from EXAFS analysis, and a good agreement is found.
TL;DR: Pd-Cu/γ-Al2O3 bimetallic catalysts were tested for the selective hydrogenation of aqueous nitrate solutions to nitrogen by XRD, SEM, EDXS and AES as mentioned in this paper.
Abstract: Pd-Cu/γ-Al2O3 bimetallic catalysts were prepared according to different impregnation sequences of γ-Al2O3 and characterized by XRD, SEM, EDXS and AES. The catalysts were tested for the selective hydrogenation of aqueous nitrate solutions to nitrogen. The reaction selectivity was found to be dependent on the catalyst preparation procedures, which affect the spatial distribution of metallic copper and palladium phases. A catalyst prepared by impregnating γ -Al2O3 with copper followed by palladium gives higher selectivity to nitrogen than a catalyst prepared by impregnating the support with palladium followed by copper. The AES examination shows that in the catalyst exhibiting a higher nitrogen production yield, a reaction zone for the liquid-phase nitrate reduction is located in the interior of particles and covered by a layer of Pd atoms.
TL;DR: In this article, the chemisorptive behavior of CO on several planar model monometallic and bimetallic Pd, Cu, and Au catalysts supported on thin film Al2O3 has been investigated using IRAS.
Abstract: The chemisorptive behavior of CO on several planar model monometallic and bimetallic Pd, Cu, and Au catalysts supported on thin film Al2O3 has been investigated using infrared reflection absorption spectroscopy (IRAS). For Pd and Cu monometallic catalysts, CO adsorption spectra indicate a high representation of low index planes, while the morphologies of smaller particles are characterized more by high densities of low coordinated step/edge defect sites. For Au particles, CO was observed to be present on the surface at conditions where low index Au single crystals have been observed to be inactive for CO adsorption, indicating the modified chemisorptive properties at step/edge sites. For the IRAS studies of supported Pd–Au and Pd–Cu catalysts, no conclusive indications of ligand effects were apparent in the CO stretching frequencies. The spectra for the bimetallics resemble combinations of both analogous monometallic catalysts, even though a significant degree of metal mixing is apparent from thermally in...
TL;DR: In this paper, the reducibility of cobalt and ruthenium was investigated in the context of temperature-programmed reduction, CO chemisorption, X-ray diffraction, and transmission electron microscopy.
TL;DR: In this article, the core-level binding energy shifts of the component metals in bimetallic clusters of various compositions in the Ni-Cu, Au-Ag, Ni-Pd, and Cu Pd systems were measured as functions of coverage or cluster size, after having characterized the clusters with respect to sizes and compositions.
Abstract: Core-level binding energies of the component metals in bimetallic clusters of various compositions in the Ni-Cu, Au-Ag, Ni-Pd, and Cu-Pd systems have been measured as functions of coverage or cluster size, after having characterized the clusters with respect to sizes and compositions. The core-level binding energy shifts, relative to the bulk metals, at large coverages or cluster size, Delta E(a), are found to be identical to those of bulk alloys. By substracting the Delta E(a) values from the observed binding energy shifts, Delta E, we obtain the shifts, Delta E(c), due to cluster size. The Delta E(c) values in all the alloy systems increase with the decrease in cluster size. These results establish the additivity of the binding energy shifts due to alloying and cluster size effects in bimetallic clusters.
TL;DR: In this article, the effects of cobalt addition on the thiophene hydrodesulfurization (HDS) reaction were investigated, and it was found that the addition of Co could improve the HDS conversion, and the high specific activity of the bimetallic nitride catalyst was believed to be related with the new Co3Mo3N phase.
Abstract: CoMo bimetallic nitride catalysts were prepared by temperature-programmed reduction of CoMo oxides with flowing ammonia, and the effects of cobalt addition on the thiophene hydrodesulfurization (HDS) reaction were investigated. MoO3 transformed into Mo2N, while cobalt oxide was just reduced to Co metal rather than Co nitride. When Co was added to Mo, the surface area decreased significantly but the new bimetallic nitride phase of Co3Mo3N was produced. The addition of Co could improve the HDS conversion, and the high specific activity of the bimetallic nitride catalyst was believed to be related with the new Co3Mo3N phase.
TL;DR: In this paper, a series of monometallic and bimetallic Pt and PtSn catalysts, modified or not by the addition of Li, was studied in the dehydrogenation of isobutane-to-isobutene reaction.
