Bimetallic Pt―Cu catalysts for glycerol oxidation with oxygen in a base-free aqueous solution

A series of carbon supported bimetallic Pt―Cu catalysts were prepared and used for glycerol oxidation with oxygen in a base-free aqueous solution. It was found that bimetallic Pt―Cu/C was more active than monometallic Pt/C towards selective oxidation of glycerol to glyceric acid. The selectivity of free glyceric acid reached 70.8% at an 86.2% conversion of glycerol over 5Pt―Cu/C. Highly dispersed bimetallic Pt―Cu nanoparticles with small particle size in dominant alloyed phase of PtCu₃ were confirmed by XRD and TEM in the bimetallic Pt―Cu/C catalyst, which is proposed to contribute to the improved performance.     

Pt/Ni wet impregnated over Al incorporated mesoporous silicates: a highly efficient catalyst for anisole hydrodeoxygenation

This work reports, formation of benzene from anisole via hydrodeoxygenation process using vapour phase fixed bed reactor. The surface properties of bimetallic catalysts such as textural properties, acidic, and Pt/Ni dispersion has established by various characterization techniques. The reaction was carried out at 370 and 420 °C with space velocity 3.3 & 6.6 h^??1, over acidic and non-acidic supported mono and bimetallic catalysts. The optimum conversion and selectivity was observed at 420 °C and WHSV?=?3.3 h^??1 for all mono and bimetallic catalysts. Pt/Ni/Al-SBA-15 acidic bimetallic catalyst shows maximum anisole conversion 59% with benzene selectivity 37% under atmospheric pressure, due to the more acidic centres and high dispersion of Pt/Ni species on the bimetallic catalyst, enhance the anisole conversion; this was proved by NH₃-TPD and HR-TEM analysis. The acidic Pt/Ni bimetallic catalyst shows higher anisole conversion as compared to the mono metallic Pt/Ni catalysts and it works predominantly through demethylation and hydrogenolysis reaction pathway.     

Mesoporous Pt–Ni catalyst and their electro catalytic activity towards methanol oxidation

Mesoporous Pt/Ni architecture has been prepared by template assisted electrochemical deposition of Pt–Ni over anodized aluminum oxide template followed by controlled de-alloying with nitric acid. Surface characteristics of the ordered bimetallic mesoporous Pt/Ni structure were systematically characterized through XRD, SEM, AFM and XPS analyses. It is designated by XPS analysis that presence of Ni significantly modifies surface characteristics and electronic states of Pt accompanied with a downshift in the d-band character of Pt. Mesoporous morphology is highly beneficial to offer readily accessible Pt catalytic sites for methanol oxidation reaction. The prepared bimetallic Pt/Ni was used as electro catalyst for DMFC. Comparison of electrocatalytic activity of bimetallic mesoporous Pt/Ni with bimetallic smooth Pt/Ni was interrogated using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy analyses. Distinctly enhanced electrocatalytic activity with improved CO tolerance associated with bimetallic mesoporous Pt/Ni electrode towards methanol oxidation stems from a synergy existing between mesoporous structure with bi-metallic composition.     

NO + H2 reaction on Pt-Ru/SiO2 catalysts: correlation between nanostructure and catalytic activity and selectivity

Nitric oxide reduction by hydrogen has been studied on Pt-Ru/SiO₂ catalysts of various Pt/Ru atomic compositions in the temperature range 298–673 K. Physical characterization showed the presence of bimetallic particles which tend to be Pt-rich. The overall activity of the bimetallic catalysts suggests a dilution of the active component (Pt) in the range 373–523 K. The addition of Ru results in a general improvement of the N₂ selectivity and significant modifications in the product distribution are observed as a function of the catalyst composition. A bimetallic particle model is proposed in which various types of surfaces are exposed including those with pure Pt atoms and/or Pt-Ru mixture. This model allows to explain the overall activity and selectivity in the whole series of catalysts.     

In Situ Generation of Two-Dimensional Au–Pt Core–Shell Nanoparticle Assemblies

Two-dimensional assemblies of Au–Pt bimetallic nanoparticles are generated in situ on polyethyleneimmine (PEI) silane functionalized silicon and indium tin oxide (ITO) coated glass surfaces. Atomic force microscopy (AFM), UV–Visible spectroscopy, and electrochemical measurements reveal the formation of core–shell structure with Au as core and Pt as shell. The core–shell structure is further supported by comparing with the corresponding data of Au nanoparticle assemblies. Static contact angle measurements with water show an increase in hydrophilic character due to bimetallic nanoparticle generation on different surfaces. It is further observed that these Au–Pt core–shell bimetallic nanoparticle assemblies are catalytically active towards methanol electro-oxidation, which is the key reaction for direct methanol fuel cells (DMFCs).     

