Infrared spectroscopy on size-controlled synthesized Pt-based nano-catalysts (original) (raw)
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Nanosized Composite Pt-Ru Catalysts for Production of Modern Modified Fuels
Chemical Engineering & Technology, 2019
Ce/(q+a)-Al 2 O 3 nanosized catalyst was developed for selective catalytic oxidation of CH 4 to synthesis gas. The process was carried out entirely with the formation of synthesis gas at high selectivity by H 2 and CO with H 2 :CO = 2.0 ratio only at Pt:Ru = 2:1 or 1:1 atomic ratio and short contact time on Pt-, Ru-, and Pt-Ru low-percentage catalysts. Samples, which were reduced by H 2 at high temperature, presented a mixture of Pt-, Ru-, and Pt-Ru nanosized particles, its alloy in the mixed catalysts. The correlation between experimental results and data of physicochemical research was established. The activity together with physicochemical properties and quantum chemical calculations for the developed lowpercentage Pt-Ru catalysts was investigated.
Preparation and characterization of supported Pt–Ru catalysts with a high Ru content
Journal of Power Sources, 2006
Pt-Ru nanoparticles supported on high surface area carbon were synthesized by reduction of the precursors with sodium formate, a modification of the reduction method with formic acid developed in this laboratory, which allows the incorporation of higher amounts of Ru. The catalysts were characterized by EDX and XRD. Electrochemical experiments involved cyclic voltammetry, linear sweep voltammetry and current-potential curves for the oxidation of hydrogen and carbon monoxide using an ultrathin layer rotating disc electrode. Levich and Tafel plots were used to examine the mechanism of the reactions. The results were compared with those obtained using a commercial Pt-Ru catalyst.
Displacement Pt on Ru nanoparticle
The displacement reaction of Pt on Ru to form a Ru core and Pt shell (Ru@Pt) bimetallic structure is investigated by immersing the carbon-supported Ru nanoparticles in hexachloroplatinic acids with pH of 1, 2.2, and 8, followed by a hydrogen reduction treatment. Results from inductively coupled plasma mass spectrometry suggest that the dissolution of Ru is mostly caused by the reduction of Pt cations. Images from transmission electron microscopy demonstrate a uniform distribution of Ru@Pt in size of 3-5 nm. Spectra from X-ray absorption near edge structure and extended X-ray absorption fine structure confirm that the pH value of hexachloroplatinic acid determines the type of ligands complexing the Pt cations that affects their activity and consequently the severity of displacement reaction and alloying degree of Ru@Pt nanoparticles. As a result, the samples from pH 1 bath reveal a desirable core-shell structure that displays a reduced onset potential in CO stripping and stable catalytic performance for H 2 oxidation while the samples from pH 8 bath indicate the formation of Pt clusters on the Ru surface that leads to poor CO stripping and H 2 oxidation characteristics.
Journal of Physical Chemistry C, 2012
The modification of carbon-supported Pt nanoparticles, high performance (HP) 20% Pt on Vulcan XC-72 carbon black (Pt/C electrocatalyst), by spontaneous deposition of Ru species is examined employing electrochemical and structural techniques. Thin-layer electrodes were prepared by applying aqueous catalyst inks of Pt/C on glassy carbon (GC) disks. Ru deposition was carried out by immersion of the prepared electrode in deaerated RuCl 3 / HClO 4 solutions. The subsequent cyclic voltammetry experiments of the modified electrocatalysts (Ru(Pt)/C) were performed in 0.5 M H 2 SO 4 to determine the Ru coverage and the electroactive surface. CO stripping voltammetry showed the promotional effect of Ru(Pt)/C for the CO oxidation compared to Pt/C. The structural characterization of the modified electrocatalysts was performed by transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analyses, fast Fourier transform (FFT), selected-area electron diffraction (SAED), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). TEM observations revealed no appreciable signals of Ru agglomerates, and EDX confirmed the regular incorporation of Ru species to the nanoparticles. XRD analyses showed the characteristic profile of the Pt face-centered cubic (FCC) structure and the absence of crystalline Ru or Ru oxides. The application of the Williamson−Hall models indicated that Ru incorporation did not significantly affect the internal strain of the Pt nanoparticles, the increase of the crystallite size being attributed to an epitaxial growth of the Ru deposit. XPS measurements reported the presence of nonreducible RuO 2 and hydrous RuO 2 (RuO x H y) as the main Ru species in Ru(Pt)/C, the hydrous species justifying the promotional effect for the CO oxidation.
Materials Chemistry and Physics, 2011
The electrodeposition of Pt and Ru on a oxidized graphite cloth from H 2 PtCl 6 and RuCl 3 solution containing trisodium citrate (Cit), disodium tartrate (Tar) and disodium dihydrogen ethylenediaminetetraacetate (Na 2 H 2 EDTA) as complexants was investigated. SEM image of the electrode prepared without complexant showed a continuous compact and rough deposit that covers the entire graphite fibers surface displaying the structure of a coating film, whereas particles with uniform size and globular shape regularly distributed over the support were obtained when the complexants were added to the solution. Thus, EDX and XRD analysis revealed changes in Pt-Ru catalyst composition. It was concluded from electrocatalytic activity measurements that the electrodes prepared using chelating compounds exhibited better CO tolerance and performance for methanol oxidation than that without complexant.
