Characterization of bimetallic catalysts

Preparation and characterization of bimetallic catalysts supported on mesoporous silica Blms... 

Synthesis and characterization of bimetallic catalysts by reaction of organometallics with supported metal particles... 

Recently characterization of bimetallic nanoparticles by EXAFS were extensively reported [122-124,176], Structural transformation of bimetallic Pd/Pt nanoparticles, which were prepared by a sequential loading of H2PtClg onto the Pd loaded catalyst, was investigated with EXAFS at high temperatures [176], The results of EXAFS at Pd K and Pt L-III edges showed that Pt was surface-enriched or anchored on the Pd metal core with an increase of the Pt content. The structure of the obtained bimetallic Pd/Pt nanoparticles seemed to be retained upon heating up to 1273 K under ambient condition [176], Pt/ Au bimetallic nanoparticles can be prepared by polyol method and stabilized by PVP [122], XANES and EXAFS studies were also performed on the samples and their results supported the idea of a Pt-core/Au-shell structure with the elements segregated from each other [122],... 

Ffirai and Toshima have published several reports on the synthesis of transition-metal nanoparticles by alcoholic reduction of metal salts in the presence of a polymer such as polyvinylalcohol (PVA) or polyvinylpyrrolidone (PVP). This simple and reproducible process can be applied for the preparation of monometallic [32, 33] or bimetallic [34—39] nanoparticles. In this series of articles, the nanoparticles are characterized by different techniques such as transmission electronic microscopy (TEM), UV-visible spectroscopy, electron diffraction (EDX), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) or extended X-ray absorption fine structure (EXAFS, bimetallic systems). The great majority of the particles have a uniform size between 1 and 3 nm. These nanomaterials are efficient catalysts for olefin or diene hydrogenation under mild conditions (30°C, Ph2 = 1 bar)- In the case of bimetallic catalysts, the catalytic activity was seen to depend on their metal composition, and this may also have an influence on the selectivity of the partial hydrogenation of dienes. 

To summarize, TPR is a highly useful technique, which provides a quick characterization of metallic catalysts. It gives information on the phases present after impregnation and on the eventual degree of reduction. For bimetallic catalysts, TPR patterns often indicate whether or not the two components are mixed. In favorable cases, where the catalyst particles are uniform, TPR yields activation energies for the reduction as well as information on the mechanism of reduction. 

Chapter 4, by Batzill and his coworkers, describes modern surface characterization techniques that include photoelectron diffraction and ion scattering as well as scanning probe microscopies. The chapter by Hayden discusses model hydrogen fuel cell electrocatalysts, and the chapter by Ertl and Schuster addresses the electrochemical nano structuring of surfaces. Henry discusses adsorption and reactions on supported model catalysts, and Goodman and Santra describe size-dependent electronic structure and catalytic properties of metal clusters supported on ultra-thin oxide films. In Chapter 9, Markovic and his coworkers discuss modern physical and electrochemical characterization of bimetallic nanoparticle electrocatalysts. 

Simply changing the solvent in the Pd-based catalytic system from water to a mixture of water and a perfluorocarboxylic acid (some water is necessary for the reaction see Scheme 6) had no significant effect on product composition formic acid was still the principal product from methane. However, the addition of Cu or Cu chloride to the reaction mixture had a dramatic effect. Methanol and its ester now became the preferred products, with virtually no acetic and little formic acid being formed [40 b]. The activation parameters for the overall reaction determined under the condition when the rate was first order in both methane and carbon monoxide were A = 2 X [O sfa = 15.3 kcal mol . Since methyl trifluoro-acetate is both volatile and easily hydrolyzed back to the acid and methanol, it should be possible to design a system where the acid is recycled and methanol is the end product. Lee and co-workers have recently reported on the further characterization of the catalyst in this bimetallic Pd/Cu system [41]. 

Obviously a controlled preparation of bimetallic catalysts is needed in order to imderstand its role upon activity, selectivity and deactivation resistance. On this way, the controlled formation of surface bimetallic particles has been reported in catalysts prepared by the redox method [1]. In the present work, in order to define the role of the redox method in the surface properties of the R-Au alumina supported catalysts, we report the preparation, characterization and catalytic properties of a set of bimetallic catalysts with different gold content. The catalysts were evaluated using methylcyclopentane (MCP) hydrogenolysis as the test reaction. 

In case of bimetallic catalysts, other properties, such as surface composition and the potential stabilization of one of the metal components in ionic form, are the most crucial determining the performance of the catalyst. It is noteworthy that combination of modern methods enables the chemist to characterize both active sites of supported metals and the reaction intermediates formed. Additionally, quantum chemical calculations become more and more powerful tools in understanding chemical interaction controlling and governing both the catalyst structure and the catalytic performance. ... 

Characterization of Supported Metal Catalysts. - Chemisorption of different probe molecules and Temperature Programmed Reduction (TPR) studies are frequently used to study the metal dispersion, surface composition and oxidation state of metals in mono- and bimetallic supported catalysts. Combined use of CO, hydrogen and oxygen chemisorption as well as oxygen-hydrogen titration can provide information about the dispersion and surface composition of metal nanoclusters. TPR studies of bimetallic catalysts can give information about the type, the reducibility, and the oxidation state of metal components. In addition, the position of TPR peaks can be used to characterize the type of interactions of the metal species in the catalysts. - ... 

P-15 - Preparation and characterization of bimetallic Pt-Zn catalysts supported on zeolite NaX... 

Silica (Degussa Aerosil, 200 m /g) was used as the support material. Conventional electron microscopy (CTEM) was performed on a Oeol 100 CX microscope. It was used to determine the particles size of both supported monometallic and bimetallic catalysts. Scanning Transmission Electron Microscope (STEM) HB 5 from Vacuum Generator was used to characterize the bimetallic catalysts. Infrared spectra were obtained with a Nicolet 10 MX-1 Fourier transform instrument. It was used to characterize the alkyl groups evolution on the surface during reaction between Rh/Si02 and Sn(n-C Hg). ... 

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