Reducibility and CO hydrogenation over Pt and Pt-Co bimetallic catalysts encaged in NaY-zeolite

Temperature programmed techniques (TPR, TPD) and X-ray diffraction (XRD) have been used to study ion migration and location as well as reducibility of platinum and cobalt ions encapsulated in Pt/NaY, Co/NaY and Pt-Co/NaY zeolites prepared by ion exchange. The temperature required to reduce Co²⁺ in NaY was significantly lowered by the presence of Pt and dependent upon the relative locations of Pt and Co ions in zeolite cages. The exact location was controlled by the calcination condition and the metal contents. For bimetallic catalyst with low Pt content (0.5 wt% Pt and 0.9 wt% Co), the TPR results indicated that reduction of Co²⁺ ions in the vicinity of Pt shifted toward lower temperature, while that of Co²⁺ staying alone was not affected. With high Pt loading (4.5 wt% Pt, 0.7 and 2.6 wt% Co), however, most of the Co²⁺ ions were reduced by means of Pt at temperature below 723 K after calcination at 573 K. The temperature for Pt reduction in bimetallic catalysts was somewhat higher than Pt/NaY and increased with Co atomic fraction, indicating that mixed oxide, PtCo _x O _y , might be formed during calcination. After reduction in hydrogen at 723 K, highly dispersed metal particles were formed. These fine particles were most probably confined inside zeolite cages as indicated by the absence of XRD peak for all samples after calcination and reduction. Surface composition of the bimetallic particles may be different for catalysts with similar Pt content but different Co loading. Accordingly, H/Pt ratios of 1.0 and 0.72 for catalysts with low and high Co content, respectively, were shown by hydrogen chemisorption. It was further supported by the increase in TPD peak intensity with Co loading in the high temperature range, which was related to the reoxidation of Co in bimetallic particles by surface hydroxyl groups. Preliminary results on CO hydrogenation demonstrated that activity and methanol selectivity were higher on Pt-Co bimetallic catalysts than either over monometallic Pt or Co catalyst, which was consistent with the Pt enhanced Co reduction and formation of Pt-Co bimetallic particles.     

Autothermal reforming of n-dodecane, toluene, and their mixture on mono- and bimetallic noble metal zirconia catalysts

Autothermal reforming (ATR) of higher hydrocarbons and their mixture was studied on zirconia-supported mono- (Rh, Pd, or Pt) and bimetallic (RhPt) catalysts. ATR reactions predominated on Rh-containing catalysts at 700–900 °C, whereas thermal cracking predominated on Pt and the support. The thermal stability of Rh was improved when Rh was combined with Pt in the bimetallic catalyst.     

Dendrimer templates for heterogeneous catalysts: Bimetallic Pt–Au nanoparticles on oxide supports

Polyamidoamine (PAMAM) dendrimers were used to template Pt, Au, and bimetallic Pt–Au dendrimer encapsulated nanoparticles (DENs) in solution. Adjusting the solution pH allowed for slow, spontaneous adsorption of the nanoparticles onto silica, alumina, and titania. After dendrimer removal, the catalysts were characterized with infrared spectroscopy of adsorbed CO and tested with CO oxidation catalysis. Infrared spectroscopy of the monometallic Pt catalysts showed a slight shift in the CO stretching frequency for the different supports. For the bimetallic catalysts, infrared spectra showed CO adsorbed on both Pt and on Au sites. Spectra collected during CO desorption showed substantial interactions between the two bands, confirming the presence of bimetallic particles on all the supports. The bimetallic catalysts were found to be more active than the monometallic catalysts and had lower apparent activation energies. The titania supported Pt–Au catalyst was resistant to deactivation during an extended treatment at 300 °C. Correlations between IR spectra and catalytic activity showed differences between the mono- and bimetallic materials and implicated a bimetallic Pt–Au ensemble at the catalytic active site. This is the first study to show that DENs are appropriate precursors for studying support effects on catalysis by metal nanoparticles, although the magnitude of the effects were small.     

