Bimetallic catalysts catalysis

Nishimura, S., Ikeda, N., Ehitani, K., 2014. Selective hydrogenation of biomass derived 5-hydroxymethytturfural (HMF) to 2,5-dimethylturan (DMF) under atmospheric hydrogen pressure over carbon supported PdAu bimetallic catalyst. Catalysis Today 232, 89-98. 

Heterogeneous catalysis by metals has been of long-standing interest, with bimetallic catalysts a particular focus.Transition metal carbonyls have... 

Surface Chemistry and Catalysis on Some Platinum-Bimetallic Catalysts... 

Bahome, M. C., Jewell, K., Padayachy, L. L., Padayachy, K., Hildebrandt, D., Glasser, D., Datye, A. K., and Coville, N. J. 2007. Fe-Ru small particle bimetallic catalysts supported on carbon nano tubes for use in Fischer-Tropsch synthesis. Applied Catalysis A General 328 243-51. 

CO oxidation catalysis showed that, for all the supports, the bimetallic catalyst was more active at low temperatures than the corresponing monometallic and cometallic catalysts. Apparent activation energies for monometallic Pt and Au catalysts were very consistent, near 32 and 80 kJ/mole, respectively. The s)uiergism for PtieAuie catalysts also shows up in the apparent activation energies for these catalysts, which were consistently around 23 kJ/mole. 

J. Barbier, Redox method of bimetallic catalysts. In Handbook of Heterogeneous Catalysis edited by G. ErtI, H. Knozinger, and J. Weitkamp (Wiley-VCH, Weinheim 1997) pp. 257-264. 

On the other hand, hi- or multi-metallic supported systems have been attracting considerable interest in research into heterogeneous catalysis as a possible way to modulate the catalytic properties of the individual monometalUc counterparts [12, 13]. These catalysts usually show new catalytic properties that are ascribed to geometric and/or electronic effects between the metalUc components. Of special interest is the preparation of supported bimetallic catalysts using metal carbonyls as precursors, since the milder conditions used, when compared with conventional methods, can render catalysts with homogeneous bimetallic entities of a size and composition not usually achieved when conventional salts are employed as precursors. The use of these catalysts as models can lead to elucidation of the relationships between the structure and catalytic behavior of bimetalUc catalysts. 

In support of the conclusion based on silver, series of 0.2, 0.5, 1.0, 2.0, and 5.0 % w/w of platinum, iridium, and Pt-Ir bimetallic catalysts were prepared on alumina by the HTAD process. XRD analysis of these materials showed no reflections for the metals or their oxides. These data suggest that compositions of this type may be generally useful for the preparation of metal supported oxidation catalysts where dispersion and dispersion maintenance is important. That the metal component is accessible for catalysis was demonstrated by the observation that they were all facile dehydrogenation catalysts for methylcyclohexane, without hydrogenolysis. It is speculated that the aerosol technique may permit the direct, general synthesis of bimetallic, alloy catalysts not otherwise possible to synthesize. This is due to the fact that the precursors are ideal solutions and the synthesis time is around 3 seconds in the heated zone. 

A renewed industrial interest in catalysis by alloys or more generally by bimetallic catalysts (see, e.g., 6). 

For a further discussion of the structure and properties of bimetallic systems, see Sections 2.6 and 3.2.3 for the preparation of bimetallic catalysts, see Section 4.6 and for the mechanisms by which they work in oxidations, see Section 8.2.2. Most textbooks of physical chemistry have sections on adsorption and catalysis, but they frequently focus on studies made under ultra-high vacuum conditions with single crystal surfaces. While this work produces beautiful pictures, it has limited relevance to the more mundane world of practical catalysis. Other introductory treatments of about the level of this chapter, or slightly more advanced, are available,5,7,11 as are deeper discussions of the kinetics of catalysed reactions.12 14 Industrial processes using catalysts have also been described in detail.15,16... 

In heterogeneous catalysis, the first tests on UPD were performed on bulk catalysts which allows, for the preparation of the bimetallic catalyst, easy control of the electrochemical potential by an external device (potentiostat). In the same way all electrochemical techniques, particularly the control of catalyst potential required for submonolayer deposition, can be extrapolated to metallic catalysts supported on conductive materials such as carbon or carbides [8]. 

The recent accomplishments of near-edge X-ray absorption spectroscopy in catalysis studies are already quite impressive, in particular if one considers the limited availability of suitable X-ray spectrometers. Developments of catalytic interest have concerned the Shell Higher Olefin process, size effects, metal-support interaction, mono- and bimetallic catalysts (in particular the PtRe/Al203 system), the reactivity of supported metal catalysts, dynamical and in situ catalyst studies, and a variety of oxide and sulfide catalysts. Other catalytic problems are now coming within easy experimental reach, such as the study of sulfur poisoning and the nature of coking. 

Asymmetric catalysis by bimetallic catalysts is currently a research field of great interest. There have been few studies of the interaction between bidentate Lewis acids and carbonyl groups [22a]. Reilly and Oh [22c] have reported the only example of such an asymmetric Diels-Alder reaction catalyzed by a 1 1 complex of N-tosyltrypto-phan [17-19] with l,8-naphthalenediylbis(dichloroborane), in which the two Lewis-acidic sites work in a cooperative manner (Eq. 22). 

The understanding of the interaction of S with bimetallic surfaces is a critical issue in two important areas of heterogeneous catalysis. On one hand, hydrocarbon reforming catalysts that combine noble and late-transition metals are very sensitive to sulphur poisoning [6,7]. For commercial reasons, there is a clear need to increase the lifetime of this type of catalysts. On the other hand. Mo- and W-based bimetallic catalysts are frequently used for hydrodesulphurization (HDS) processes in oil refineries [4,5,7,8]. In order to improve the quality of fuels and oil-derived feedstocks there is a general desire to enhance the activity of HDS catalysts. These facts have motivated many studies investigating the adsorption of S on well-defined bimetallic surfaces prepared by the deposition of a metal (Co, Ni, Cu, Ag, Au, Zn, A1 or Sn) onto a single-crystal face of anodier metal (Mo, Ru, Pt, W or Re) [9-29]. 

The review is broken into three broad sections, each containing three separate topics. The first section highlights three dramatic successes in the application of DFT to heterogeneous catalysis, followed by a discussion of the accuracy of DFT. The second section reviews three areas within heterogeneous catalysis that have attracted large volumes of theoretical effort in recent years, namely ab initio thermodynamics, the catalytic activity of nanoclusters of gold, and the development of bimetallic catalysts. The third section provides recent... 

The success stories reviewed above are, of course, just several of a larger number of areas of heterogeneous catalysis in which DFT-based calculations have made valuable contributions in recent years. In this section, three topics that have attracted considerable attention are described, ab initio thermodynamics, the catalytic activity of nanoclusters of gold, and computational efforts to screen bimetallic catalysts. Again, the choice of these topics does not indicate that they are the only topics of interest in the community, but they give a good representation of current approaches. 

Fox, E.B., Velu, S., Engelhard, M.H., Chin, Y.-H., Miller, J.T., Kropf, J., and Song, C. Characterization of Ce02-supported Cu-Pd bimetallic catalyst for the oxygen-assisted water-gas shift reaction. Journal of Catalysis, 2008, 260 (2), 358. 

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