Abstract: A series of monometallic and bimetallic Pt and PtSn catalysts, modified or not by the addition of Li, was studied in the dehydrogenation of isobutane to isobutene reaction. Special emphasis was devoted to the behavior of catalysts obtained following different preparation procedures. In relation to the addition of lithium, a strong dependence of the catalytic properties on the order in which Li was added was observed. Two alternatives were analyzed: (a) the support was modified by adding lithium onto it, and then it was impregnated with the metallic precursors; (b) the support was impregnated with the metallic precursors and afterward lithium was added. The application of surface organometallic chemistry on metals (SOMC/M) techniques for the preparation of PtSn bimetallic catalysts led to solids having a better performance than when conventional techniques (successive impregnations with inorganic precursors) were used. Selectivities close to 100% at a high level of activity were obtained when lithium was ...
TL;DR: In this article, a series of Nb1.0Mo1.5OC and Nb 1.0MoxOC catalysts were synthesized from oxide precursors in a flow of 20% CH4/H2 reactant gas mixture.
Abstract: A series of Nb1.0MoxOC (x = 0.67−2.0) catalysts were prepared by a temperature-programmed reaction technique. The catalysts were synthesized from oxide precursors in a flow of 20% CH4/H2 reactant gas mixture, while the temperature was increased linearly at 5 K/min (8.3 × 10-2 K s-1). The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), elemental analysis, CO chemisorption, surface area measurements, and temperature-programmed reduction. XRD patterns of the fresh catalysts indicated that Nb1.0Mo1.5OC and Nb1.0Mo1.75OC consisted of pure bimetallic carbide phases, while the other compositions showed impurity phases of NbO2 or Mo2C at high concentrations of Nb and Mo, respectively, in the starting oxide. The hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) activity of these materials was studied in a high-pressure reactor system. The reactions were carried out at 3.1 MPa and 643 K using model liquid comp...
TL;DR: In this article, a bimetallic system of Co with Sn, Pd, Ru, Fe, Ni, W and Pt was studied for the metal-mediated synthesis of single-walled carbon nanotubes (SWT), and compared with Co alone.
Abstract: Bimetallic systems of Co with Sn, Pd, Ru, Fe, Ni, W and Pt were studied for the metal-mediated synthesis of single-walled carbon nanotubes (SWT), and compared with Co alone. The materials were characterized by TEM, XRD and H2 chemisorption. Sn, Ru, Fe and Pd decrease the catalytic effect of Co, whereas W or Ni have little effect on Co. By contrast, a synergy exists between Co and Pt for the SWT formation. The highest SWT yield was obtained with Co/Pt=3/1 (at/at), but the selective catalytic phase is actually the definite CoPt compound identified by XRD. After activation at 673 K under hydrogen, 1/3 to 1/2 of the bimetallic surface becomes accessible for hydrogen. The CoPt(3/1)/SWT composite is active and selective for the liquid-phase hydrogenation of cinnamaldehyde to cinnamyl alcohol.
TL;DR: In this article, the TPR method for surface oxide reduction after exposing the catalyst to N 2 O decomposition for the determination of the active phase is in good agreement with the frontal H 2 chemisorption method on rhodium, copper and bimetallic catalysts.
Abstract: Rh Cu supported on alumina were selected for the dehydrogenation of cyclohexanol. Highly dispersed Rh Cu supported on alumina were obtained and characterized after reduction. The metallic surface area was determined by frontal H 2 chemisorption and by N 2 O decomposition followed by TPR. The TPR method for surface oxide reduction after exposing the catalyst to N 2 O decomposition for the determination of the active phase is in good agreement with the frontal H 2 chemisorption method on rhodium, copper and bimetallic catalysts. The temperature and time exposition are important parameters for a complete oxidation of the monolayer, in particular for lower concentration of copper. An exposition time of 20 h is needed to complete a monolayer oxidation. Metallic copper is oxidized to Cu 1+ and Cu 2+ although not all Cu 2+ is reduced to Cu 1+ without oxidation of a sublayer. For the bimetallic catalysts Rh Cu a complete monolayer was attained. The TOF values were calculated based on the total active sites which give correct interpretation of the activity. The activity decreases when copper is added to rhodium which was attributed to an ensemble effect. For lower contents the selectivity of ketone was enhanced, which could be explained by simultaneous geometric and electronic effects. The selectivity on the monometallic catalysts prevails toward cyclohexene formation, indicating strong influence of the acidic sites. However, for the bimetallic catalysts it changed drastically toward dehydrogenation. The second metal affects the surface sites enhancing the metallic or bimetallic formation for dehydrogenation. This phenomena explains the electronic effect on bimetallic Rh Cu systems.