Comparison of H2 production from ethanol and ethylene glycol on M/Pt(1 1 1) (M = Ni, Fe, Ti) bimetallic surfaces

The reactions of ethylene glycol and ethanol have been studied on Fe/Pt(1 1 1) and Ti/Pt(1 1 1) bimetallic surfaces utilizing temperature programmed desorption (TPD). These results are compared to our previous studies on Ni/Pt(1 1 1) to illustrate the trend in the reforming activity on 3d-Pt bimetallic surfaces. The oxygenates decomposed on these surfaces to produce mainly H₂ and CO. The bimetallic surfaces were prepared by thermal evaporation of Fe or Ti onto Pt(1 1 1), using Auger electron spectroscopy (AES) to monitor surface compositions. Surfaces prepared by deposition of a monolayer of Fe or Ti on Pt(1 1 1), designated Fe–Pt–Pt(1 1 1) or Ti–Pt–Pt(1 1 1), displayed higher reforming activity for both ethylene glycol and ethanol than the corresponding subsurface monolayer Pt–Fe–Pt(1 1 1) and Pt–Ti–Pt(1 1 1) structures or clean Pt(1 1 1). The reforming yield increased as the surface d-band center, calculated from density functional theory (DFT), shifted closer to the Fermi level. The reforming selectivity of oxygenates, especially ethanol, began to decrease as the d-band center shifted closer to the Fermi level. Combining results in the current work with previous studies on Ni/Pt(1 1 1), a general criterion can be formulated for selecting 3d-Pt bimetallic surfaces with desirable reforming activity and selectivity.     

Correlating Low-temperature Hydrogenation Activity of Co/Pt(111) Bimetallic Surfaces to Supported Co/Pt/γ-Al2O3 Catalysts

The low-temperature self-hydrogenation (disproportionation) of cyclohexene was used as a probe reaction to correlate the reactivity of Co/Pt(111) bimetallic surfaces with supported Co/Pt/γ-Al₂O₃ catalysts. Temperature-programmed desorption (TPD) experiments show that cyclohexene undergoes self-hydrogenation on the ~1 ML Co/Pt(111) surface at ~219 K, which does not occur on either pure Pt(111) or a thick Co film on Pt(111). Supported catalysts with a 1:1 atomic ratio of Co:Pt were synthesized on a high surface area γ-Al₂O₃ to verify the bimetallic effect on the self-hydrogenation of cyclohexene. EXAFS experiments confirmed the presence of Co–Pt bonds in the catalyst. Using FTIR in a batch reactor configuration, the bimetallic catalyst showed a higher activity toward the self-hydrogenation of cyclohexene at room temperature than either Pt/γ-Al₂O₃ or Co/γ-Al₂O₃ catalysts. The comparison of Co/Pt(111) and Co/Pt/γ-Al₂O₃ provided an excellent example of correlating the self-hydrogenation activity of cyclohexene on bimetallic model surfaces and supported catalysts.     

Observation of anomalous reactivities of Ni/Pt(111) bimetallic surfaces

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. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reactions of methylcyclopentane on Rh–Pt catalyst prepared by underpotential deposition of Rh on Pt/SiO2

Rh was deposited on to a well-characterized 3.1% Pt/SiO₂ (InCat-1) parent catalyst by underpotential deposition method to obtain a model Rh–Pt bimetallic catalyst. TEM and EDS was used to determine its mean particle size and bulk composition: the particles of ca. 3 nm contained ca. 60% Pt and 40% Rh. The Rh–Pt catalyst was tested in methylcyclopentane (MCP) reaction between 513 K and 603 K and 60–480 Torr H₂ pressure (with 10 Torr MCP). The parent Pt/SiO₂ as well as a 5% Rh/SiO₂ catalyst were also studied for comparison. Four subsequent treatments with O₂ and H₂ up to T = 673 K were applied on the bimetallic catalyst before the catalytic runs. The overall activity showed positive hydrogen order on all samples, bimetallic Rh–Pt resulting in the lowest TOF values. Ring opening and hydrogenolysis products, as well as unsaturated hydrocarbons were formed from MCP. The selectivity of ring opening products and fragments over Rh–Pt catalyst was between the values observed on Pt and Rh, while the selectivity towards benzene formation was highest on the bimetallic sample, especially at higher temperatures. “Selective” ring opening occurred on all samples, resulting mostly in 2 and 3-methylpentane and less hexane. Different pretreatments with H₂ and O₂ affected slightly the dispersion values and the catalytic behavior of Rh–Pt sample. The selectivities of the Rh–Pt catalyst being between the values observed for Pt/SiO₂ and Rh/SiO₂ indicates that the sample studied represented a real bimetallic catalyst, resembling both components and exhibiting at the same time, new properties in addition to those, characteristic of Pt or Rh. Dedicated to Konrad Hayek.     