Size-Selected Synthesis of PtRu Nano-Catalysts: Reaction and Size Control Mechanism
Journal of the American Chemical Society, 2004
A rapid synthesis method for the preparation of PtRu colloids and their subsequent deposition on high surface area carbons is presented. The reaction mechanism is shown to involve the oxidation of the solvent, ethylene glycol, to mainly glycolic acid or, depending on the pH, its anion, glycolate, while the Pt(+IV) and Ru(+III) precursor salts are reduced. Glycolate acts as a stabilizer for the PtRu colloids and the glycolate concentration, and hence the size of the resulting noble metal colloids is controlled via the pH of the synthesis solution. Carbon-supported PtRu catalysts of controlled size can be prepared within the range of 0.7-4 nm. Slow scan X-ray diffraction and high-resolution transmission electron microscopy show the PtRu catalysts to be crystalline. The Ru is partly dissolved in the face-centered cubic Pt lattice, but the catalysts also consist of a separate, hexagonal Ru phase. The PtRu catalysts appear to be of the same composition independent of the catalyst size in the range of 1.2-4 nm. Particular PtRu catalysts prepared in this work display enhanced activities for the CH 3OH electro-oxidation reaction when compared to two commercial catalysts.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1998
The CO monolayer adsorption and electro-oxidation is investigated on model electrodes consisting of small Pt clusters (2-8 nm size) supported on polycrystalline gold in 0.1 M HCIO 4. The study is performed by in situ infrared spectroscopy and cyclic voltammetry. The electrodes were prepared from an aqueous Pt colloid and polyerystalline gold. The size and size distribution oI the clusters is determined by TEM images. The cyclic voltammogram of the CO monolayer oxidation on 3 nm Pt particles exhibits three oxidation peaks located at 100 to 500 mVRHE higher potentials compared to a polycrystalline Pt electrode. A pronounced influence of the Pt particle coverage on the stretching vibration of linearly bonded CO is also found: while at low Pt coverages the band is located at 2013 cm-1 an upwards shift to 2060 cm-1 is observed when incre-_sing the particle coverage. A particle size effect on the vibrational frequency can also be established by using electrodes prepared from an aged Pt colloid. TEM analysis of this colloid showed particle sizes of 2.2 nm (primary size) and 8.5 nm (secondary size) and aggregates of the larger particles. At low Pt particle coverage, two bands can be distinguished: a band at 2013cm-~ is attributed to CO adsorbed on the small primary particles while a second band at 2046 cm-~ is assigned to linearly bonded CO adsorbed on the larger particles and on the aggregates. The importance of the lateral dipole field interactions between the adsorbed vibrating molecules is discussed and also the dependence of the vibrational frequency on the coordination of the adsorbate Pt site. Both interactions are too weak to account for the pronounced vibrational shifts in comparison with CO bonded on polycrystalline Pt and therefore the results are tentatively explained by particle-substrate interaction.
The control of Pt and Ru nanoparticle size on high surface area supports
Phys. Chem. Chem. Phys., 2014
Supported Ru and Pt nanoparticles were synthesized by the method of strong electrostatic adsorption and subsequently treated to achieve a series of catalysts with particle sizes ranging from 1 to 8 nm. This methodology allows the control of particle size applicable to high surface area supports with common metal precursors.
Method for Preparing Carbon Supported Pt-Ru Nanoparticles with Controlled Internal Structure
Chemistry of Materials, 2009
A polyol method for depositing highly dispersed PtRu nanoparticles with controlled size and internal composition on carbon supports is described. Through a judicious selection of the polyol, reaction pH and temperature, and modality of combining the reactants, it was possible to control not only the size and dispersion of the bimetallic nanoparticles but also the relative spatial distribution of the two elements. The method yields reproducibly high metal-loading electrocatalysts in which the Pt:Ru ratio in both the surface and the interior of the particles can be tailored. The strategy described represents a viable experimental approach for controlling the internal composition of other bi-or multimetallic systems.
Langmuir, 2007
The chemical state and formation mechanism of Pt-Ru nanoparticles (NPs) synthesized by using ethylene glycol (EG) as a reducing agent and their stability have been examined by in situ X-ray absorption spectroscopy (XAS) at the Pt L III and Ru K edges. It appears that the reduction of Pt(IV) and Ru(III) precursor salts by EG is not a straightforward reaction but involves different intermediate steps. The pH control of the reaction mixture containing Pt(IV) and Ru(III) precursor salts in EG to 11 led to the reduction of Pt(IV) to Pt(II) corresponding to [PtCl 4 ] 2whereas Ru III Cl 3 is changed to the [Ru(OH) 6 ] 3species. Refluxing the mixture containing [PtCl 4 ] 2and [Ru(OH) 6 ] 3species at 160°C for 0.5 h produces Pt-Ru NPs as indicated by the presence of Pt and Ru in the first coordination shell of the respective metals. No change in XAS structural parameters is found when the reaction time is further increased, indicating that the Pt-Ru NPs formed are extremely stable and less prone to aggregation. XAS structural parameters suggest a Pt-rich core and a Ru-rich shell structure for the final Pt-Ru NPs. Due to the inherent advantages of the EG reduction method, the atomic distribution and alloying extent of Pt and Ru in the Pt-Ru NPs synthesized by the EG method are higher than those of the Pt-Ru/C NPs synthesized by a modified Watanabe method.