TL;DR: In this paper, the surface reactivities of Ni/Pt(111) bimetallic model catalysts using ethylene and cyclohexene as probing molecules were investigated using high-resolution electron energy loss spectroscopy (HREELS), Auger electron spectroscope (AES), temperature-programmed desorption (TPD), and low-energy electron diffraction (LEED).
Abstract: We have investigated the surface reactivities of Ni/Pt(111) bimetallic model catalysts using ethylene and cyclohexene as probing molecules. The bimetallic surfaces were generated by evaporating Ni onto a Pt(111) single- crystal surface held at 600 K. The surface chemistry was investigated using high-resolution electron energy loss spectroscopy (HREELS), Auger electron spectroscopy (AES), temperature-programmed desorption (TPD) and low-energy electron diffraction (LEED). The reactivities of the bimetallic surfaces were compared with those of the clean Pt(111) surface and a thick Ni(111) film on the Pt(111) substrate. Formation of the bimetallic surface led to a significantly reduced reactivity towards the decomposition of ethylene when compared to either Pt(111) or Ni(111)/Pt(111) surfaces. Furthermore, although the surface reactivity towards cyclohexene was retained for the bimetallic surface, the decomposition mechanism was distinctly altered from that of either Pt(111) or Ni(111)/Pt(111) surfaces.
Patent•
14 Jul 1997
TL;DR: In this article, the authors describe shell catalysts which contain, on powdered or shaped supports, one or more metals from groups VIII and IB of the Periodic Table of Elements.
Abstract: Disclosed are shell catalysts which contain, on powdered or shaped supports, one or more metals from groups VIII and IB of the Periodic Table of Elements. The catalysts are obtained by coating the support with the catalytically active metals in aqueous solutions of mono- or bimetallic colloids of these metals, wherein the colloids are stabilized by highly hydrophilic surfactants.
TL;DR: In this article, the performance of bimetallic catalysts was compared with those of monometallic Pt/Al2O3 catalysts using H2PtCl6or [Pt(NH3)4]Cl2 precursors.
TL;DR: In this paper, the structure, thermal stability, and catalytic behavior of a novel highly dispersed silica-supported Pd/Sn catalyst prepared by an organometallic route have been examined by X-ray photoelectron, Xray diffraction, and Xray absorption, fine structure spectroscopies, the latter two measurements being carried out with an in situ reaction cell.
Abstract: The structure, thermal stability, and catalytic behavior of a novel highly dispersed silica-supported Pd/Sn catalyst prepared by an organometallic route have been examined by X-ray photoelectron, X-ray diffraction, and X-ray absorption, fine structure spectroscopies, the latter two measurements being carried out with an in situ reaction cell. Additional reactor measurements were performed on a more Sn-rich catalyst and on a pure Pd catalyst. Varying the temperature of reduction induced large variations in catalytic performance toward ethyne-coupling reactions. These changes are understandable in terms of the destruction of SnO2-like structures surrounding the Pd core, yielding a skin of metallic Sn which subsequently undergoes intermixing with Pd. The overall thermal and catalytic behavior of these highly dispersed materials accords well with the analogous single-crystal model system.
TL;DR: In this article, the evolution of surface species under hydrogen from 473 to 873 K has been studied by in situ FTIR spectroscopy, mass spectrometry analysis of products evolved, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive Xray analysis (EDX), electron nanodiffraction, and Xray photoelectron spectroscope (XPS), the genesis of supported PtSn alloy as the only metallic phase on surface is shown for both supports.
Abstract: Platinum-tin catalysts supported on either silica or γ-alumina have been prepared from [PtCl(SnCl 3 (PPh 3 ) 2 ] bimetallic complex. The evolution of surface species under hydrogen from 473 to 873 K has been studied by in situ FTIR spectroscopy, mass spectrometry analysis of products evolved, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), electron nanodiffraction, and X-ray photoelectron spectroscopy (XPS). The genesis of supported PtSn alloy as the only metallic phase on surface is shown for both supports. Catalytic performance and catalyst stability on the reaction between CO 2 , C 2 H 4 and H 2 O to give lactic acid is reported. The characteristics of silica-supported catalysts contrast with those of alumina-supported ones.
TL;DR: In this paper, a general model for the reduction of graphite supported catalysts has been suggested, based on X-ray diffraction to define the structure of the calcined precursors, magnetic measurements to determine the amount of metallic cobalt formed after reduction, and analysis of the gaseous medium during the reduction.