Synergistic activity of gold-platinum alloy nanoparticle catalysts

The understanding of the composition–activity relationship is essential for the exploitation of the synergistic properties of multimetallic nanoparticles in catalytic reactions. This paper focuses on the discussion of findings from the investigation of bimetallic gold-platinum (AuPt) nanoparticles of different compositions. Infrared spectroscopic data for CO adsorption on silica-supported AuPt nanoparticles reveal that the surface binding sites are dependent on the bimetallic composition. The analysis of this dependence further led to the conclusion that the relative Au-atop and Pt-atop sites for the linear CO adsorption on the nanoparticle surface are not only correlated with the bimetallic composition, but also with the electronic effect as a result of the d-band shift of Pt in the bimetallic nanocrystals, which is the first demonstration of the nanoscale core–surface property correlation for the bimetallic nanoparticles over a wide range of bimetallic composition. A further examination of the electrocatalysis data for methanol oxidation reaction on carbon-supported AuPt nanoparticle catalysts reveal important insights into the participation of CO or OH adsorption on Au sites and the catalytic activity of Pt in the AuPt alloys with relatively high Au concentration. Implications of these findings to synergistic correlation of the bifunctional activity of the bimetallic nanoparticle catalysts with the bimetallic composition are also discussed.     

Pt/Co和Pt/Ni双金属纳米溶胶制备及催化制氢

采用化学共还原法制备聚乙烯吡咯烷酮(PVP)稳定的Pt/Co和Pt/Ni双金属纳米溶胶,采用UV-Vis、TEM等对所合成的Pt/Co和Pt/Ni双金属纳米溶胶进行表征,研究了化学组成对双金属纳米溶胶催化剂催化NaBH4水解制氢的影响. 结果表明,所制双金属纳米溶胶的平均粒径约为2.0 nm,双金属纳米溶胶的催化能力高于单金属Pt, Co, Ni纳米溶胶,Pt/Co和Pt/Ni双金属纳米颗粒优异的催化性能可归因于电荷转移效应,Co或者Ni原子与Pt原子之间发生的电荷转移效应使得Pt原子带负电而Co或者Ni原子带正电,荷电的Pt和Co、Ni原子成为催化反应的活性中心,促进了催化反应的进行.     

Preparation and characterization of the bimetallic Pt–Au/ZnO/Al2O3 catalysts: Influence of Pt–Au molar ratio on the catalytic activity for toluene oxidation

The bimetallic Pt–Au catalysts supported on ZnO/Al₂O₃ with different Pt/Au molar ratios were prepared by impregnation (IMP) method using a mixed solution of Pt and Au precursor. These were characterized by X-ray diffraction (XRD), CO chemisorption, temperature programmed reduction (TPR), and transmission electron microscopy (TEM) equipped energy dispersive spectroscopy (EDS). Catalytic activity for complete oxidation of toluene was measured using a flow reactor under atmospheric pressure. In the results, the aggregation of Au particles depended on the molar ratio in the bimetallic Pt–Au catalyst, and Pt particles was well dispersed homogeneously even by the IMP method. The Pt₇₅Au₂₅ and Pt₆₇Au₃₃ catalysts concurrently coated with Pt and Au precursors by IMP method showed higher activity than monometallic Pt and Au catalyst for toluene oxidation. Also, in order of the catalytic activity for toluene was very good agreement compare with the TPR results. The Au particles might promote the toluene oxidation over the bimetallic catalyst concurrently coated with Pt and Au particles. Therefore, the size of Pt and Au particles and catalytic activity were confirmed to be correlated to molar ratio of Pt and Au loaded.     

Deactivation characteristics inn-heptane reforming reaction catalyzed over small Pt,Ir and Pt-Ir bimetallic clusters in NaY

The deactivation characteristics of highly dispersed (about 1 nm) Pt, Ir and Pt-Ir bimetallic clusters in NaY were studied by hydrogen chemisorption, coke analysis and temperature programmed oxidation of used catalyst inn-heptane reforming reaction. As the Ir content was increased, the amount of coke decreased. Most of coke was located around the metal cluster and this coke decreased the selectivity of dehydrocyclization inn-heptane reaction. The higher activity and more improved activity maintenance of Pt-Ir/NaY bimetallic catalysts than those of Pt/NaY are related to the less amount of coke formation.     

Hydrogenation of Citral using Monometallic Pt and Bimetallic Pt‐Ru Catalysts on a Mesoporous Support in Supercritical Carbon Dioxide Medium

Supercritical carbon dioxide was shown to be a suitable reaction medium for the highly efficient hydrogenation of citral using monometallic Pt and bimetallic Pt‐Ru supported on a mesoporous material, MCM‐48, as catalyst. A remarkable change in the product distribution was observed after the addition of Ru to the monometallic Pt catalyst in supercritical carbon dioxide. The monometallic Pt catalyst was found to be highly selective to the unsaturated alcohol (geraniol+nerol) at a temperature of 323 K within 2 h whereas the bimetallic catalyst becomes selective to the partially saturated aldehyde (citronellal) under the same reaction conditions. Phase behavior plays an important role in the product distribution. Highest conversion and high selectivity to citronellal were achieved in the homogeneous phase for the Pt‐Ru catalyst while on the other hand the unsaturated alcohol (geraniol+nerol) was produced in the heterogeneous phase for the monometallic Pt catalyst. An XPS study offers strong evidence of the electronic modification of Pt after the addition of Ru in the bimetallic catalyst. The change in product distribution on the Pt‐Ru bimetallic catalyst may be explained by the appreciable interaction between the medium and the metal particles promoted by the presence of metallic Ru.     

Effect of palladium on sulfur resistance in Pt–Pd bimetallic catalysts

The interactions of H₂ and H₂S molecules with Pt–Pd bimetallic catalysts were investigated at the molecular level using a DFT (density functional theory) approach to better understand the structures and properties of active sites, and the relations between structural changes and sulfur resistance. It was found that when alloying the Pt catalyst with a small amount of Pd at a particular surface atomic ratio range, both H₂ and H₂S showed different adsorption properties compared to those on monometallic Pt or Pd catalyst. The adsorptions of both H₂ and H₂S were enhanced, but the adsorption energy of H₂ increased more than that of H₂S, indicating that the adsorption of H₂S became less favorable compared with H₂ on the bimetallic Pt–Pd catalyst surface. The desorption energy of hydrogen from monometallic Pt or Pd, as well as bimetallic Pt–Pd supported on zeolite, were calculated by temperature-programmed desorption (TPD), the values were compared against the DFT results to explain experimentally and theoretically why the bimetallic Pt–Pd catalyst has better sulfur resistance than monometallic Pt catalyst.     

Oxygen Reduction on Structurally Well Defined,Bimetallic PtRu Surfaces: Monolayer PtxRu1−x/Ru(0001) Surface Alloys Versus Pt Film Covered Ru(0001)

The electrocatalytic activity of different, structurally well defined bimetallic PtRu surfaces in the oxygen reduction reaction was investigated by a combination of scanning tunnelling microscopy and electrochemical measurements performed under controlled mass transport conditions in a flow cell. We compare the effect of pseudomorphic Pt cover layers, mimicking the situation in a core–shell Pt/Ru nanoparticle, and of mixed Pt_xRu_1?x monolayer surface alloys, reflecting the situation in an alloyed nanoparticle. The results unambiguously demonstrate that these bimetallic surfaces can reach activities well in excess of that of Pt(111), both for the film surfaces and the surface alloys, by optimizing the Pt surface content (surface alloys) or the Pt film thickness (film surfaces). The results are compared with simulated kinetic current–potential profiles based on existent density functional theory calculations (Greeley and Nørskov, J Phys Chem C 113:4932, 2009; Lischka et al., Electrochim Acta 52:2219, 2007) revealing very good agreement in trends. Potential and limits of this approach are discussed.     

Electrochemical and structural characterization of carbon-supported Pt-Pd bimetallic electrocatalysts prepared by electroless deposition

Electrochemical and structural characteristics of various Pt-Pd/C bimetallic catalysts prepared by electroless deposition (ED) methods have been investigated. Structural analysis was conducted by X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, scanning transmission electron microscopy, and energy dispersive X-ray spectroscopy (EDS). Monometallic Pt or Pd particles were not detected by EDS, indicating the ED methodology formed only bimetallic particles. The size of the Pt-Pd bimetallic particles was smaller than those of a commercially available Pt/C catalyst. The morphology of the Pt on Pd/C catalysts was identified and corresponded to Pd particles partially encapsulated by Pt.The electrochemical characteristics of the lowest Pd loading catalyst (7.0% Pt on 0.5% Pd/C) for the oxygen reduction reaction (ORR) have been investigated by the rotating ring disk electrode technique. The electrochemical activity was equal or lower than the commercially available Pt/C catalyst; however, the amount of hydrogen peroxide observed at the ring was reduced by the Pd, suggesting that such a catalyst has the potential to decrease ionomer degradation in applications. The Pt on Pd/C catalysts also show a higher tolerance to ripening induced by potential cycling. Therefore, catalyst suitability cannot be judged solely by its initial performance; information related to specific degradation mechanisms is also needed for a more complete assessment.